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Chapter 2-Static Routing
CCNA Exploration 4.0
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Objectives
Define the general role a router plays in networks. Describe the directly connected networks, different router
interfaces
Examine directly connected networks in the routing tableand use the CDP protocol
Describe static routes with exit interfaces Describe summary and default route Examine how packets get forwarded when using static
routes Identify how to manage and troubleshoot static routes
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Role of the Router
The router is a special-purpose computer that plays a key role inthe operation of any data network. Routers are primarilyresponsible for interconnecting networks by:
Determining the best path to send packets.
Forwarding packets toward their destination.
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Introducing the topology
Topology Lab Three 1800 series routers connected via WAN links.
Each router connected to a LAN represented by a switch anda PC.
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Cable for LAN/WAN interfaces
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Examining Router Interfaces
Examining Router Interfaces show ip route command used to view routing table
show interfaces command used to show status of an interface
show ip Interface brief command used to show a portion of theinterface information
show running-config command used to show configuration file inRAM
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Configuring an Ethernet Interface
Configuring an Ethernet interface By default all serial and Ethernet interfaces are admintrative down.
To enable an interface use the no shutdown command.
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Logging Synchronous Command
In order to keep the unsolicited output separate from your input,enter line configuration mode for the consoled port and add thelogging synchronous command.
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Configuring a Serial Interfaces
Configuring a Serial interface Enter interface configuration mode
Enter in the ip address and subnet mask
Enter in the clock rate(DCE) and no shut down command
Example:
R1(config)#interface serial 0/0 R1(config-if)#ip address 172.16.2.1 255.255.255.0
R1(config-if)#clock rate 64000
R1(config-if)#no shutdown
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Verifying Changes to the Routing Table
The routing table consists of a list of "known" network addressesthese addresses that are directly connected, configuredstatically, and learned dynamically.
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Verifying Changes to the Routing Table
Observing Routes as They are Added to the Routing Table debug ip routing command will let us see any changes that
the router performs when adding or removing routes.
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Devices on Directly Connected Networks
When a router only has its interfaces configured, and the routingtable contains the directly connected networks but no otherroutes, only devices on those directly connected networks arereachable.
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Devices on Directly Connected Networks
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Cisco Discovery Protocol (CDP)
Network discovery with CDP
CDP is an information-gathering tool used by network administrators toget information about directly connected Cisco devices.
CDP is a proprietary tool that enables you to access a summary ofprotocol and address information about Cisco devices that are directlyconnected.
These advertisements contain information such as the types of devicesthat are connected, the router interfaces they are connected to, theinterfaces used to make the connections, and the model numbers ofthe devices.
Concept of neighbors
2 types of neighbors
Layer 3 neighbors.
Layer 2 neighbors.
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Cisco Discovery Protocol (CDP)
CDP Operation
CDP runs at the Data Link layer connecting the physical media to theupper-layer protocols (ULPs).
Cisco network devices, such as routers that support different Networklayer protocols (for example, IP and Novell IPX), can learn about eachother
CDP provides the following information about each CDP neighbordevice:
Device identifiers
Address list
Port identifier Capabilities list
Platform
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Default Setting
Feature Default Setting
CDP global state Enabled
CDP interface state Enabled
CDP holdtime (packet holdtime inseconds)
180
CDP timer (packets sent every x seconds) 60
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Using CDP for Network Discovery
The information gathered by the CDP protocol can be examinedwith the show cdp neighbors command.
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Using CDP for Network Discovery
Field Definition
Device ID The name of the neighbor device and either theMAC address or the serial number of thisdevice.
Local Intrfce The protocol being used by the connectivitymedia.
Holdtme The remaining amount of time (in seconds) thecurrent device will hold the CDP advertisement
from a sending router before discarding it.
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Using CDP for Network Discovery
Capability(CapabilityCodes)
Capability (type of routing device) of the listedneighboring device.The capability types that can be discovered are:RRouterTTransparent bridge
BSource-routing bridgeSSwitchHHostI device is using IGMPrRepeater
Platform The product number of the device.
Port ID The protocol and port number of the device.
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Using CDP for Network Discovery
To disable CDP on aspecific interfaceafter it has beenenabled, use the noCDP enable
command in interfaceconfiguration mode.
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CDP Commands
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CDP Commands
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CDP Commands
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CDP Commands
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STATIC ROUTING
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Purpose and Command Syntax of ip route
Static routes are commonly used when routing from a network toa stub network.
A stub network is a network accessed by a single route.
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ip route command
RTR(config)# ip routeprefix mask {address |
interface} [distance] [tag tag] [permanent]
prefix IP route prefix for the destination.
mask Prefix mask for the destination.
address IP address of the next hop that can be used to reach
that network.
interface Network interface to use (exit-interface)
distance (Optional) An administrative distance.
tag tag (Optional) Tag value that can be used as a "match" value
for controlling redistribution via route maps. (CCNP Advanced Routing)
Permanent (Optional) Specifies that the route will not be removed,even if the interface shuts down. (CCNP Advanced Routing)
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Configuring Static Routes
Installing a Static Route in the Routing Table
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Configuring Static Routes
Configuring Routes to Two More Remote Networks
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Routing Table Principles and Static Routes
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Routing Table Principles and Static Routes
Applying the Principles
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Resolving to an Exit Interface
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Resolving to an Exit Interface
Exit Interface is Down
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Configuring a Static Route with an Exit Interface
Static routes can be configured with an exit interface, which
allows the routing table to resolve the exit interface in a singlesearch instead of two searches.
d
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ip route command
RTR(config)# ip routeprefix mask {address |
interface} [distance] [tag tag] [permanent]
prefix IP route prefix for the destination.
mask Prefix mask for the destination.
address IP address of the next hop that can be used to reach
that network. interface Network interface to use (exit-interface)
distance (Optional) An administrative distance.
tag tag (Optional) Tag value that can be used as a "match" value
for controlling redistribution via route maps. (CCNP Advanced Routing) Permanent (Optional) Specifies that the route will not be removed,
even if the interface shuts down. (CCNP Advanced Routing)
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Configuring a Static Route with an Exit Interface
Static Route and an Exit Interface
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Modifying Static Routes
There are times when a previously configured static route needs to be
modified: The destination network no longer exists, and therefore the static route
should be deleted.
There is a change in the topology, and either the intermediate addressor the exit interface has to be changed.
V if i h S i R C fi i
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Verifying the Static Route Configuration
Verifying the Static Route Configuration
Use the following commands Step 1 show running-config.
Step 2 verify static route has been entered correctly.
Step 3 show ip route.
Step 4 verify route was configured in routing table. Step 5 issue ping command to verify packets can reach
destination and that Return path is working.
S i R i h E h I f
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Static Routes with Ethernet Interfaces
Ethernet interfaces and ARP. If a static route is configured on an
Ethernet link If the packet is sent to the next-hop router then the destination MAC
address will be the address of the next hops Ethernet interface
This is found by the router consulting the ARP table. If an entryisnt found then an ARP request will be sent out
S i R i h E h I f
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Static Routes with Ethernet Interfaces
Static routes and Ethernet exit interfaces
With Ethernet networks, there may be many different devices sharingthe same multi-access network, including hosts and even multiplerouters. Thefore, router does not know the next-hop IP address andtherefore it cannot determine the destination MAC address for theEthernet frame.
S St ti R t
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Summary Static Routes
Route Summarization
Summarizing Routes to Reduce the Size of the Routing Table Multiple static routes can be summarized into a single static route if:
The destination networks can be summarized into a single networkaddress, and
The multiple static routes all use the same exit-interface or next-hop IP address
S St ti R t
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Summary Static Routes
Configuring a Summary Route
Configuring a summaryroute
Step 1: Delete thecurrent static route
Step 2: Configure thesummary static route
Step 3: Verify the newstatic route
D f lt St ti R t
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Default Static Route
A default static route is a route that will match all packets. Default static
routes are used: When no other routes in the routing table match the packet's
destination IP address. In other words, when a more specific matchdoes not exist. A common use is when connecting a company'sedge router to the ISP network.
When a router has only one other router to which it is connected.This condition is known as a stub router.
Using command: ip route 0.0.0.0 0.0.0.0 {exit Interface, IPNextHop}
D f lt St ti R t
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Default Static Route
Verifying a Default Static Route
St ti R t d P k t F di
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Static Routes and Packet Forwarding
Static Routes and Packet Forwarding
St ti R t d P k t F di
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Static Routes and Packet Forwarding
Static Routes and Packet Forwarding
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Static Routes and Packet Forwarding
Static Routes and Packet Forwarding
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Static Routes and Packet Forwarding
Static Routes and Packet Forwarding
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Static Routes and Packet Forwarding
Static Routes and Packet Forwarding
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Static Routes and Packet Forwarding
Static Routes and Packet Forwarding
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Static Routes and Packet Forwarding
Troubleshooting a Missing Route
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Troubleshooting a Missing Route
Troubleshooting a Missing Route
Tools that can be used to isolate routing problems include: Ping tests end to end connectivity
Traceroute used to discover all of the hops (routers) along thepath between 2 points
Show IP route used to display routing table & ascertain forwardingprocess
Show ip interface brief- used to show status of router interfaces
Show cdp neighbors detail used to gather configurationinformation about directly connected neighbors
Summary
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Summary
Routers
Operate at layer 3 Functions include best path selection & forwarding
packets Connecting Networks
WANs
Serial cables are connected to router serial ports. In the lab environment clock rates must be configured for
DCE
LANs Straight through cables or cross over cables are used to
connect to fastethernet port. (The type of cable useddepends on what devices are being connected)
Cisco Discovery Protocol A layer 2 proprietary protocol Used to discover information about directly connected
Cisco devices
Summary
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Summary
Static Routes
This is a manually configured path that specifies how therouter will get to a certain point using a certain path.
Summary static routes This is several static routes that have been condensed into a
single static route.
Default route It is the route packets use if there is no other possible matchfor their destination in the routing table.
Forwarding of packets when static route are used Zinins 3 routing principles describe how packets are
forwarded
Troubleshooting static routes may require some of thefollowing commands: Ping Traceroute Show IP route Show ip interface brief Show cdp neighbors detail
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