Exp_2-Ch_9-EIGRP-.ppt

© 2007 Cisco Systems, Inc. All rights reserved. Cisco PublicITE PC v4.0Chapter 1 1

EIGRP

Routing Protocols and Concepts – Chapter 9

ITE PC v4.0Chapter 1 2© 2007 Cisco Systems, Inc. All rights reserved. Cisco Public

Introduction


EIGRP

Roots of EIGRP: IGRP-Developed in 1985 to overcome RIPv1’s limited hop count

-Distance vector routing protocol

-Metrics used by IGRP

bandwidth (used by default)

Delay (used by default)

Reliability (not used by default)

Load (not used by default)

-Discontinued support starting with IOS 12.2(13)T & 12.2(R1s4)S


EIGRP EIGRP is a distance vector, classless routing protocol that was

released in 1992 with IOS 9.21. As its name suggests, EIGRP is an enhancement of Cisco

IGRP (Interior Gateway Routing Protocol). Both are Cisco proprietary protocols and only operate on Cisco

routers. The main purpose in Cisco's development of EIGRP was to

create a classless version of IGRP. EIGRP includes several features that are not commonly found in other distance vector routing protocols like RIP (RIPv1 and RIPv2) and IGRP. These features include:

–Reliable Transport Protocol (RTP)–Bounded Updates–Diffusing Update Algorithm (DUAL)–Establishing Adjacencies–Neighbor and Topology Tables

Although EIGRP may act like a link-state routing protocol, it is still a distance vector routing protocol.


EIGRP The Algorithm

–EIGRP uses the Diffusing Update Algorithm (DUAL).

–EIGRP does not send periodic updates and route entries do not age out.

–Only changes in the routing information, such as a new link or a link becoming unavailable cause a routing update to occur.


EIGRP Path Determination

–EIGRP's DUAL maintains a topology table separate from the routing table, which includes both the best path to a destination network and any backup paths that DUAL has determined to be loop-free.

–If a route becomes unavailable, DUAL will search its topology table for a valid backup path.

•If one exists, that route is immediately entered into the routing table.

•If one does not exist, DUAL performs a network discovery process to see if there happens to be a backup path that did not meet the requirement of the feasibility condition.


EIGRP Convergence

–EIGRP does not use holddown timers.

–Instead, loop-free paths are achieved through a system of route calculations (diffusing computations) that are performed in a coordinated fashion among the routers.

–The detail of how this is done is beyond the scope of this course, but the result is faster convergence than traditional distance vector routing protocols.


EIGRPProtocol Dependent Modules (PDM) EIGRP uses PDM to route several

different protocols i.e. IP, IPX & AppleTalk PDMs are responsible for the specific

routing task for each network layer protocol

–As you can see in the figure, EIGRP uses different EIGRP packets and maintains separate neighbor, topology, and routing tables for each Network layer protocol.

How do people route IPX or Appletalk today if they still get either IPX or Appletalk?


EIGRPReliable Transport Protocol (RTP) Purpose of RTP

–Used by EIGRP to transmit and receive EIGRP packets– EIGRP was designed as a Network layer independent routing protocol; therefore, it cannot use the services of UDP or TCP because IPX and Appletalk do not use protocols from the TCP/IP protocol suite.

Characteristics of RTP–Involves both reliable & unreliable delivery of EIGRP packet

Reliable delivery requires acknowledgment from destinationUnreliable delivery does not require an acknowledgement from destination

–Packets can be sent UnicastMulticast

–Using address 224.0.0.10


EIGRPEIGRP’s 5 Packet Types

Hello packets–Used to discover & form adjacencies with neighbors

–EIGRP hello packets are multicasts and use unreliable delivery.

•Hello•Update•ACK•Query•Reply


EIGRP Update packets

–Update packets are used to propagate routing information

–Update packets are sent only when necessary.

–EIGRP updates are sent only to those routers that require it.

–When a new neighbor is discovered, unicast update packets are sent so that the neighbor can build up its topology table.

–In other cases, such as a link-cost change, updates are multicast.

–Updates always are transmitted reliably

Acknowledgement packets–Used to acknowledge receipt of update, query & reply packets

–An acknowledgment packet is a hello packet that has no data.

–EIGRP acknowledgement packets are always sent as an unreliable unicast


•R2 has lost connectivity to the LAN attached to its FastEthernet interface. •R2 immediately sends an unicast Update to R1 and R3 noting the downed route. •R1 and R3 respond with an unicast acknowledgement.


EIGRP Query & Reply packets

Used by DUAL for searching for networks

Queries and replies use reliable delivery.

Query packets can use

Multicast

Reply packet use only

unicast


•R2 has lost connectivity to the LAN and it sends out queries to all EIGRP neighbors.

•All neighbors must send a reply regardless of whether or not they have a route to the downed network.


EIGRP

Query Update Reply Hello Acknowledge

Reliable Reliable Reliable Unreliable(not require acknowledgment )

Unreliable(a hello packet that has no data )

multicast Multicast & unicast

unicast multicast unicast


EIGRP Purpose of Hello Protocol

–To discover neighbors & establish adjacencies with neighbor routers

Characteristics of hello protocol–Time interval for sending hello packet

5 seconds - high bandwidth (greater than T1) 60 seconds - multipoint circuits T1 bandwidth or slower

-Holdtime

This is the maximum time router should wait before declaring a neighbor down

Default holdtime

–3 times hello interval

»15 seconds

»180 seconds


EIGRPEIGRP Bounded Updates

EIGRP only sends update when there is a change in route status

Partial update

–A partial update includes only the route information that has changed

– the whole routing table is NOT sent

Bounded update

–When a route changes, only those devices that are impacted will be notified of the change

EIGRP’s use of partial bounded updates minimizes use of bandwidth


EIGRP

Diffusing Update Algorithm (DUAL)–Purpose

•EIGRP’s primary method for preventing routing loops

•And also hold-down timers and split horizon, too.

–Advantage of using DUAL

•Provides for fast convergence time by keeping a list of loop-free backup routes

–DUAL maintains a list of backup routes it has already determined to be loop-free. If the primary route in the routing table fails, the best backup route is immediately added to the routing table.


EIGRP

Administrative Distance (AD)–Defined as the trustworthiness of the source route

EIGRP default administrative distances–Summary routes = 5

–Internal routes = 90

–Imported routes = 170


EIGRPAuthentication

EIGRP can

– Encrypt routing information

– Authenticate routing information

It is good practice to authenticate transmitted routing information.

– This practice ensures that routers will only accept routing information from other routers that have been configured with the same password or authentication information.

Note: Authentication does not encrypt the router's routing table.

http://www.ciscopress.com/articles/article.asp?p=1171169&seqNum=3


EIGRPNetwork Topology

Topology used is the same as previous chapters with the addition of an ISP router

–ISP router does not physically exist

EIGRP will automatically summarizes at classful boundaries, similar to RIP.


Basic EIGRP Configuration Autonomous System (AS) & Process IDs

–This is a collection of networks under the control of a single authority (reference RFC 1930)

–AS Numbers are assigned by IANA

–Entities needing AS numbersISPInternet Backbone prodiersInstitutions connecting to other institutions using AS numbersThese ISPs and large institutions use the exterior gateway routing protocol or BGP, to propagate routing information.


Basic EIGRP Configuration EIGRP autonomous system

number actually functions as a process ID

–The vast majority of companies and institutions with IP networks do not need an AS number

–The ISP is responsible for the routing of packets within its autonomous system and between other autonomous systems.

Process ID represents an instance of the routing protocol running on a router

ExampleRouter(config)#router eigrp autonomous-system


Basic EIGRP ConfigurationThe router eigrp command

The global command that enables eigrp is

router eigrp autonomous-system

-All routers in the EIGRP routing domain must use the same process ID number (autonomous-system number)


Basic EIGRP ConfigurationThe Network Command

Functions of the network command–Enables interfaces to transmit & receive EIGRP updates

–Includes network or subnet in EIGRP updates

Example–Router(config-router)#network network-address

The network-address is the classful network address for this interface.

a single classful network statement is used on R1 to include both 172.16.1.0/24 and 172.16.3.0/30 subnets:

When EIGRP is configured on R2, DUAL sends a notification message to the console stating that a neighbor relationship with another EIGRP router has been established.


Basic EIGRP Configuration The network Command with a Wildcard Mask

-This option is used when you want to configure EIGRP to advertise specific subnets

-Example

Router(config-router)#network network-address [wildcard-mask]

192.168.10.8 – 192.168.10.11


Basic EIGRP Configuration Router(config-router)#network network-address [wildcard-mask]

Think of a wildcard mask as the inverse of a subnet mask.

The inverse of subnet mask 255.255.255.252 is 0.0.0.3.

To calculate the inverse of the subnet mask, subtract the subnet mask from 255.255.255.255:

255.255.255.255

- 255.255.255.252

---------------

0. 0. 0. 3

Wildcard mask


Basic EIGRP ConfigurationVerifying EIGRP

EIGRP routers must establish adjacencies with their neighbors before any updates can be sent or received

Command used to view neighbor table and verify that EIGRP has established adjacencies with neighbors is

show ip eigrp neighbors

H column - Lists the neighbors in the order they were learned.

SRTT (Smooth Round Trip Timer)

Queue Count - Should always be zero.

RTO (Retransmit Interval) - Used by RTP to manage reliable EIGRP packets.

Sequence Number - Used to track updates, queries, and reply packets.


EIGRP

The show ip protocols command is also used to verify that EIGRP is enabled

Remember, the process ID must be the same on all routers for EIGRP to establish neighbor adjacencies and share routing information.

EIGRP's internal and external administrative distances are also displayed:

–Distance: internal 90 external 170


Basic EIGRP Configuration

Examining the Routing Table

The show ip route command is also used to verify EIGRP

–EIGRP routes are denoted in a routing table by the letter “D”–EIGRP is a classless routing protocol (includes the subnet mask in the routing update), it supports VLSM and CIDR.

By default , EIGRP automatically summarizes routes at major network boundary

–We can disable the automatic summarization with the no auto-summary command. We will examine this in more detail in a later.

We will configure the bandwidth later.


EIGRP Null0 Summary Route EIGRP has automatically included a summary route to Null0

(192.168.10.0/24 and 172.16.0.0/16)

–Null0 is not a physical interface

–In the routing table summary routes are sourced from Null0

Reason: routes are used for advertisement purposes

–EIGRP will automatically include a null0 summary route as child route when 2 conditions are met

At least one subnet is learned via EIGRP

Automatic summarization is enabled

If the packet matches the level 1 parent - the classful network address - but none of the subnets, the packet is discarded.


Basic EIGRP Configuration

R3’s routing table shows that the 172.16.0.0/16 network is automatically summarized by R1 & R3

–R1 and R2 are not propagating the individual subnets because of automatic summarization.

[Tony] We will configure the bandwidth later. Once the bandwidth is reconfigured, you will not see the equal-cost route on R3.


EIGRP Metric CalculationEIGRP Composite Metric & the K Values EIGRP uses the following values in its composite metric

-Bandwidth, delay, reliability, and load (reliability and load are not used)

The composite metric used by EIGRP– formula used has values K1 K5

K1 & K3 = 1K2, K4, K5 = 0


EIGRP Metric Calculation

Using the Bandwidth Command

Modifying the interface bandwidth-Router(config-if)#bandwidth kilobits

Verifying bandwidth –Use the show interface command

Note – bandwidth command does not change the link’s physical bandwidth

–The bandwidth command only modifies the bandwidth metric used by routing protocols such as EIGRP and OSPF.



The EIGRP metric can be determined by examining the

bandwidth delay

The value before change the bandwidth is

2172416



EIGRP uses the lowest bandwidth (BW)in its metric calculation

Calculated BW = reference BW / lowest BW(kbps)

Delay – EIGRP uses the cumulative sum of all outgoing interfaces

Calculated Delay = the sum of outgoing interface delays

EIGRP Metric = calculated BW + calculated delay



10,000,000 is divided by 1024. If the result is not a whole number, then the value is rounded down. In this case, 10,000,000 divided by 1024 equals 9765.625. The .625 is dropped before multiplying by 256. The bandwidth portion of the composite metric is 2,499,840.


End of part 1


DUAL Concepts

The Diffusing Update Algorithm (DUAL) is used to prevent looping

–Successor

–Feasible Distance (FD)

–Feasible Successor (FS)

–Reported Distance (RD) or Advertised Distance (AD)

–Feasible Condition or Feasibility Condition (FC)


DUAL Concepts

Successor

The best least cost route to a destination found in the routing table

Feasible distance

The lowest calculated metric along a path to a destination network

2 commands can be used to find the “successor” and “feasible distance”:

–show ip route

–show ip eigrp topology


DUAL Concepts

EIGRP Topology Table dissected


DUAL ConceptsFeasible Successors, Feasibility Condition & Reported

Distance Feasible Successor

–This is a loop free backup route to the same destination as successor route

–If the link between R2 and R3 failed, the R1 will become the successor for sending traffic to 192.168.1.0


EIGRP technologies (cont.)

Advertised or Destination Feasible Dist. Reported. Dist. Neighbor

172.30.1.0 40 30 X In Topology Table

172.30.1.0 31 21 Y In Routing Table

172.30.1.0 230 220 Z Not in Topology Table

Current Successor = 31 RD of RTY= 21

Feasible Successor, FC: RD30 < FD31

FD to 172.30.1.0 is 31 via Router Y

172.30.1.0

RTZ is NOT Feasible Successor, FC: RD220 not< FD31


Verifying basic EIGRP


1) If feasible successor exists:

If current successor route fails, feasible successor becomes the current successor, i.e. the current route.

Routing of packets continue with little delay.

2) If no feasible successor exists:

This may be because the Reported Distance is greater than the Feasible Distance.

Before this route can be installed, it must be placed in the active state and recomputed.

Routing of packets continue but with more of a delay.

What if the successor fails?


DUAL Concepts

Feasibility Condition (FC)

–Met when a neighbor’s reported distance (RD) is less than the local router’s FD to the same destination network–The reported distance is simply an EIGRP neighbor's feasible distance to the same destination network.

–The reported distance is the metric that a router reports to a neighbor about its own cost to that network.


DUAL Concepts Reported distance (RD)

–The metric that a router reports to a neighbor about its own cost to that network–R2 examines the reported distance (RD) of 2172416 from R1. Because the reported distance (RD) of R1 is less than R2's own feasible distance (FD) of 3014400, R1 meets the feasibility condition. R1 is now a feasible successor for R2 to the 192.168.1.0/24 network.

Why isn't R1 the successor if its reported distance (RD) is less than R2's feasible distance (FD) to 192.168.1.0/24?

–Because the total cost for R2, its feasible distance (FD), to reach 192.168.1.0/24 is greater through R1 than it is through R3.


DUAL Concepts

EIGRP Topology table–Viewed using the show ip eigrp topology command

Contents of table include:

– all successor routes

– all feasible successor routes


DUAL Concepts

EIGRP Topology Table dissected

P - This route is in the passive state. When DUAL is not performing its diffusing computations to determine a path for a network, the route will be in a stable mode, known as the passive state. A - If DUAL is recalculating or searching for a new path, the route will be in an active state.

All routes in the topology table should be in the passive state for a stable routing domain.

if there is not a second entry, then there are no feasible successors


DUAL Concepts

Finite State Machines (FSM)

To examine output from EIGRP’s finite state machine us the debug eigrp fsm command


More EIGRP ConfigurationsThe Null0 Summary Route

By default, EIGRP uses the Null0 interface to discard any packets that match the parent route but do not match any of the child routes

EIGRP automatically includes a null0 summary route as a child route whenever both of the following conditions exist

–One or subnets exists that was learned via EIGRP

–Automatic summarization is enabled


More EIGRP Configurations Regardless of whether classful or classless

routing behavior is being used, the null0 summary will potentially be used and denying the use of any supernet or default route.

Disabling Automatic Summarization

–The no auto-summary command is used to disable automatic summarization

•This causes all EIGRP neighbors to send updates that will not be automatically summarized

this will cause changes in both

-routing tables

-topology tables


More EIGRP Configurations The no auto-summary command


Manual Summarization EIGRP can be configured to

summarize routes, whether or not automatic summarization (auto-summary) is enabled.

–EIGRP is a classless routing protocol & include subnet mask in update

Command used to configure manual summarization

–Router(config-if)#ip summary-address eigrp as-number network-address subnet-mask


More EIGRP ConfigurationsEIGRP Default Routes

“quad zero” static default route

-Can be used with any currently supported routing protocol

-Is usually configured on a router that is connected a network outside the EIGRP domain (for example, to an ISP. )

EIGRP & the “Quad zero” static default route

–Requires the use of the redistribute static command to include the static default route in EIGRP routing updates to other routers.


More EIGRP Configurations In the routing tables for R1

and R3, notice the routing source and administrative distance for the new static default route. The entry for the static default route on R1 is the following:

D*EX 0.0.0.0/0 [170/3651840] via 192.168.10.6, 00:01:08, Serial0/1

–D: This static route was learned from an EIGRP routing update.–*: The route is a candidate for a default route.–EX: The route is an external EIGRP route, in this case a static route outside of the EIGRP routing domain.–170: This is the administrative distance of an external EIGRP route.


More EIGRP Configurations Configuring Hello Intervals and Hold Times

-Hello intervals and hold times are configurable on a per-interface basis

-The command to configure hello interval is

Router(config-if)#ip hello-interval eigrp as-number seconds

Changing the hello interval also requires changing the hold time to a value greater than or equal to the hello interval

-The command to configure hold time value is

Router(config-if)#ip hold-time eigrp as-number secondsDefaults For low-speed, NBMA networks: 60 seconds For all other networks: 5 seconds

Defaults For low-speed, NBMA networks: 180 seconds For all other networks: 15 seconds


Summary Background & History

–EIGRP is a derivative of IGRP

EIGRP is a Cisco proprietary distance vector routing protocol released in 1994

EIGRP terms and characteristics–EIGPR uses RTP to transmit & receive EIGRP packets

–EIGRP has 5 packet type:

Hello packets

Update packets

Acknowledgement packets

Query packets

Reply packets

–Supports VLSM & CIDR


Summary

EIGRP terms and characteristics

–EIGRP uses a hello protocol

Purpose of hello protocol is to discover & establish adjacencies

–EIGRP routing updates

Aperiodic

Partial and bounded

Fast convergence


Summary

EIGRP commands–The following commands are used for EIGRP configuration

RtrA(config)#router eigrp [autonomous-system #]RtrA(config-router)#network network-number

–The following commands can be used to verify EIGRPShow ip protocolsShow ip eigrp neighborsShow ip route


Summary

EIGRP metrics include

–Bandwidth (default)

–Delay (default)

–Reliability

–Load


Summary DUAL

–Purpose of DUALTo prevent routing loops

–SuccessorPrimary route to a destination

–Feasible successorBackup route to a destination

–Feasible distanceLowest calculated metric to a destination

–Reported distanceThe distance towards a destination as advertised by an upstream neighbor


Summary Choosing the best route

–After router has received all updates from directly connected neighbors, it can calculate its DUAL

1st metric is calculated for each route

2nd route with lowest metric is designated successor & is placed in routing table

3rd feasible successor is found

–Criteria for feasible successor: it must have lower reported distance to the destination than the installed route’s feasible distance

–Feasible routes are maintained in topology table


Summary

Automatic summarization

–On by default

–Summarizes routes on classful boundary

–Summarization can be disabled using the following command

RtrA(config-if)#no auto-summary

Exp_2-Ch_9-EIGRP-.ppt

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