ccnapresentation-print .ppt

Data Networks

Sharing data through the use of floppy disks is not an efficient or cost-effective manner in which to operate businesses.

Businesses needed a solution that would successfully address the following three problems:
How to avoid duplication of equipment and resources How to communicate efficiently How to set up and manage a network
Businesses realized that networking technology could increase productivity while saving money.

Networking Devices

Equipment that connects directly to a network segment is referred to as a device.

These devices are broken up into two classifications.
end-user devices network devices
End-user devices include computers, printers, scanners, and other devices that provide services directly to the user.

Network devices include all the devices that connect the end-user devices together to allow them to communicate.

Network Interface Card

A network interface card (NIC) is a printed circuit board that provides network communication capabilities to and from a personal computer. Also called a LAN adapter.

Networking Device Icons

Repeater

A repeater is a network device used to regenerate a signal.

Repeaters regenerate analog or digital signals distorted by transmission loss due to attenuation. A repeater does not perform intelligent routing.

Hub

Hubs concentrate connections. In other words, they take a group of hosts and allow the network to see them as a single unit.

This is done passively, without any other effect on the data transmission.

Active hubs not only concentrate hosts, but they also regenerate signals.

Bridge

Bridges convert network transmission data formats as well as perform basic data transmission management. Bridges, as the name implies, provide connections between LANs. Not only do bridges connect LANs, but they also perform a check on the data to determine whether it should cross the bridge or not. This makes each part of the network more efficient.

Workgroup Switch

Workgroup switches add more intelligence to data transfer management.

Switches can determine whether data should remain on a LAN or not, and they can transfer the data to the connection that needs that data.

Router

Routers have all capabilities of the previous devices. Routers can regenerate signals, concentrate multiple connections, convert data transmission formats, and manage data transfers.They can also connect to a WAN, which allows them to connect LANs that are separated by great distances.

The Cloud

The cloud is used in diagrams to represent where the connection to the internet is.

It also represents all of the devices on the internet.

Network Topologies

Network topology defines the structure of the network.

One part of the topology definition is the physical topology, which is the actual layout of the wire or media.

The other part is the logical topology,which defines how the media is accessed by the hosts for sending data.

Physical Topologies

Bus Topology

A bus topology uses a single backbone cable that is terminated at both ends.

All the hosts connect directly to this backbone.

Ring Topology

A ring topology connects one host to the next and the last host to the first.

This creates a physical ring of cable.

Star Topology

A star topology connects all cables to a central point of concentration.

Extended Star Topology

An extended star topology links individual stars together by connecting the hubs and/or switches.This topology can extend the scope and coverage of the network.

Hierarchical Topology

A hierarchical topology is similar to an extended star.

Mesh Topology

A mesh topology is implemented to provide as much protection as possible from interruption of service.

Each host has its own connections to all other hosts. Although the Internet has multiple paths to any one location, it does not adopt the full mesh topology.

LANs, MANs, & WANs

One early solution was the creation of local-area network (LAN) standards which provided an open set of guidelines for creating network hardware and software, making equipment from different companies compatible.

What was needed was a way for information to move efficiently and quickly, not only within a company, but also from one business to another.

The solution was the creation of metropolitan-area networks (MANs) and wide-area networks (WANs).

Examples of Data Networks

Wireless LAN Organizations and Standards

In cabled networks, IEEE is the prime issuer of standards for wireless networks. The standards have been created within the framework of the regulations created by the Federal Communications Commission (FCC).

A key technology contained within the 802.11 standard is Direct Sequence Spread Spectrum (DSSS).

Cellular Topology for Wireless

SANs

A SAN is a dedicated, high-performance network used to move data between servers and storage resources.

Because it is a separate, dedicated network, it avoids any traffic conflict between clients and servers.

Virtual Private Network

A VPN is a private network that is constructed within a public network infrastructure such as the global Internet. Using VPN, a telecommuter can access the network of the company headquarters through the Internet by building a secure tunnel between the telecommuters PC and a VPN router in the headquarters.

Bandwidth

Measuring Bandwidth

Why do we need the OSI Model?

To address the problem of networks increasing in size and in number, the International Organization for Standardization (ISO) researched many network schemes and recognized that there was a need to create a network model that would help network builders implement networks that could communicate and work together and therefore, released the OSI reference model in 1984.

Dont Get Confused.

ISO - International Organization for Standardization

OSI - Open System Interconnection

IOS - Internetwork Operating System

The ISO created the OSI to make the IOS more efficient. The ISO acronym is correct as shown.

To avoid confusion, some people say International Standard Organization.

The OSI Reference Model

7 Application

6 Presentation

5 Session

4 Transport

3 Network

2 Data Link

1 Physical

The OSI Model will be used throughout your entire networking career!

Memorize it!

Layer 7 - The Application Layer

7 Application

6 Presentation

5 Session

4 Transport

3 Network

2 Data Link

1 Physical

This layer deal with networking applications.

Examples:

Email

Web browsers

PDU - User Data

Layer 6 - The Presentation Layer

7 Application

6 Presentation

5 Session

4 Transport

3 Network

2 Data Link

1 Physical

This layer is responsible for presenting the data in the required format which may include:

Encryption

Compression

PDU - Formatted Data

Layer 5 - The Session Layer

7 Application

6 Presentation

5 Session

4 Transport

3 Network

2 Data Link

1 Physical

This layer establishes, manages, and terminates sessions between two communicating hosts.

Example:

Client Software

( Used for logging in)

PDU - Formatted Data

Layer 4 - The Transport Layer

7 Application

6 Presentation

5 Session

4 Transport

3 Network

2 Data Link

1 Physical

This layer breaks up the data from the sending host and then reassembles it in the receiver.

It also is used to insure reliable data transport across the network.

PDU - Segments

Layer 3 - The Network Layer

7 Application

6 Presentation

5 Session

4 Transport

3 Network

2 Data Link

1 Physical

Sometimes referred to as the Cisco Layer.

Makes Best Path Determination decisions based on logical addresses (usually IP addresses).

PDU - Packets

Layer 2 - The Data Link Layer

7 Application

6 Presentation

5 Session

4 Transport

3 Network

2 Data Link

1 Physical

This layer provides reliable transit of data across a physical link.

Makes decisions based on physical addresses (usually MAC addresses).

PDU - Frames

Layer 1 - The Physical Layer

7 Application

6 Presentation

5 Session

4 Transport

3 Network

2 Data Link

1 Physical

This is the physical media through which the data, represented as electronic signals, is sent from the source host to the destination host.

Examples:

CAT5 (what we have)

Coaxial (like cable TV)

Fiber optic

PDU - Bits

OSI Model Analogy
Application Layer - Source Host

After riding your new bicycle a few times in NewYork, you decide that you want to give it to a friend who lives in Munich,Germany.

OSI Model Analogy
Presentation Layer - Source Host

Make sure you have the proper directions to disassemble and reassemble the bicycle.

OSI Model Analogy
Session Layer - Source Host

Call your friend and make sure you have his correct address.

OSI Model Analogy
Transport Layer - Source Host

Disassemble the bicycle and put different pieces in different boxes. The boxes are labeled

1 of 3, 2 of 3, and 3 of 3.

OSI Model Analogy
Network Layer - Source Host

Put your friend's complete mailing address (and yours) on each box.Since the packages are too big for your mailbox (and since you dont have enough stamps) you determine that you need to go to the post office.

OSI Model Analogy
Data Link Layer Source Host

NewYork post office takes possession of the boxes.

OSI Model Analogy
Physical Layer - Media

The boxes are flown from USA to Germany.

OSI Model Analogy
Data Link Layer - Destination

Munich post office receives your boxes.

OSI Model Analogy
Network Layer - Destination

Upon examining the destination address, Munich post office determines that your boxes should be delivered to your written home address.

OSI Model Analogy
Transport Layer - Destination

Your friend calls you and tells you he got all 3 boxes and he is having another friend named BOB reassemble the bicycle.

OSI Model Analogy
Session Layer - Destination

Your friend hangs up because he is done talking to you.

OSI Model Analogy
Presentation Layer - Destination

BOB is finished and presents the bicycle to your friend. Another way to say it is that your friend is finally getting him present.

OSI Model Analogy
Application Layer - Destination

Your friend enjoys riding his new bicycle in Munich.

Host Layers

7 Application

6 Presentation

5 Session

4 Transport

3 Network

2 Data Link

1 Physical

These layers only exist in the source and destination host computers.

Media Layers

7 Application

6 Presentation

5 Session

4 Transport

3 Network

2 Data Link

1 Physical

These layers manage the information out in the LAN or WAN between the source and destination hosts.

Data Flow Through a Network

LAN Physical Layer

Various symbols are used to represent media types.

The function of media is to carry a flow of information through a LAN.Networking media are considered Layer 1, or physical layer, components of LANs.

Each media has advantages and disadvantages.

Some of the advantage or disadvantage comparisons concern:
Cable length Cost Ease of installation Susceptibility to interference
Coaxial cable, optical fiber, and even free space can carry network signals. However, the principal medium that will be studied is Category 5 unshielded twisted-pair cable (Cat 5 UTP)

Unshielded Twisted Pair (UTP) Cable

UTP Implementation

EIA/TIA specifies an RJ-45 connector for UTP cable.

The RJ-45 transparent end connector shows eight colored wires.

Four of the wires carry the voltage and are considered tip (T1 through T4).

The other four wires are grounded and are called ring (R1 through R4).

The wires in the first pair in a cable or a connector are designated as T1 & R1

Connection Media

The registered jack (RJ-45) connector and jack are the most common.

In some cases the type of connector on a network interface card (NIC) does not match the media that it needs to connect to.

The attachment unit interface (AUI) connector allows different media to connect when used with the appropriate transceiver.

A transceiver is an adapter that converts one type of connection to another.

Ethernet Standards

The Ethernet standard specifies that each of the pins on an RJ-45 connector have a particular purpose. A NIC transmits signals on pins 1 & 2, and it receives signals on pins 3 & 6.

Remember

A straight-thru cable has T568B on both ends. A crossover (or cross-connect) cable has T568B on one end and T568A on the other. A console cable had T568B on one end and reverse T568B on the other, which is why it is also called a rollover cable.

Straight-Thru or Crossover

Use straight-through cables for the following cabling:
Switch to router Switch to PC or server Hub to PC or server
Use crossover cables for the following cabling:
Switch to switch Switch to hub Hub to hub Router to router PC to PC Router to PC

Sources of Noise on Copper Media

Noise is any electrical energy on the transmission cable that makes it difficult for a receiver to interpret the data sent from the transmitter. TIA/EIA-568-B certification of a cable now requires testing for a variety of types of noise.Twisted-pair cable is designed to take advantage of the effects of crosstalk in order to minimize noise. In twisted-pair cable, a pair of wires is used to transmit one signal.The wire pair is twisted so that each wire experiences similar crosstalk. Because a noise signal on one wire will appear identically on the other wire, this noise be easily detected and filtered at receiver.Twisting one pair of wires in a cable also helps to reduce crosstalk of data or noise signals from adjacent wires.

Shielded Twisted Pair (STP) Cable

Coaxial Cable

Fiber Optic Cable

Fiber Optic Connectors

Connectors are attached to the fiber ends so that the fibers can be connected to the ports on the transmitter and receiver.

The type of connector most commonly used with multimode fiber is the Subscriber Connector (SC connector).On single-mode fiber, the Straight Tip (ST) connector is frequently used

Fiber Optic Patch Panels

Fiber patch panels similar to the patch panels used with copper cable.

Cable Specifications

10BASE-T

The T stands for twisted pair.

10BASE5

The 5 represents the fact that a signal can travel for approximately 500 meters 10BASE5 is often referred to as Thicknet.

10BASE2

The 2 represents the fact that a signal can travel for approximately 200 meters 10BASE2 is often referred to as Thinnet.

All 3 of these specifications refer to the speed of transmission at 10 Mbps and a type of transmission that is baseband, or digitally interpreted. Thinnet and Thicknet are actually a type of networks, while 10BASE2 & 10BASE5 are the types of cabling used in these networks.

Ethernet Media Connector Requirements

LAN Physical Layer Implementation

Ethernet in the Campus

WAN Physical Layer

WAN Serial Connection Options

Serial Implementation of DTE & DCE

When connecting directly to a service provider, or to a device such as a CSU/DSU that will perform signal clocking, the router is a DTE and needs a DTE serial cable.

This is typically the case for routers.

Back-to-Back Serial Connection

When performing a back-to-back router scenario in a test environment, one of the routers will be a DTE and the other will be a DCE.

Repeater

A repeater is a network device used to regenerate a signal.

Repeaters regenerate analog or digital signals distorted by transmission loss due to attenuation.Repeater is a Physical Layer device

The 4 Repeater Rule

The Four Repeater Rule for 10-Mbps Ethernet should be used as a standard when extending LAN segments.

This rule states that no more than four repeaters can be used between hosts on a LAN.

This rule is used to limit latency added to frame travel by each repeater.

Hub

Hubs concentrate connections.In other words, they take a group of hosts and allow the network to see them as a single unit.

Hub is a physical layer device.

Network Interface Card

The function of a NIC is to connect a host device to the network medium.

A NIC is a printed circuit board that fits into the expansion slot on the motherboard or peripheral device of a computer. The NIC is also referred to as a network adapter.

NICs are considered Data Link Layer devices because each NIC carries a unique code called a MAC address.

MAC Address

MAC address is 48 bits in length and expressed as twelve hexadecimal digits.MAC addresses are sometimes referred to as burned-in addresses (BIA) because they are burned into read-only memory (ROM) and are copied into random-access memory (RAM) when the NIC initializes.

Bridge

Bridges are Data Link layer devices.Connected host addresses are learned and stored on a MAC address table.Each bridge port has a unique MAC address

Bridges

Bridging Graphic

Switch

Switches are Data Link layer devices.

Each Switch port has a unique MAC address.

Connected host MAC addresses are learned and stored on a MAC address table.

Switching Modes

cut-through

A switch starts to transfer the frame as soon as the destination MAC address is received. No error checking is available.

Must use synchronous switching.

store-and-forward

At the other extreme, the switch can receive the entire frame before sending it out the destination port. This gives the switch software an opportunity to verify the Frame Check Sum (FCS) to ensure that the frame was reliably received before sending it to the destination.

Must be used with asynchronous switching.

fragment-free

A compromise between the cut-through and store-and-forward modes.

Fragment-free reads the first 64 bytes, which includes the frame header, and switching begins before the entire data field and checksum are read.

Full Duplex

Another capability emerges when only two nodes are connected. In a network that uses twisted-pair cabling, one pair is used to carry the transmitted signal from one node to the other node. A separate pair is used for the return or received signal. It is possible for signals to pass through both pairs simultaneously. The capability of communication in both directions at once is known as full duplex.

Switches MAC Tables

Switches Parallel Communication

Microsegmentation

A switch is simply a bridge with many ports. When only one node is connected to a switch port, the collision domain on the shared media contains only two nodes. The two nodes in this small segment, or collision domain, consist of the switch port and the host connected to it. These small physical segments are called micro segments.

Peer-to-Peer Network

In a peer-to-peer network, networked computers act as equal partners, or peers.

As peers, each computer can take on the client function or the server function.

At one time, computer A may make a request for a file from computer B, which responds by serving the file to computer A. Computer A functions as client, while B functions as the server. At a later time, computers A and B can reverse roles.

In a peer-to-peer network, individual users control their own resources. Peer-to-peer networks are relatively easy to install and operate. As networks grow, peer-to-peer relationships become increasingly difficult to coordinate.

Client/Server Network

In a client/server arrangement, network services are located on a dedicated computer called a server.

The server responds to the requests of clients.

The server is a central computer that is continuously available to respond to requests from clients for file, print, application, and other services.

Most network operating systems adopt the form of a client/server relationship.

Why Another Model?

Although the OSI reference model is universally recognized, the historical and technical open standard of the Internet is Transmission Control Protocol / Internet Protocol (TCP/IP).

The TCP/IP reference model and the TCP/IP protocol stack make data communication possible between any two computers, anywhere in the world, at nearly the speed of light.

The U.S. Department of Defense (DoD) created the TCP/IP reference model because it wanted a network that could survive any conditions, even a nuclear war.

Dont Confuse the Models

Application

Transport

Internet

Network Access

7 Application

6 Presentation

5 Session

4 Transport

3 Network

2 Data Link

1 Physical

2 Models
Side-By-Side

Application

Transport

Internet

Network Access

7 Application

6 Presentation

5 Session

4 Transport

3 Network

2 Data Link

1 Physical

The Application Layer

The application layer of the TCP/IP model handles high-level protocols, issues of representation, encoding, and dialog control.

The Transport Layer

The transport layer provides transport services from the source host to the destination host. It constitutes a logical connection between these endpoints of the network. Transport protocols segment and reassemble upper-layer applications into the same data stream between endpoints.

The transport layer data stream provides end-to-end transport services.

The Internet Layer

The purpose of the Internet layer is to select the best path through the network for packets to travel. The main protocol that functions at this layer is the Internet Protocol (IP). Best path determination and packet switching occur at this layer.

The Network Access Layer

The network access layer is also called the host-to-network layer. It the layer that is concerned with all of the issues that an IP packet requires to actually make a physical link to the network media. It includes LAN and WAN details, and all the details contained in the OSI physical and data-link layers. NOTE: ARP & RARP work at both the Internet and Network Access Layers.

Comparing TCP/IP & OSI Models

NOTE: TCP/IP transport layer using UDP does not always guarantee reliable delivery of packets as the transport layer in the OSI model does.

Introduction to the Transport Layer

The primary duties of the transport layer, Layer 4 of the OSI model, are to transport and regulate the flow of information from the source to the destination, reliably and accurately.

End-to-end control and reliability are provided by sliding windows, sequencing numbers, and acknowledgments.

More on The Transport Layer

The transport layer provides transport services from the source host to the destination host.

It establishes a logical connection between the endpoints of the network.
Transport services include the following basic services: Segmentation of upper-layer application data Establishment of end-to-end operations Transport of segments from one end host to another
end host
Flow control provided by sliding windows Reliability provided by sequence numbers and
acknowledgments

Flow Control

As the transport layer sends data segments, it tries to ensure that data is not lost.

A receiving host that is unable to process data as quickly as it arrives could be a cause of data loss.

Flow control avoids the problem of a transmitting host overflowing the buffers in the receiving host.

3-Way Handshake

TCP requires connection establishment before data transfer begins.

For a connection to be established or initialized, the two hosts must synchronize their Initial Sequence Numbers (ISNs).

Basic Windowing

Data packets must be delivered to the recipient in the same order in which they were transmitted to have a reliable, connection-oriented data transfer.

The protocol fails if any data packets are lost, damaged, duplicated, or received in a different order.

An easy solution is to have a recipient acknowledge the receipt of each packet before the next packet is sent.

Sliding Window

Sliding Window
with Different Window Sizes

TCP Sequence & Acknowledgement

TCP

Transmission Control Protocol (TCP) is a connection-oriented Layer 4 protocol that provides reliable full-duplex data transmission.

TCP is part of the TCP/IP protocol stack. In a connection-oriented environment, a connection is established between both ends before the transfer of information can begin.

TCP is responsible for breaking messages into segments, reassembling them at the destination station, resending anything that is not received, and reassembling messages from the segments.TCP supplies a virtual circuit between end-user applications.

The protocols that use TCP include:
FTP (File Transfer Protocol) HTTP (Hypertext Transfer Protocol) SMTP (Simple Mail Transfer Protocol) Telnet

TCP Segment Format

UDP

User Datagram Protocol (UDP) is the connectionless transport protocol in the TCP/IP protocol stack.

UDP is a simple protocol that exchanges datagrams, without acknowledgments or guaranteed delivery. Error processing and retransmission must be handled by higher layer protocols.

UDP uses no windowing or acknowledgments so reliability, if needed, is provided by application layer protocols. UDP is designed for applications that do not need to put sequences of segments together.

The protocols that use UDP include:
TFTP (Trivial File Transfer Protocol) SNMP (Simple Network Management Protocol) DHCP (Dynamic Host Control Protocol) DNS (Domain Name System)

UDP Segment Format

Well Known Port Numbers

The following port numbers should be memorized:

NOTE:

The curriculum forgot to mention one of the most important port numbers.

Port 80 is used for HTTP or WWW protocols. (Essentially access to the internet.)

SNMP Managed Network

Base 2 Number System

101102 = (1 x 24 = 16) + (0 x 23 = 0) + (1 x 22 = 4) +

(1 x 21 = 2) + (0 x 20 = 0) = 22

Converting Decimal to Binary

Convert 20110 to binary:

201 / 2 = 100 remainder 1

100 / 2 = 50 remainder 0

50 / 2 = 25 remainder 0

25 / 2 = 12 remainder 1

12 / 2 = 6 remainder 0




When the quotient is 0, take all the remainders in reverse order for your answer: 20110 = 110010012

Network and Host Addressing

Using the IP address of the destination network, a router can deliver a packet to the correct network.

When the packet arrives at a router connected to the destination network, the router uses the IP address to locate the particular computer connected to that network.

Accordingly, every IP address has two parts.

Network Layer Communication Path

A router forwards packets from the originating network to the destination network using the IP protocol. The packets must include an identifier for both the source and destination networks.

Internet Addresses

IP Addressing is a hierarchical structure.An IP address combines two identifiers into one number. This number must be a unique number, because duplicate addresses would make routing impossible.The first part identifies the system's network address.The second part, called the host part, identifies which particular machine it is on the network.

IP Address Classes

IP addresses are divided into classes to define the large, medium, and small networks.

Class A addresses are assigned to larger networks.

Class B addresses are used for medium-sized networks, &

Class C for small networks.

Identifying Address Classes

Address Class Prefixes

To accommodate different size networks and aid in classifying these networks, IP addresses are divided into groups called classes.This is classful addressing.

Network and Host Division

Each complete 32-bit IP address is broken down into a network part and a host part. A bit or bit sequence at the start of each address determines the class of the address. There are 5 IP address classes.

Class A Addresses

The Class A address was designed to support extremely large networks, with more than 16 million host addresses available. Class A IP addresses use only the first octet to indicate the network address. The remaining three octets provide for host addresses.

Class B Addresses

The Class B address was designed to support the needs of moderate to large-sized networks.A Class B IP address uses the first two of the four octets to indicate the network address. The other two octets specify host addresses.

Class C Addresses

The Class C address space is the most commonly used of the original address classes.This address space was intended to support small networks with a maximum of 254 hosts.

Class D Addresses

The Class D address class was created to enable multicasting in an IP address. A multicast address is a unique network address that directs packets with that destination address to predefined groups of IP addresses. Therefore, a single station can simultaneously transmit a single stream of data to multiple recipients.

Class E Addresses

A Class E address has been defined. However, the Internet Engineering Task Force (IETF) reserves these addresses for its own research. Therefore, no Class E addresses have been released for use in the Internet.

IP Address Ranges

The graphic below shows the IP address range of the first octet both in decimal and binary for each IP address class.

IPv4

As early as 1992, the Internet Engineering Task Force (IETF) identified two specific concerns: Exhaustion of the remaining, unassigned IPv4 network addresses and the increase in the size of Internet routing tables.

Over the past two decades, numerous extensions to IPv4 have been developed. Two of the more important of these are subnet masks and classless interdomain routing (CIDR).

Finding the Network Address with ANDing

By ANDing the Host address of 192.168.10.2 with 255.255.255.0

(its network mask) we obtain the network address of 192.168.10.0

Network Address

Broadcast Address

Network/Broadcast Addresses
at the Binary Level

An IP address that has binary 0s in all host bit positions is reserved for the network address, which identifies the network. An IP address that has binary 1s in all host bit positions is reserved for the broadcast address, which is used to send data to all hosts on the network. Here are some examples:

ClassNetwork AddressBroadcast Address

A100.0.0.0100.255.255.255

B150.75.0.0150.75.255.255

C200.100.50.0200.100.50.255

Public IP Addresses

Unique addresses are required for each device on a network.

Originally, an organization known as the Internet Network Information Center (InterNIC) handled this procedure.

InterNIC no longer exists and has been succeeded by the Internet Assigned Numbers Authority (IANA).

No two machines that connect to a public network can have the same IP address because public IP addresses are global and standardized.

All machines connected to the Internet agree to conform to the system.

Public IP addresses must be obtained from an Internet service provider (ISP) or a registry at some expense.

Private IP Addresses

Private IP addresses are another solution to the problem of the impending exhaustion of public IP addresses.As mentioned, public networks require hosts to have unique IP addresses.

However, private networks that are not connected to the Internet may use any host addresses, as long as each host within the private network is unique.

Mixing Public and
Private IP Addresses

Private IP addresses can be intermixed, as shown in the graphic, with public IP addresses.This will conserve the number of addresses used for internal connections. Connecting a network using private addresses to the Internet requires translation of the private addresses to public addresses. This translation process is referred to as Network Address Translation (NAT).

Introduction to Subnetting

Subnetting a network means to use the subnet mask to divide the network and break a large network up into smaller, more efficient and manageable segments, or subnets.

With subnetting, the network is not limited to the default Class A, B, or C network masks and there is more flexibility in the network design.

Subnet addresses include the network portion, plus a subnet field and a host field.The ability to decide how to divide the original host portion into the new subnet and host fields provides addressing flexibility for the network administrator.

The 32-Bit
Binary IP Address

Numbers That Show Up In Subnet Masks (Memorize Them!)

Addressing with Subnetworks

Obtaining an Internet Address

Static Assignment of an IP Address

Static assignment works best on small networks.

The administrator manually assigns and tracks IP addresses for each computer, printer, or server on the intranet.

Network printers, application servers, and routers should be assigned static IP addresses.

ARP
(Address Resolution Protocol)

Fig. 32 How does ARP work? (TI1332EU02TI_0004 The Network Layer, 47)

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Host A

Host B

IP Address: 128.0.10.4

HW Address: 080020021545

ARP Reply

ARP Request - Broadcast to all hosts

What is the hardware address for IP address 128.0.10.4?

Fig. 33 The ARP command (TI1332EU02TI_0004 The Network Layer, 47)

host B would reply

no one would reply

Fig. 34 Proxy-ARP concept (TI1332EU02TI_0004 The Network Layer, 49)

B

A

1 Network = 1 Broadcast Domain

Broadcast: ARP request

B

A

Router

2 Networks = 2 Broadcast Domains

Broadcast: ARP request

Broadcast Message to all:

If your IP address matches B

then please tell me your

Ethernet address

Yes, I know the destination

network, let me give you my

Ethernet address

I take care, to forward

IP packets to B

A

Router R

B

A

B

RARP

Reverse Address Resolution Protocol (RARP) associates a known MAC addresses with an IP addresses.

A network device, such as a diskless workstation, might know its MAC address but not its IP address. RARP allows the device to make a request to learn its IP address.

Devices using RARP require that a RARP server be present on the network to answer RARP requests.

BootP

The bootstrap protocol (BOOTP) operates in a client-server environment and only requires a single packet exchange to obtain IP information.

However, unlike RARP, BOOTP packets can include the IP address, as well as the address of a router, the address of a server, and vendor-specific information.

One problem with BOOTP, however, is that it was not designed to provide dynamic address assignment. With BOOTP, a network administrator creates a configuration file that specifies the parameters for each device.The administrator must add hosts and maintain the BOOTP database.

Even though the addresses are dynamically assigned, there is still a one to one relationship between the number of IP addresses and the number of hosts.

This means that for every host on the network there must be a BOOTP profile with an IP address assignment in it. No two profiles can have the same IP address.

DHCP

Dynamic host configuration protocol (DHCP) is the successor to BOOTP.

Unlike BOOTP, DHCP allows a host to obtain an IP address dynamically without the network administrator having to set up an individual profile for each device.

All that is required when using DHCP is a defined range of IP addresses on a DHCP server.As hosts come online, they contact the DHCP server and request an address.

The DHCP server chooses an address and leases it to that host.

With DHCP, the entire network configuration of a computer can be obtained in one message.

This includes all of the data supplied by the BOOTP message, plus a leased IP address and a subnet mask.

The major advantage that DHCP has over BOOTP is that it allows users to be mobile.

Introduction to Routers

A router is a special type of computer. It has the same basic components as a standard desktop PC. However, routers are designed to perform some very specific functions. Just as computers need operating systems to run software applications, routers need the Internetwork Operating System software (IOS) to run configuration files. These configuration files contain the instructions and parameters that control the flow of traffic in and out of the routers. The many parts of a router are shown below:

RAM

Random Access Memory, also called dynamic RAM (DRAM)

RAM has the following characteristics and functions:
Stores routing tables Holds ARP cache Holds fast-switching cache Performs packet buffering (shared RAM) Maintains packet-hold queues Provides temporary memory for the configuration file of the router while the router is powered on Loses content when router is powered down or restarted

NVRAM

Non-Volatile RAM

NVRAM has the following characteristics and functions:
Provides storage for the startup configuration file Retains content when router is powered down or restarted

Flash

Flash memory has the following characteristics and functions:
Holds the operating system image (IOS) Allows software to be updated without removing and replacing chips on the processor Retains content when router is powered down or restarted Can store multiple versions of IOS software
Is a type of electronically erasable, programmable ROM (EEPROM)

ROM

Read-Only Memory

ROM has the following characteristics and functions:
Maintains instructions for power-on self test (POST) diagnostics Stores bootstrap program and basic operating system software Requires replacing pluggable chips on the motherboard for software upgrades

Interfaces

Interfaces have the following characteristics and functions:
Connect router to network for frame entry and exit Can be on the motherboard or on a separate module
Types of interfaces:
EthernetFast EthernetSerialToken ringISDN BRILoopbackConsoleAux

Internal Components of a 2600 Router

External Components of a 2600 Router

External Connections

Fixed Interfaces

When cabling routers for serial connectivity, the routers will either have fixed or modular ports. The type of port being used will affect the syntax used later to configure each interface. Interfaces on routers with fixed serial ports are labeled for port type and port number.

Modular Serial Port Interfaces

Interfaces on routers with modular serial ports are labeled for port type, slot, and port number.The slot is the location of the module.To configure a port on a modular card, it is necessary to specify the interface using the syntax port type slot number/port number. Use the label serial 0/1, when the interface is serial, the slot number where the module is installed is slot 0, and the port that is being referenced is port 1.

Routers & DSL Connections

The Cisco 827 ADSL router has one asymmetric digital subscriber line (ADSL) interface. To connect a router for DSL service, use a phone cable with RJ-11 connectors. DSL works over standard telephone lines using pins 3 and 4 on a standard RJ-11 connector.

Computer/Terminal Console Connection

Modem Connection to Console/Aux Port

HyperTerminal Session Properties

Establishing a
HyperTerminal Session

Take the following steps to connect a terminal to the console port on the router:

First, connect the terminal using the RJ-45 to RJ-45 rollover cable and an RJ-45 to DB-9 or RJ-45 to DB-25 adapter.

Then, configure the terminal or PC terminal emulation software for 9600 baud, 8 data bits, no parity, 1 stop bit, and no flow control.

Cisco IOS

Cisco technology is built around the Cisco Internetwork Operating System (IOS), which is the software that controls the routing and switching functions of internetworking devices.

A solid understanding of the IOS is essential for a network administrator.

The Purpose of Cisco IOS

As with a computer, a router or switch cannot function without an operating system. Cisco calls its operating system the Cisco Internetwork Operating System or Cisco IOS.

It is the embedded software architecture in all of the Cisco routers and is also the operating system of the Catalyst switches.

Without an operating system, the hardware does not have any capabilities.

The Cisco IOS provides the following network services:
Basic routing and switching functions Reliable and secure access to networked resources Network scalability

Router Command Line Interface

Setup Mode

Setup is not intended as the mode for entering complex protocol features in the router. The purpose of the setup mode is to permit the administrator to install a minimal configuration for a router, unable to locate a configuration from another source.

In the setup mode, default answers appear in square brackets [ ] following the question. Press the Enter key to use these defaults.

During the setup process, Ctrl-C can be pressed at any time to terminate the process. When setup is terminated using Ctrl-C, all interfaces will be administratively shutdown.

When the configuration process is completed in setup mode, the following options will be displayed:

[0] Go to the IOS command prompt without saving this config.
[1] Return back to the setup without saving this config.
[2] Save this configuration to nvram and exit.
Enter your selection [2]:

Operation of Cisco IOS Software

The Cisco IOS devices have three distinct operating environments or modes:
ROM monitor Boot ROM Cisco IOS
The startup process of the router normally loads into RAM and executes one of these operating environments. The configuration register setting can be used by the system administrator to control the default start up mode for the router.

To see the IOS image and version that is running, use the show version command, which also indicates the configuration register setting.

IOS File System Overview

Initial Startup of Cisco Routers

A router initializes by loading the bootstrap, the operating system, and a configuration file.

If the router cannot find a configuration file, it enters setup mode.

Upon completion of the setup mode a backup copy of the configuration file may be saved to nonvolatile RAM (NVRAM).

The goal of the startup routines for Cisco IOS software is to start the router operations. To do this, the startup routines must accomplish the following:
Make sure that the router hardware is tested and functional. Find and load the Cisco IOS software. Find and apply the startup configuration file or enter the setup mode.
When a Cisco router powers up, it performs a power-on self test (POST). During this self test, the router executes diagnostics from ROM on all hardware modules.

After the Post

After the POST, the following events occur as the router initializes:

Step 1

The generic bootstrap loader in ROM executes. A bootstrap is a simple set of instructions that tests hardware and initializes the IOS for operation.

Step 2

The IOS can be found in several places. The boot field of the configuration register determines the location to be used in loading the IOS. If the boot field indicates a flash or network load, boot system commands in the configuration file indicate the exact name and location of the image.

Step 3

The operating system image is loaded.

Step 4

The configuration file saved in NVRAM is loaded into main memory and executed one line at a time. The configuration commands start routing processes, supply addresses for interfaces, and define other operating characteristics of the router.

Step 5

If no valid configuration file exists in NVRAM, the operating system searches for an available TFTP server. If no TFTP server is found, the setup dialog is initiated.

Step in Router Initialization

Router LED Indicators

Cisco routers use LED indicators to provide status information. Depending upon the Cisco router model, the LED indicators will vary. An interface LED indicates the activity of the corresponding interface. If an LED is off when the interface is active and the interface is correctly connected, a problem may be indicated. If an interface is extremely busy, its LED will always be on. The green OK LED to the right of the AUX port will be on after the system initializes correctly.

Enhanced
Cisco IOS Commands

The show version Command

The show version command displays information about the Cisco IOS software version that is currently running on the router. This includes the configuration register and the boot field settings.

The following information is available from the show version command:

IOS version and descriptive information
Bootstrap ROM version Boot ROM version Router up time Last restart method System image file and location Router platform Configuration register setting
Use the show version command to identify router IOS image and boot source. To find out the amount of flash memory, issue the show flash command.

Router User Interface Modes

The Cisco command-line interface (CLI) uses a hierarchical structure. This structure requires entry into different modes to accomplish particular tasks.

Each configuration mode is indicated with a distinctive prompt and allows only commands that are appropriate for that mode.

As a security feature the Cisco IOS software separates sessions into two access levels, user EXEC mode and privileged EXEC mode. The privileged EXEC mode is also known as enable mode.

Overview of Router Modes

Router Modes

User Mode Commands

Privileged Mode Commands

NOTE:

There are many more commands available in privileged mode.

Specific Configuration Modes

CLI Command Modes

All command-line interface (CLI) configuration changes to a Cisco router are made from the global configuration mode. Other more specific modes are entered depending upon the configuration change that is required.

Global configuration mode commands are used in a router to apply configuration statements that affect the system as a whole.

The following command moves the router into global configuration mode

Router#configure terminal (or config t)
Router(config)#

When specific configuration modes are entered, the router prompt changes to indicate the current configuration mode.

Typing exit from one of these specific configuration modes will return the router to global configuration mode. Pressing Ctrl-Z returns the router to all the way back privileged EXEC mode.

Configuring a Routers Name

A router should be given a unique name as one of the first configuration tasks.

This task is accomplished in global configuration mode using the following commands:

Router(config)#hostname Tokyo
Tokyo(config)#

As soon as the Enter key is pressed, the prompt changes from the default host name (Router) to the newly configured host name (which is Tokyo in the example above).

Setting
the Clock
with Help

Message Of The Day (MOTD)

A message-of-the-day (MOTD) banner can be displayed on all connected terminals.

Enter global configuration mode by using the command config t

Enter the command

banner motd # The message of the day goes here #.

Save changes by issuing the command copy run start

Configuring a Console Password

Passwords restrict access to routers.

Passwords should always be configured for virtual terminal lines and the console line.

Passwords are also used to control access to privileged EXEC mode so that only authorized users may make changes to the configuration file.

The following commands are used to set an optional but recommended password on the console line:

Router(config)#line console 0
Router(config-line)#password
Router(config-line)#login

Configuring a Modem Password

If configuring a router via a modem you are most likely connected to the aux port.

The method for configuring the aux port is very similar to configuring the console port.

Router(config)#line aux 0

Configuring Interfaces

An interface needs an IP Address and a Subnet Mask to be configured.

All interfaces are shutdown by default.

The DCE end of a serial interface needs a clock rate.

Router#config t
Router(config)#interface serial 0/1

Router(config-if)#ip address 200.100.50.75 255.255.255.240
Router(config-if)#clock rate 56000 (required for serial DCE only)
Router(config-if)#no shutdown

Router(config-if)#exit

Router(config)#int f0/0
Router(config-if)#ip address 150.100.50.25 255.255.255.0

Router(config-if)#no shutdown

Router(config-if)#exit

Router(config)#exit

Router#

On older routers, Serial 0/1 would be just Serial 1 and f0/0 would be e0.

s = seriale = Ethernetf = fast Ethernet

Configuring a Telnet Password

A password must be set on one or more of the virtual terminal (VTY) lines for users to gain remote access to the router using Telnet.

Typically Cisco routers support five VTY lines numbered 0 through 4.

The following commands are used to set the same password on all of the VTY lines:

Router(config)#line vty 0 4

Examining the show Commands

There are many show commands that can be used to examine the contents of files in the router and for troubleshooting. In both privileged EXEC and user EXEC modes, the command show ? provides a list of available show commands. The list is considerably longer in privileged EXEC mode than it is in user EXEC mode.

show interfaces Displays all the statistics for all the interfaces on the router. show int s0/1 Displays statistics for interface Serial 0/1

show controllers serial Displays information-specific to the interface hardware

show clock Shows the time set in the router

show hosts Displays a cached list of host names and addresses

show users Displays all users who are connected to the router

show history Displays a history of commands that have been entered

show flash Displays info about flash memory and what IOS files are stored there

show version Displays info about the router and the IOS that is running in RAM

show ARP Displays the ARP table of the router

show start Displays the saved configuration located in NVRAM

show run Displays the configuration currently running in RAM

show protocol Displays the global and interface specific status of any configured

Layer 3 protocols

Ethernet Overview

Ethernet is now the dominant LAN technology in the world.

Ethernet is not one technology but a family of LAN technologies.

All LANs must deal with the basic issue of how individual stations (nodes) are named, and Ethernet is no exception.

Ethernet specifications support different media, bandwidths, and other Layer 1 and 2 variations.

However, the basic frame format and addressing scheme is the same for all varieties of Ethernet.

Ethernet and the OSI Model

Ethernet operates in two areas of the OSI model, the lower half of the data link layer, known as the MAC sublayer and the physical layer

Ethernet Technologies
Mapped to the OSI Model

Layer 2 Framing

Framing is the Layer 2 encapsulation process.

A frame is the Layer 2 protocol data unit.

The frame format diagram shows different groupings of bits (fields) that perform other functions.

Ethernet and IEEE Frame Formats are Very Similar

3 Common Layer 2 Technologies

Ethernet

Uses CSMA/CD logical bus topology (information flow is on a linear bus) physical star or extended star (wired as a star)

Token Ring

logical ring topology (information flow is controlled in a ring) and a physical star topology (in other words, it is wired as a star)

FDDI

logical ring topology (information flow is controlled in a ring) and physical dual-ring topology(wired as a dual-ring)

Collision Domains

To move data between one Ethernet station and another, the data often passes through a repeater.

All other stations in the same collision domain see traffic that passes through a repeater.

A collision domain is then a shared resource. Problems originating in one part of the collision domain will usually impact the entire collision domain.

CSMA/CD Graphic

Backoff

After a collision occurs and all stations allow the cable to become idle (each waits the full interframe spacing), then the stations that collided must wait an additional and potentially progressively longer period of time before attempting to retransmit the collided frame.

The waiting period is intentionally designed to be random so that two stations do not delay for the same amount of time before retransmitting, which would result in more collisions.

Hierarchical Addressing Using
Variable-Length Subnet Masks


*

Prefix Length and Network Mask

Range of Addresses: 192.168.1.64 through 192.168.1.79
Have the first 28 bits in common, which is represented by a /28 prefix length28 bits in common can also be represented in dotted decimal as 255.255.255.240
In the IP network number that accompanies the network mask, when the host bits of the IP network number are:
All binary zeros that address is the bottom of the address rangeAll binary ones that address is the top of the address range
Binary ones in the network mask represent network bits in the accompanying IP address; binary zeros represent host bits

11000000.10101000.00000001.0100xxxxIP Address

11111111.11111111.11111111.11110000Network Mask

Fourth Octet
6401000000650100000166010000106701000011680100010069010001017001000110710100011172010010007301001001740100101075010010117601001100770100110178010011107901001111

Implementing VLSM

Range Of Addresses for VLSM

Breakdown Address Space for Largest Subnet

Breakdown Address Space for Ethernets at Remote Sites

Break Down Remaining Address Space for Serial Subnets

Calculating VLSM: Binary

Route Summarization and Classless Interdomain Routing


*

What Is Route Summarization?

Summarizing Within an Octet

Summarizing Addresses in a VLSM-Designed Network

Classless Interdomain Routing
CIDR is a mechanism developed to alleviate exhaustion of addresses and reduce routing table size.Block addresses can be summarized into single entries without regard to the classful boundary of the network number.Summarized blocks are installed in routing tables.

What Is CIDR?
Addresses are the same as in the route summarization figure, except that
Class B network 172 has been replaced by Class C network 192.

CIDR Example

Anatomy of an IP Packet

IP packets consist of the data from upper layers plus an IP header. The IP header consists of the following:

Administrative Distance

The administrative distance is an optional parameter that gives a measure of the reliability of the route. The range of an AD is 0-255 where smaller numbers are more desireable.

The default administrative distance when using next-hop address is 1, while the default administrative distance when using the outgoing interface is 0. You can statically assign an AD as follows:

Router(config)#ip route 172.16.3.0 255.255.255.0 172.16.4.1 130

Sometimes static routes are used for backup purposes. A static route can be configured on a router that will only be used when the dynamically learned route has failed. To use a static route in this manner, simply set the administrative distance higher than that of the dynamic routing protocol being used.

Configuring Default Routes

Default routes are used to route packets with destinations that do not match any of the other routes in the routing table.

A default route is actually a special static route that uses this format:

ip route 0.0.0.0 0.0.0.0 [next-hop-address | outgoing interface]

This is sometimes referred to as a Quad-Zero route.

Example using next hop address:

Router(config)#ip route 0.0.0.0 0.0.0.0 172.16.4.1

Example using the exit interface:

Router(config)#ip route 0.0.0.0 0.0.0.0 s0/0

Verifying Static
Route Configuration

After static routes are configured it is important to verify that they are present in the routing table and that routing is working as expected.

The command show running-config is used to view the active configuration in RAM to verify that the static route was entered correctly.

The show ip route command is used to make sure that the static route is present in the routing table.

Path Determination Graphic

What is

an optimal

route ?

Router

Router

Router

Router

Router

Switch

Switch

Routing Protocol

Routing Protocols

Routing protocols includes the following:

processes for sharing route information allows routers to communicate with other routers to update and maintain the routing tables

Examples of routing protocols that support the IP routed protocol are:

RIP, IGRP,

OSPF, BGP,

and EIGRP.

Routed Protocols

Protocols used at the network layer that transfer data from one host to another across a router are called routed or routable protocols. The Internet Protocol (IP) and Novell's Internetwork Packet Exchange (IPX) are examples of routed protocols. Routers use routing protocols to exchange routing tables and share routing information. In other words, routing protocols enable routers to route routed protocols.

Autonomous System

AS 2000

AS 3000

AS 1000

An Autonomous System (AS) is a group of IP networks, which has a single and clearly defined external routing policy.

Fig. 48 IGP and EGP (TI1332EU02TI_0004 The Network Layer, 67)

IGP

Interior Gateway Protocols are

used for routing decisions

within an Autonomous System.

Exterior Gateway

Protocols are used

for routing between

Autonomous Systems

EGP

IGP

Interior Gateway Protocol

(IGP)

Interior Gateway Protocol

(IGP)

AS 1000

AS 2000

AS 3000

Fig. 49 The use of IGP and EGP protocols (TI1332EU02TI_0004 The Network Layer, 67)

Exterior Gateway

Protocol (EGP)

EGP

EGP

EGP

IGP and EGP

An autonomous system is a network or set of networks under common administrative control, such as the cisco.com domain.

Categories of Routing Protocols

Most routing algorithms can be classified into one of two categories:
distance vector link-state
The distance vector routing approach determines the direction (vector) and distance to any link in the internetwork.

The link-state approach, also called shortest path first, recreates the exact topology of the entire internetwork.

Distance Vector
Routing Concepts

Distance Vector Routing (DVR)

Destination

192.16.1.0

192.16.5.0

192.16.7.0

Distance

1

1

2

Router B

Router C

Router A

Router D

2 Hops

1 Hop

1 Hop

Routing table contains the addresses

of destinations and the distance

of the way to this destination.

Flow of routing

information

192.16.1.0

192.16.7.0

192.16.5.0

Routing Tables Graphic

Distance Vector
Topology Changes

Router Metric Components


Router C

Router A

Router D

Router B

192.16.1.0

192.16.2.0

192.16.4.0

192.16.5.0

192.16.6.0

192.16.6.0

192.16.7.0

192.16.2.0

192.16.3.0

192.16.4.0

0

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192.16.5.0

192.16.3.0

192.16.2.0

192.16.4.0

192.16.6.0

192.16.4.0

192.16.5.0

192.16.6.0

192.16.6.0

192.16.7.0

192.16.1.0

192.16.2.0

192.16.2.0

192.16.3.0

192.16.4.0

192.16.3.0

192.16.4.0

192.16.1.0

192.16.5.0

192.16.6.0

192.16.3.0

192.16.2.0

192.16.7.0

192.16.5.0

192.16.4.0

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C

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D

C

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L

Locally connected


Fig. 53 Distribution of routing information with distance vector routing protocol (cont.) (TI1332EU02TI_0004 The Network Layer, 71)

192.16.4.0

192.16.5.0

192.16.6.0

192.16.6.0

192.16.7.0

192.16.1.0

192.16.2.0

192.16.2.0

192.16.3.0

192.16.4.0

192.16.3.0

192.16.4.0

192.16.1.0

192.16.5.0

192.16.6.0

192.16.3.0

192.16.2.0

192.16.7.0

192.16.5.0

192.16.4.0

192.16.5.0

192.16.6.0

192.16.7.0

192.16.1.0

192.16.3.0

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192.16.4.0

192.16.5.0

192.16.6.0

192.16.6.0

192.16.7.0

192.16.1.0

192.16.2.0

192.16.2.0

192.16.3.0

192.16.4.0

192.16.3.0

192.16.4.0

192.16.1.0

192.16.5.0

192.16.6.0

192.16.3.0

192.16.2.0

192.16.7.0

192.16.5.0

192.16.4.0

192.16.5.0

192.16.6.0

192.16.7.0

192.16.1.0

192.16.3.0

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RIPv1

Distance Vector Routing Protocol,

classful

Distribution of Routing Tables via broadcast

to adjacent routers

Only one kind of metric:

Number of Hops

Connections with different

bandwidth can not be weighted

Routing loops can occur

-> bad convergence in case of a failure

Count to infinity problem

(infinity = 16)

Maximum network size is limited

by the number of hops

Fig. 59 Properties of RIPv1 (TI1332EU02TI_0004 The Network Layer, 81)

RIP Characteristics

200.14.13.0/24

130.24.13.0/24

Port 2

200.14.13.2/24

Port 1

130.24.13.1/24

130.24.36.0/24

130.24.25.0/24

RIP-1 permits only a Single Subnet Mask

Fig. 60 RIP-1 permits only a single subnet mask (TI1332EU02TI_0004 The Network Layer, 83)

Router A

RIP-1: 130.24.36.0

RIP-1: 130.24.36.0

RIP-1: 130.24.0.0

Router Configuration

The router command starts a routing process.

The network command is required because it enables the routing process to determine which interfaces participate in the sending and receiving of routing updates.

An example of a routing configuration is:

GAD(config)#router rip
GAD(config-router)#network 172.16.0.0

The network numbers are based on the network class addresses, not subnet addresses or individual host addresses.

Configuring RIP Example

Verifying RIP Configuration

The debug ip rip Command

Most of the RIP configuration errors involve an incorrect network statement, discontiguous subnets, or split horizons. One highly effective command for finding RIP update issues is the debug ip rip command. The debug ip rip command displays RIP routing updates as they are sent and received.

Problem: Routing Loops

Routing loops can occur when inconsistent routing tables are not updated due to slow convergence in a changing network.

Problem: Counting to Infinity

Solution: Define a Maximum

Solution: Split Horizon

Route Poisoning

Route poisoning is used by various distance vector protocols in order to overcome large routing loops and offer explicit information when a subnet or network is not accessible. This is usually accomplished by setting the hop count to one more than the maximum.

Triggered Updates

New routing tables are sent to neighboring routers on a regular basis.

For example, RIP updates occur every 30 seconds.

However a triggered update is sent immediately in response to some change in the routing table.

The router that detects a topology change immediately sends an update message to adjacent routers that, in turn, generate triggered updates notifying their adjacent neighbors of the change.

When a route fails, an update is sent immediately rather than waiting on the update timer to expire.

Triggered updates, used in conjunction with route poisoning, ensure that all routers know of failed routes before any holddown timers can expire.

Triggered Updates Graphic

Solution: Holddown Timers

IGRP

Interior Gateway Routing Protocol (IGRP) is a proprietary protocol developed by Cisco.

Some of the IGRP key design characteristics emphasize the following:
It is a distance vector routing protocol. Routing updates are broadcast every 90 seconds.Bandwidth, load, delay and reliability are used to
create a composite metric.

IGRP Stability Features

IGRP has a number of features that are designed to enhance its stability, such as:
Holddowns Split horizons Poison reverse updates
Holddowns
Holddowns are used to prevent regular update messages from inappropriately reinstating a route that may not be up.

Split horizons
Split horizons are derived from the premise that it is usually not useful to send information about a route back in the direction from which it came.

Poison reverse updates
Split horizons prevent routing loops between adjacent routers, but poison reverse updates are necessary to defeat larger routing loops.

Today, IGRP is showing its age, it lacks support for variable length subnet masks (VLSM). Rather than develop an IGRP version 2 to correct this problem, Cisco has built upon IGRP's legacy of success with Enhanced IGRP.

Configuring IGRP

Routing Metrics Graphics

Link State Concepts

Link State Topology Changes

LSP:

My links to

R2 and R4 are up

LSP: My links to

R1 and R3 are up,

my link to R4 is down.

LSP: My links to

R2 and R4 are up.

LSP:

My links to R1 and R3 are up.

My link to R2 is down.

Link State Routing (LSR)

LSP....link state packet

SPF... shortest path first

Router 1

Router 4

Router 2

Router 3

SPF

Routing

Table

Link State Concerns

2

1

4

2

4

1

B - 2

C - 1

A - 2

D - 4

A - 1

D - 2

E - 4

C - 2

B - 4

E - 1

C - 4

D - 1

Router A

Router B

Router C

Router D

Router E

Link State Database

Link State Routing (LSR)

Router A

Router C

Router B

Router D

Router E

A

C

B

D

E

A

D

E

C

B

D

A

E

B

C

E

C

B

A

D

Link State Routing Features

Link-state algorithms are also known as Dijkstras algorithm or as SPF (shortest path first) algorithms.

Link-state routing algorithms maintain a complex database of topology information.

The distance vector algorithm are also known as Bellman-Ford algorithms. They have nonspecific information about distant networks and no knowledge of distant routers.

A link-state routing algorithm maintains full knowledge of distant routers and how they interconnect. Link-state routing uses:
Link-state advertisements (LSAs)
A link-state advertisement (LSA) is a small packet of routing information

that is sent between routers.
Topological database
A topological database is a collection of information gathered from LSAs.
SPF algorithm
The shortest path first (SPF) algorithm is a calculation performed on the

database resulting in the SPF tree.
Routing tables A list of the known paths and interfaces.

Link State Routing

Comparing Routing Methods

OSPF (Open Shortest Path First) Protocol


*

OSPF is a Link-State Routing Protocols
Link-state (LS) routers recognize much more information about the network than their distance-vector counterparts,Consequently LS routers tend to make more accurate decisions.Link-state routers keep track of the following:Their neighboursAll routers within the same areaBest paths toward a destination

Link-State Data Structures
Neighbor table: Also known as the adjacency database
(list of recognized neighbors)Topology table: Typically referred to as LSDB
(routers and links in the area or network) All routers within an area have an identical LSDBRouting table:Commonly named a forwarding database
(list of best paths to destinations)

OSPF vs. RIP

RIP is limited to 15 hops, it converges slowly, and it sometimes chooses slow routes because it ignores critical factors such as bandwidth in route determination. OSPF overcomes these limitations and proves to be a robust and scalable routing protocol suitable for the networks of today.

OSPF Terminology

The next several slides explain various OSPF terms -one per slide.

OSPF Term: Link

OSPF Term: Link State

OSPF Term: Area

OSPF Term: Link Cost

OSPF Term: Forwarding Database

OSPF Term: Adjacencies Database

OSPF Terms: DR & BDR

Link-State Data Structure:
Network Hierarchy
Link-state routing requires a hierachical
network structure that is enforced by OSPF.This two-level hierarchy consists of the following: Transit area (backbone or area 0) Regular areas (nonbackbone areas)

OSPF Areas

Area Terminology

LS Data Structures: Adjacency Database
Routers discover neighbors by exchanging
hello packets.Routers declare neighbors to be up after checking
certain parameters or options in the hello packet.Point-to-point WAN links:Both neighbors become fully adjacent.LAN links:Neighbors form an adjacency with the DR and BDR.Maintain two-way state with the other routers (DROTHERs).Routing updates and topology information are only passed between adjacent routers.

OSPF Adjacencies

Routers build logical adjacencies between each other using the Hello Protocol. Once an adjacency is formed:
LS database packets are exchanged to synchronize
each others LS databases. LSAs are flooded reliably throughout the area or network
using these adjacencies.

Open Shortest Path First Calculation
Routers find the best paths to destinations by applying Dijkstras SPF algorithm to the link-state database as follows:Every router in an area has the identical
link-state database.Each router in the area places itself into
the root of the tree that is built.The best path is calculated with respect to the
lowest total cost of links to a specific destination.Best routes are put into the forwarding database.

OSPF Packet Types

OSPF Packet Header Format

Neighborship

Establishing Bidirectional Communication

Establishing Bidirectional Communication (Cont.)

Establishing Bidirectional Communication

Discovering the Network Routes

Adding the Link-State Entries

Adding the Link-State Entries (Cont.)

Adding the Link-State Entries

Maintaining Routing Information
Router A notifies all OSPF DRs on 224.0.0.6

Maintaining Routing Information (Cont.)
Router A notifies all OSPF DRs on 224.0.0.6 DR notifies others on 224.0.0.5

Maintaining Routing Information
Router A notifies all OSPF DRs on 224.0.0.6 DR notifies others on 224.0.0.5

Configuring Basic OSPF: Single Area

router ospf process-id

Router(config)#
Turns on one or more OSPF routing processes in the IOS software.
network address inverse-mask area [area-id]

Router(config-router)#
Router OSPF subordinate command that defines the interfaces (by network number) that OSPF will run on. Each network number must be defined to a specific area.

Configuring OSPF on Internal Routers of a Single Area

Verifying OSPF Operation

show ip protocols

Router#
Verifies the configured IP routing protocol processes, parameters and statistics
show ip route ospf

Router#
Displays all OSPF routes learned by the router
show ip ospf interface

Router#
Displays the OSPF router ID, area ID and adjacency information

Verifying OSPF Operation (Cont.)

show ip ospf

Router#
Displays the OSPF router ID, timers, and statistics
show ip ospf neighbor [detail]

Router#
Displays information about the OSPF neighbors, including Designated Router (DR) and Backup Designated Router (BDR) information on broadcast networks

The show ip route ospf Command

RouterA# show ip route ospf

Codes:C - connected, S - static, I - IGRP, R - RIP, M - mobile,
B - BGP, D - EIGRP, EX - EIGRP external, O - OSPF,
IA - OSPF inter area, E1 - OSPF external type 1,
E2 - OSPF external type 2, E - EGP, i - IS-IS, L1 - IS-IS

level-1, L2 - IS-IS level-2, * - candidate default

Gateway of last resort is not set

10.0.0.0 255.255.255.0 is subnetted, 2 subnets

O 10.2.1.0 [110/10] via 10.64.0.2, 00:00:50, Ethernet0

The show ip ospf interface Command

RouterA# show ip ospf interface e0

Ethernet0 is up, line protocol is up

Internet Address 10.64.0.1/24, Area 0

Process ID 1, Router ID 10.64.0.1, Network Type BROADCAST, Cost: 10

Transmit Delay is 1 sec, State DROTHER, Priority 1

Designated Router (ID) 10.64.0.2, Interface address 10.64.0.2

Backup Designated router (ID) 10.64.0.1, Interface address 10.64.0.1

Timer intervals configured, Hello 10, Dead 40, Wait 40, Retransmit 5

Hello due in 00:00:04

Neighbor Count is 1, Adjacent neighbor count is 1

Adjacent with neighbor 10.64.0.2 (Designated Router)

Suppress hello for 0 neighbor(s)

The show ip ospf neighbor Command

RouterB# show ip ospf neighbor

Neighbor ID Pri State Dead Time Address Interface

10.64.1.1 1 FULL/BDR 00:00:31 10.64.1.1 Ethernet0

10.2.1.1 1 FULL/- 00:00:38 10.2.1.1 Serial0

show ip protocol

show ip route

show ip ospf neighbor detail

show ip ospf database

OSPF Network Types - 1

Point-to-Point Links
Usually a serial interface running either PPP
or HDLC May also be a point-to-point subinterface
running Frame Relay or ATM No DR or BDR election required OSPF autodetects this interface type OSPF packets are sent using multicast 224.0.0.5

Multi-access Broadcast Network
Generally LAN technologies like Ethernet and Token Ring DR and BDR selection required All neighbor routers form full adjacencies with the DR and
BDR only Packets to the DR use 224.0.0.6 Packets from DR to all other routers use 224.0.0.5

Electing the DR and BDR
Hello packets are exchanged via IP multicast. The router with the highest OSPF priority is
selected as the DR. Use the OSPF router ID as the tie breaker. The DR election is nonpreemptive.

Setting Priority for DR Election

ip ospf priority number
This interface configuration command assigns the OSPF priority to an interface.Different interfaces on a router may be assigned different values.The default priority is 1. The range is from 0 to 255.0 means the router is a DROTHER; it cant be the DR or BDR.
Router(config-if)#

OSPF Network Types - 2

Creation of Adjacencies

RouterA# debug ip ospf adj

Point-to-point interfaces coming up: No election

%LINK-3-UPDOWN: Interface Serial1, changed state to up

OSPF: Interface Serial1 going Up

OSPF: Rcv hello from 192.168.0.11 area 0 from Serial1 10.1.1.2

OSPF: End of hello processing

OSPF: Build router LSA for area 0, router ID 192.168.0.10

OSPF: Rcv DBD from 192.168.0.11 on Serial1 seq 0x20C4 opt 0x2 flag 0x7 len 32 state INIT

OSPF: 2 Way Communication to 192.168.0.11 on Serial1, state 2WAY

OSPF: Send DBD to 192.168.0.11 on Serial1 seq 0x167F opt 0x2 flag 0x7 len 32

OSPF: NBR Negotiation Done. We are the SLAVE

OSPF: Send DBD to 192.168.0.11 on Serial1 seq 0x20C4 opt 0x2 flag 0x2 len 72

Creation of Adjacencies (Cont.)

RouterA# debug ip ospf adj

Ethernet interface coming up: Election

OSPF: 2 Way Communication to 192.168.0.10 on Ethernet0, state 2WAY

OSPF: end of Wait on interface Ethernet0

OSPF: DR/BDR election on Ethernet0

OSPF: Elect BDR 192.168.0.12

OSPF: Elect DR 192.168.0.12

DR: 192.168.0.12 (Id) BDR: 192.168.0.12 (Id)

OSPF: Send DBD to 192.168.0.12 on Ethernet0 seq 0x546 opt 0x2 flag 0x7 len 32

OSPF: DR/BDR election on Ethernet0

OSPF: Elect BDR 192.168.0.11

OSPF: Elect DR 192.168.0.12

DR: 192.168.0.12 (Id) BDR: 192.168.0.11 (Id)

Overview

Enhanced Interior Gateway Routing Protocol (EIGRP) is a Cisco-proprietary routing protocol based on Interior Gateway Routing Protocol (IGRP).

Unlike IGRP, which is a classful routing protocol, EIGRP supports CIDR and VLSM.

Compared to IGRP, EIGRP boasts faster convergence times, improved scalability, and superior handling of routing loops.

Furthermore, EIGRP can replace Novell Routing Information Protocol (RIP) and AppleTalk Routing Table Maintenance Protocol (RTMP), serving both IPX and AppleTalk networks with powerful efficiency.

EIGRP is often described as a hybrid routing protocol, offering the best of distance vector and link-state algorithms.

Comparing EIGRP with IGRP

IGRP and EIGRP are compatible with each other.

EIGRP offers multiprotocol support, but IGRP does not.

EIGRP and IGRP use different metric calculations.

EIGRP scales the metric of IGRP by a factor of 256.

IGRP has a maximum hop count of 255.

EIGRP has a maximum hop count limit of 224.

Enabling dissimilar routing protocols such as OSPF and RIP to share information requires advanced configuration. Redistribution, the sharing of routes, is automatic between IGRP and EIGRP as long as both processes use the same autonomous system (AS) number.

EIGRP & IGRP Metric Calculation

Comparing EIGRP with IGRP

EIGRP Concepts & Terminology

EIGRP routers keep route and topology information readily available in RAM, so they can react quickly to changes.

Like OSPF, EIGRP saves this information in several tables and databases.

EIGRP saves routes that are learned in specific ways.

Routes are given a particular status and can be tagged to provide additional useful information.

EIGRP maintains three tables:
Neighbor table Topology table Routing table

Neighbor Table

The neighbor table is the most important table in EIGRP.

Each EIGRP router maintains a neighbor table that lists adjacent routers. This table is comparable to the adjacency database used by OSPF. There is a neighbor table for each protocol that EIGRP supports.

When a neighbor sends a hello packet, it advertises a hold time. The hold time is the amount of time a router treats a neighbor as reachable and operational. In other words, if a hello packet is not heard within the hold time, then the hold time expires.

When the hold time expires, the Diffusing Update Algorithm (DUAL), which is the EIGRP distance vector algorithm, is informed of the topology change and must recalculate the new topology.

Topology Table

The topology table is made up of all the EIGRP routing tables in the autonomous system.

DUAL takes the information supplied in the neighbor table and the topology table and calculates the lowest cost routes to each destination. By tracking this information, EIGRP routers can identify and switch to alternate routes quickly.

The information that the router learns from the DUAL is used to determine the successor route, which is the term used to identify the primary or best route.

A copy is also placed in the topology table.

Every EIGRP router maintains a topology table for each configured network protocol. All learned routes to a destination are maintained in the topology table.

Routing Table

The EIGRP routing table holds the best routes to a destination. This information is retrieved from the topology table. Each EIGRP router maintains a routing table for each network protocol.

A successor is a route selected as the primary route to use to reach a destination.DUAL identifies this route from the information contained in the neighbor and topology tables and places it in the routing table.

There can be up to four successor routes for any particular route. These can be of equal or unequal cost and are identified as the best loop-free paths to a given destination.

A copy of the successor routes is also placed in the topology table.

A feasible successor (FS) is a backup route.These routes are identified at the same time the successors are identified, but they are only kept in the topology table. Multiple feasible successors for a destination can be retained in the topology table although it is not mandatory.

EIGRP Data Structure

Like OSPF, EIGRP relies on different types of packets to maintain its various tables and establish complex relationships with neighbor routers. The five EIGRP packet types are:
Hello Acknowledgment Update Query Reply
EIGRP relies on hello packets to discover, verify, and rediscover neighbor routers.

Rediscovery occurs if EIGRP routers

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