nt 2 lecture 2 eigrp

8/14/2019 Nt 2 Lecture 2 Eigrp

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NT 2 Lecture 2

EIGRP


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What is EIGRP?EIGRP is an advanced distance-vector

routing protocol that relies on featurescommonly associated with link-stateprotocols.

EIGRP uses Link State's partial updatesand neighbor discovery.

EIGRP's advanced features supports IP,IPX and AppleTalk.

EIGRP uses RTP (Reliable TransportProtocol) to transport its routingupdates


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IGRP and EIGRP MetricCalculation - 1

The composite metric is calculatedwith the following formula:

By default, k1=k3=1 andk2=k4=k5=0. The default composite

metric for EIGRP, adjusted for scalingfactors, is as follows:


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IGRP and EIGRP MetricCalculation - 2

BWmin is in kbps and the sum of delays are in 10s of

microseconds.

Example

The bandwidth and delay for an Ethernet interfaceare 10 Mbps and 1ms, respectively.

The calculated EIGRP BW metric is as follows:

256 107/BW = 256 107/10,000

= 256 10000 = 256000


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Using EIGRP with IGRP


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EIGRP Neighbor Discovery -1

EIGRP routers actively establish relationships with theirneighbors, similar to what Link State routers do.

EIGRP routers establish adjacencies with neighbor routers byusing small hello packets.

The Hello protocol uses a multicast address of224.0.0.10,and all routers periodically send hellos.


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EIGRP Neighbor Discovery - 2

On hearing hellos, the router creates a table ofits neighbors.

The continued receipt of these packetsmaintains the neighbor table

To become a neighbor, the followingconditions must be met: The router must hear a hello packet or an ACK from

a neighbor. The AS number in the packet header must be the

same as that of the receiving router. The neighbors metric settings must be the same. Each Layer 3 protocol has its own neighbor table.


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Neighbor Discovery - 3


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Neighbor Discovery - 4

By forming adjacencies, EIGRProuters do the following:

Dynamically learn of new routesthat join their network

Identify routers that become either

unreachable or inoperableRediscover routers that hadpreviously been unreachable


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EIGRP Timers

EIGRP updates are set only when necessaryand are sent only to neighboring routers.

There is no periodic update timer.

EIGRP use hello packets to learn ofneighboring routes.

The holdtime to maintain a neighboradjacency is three times the hello time.

For hello is not received with the holdtime,the neighbor is removed from the table.


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Default Hello Intervals andHold Time for EIGRP


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a s n e e g orTable?


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Dual Terminology - 1

AD (Advertised distance) is the metric thatis reported by the neighbor router(s).

FD (Feasible Distance) Feasible distanceis the metric that is reported by neighborrouter(s), plus the cost associated with theforwarding link from the local interface to theneighbor router(s). When multiple pathsexist, the local FD is the lowest-cost metric toa remote network.

Feasibility Condition If the AD from agiven neighbor is less than the locallycalculated FD, that neighbor meets thecriteria to become the feasible successor.


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Dual Terminology - 2

Successor - A successor is a neighboring router thatis currently being used for packet forwarding; itprovides the least-cost route to the destination andis not part of a routing loop

Feasible successor - A feasible successor is a

backup route. Feasible successors provide the nextlowest-cost path without introducing routing loops.Feasible successor routes can be used in case theexisting route fails. Packets to the destinationnetwork are immediately forwarded to the feasible

successor, which at that point is promoted to thestatus of successor


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successors an eas e

successors - 1


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EIGRP successors and feasiblesuccessors - 2


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EIGRP successors and feasiblesuccessors - 3


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Dual Example 1a


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Dual Example 1bIn the previous slide, EIGRP's composite metric is

replaced by a link cost to simplify calculations.RTA's topology table includes a list of all routesadvertised by neighbors.

For each network, RTA keeps the real (computed)cost of getting to that network and also keeps the

advertised cost (reported distance) from itsneighbor.


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Dual Example 1c

RTY is the successor to network 24, byvirtue of its lowest computed cost 31. Thisvalue is also the FD to Network 24.

RTA follows a three-step process to select a

feasible successor to become a successorfor Network 24: Determine which neighbors have a reported

distance (RD) (=AD) to Network 24 that is lessthan 31.

RTX's RD is 30 < 31, meet FC and is a feasiblesuccessor.

RTZ's RD is 220 > 31, not meet FC, and cannotbe a FS.


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Dual Example 2a

(a) Is the Destination Network


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Dual Example 2b

In this example, (a) is the destinationnetwork,

From C point of view, if it goes to (a) via B,the FD is 3 and the AD is 1. Others entries

are computed in the same manner.Note in the example that router D does nothave a feasible successor identified. The FDfor router D to router A is 2 and the AD viarouter C is 3. Because the AD is larger than

the FD, no feasible successor is placed inthe topology table.


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Dual Example 2c

Router C has a feasible successoridentified because the AD for the

next hop router is less than the FDfor the successor.

How about router E?


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EIGRP Convergence - 1

In the context of routing protocols,convergence refers to the speed and ability ofa group of internetworking devices running aspecific routing protocol to agree on the

topology of an internetwork after a change inthat topology.

DUAL results in EIGRP's exceptionally fastconvergence. Why?

The FS provides the capability to make animmediate switchover to a backup route!


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EIGRP Convergence - 2


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EIGRP Neighbor Tables

The most important table in EIGRP is the neighbortable and relationships tracked in the neighbortable are the basis for all the EIGRP routing updateand convergence activity.

The neighbor table contains information aboutadjacent neighboring EIGRP routers.

A neighbor table is used to support reliable,sequenced delivery of packets.

An EIGRP router can maintain multiple neighbortables, one for each PDM running (e.g., IP, IPX, andAppleTalk) routed protocols.


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EIGRP Packet Types - 1

Hello packets assist in the discovery ofEIGRP neighbors. The packets are multicastto 224.0.0.10.

An acknowledgment packetacknowledges the reception of an updatepacket. An acknowledgment packet is ahello packet with no data. Acknowledgment

packets are sent to the unicast address ofthe sender of the update packet.


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Update packets contain the routing informationof destinations. Update packets are unicast tonewly discovered neighbors; otherwise, updatepackets are multicast to 224.0.0.10 when a link

metric changes. Update packets areacknowledged to ensure reliable transmission.

Query packets are sent to find feasiblesuccessors to a destination. Query packets are

always multicast.


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Reply packets are sent torespond to query packets.

Reply packets provide a feasiblesuccessor to the sender of the query.

Reply packets are unicast to thesender of the query packet.

EIGRP Topo ogy Ta e


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EIGRP Topo ogy Ta e -1

EIGRP uses its topology table to store all the informationit needs to calculate a set of distances and vectors to allreachable destinations.

EIGRP maintains a separate topology table for eachrouted protocol.

EIGRP sorts the topology table so that the successorroutes are at the top, followed by feasible successors.

Entries in the topology table can be in one of twostates: active or passive.

A passive route is one that is stable and available foruse. An active route is a route in the process of beingrecomputed by DUAL.


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EIGRP Topology Table - 2


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EIGRP Routing TableThe routing table contains the routes installed by

DUAL as the best loop-free paths to a givendestination

EIGRP will maintain up to four routes per destination.These routes can be of equal or unequal cost.

EIGRP routers maintain a separate routing table for

each routed protocol.


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Configuring EIGRP

To enable EIGRP and define the autonomous system:router(config)# router eigrpautonomous-system-number

This statement identifies the locally connectednetwork that should be advertised to EIGRPneighbors.router(config-router)# networknetwork-number

When using serial links, it is important to use thebandwidth on the interface to change the bandwidth

used for calculating routing metrics. If you do notchange the bandwidth for these interfaces EIGRPassumes the default bandwidth on the link (?) insteadof the true bandwidth.

router(config-if)# bandwidthkilobits


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EIGR Route Summarization - 1

EIGRP automatically summarizes routes.The summary routes are advertised at the class A,B,or C boundaries.

Autosummarization occurs when a router is on the

boundary of different major networks.


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EIGRP Route Summarization - 2

However, if you have discontiguous

subnetworks, auto-summarization must bedisabled for routing to work properly.

In here, even though RTC is connected onlyto the subnet 2.1.1.0, it will advertise that itis connected to the entire Class A network,

2.0.0.0


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EIGRP Route Summarization - 3

By default, EIGRPs interfaces do not use VLSM.To turn off auto-summarization, use the following command:

router(config-router)#no auto-summary

anua ummar za on


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anua ummar za on- 1

EIGRP also enables you to manuallyconfigure a summary routes on anyrouter a per-interface basis.

You first select the interface thatwill propagate the route summary.

Then you can define the summary

address with the ip summary-address eigrp command.


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EIGRP Manual Summarization- 2

l i i


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EIGRP Manual Summarization- 3

When configured, RTC will add a summaryroute to its table, as follows:

The benefits of EIGRP manualsummarization: support future growth in networks; preserve bandwidth and CPU utilization.

flexibility in where apply summarization.

U l C L d B l i


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Unequal Cost Load Balancing- 1

EIGRP also supports unequal-costload balancing.

This is achieved by using thevariance command ( the same asIGRP we have come across in Lab.)

Unequal Cost Load Balancing


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Unequal Cost Load Balancing- 2


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Recap: EIGRP New Technologies overIGRP

Neighbor discovery and recovery

Reliable Transport Protocol

Dual Finite State Machine

Protocol specific modules


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Recap: EIGRP Advantages

Rapid convergence

Efficient use of bandwidth Partial, bounded updates Minimal consumption of bandwidth

when the network is stable

Support for VLSM and CIDR

Multiple network-layer supportIndependence from routed protocols

nt 2 lecture 2 eigrp

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