Sem5 eigrp chp6

1

Mälardalens högskolaMälardalens högskola

Advanced RoutingAdvanced RoutingCh. 6 EIGRPCh. 6 EIGRP

Stefan LöfgrenStefan Löfgren

2

EIGRPEIGRP

Cisco proprietary, released in 1994Cisco proprietary, released in 1994 Based on IGRPBased on IGRP EIGRP is an EIGRP is an advanced distance-vectoradvanced distance-vector

routing protocol that relies on features routing protocol that relies on features commonly associated with link-state commonly associated with link-state protocols. (sometimes called a protocols. (sometimes called a hybrid hybrid routing protocolrouting protocol))

Supports VLSM and CIDRSupports VLSM and CIDR Can route Novell IPX and Apple Can route Novell IPX and Apple

AppleTalk, AppleTalk, Like IGRP, EIGRP supports Like IGRP, EIGRP supports unequal-cost load balancing (unlike OSPF).unequal-cost load balancing (unlike OSPF).

3

EIGRPEIGRP

Routing tables are Routing tables are notnot exchanged on a periodic basis. exchanged on a periodic basis. Uses Hello protocols to create and maintain neighbor Uses Hello protocols to create and maintain neighbor

relationships and to determine when a link is down. (Like relationships and to determine when a link is down. (Like link-state)link-state)– Hellos everyHellos every 5 seconds5 seconds, with a , with a hold timer of 15 secondshold timer of 15 seconds

– Links less than T1 speed, Links less than T1 speed, Hellos are every 60 secondsHellos are every 60 seconds, , hold hold timer of 180 secondstimer of 180 seconds

When a change in topology occurs, EIGRP does When a change in topology occurs, EIGRP does notnot flood flood updates like link-state protocols, but immediately sends updates like link-state protocols, but immediately sends those changes to its neighbors.those changes to its neighbors.

Has speed and efficiency of routing updates like a link-Has speed and efficiency of routing updates like a link-state protocol, along with a topology database.state protocol, along with a topology database.

4

OSPF versus EIGRPOSPF versus EIGRPOSPFOSPF EIGRPEIGRP

Supports CIDR and VLSM, Supports CIDR and VLSM, rapid convergence, partial rapid convergence, partial updates, neighbor discoveryupdates, neighbor discovery

Supports CIDR and VLSM, Supports CIDR and VLSM, rapid convergence, partial rapid convergence, partial updates, neighbor discoveryupdates, neighbor discovery

Administrator can define route Administrator can define route summarizationsummarization

Automatic route-summarization Automatic route-summarization and user-defined route summariesand user-defined route summaries

Open standard; multivendor Open standard; multivendor supportsupport

Proprietary; Cisco routers onlyProprietary; Cisco routers only

Scalable; administratively Scalable; administratively defined “areas” provide defined “areas” provide manageable hierarchymanageable hierarchy

Scalable, but no hierarchical Scalable, but no hierarchical designdesign

Difficult to implementDifficult to implement

Equal-cost load balancingEqual-cost load balancing

Easy to implementEasy to implement

Unequal-cost load balancingUnequal-cost load balancing

5

EIGRP vs IGRPEIGRP vs IGRP

IGRP and EIGRP are compatible with each other, IGRP and EIGRP are compatible with each other, although EIGRP offers multiprotocol support and although EIGRP offers multiprotocol support and IGRP does notIGRP does not..– EIGRP supportsEIGRP supports

» TCP/IPTCP/IP» IPX/SPXIPX/SPX» AppleTalkAppleTalk

6

EIGRP and IGRPEIGRP and IGRP

AutomaticallyAutomatically redistributesredistributes when using same AS when using same AS number.number.

RTB runs both EIGRP and IGRP

7

Metric calculation: IGRP/EIGRPMetric calculation: IGRP/EIGRP

(with the following default constant values):(with the following default constant values):

Constant ValueConstant Value

K1K1 1 1

K2K2 0 0

K3 1K3 1

K4K4 0 0

K5K5 0 0

Notes Notes k2k2 metric effects metric effects LOADLOAD k4k4 and and k5k5 effects effects RELIABILITYRELIABILITY

metric = [K1 * bandwidth + ((K2 * bandwidth) / (256 * load)) + (K3 * delay)] * [K5/(reliability + K4)]

8

Metric CalculationMetric Calculation

When K2, K4 and K5 are 0, these portions of the When K2, K4 and K5 are 0, these portions of the equation is not factored in to the metric. equation is not factored in to the metric.

Thus, with the default constant values, K1=1 and K3=1, Thus, with the default constant values, K1=1 and K3=1, the metric equation boils down to this:the metric equation boils down to this:

metricmetric = [(1 * = [(1 * bandwidthbandwidth)) + (1 * + (1 * delaydelay)] )]

metricmetric = = bandwidthbandwidth + + delaydelay

Actually:Actually:

metricmetric = = slowestslowest bandwidthbandwidth + + sum of allsum of all delaysdelays

metric = [K1 * bandwidth + ((K2 * bandwidth) / (256 * load)) + (K3 * delay)] * [K5/(reliability + K4)]

9

The metrics used by EIGRP in making routing decisions are (The metrics used by EIGRP in making routing decisions are (lower the lower the metric the bettermetric the better):):

bandwidthbandwidth delaydelay loadload reliabilityreliability

By default, EIGRP uses only:By default, EIGRP uses only: BandwidthBandwidth DelayDelay

AnalogiesAnalogies::Think of Think of bandwidthbandwidth as the as the width of the pipewidth of the pipe andanddelaydelay as the as the length of the pipelength of the pipe..

BandwidthBandwidth is a the is a the carrying capacitycarrying capacity DelayDelay is the is the end-to-end travel timeend-to-end travel time..


10

If these are the default:If these are the default: bandwidth (default)bandwidth (default) delay (default)delay (default)

When are these used?When are these used? loadload reliabilityreliability

Only when configured by the network administrator to do so!Only when configured by the network administrator to do so!

Use Use show interfaceshow interface command to view the metrics used on a command to view the metrics used on a specific interface that is routing EIGRP. specific interface that is routing EIGRP.


11

Metric Calculation – show interfacesMetric Calculation – show interfaces

Router> show interfaces s1/0

Serial1/0 is up, line protocol is up

Hardware is QUICC Serial

Description: Out to VERIO

Internet address is 207.21.113.186/30

MTU 1500 bytes, BW 1544 Kbit, DLY 20000 usec,

rely 255/255, load 246/255

Encapsulation PPP, loopback not set

Keepalive set (10 sec)

<output omitted>

bandwidth delay

reliability load

12

BandwidthBandwidth Expressed in Expressed in kilobitskilobits ( (show interfaceshow interface)) This is a This is a static numberstatic number and used for metric calculations and used for metric calculations

only.only. Does not necessarily reflect the actual bandwidth of the Does not necessarily reflect the actual bandwidth of the

link.link. It is an It is an information parameter onlyinformation parameter only.. You cannot adjust the actual bandwidth on an interface You cannot adjust the actual bandwidth on an interface

with this command.with this command.

Metric Calculation – BandwidthMetric Calculation – Bandwidth

13

The default values:The default values: Default bandwidth of a Cisco interface depends on the type Default bandwidth of a Cisco interface depends on the type

of interface.of interface.

Default bandwidth of a Cisco Default bandwidth of a Cisco serial interface is 1544 serial interface is 1544 kilobitskilobits or 1,544,000 bps (T1), whether that interface is or 1,544,000 bps (T1), whether that interface is attached to a T1 line (1.544 Mbps) or a 56K line.attached to a T1 line (1.544 Mbps) or a 56K line.


14

Changing the bandwidth informational parameter:Changing the bandwidth informational parameter:

The bandwidth can be changed using:The bandwidth can be changed using:

Router(config-if)# Router(config-if)# bandwidthbandwidth kilobitskilobits

To restore the default value: To restore the default value:

Router(config-if)# Router(config-if)# no bandwidthno bandwidth


15

DelayDelay Like bandwidth, delay it is a Like bandwidth, delay it is a static numberstatic number.. Expressed in Expressed in microsecondsmicroseconds, , millionths of a secondmillionths of a second It is an It is an information parameter onlyinformation parameter only..

The default values:The default values: The default delay value of a Cisco interface depends upon The default delay value of a Cisco interface depends upon

the the type of interfacetype of interface..

Default delay of a Cisco Default delay of a Cisco serial interfaceserial interface is is 20,000 20,000 microsecondsmicroseconds, that of a T1 line., that of a T1 line.

IGRP/EIGRP metric uses the IGRP/EIGRP metric uses the sum of all of the delayssum of all of the delays of of all of the outbound interfaces to the destination network.all of the outbound interfaces to the destination network.

Metric Calculation – DelayMetric Calculation – Delay

16

Changing the delay informational parameter:Changing the delay informational parameter:

The delay can be changed using:The delay can be changed using:

Router(config-if)# Router(config-if)# delaydelay tens-of- tens-of- SS (microseconds)(microseconds)

Example of changing the delay on a serial interface to 30,000 Example of changing the delay on a serial interface to 30,000 microsecondsmicroseconds::

Router(config-if)# Router(config-if)# delaydelay 3000 3000

To restore the 20,000 microsecond default value: To restore the 20,000 microsecond default value:

Router(config-if)# Router(config-if)# no delayno delay

Metric Calculation – DelayMetric Calculation – Delay

17

IGRP vs EIGRP Metric CalculationIGRP vs EIGRP Metric CalculationIGRPIGRP bandwidth = (10,000,000/bandwidth = (10,000,000/bandwidthbandwidth)) delay = delay = delaydelay/10/10

EIGRPEIGRP bandwidth = (10,000,000/bandwidth = (10,000,000/bandwidthbandwidth) * 256) * 256 delay = (delay = (delaydelay/10) * 256/10) * 256

Note: The reference-bandwidth Note: The reference-bandwidth

For both IGRP and EIGRP: 10For both IGRP and EIGRP: 1077, (10,000,000/bandwidth), whereas, (10,000,000/bandwidth), whereas with OSPF it was 10with OSPF it was 108 8 (100,000,000/bandwidth)(100,000,000/bandwidth)

The differenceThe difference:: IGRP metric is 20 bits longIGRP metric is 20 bits long EIGRP metric is 32 bits longEIGRP metric is 32 bits long EIGRP metric is 256 times greater for the same routeEIGRP metric is 256 times greater for the same route EIGRP allows for finer comparison of potential routesEIGRP allows for finer comparison of potential routes

18

ReliabilityReliability Reliability is measure Reliability is measure dynamicallydynamically UsesUses error rate error rate for measurementfor measurement Reflects the Reflects the total outgoing error ratestotal outgoing error rates of the of the interfaces along interfaces along

the routethe route Calculated on a five minute weighted average, so not to allow Calculated on a five minute weighted average, so not to allow

sudden peaks and valleys to make a significant impactsudden peaks and valleys to make a significant impact

Expressed as an 8 bit numberExpressed as an 8 bit number 255255 is a 100% reliable link is a 100% reliable link 1 1 is a minimally reliable linkis a minimally reliable link

HigherHigher the better! the better!

What about Reliability and Load?What about Reliability and Load?

19

shows reliability as a fraction of 255, for example:shows reliability as a fraction of 255, for example:

rely 190/255 (or 74% reliability)rely 190/255 (or 74% reliability)



Router> show interfaces s1/0

Serial1/0 is up, line protocol is up

Hardware is QUICC Serial

Description: Out to VERIO

Internet address is 207.21.113.186/30

MTU 1500 bytes, BW 1544 Kbit, DLY 20000 usec,

rely 255/255, load 246/255

Encapsulation PPP, loopback not set

Keepalive set (10 sec)

<output omitted>

bandwidth delay

reliability load

Metric Calculation – show interfacesMetric Calculation – show interfaces

20

LoadLoad Load is measure Load is measure dynamicallydynamically UsesUses channel occupancy channel occupancy for measurementfor measurement Reflects the Reflects the total outgoing loadtotal outgoing load of the of the interfaces along the routeinterfaces along the route Calculated on a five minute weighted average, so not to allow sudden Calculated on a five minute weighted average, so not to allow sudden

peaks and valleys to make a significant impactpeaks and valleys to make a significant impact

Expressed as an 8 bit numberExpressed as an 8 bit number 255255 is a 100% loaded link is a 100% loaded link 1 1 is a minimally loaded linkis a minimally loaded link

LowerLower the better! the better!

Note: Even though load and reliability are dynamically changing values, Note: Even though load and reliability are dynamically changing values, EIGRP will EIGRP will notnot recalculate the route metric when these parameters recalculate the route metric when these parameters change.change.

What about Reliability and Load?What about Reliability and Load?

21

EIGRP TechnologiesEIGRP Technologies

Four key technologies set EIGRP apart from IGRPFour key technologies set EIGRP apart from IGRP

– Neighbor discovery and recoveryNeighbor discovery and recovery

– Reliable Transport Protocol (RTP)Reliable Transport Protocol (RTP)

– DUAL finite-state machine (FSM)DUAL finite-state machine (FSM)

– PDMsPDMs

22

Neighbor Discovery/RecoveryNeighbor Discovery/Recovery EIGRP routers EIGRP routers establish adjacenciesestablish adjacencies with neighbor routers by with neighbor routers by

using small using small hello packetshello packets. .

HellosHellos are sent every are sent every 5 seconds5 seconds by default. by default.

K valuesK values must be the must be the same between neighborssame between neighbors..

An EIGRP router assumes that, as long as it is receiving hello An EIGRP router assumes that, as long as it is receiving hello packets from known neighbors, those neighbors (and their packets from known neighbors, those neighbors (and their routes) remain viable.routes) remain viable.

Hold timeHold time tells the router how long it should consider the tells the router how long it should consider the neighbor alive if it has not received any EIGRP packets (Hello, neighbor alive if it has not received any EIGRP packets (Hello, EIGRP updates, etc.)EIGRP updates, etc.)

23

Neighbor Discovery/RecoveryNeighbor Discovery/Recovery Hold timeHold time is normally is normally three timesthree times the configured the configured Hello Hello

intervalinterval..

Both the Hello and Hold time intervals are Both the Hello and Hold time intervals are configurable on a configurable on a per interface basisper interface basis..

EIGRP routers exchange routing information the same way as EIGRP routers exchange routing information the same way as other distance vector routing protocols, but other distance vector routing protocols, but do not send do not send periodic updatesperiodic updates..

EIGRP updatesEIGRP updates are only sent when a network is are only sent when a network is added or added or removedremoved from the topology databasefrom the topology database, when the successor for , when the successor for a given network changes, or when the locally used metric is a given network changes, or when the locally used metric is updated.updated.

EIGRP, like any other distance-vector routing protocol EIGRP, like any other distance-vector routing protocol uses uses split-horizon.split-horizon.

24

RTPRTP

RTP (RTP (Reliable Transport Protocol)Reliable Transport Protocol)

– transport-layer protocol transport-layer protocol

EIGRP is EIGRP is protocol-independentprotocol-independent; that is, it ; that is, it doesn’t rely doesn’t rely on TCP/IPon TCP/IP to exchange routing information the way RIP, to exchange routing information the way RIP, IGRP, and OSPF do. IGRP, and OSPF do.

To stay independent of IP, EIGRP uses the transport-layer To stay independent of IP, EIGRP uses the transport-layer protocol to guarantee delivery of routing information: protocol to guarantee delivery of routing information: RTPRTP. .

RTP supports reliable and unreliable deliveryRTP supports reliable and unreliable delivery

RTP supports unicasting and multicastingRTP supports unicasting and multicasting

25

RTPRTP Initial delivery of EIGRP messages are done using Initial delivery of EIGRP messages are done using

multicast packetsmulticast packets, that is data is sent to all neighbors on a , that is data is sent to all neighbors on a segment, and every neighbor is expected to acknowledge it segment, and every neighbor is expected to acknowledge it with a unicast Hello packet.with a unicast Hello packet.

After adjacency has been formed and added to neighbor After adjacency has been formed and added to neighbor table, routers exchange routing information which is stored table, routers exchange routing information which is stored in the topology table.in the topology table.

RTP uses a mechanism of sequence numbers and RTP uses a mechanism of sequence numbers and acknowledgementsacknowledgements

RTPRTP is used for EIGRP is used for EIGRP queries, updates and replies queries, updates and replies

RTPRTP is is notnot used for EIGRP used for EIGRP Hello’s and Ack’sHello’s and Ack’s

26

DUAL FSMDUAL FSM

The centerpiece of EIGRP is DUAL, the EIGRP route-The centerpiece of EIGRP is DUAL, the EIGRP route-calculation engine. calculation engine.

– The full name of this technology is DUAL The full name of this technology is DUAL finite state finite state machine (FSM)machine (FSM). .

– This engine contains all the logic used to calculate and This engine contains all the logic used to calculate and compare routes in an EIGRP network. compare routes in an EIGRP network. Initial delivery of Initial delivery of EIGRP messages are done using EIGRP messages are done using multicast packetsmulticast packets, that is data is , that is data is sent to all neighbors on a segment, and every neighbor is expected sent to all neighbors on a segment, and every neighbor is expected to acknowledge it with a unicast Hello packet.to acknowledge it with a unicast Hello packet.

27

DUAL FSMDUAL FSM

What is FSM?

An FSM is an abstract machine, not a mechanical device An FSM is an abstract machine, not a mechanical device with moving parts.with moving parts.

FSMs define a set of possible states something can go FSMs define a set of possible states something can go through, what events causes those states, and what events through, what events causes those states, and what events result from those states.result from those states.

Designers use FSMs to describe how a device, computer Designers use FSMs to describe how a device, computer program, or routing algorithm will react to a set of input program, or routing algorithm will react to a set of input events.events.

28

Example FSMExample FSM

HUNGRY(START)

FOOD ISINEDIBLE

GET FOOD

FULL

EAT ENOUGHFOOD

NOT ENOUGHFOOD

NO FOODFOR 5

HOURS

EAT MOREFOOD EATING

29

DUAL FSMDUAL FSM DUAL selects alternate routes quickly by using the information in the DUAL selects alternate routes quickly by using the information in the

EIGRP tables. EIGRP tables.

If a link goes down, DUAL looks for a feasible successor in its If a link goes down, DUAL looks for a feasible successor in its neighbor and topology tables.neighbor and topology tables.

A A successorsuccessor is a neighboring router that is currently being used for is a neighboring router that is currently being used for packet forwarding, provides the least-cost route to the destination, and packet forwarding, provides the least-cost route to the destination, and is not part of a routing loop.is not part of a routing loop.

Feasible successorsFeasible successors provide the next lowest-cost path without provide the next lowest-cost path without introducing routing loops. introducing routing loops.

– Feasible successor routes can be used in case the existing route Feasible successor routes can be used in case the existing route fails; packets to the destination network are immediately fails; packets to the destination network are immediately forwarded to the feasible successor, which at that point, is forwarded to the feasible successor, which at that point, is promoted to the status of successor.promoted to the status of successor.

30

DUAL FSMDUAL FSM Selects a best loop-free path to a destination, the next hop Selects a best loop-free path to a destination, the next hop

being known as the being known as the successorsuccessor..

All other routers to the same destination, that also meet the All other routers to the same destination, that also meet the feasible conditionfeasible condition, meaning they are also loop-free (later), , meaning they are also loop-free (later), become become feasible successorsfeasible successors, or back-up routes., or back-up routes.

debug eigrp fsmdebug eigrp fsm

31

PDMsPDMs

PDM (Protocol-dependent module)PDM (Protocol-dependent module)

EIGRP is modularEIGRP is modular

Different PDMs can be added to EIGRP as new routed Different PDMs can be added to EIGRP as new routed protocols are enhanced or developed:protocols are enhanced or developed:

– IPv4, IPv6, IPX, and AppleTalkIPv4, IPv6, IPX, and AppleTalk

32

PDMsPDMs

Each PDM is responsible for all functions related to its Each PDM is responsible for all functions related to its specific routed protocol. specific routed protocol.

The IP-EIGRP module is responsible for the following:The IP-EIGRP module is responsible for the following:

– Sending and receiving EIGRP packets that bear IP Sending and receiving EIGRP packets that bear IP datadata

– Notifying DUAL of new IP routing information that Notifying DUAL of new IP routing information that is receivedis received

– Maintaining the results of DUAL’s routing decisions Maintaining the results of DUAL’s routing decisions in the IP routing tablein the IP routing table

– Redistributing routing information that was learned Redistributing routing information that was learned

by other IP-capable routing protocolsby other IP-capable routing protocols

33

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

Like OSPF, EIGRP keeps this information in several tables, or Like OSPF, EIGRP keeps this information in several tables, or databases.databases.

– Neighbor tableNeighbor table– Topology tableTopology table– Routing tableRouting table– SuccessorSuccessor– Feasible SuccessorFeasible Successor

We will first have an overview of all of the terminology and then see We will first have an overview of all of the terminology and then see how it works and what it all means!how it works and what it all means!

EIGRP TerminologyEIGRP Terminology

34

Neighbor TableNeighbor Table Neighbor tableNeighbor table

– Each EIGRP router maintains a neighbor table that lists adjacent Each EIGRP router maintains a neighbor table that lists adjacent routers. routers.

– This table is comparable to the adjacency database used by OSPF. This table is comparable to the adjacency database used by OSPF.

– There is a neighbor table for each protocol that EIGRP supportsThere is a neighbor table for each protocol that EIGRP supports Whenever a new neighbor is discovered, the address of that neighbor Whenever a new neighbor is discovered, the address of that neighbor

and the interface used to reach it are recorded in a new neighbor table and the interface used to reach it are recorded in a new neighbor table entry.entry.

RouterC#show ip eigrp neighbors

IP-EIGRP neighbors for process 44

H Address Interface Hold Uptime SRTT RTO Q Seq

(sec) (ms) Cnt Num

0 192.168.0.1 Se0 11 00:03:09 1138 5000 0 6

1 192.168.1.2 Et0 12 00:34:46 4 200 0 4

35

Neighbor Table includesNeighbor Table includes

RouterC#RouterC#show ip eigrp neighborsshow ip eigrp neighbors

IP-EIGRP neighbors for process 44IP-EIGRP neighbors for process 44

H H AddressAddress Interface Hold Uptime SRTT RTO Interface Hold Uptime SRTT RTO QQ Seq Seq

(sec) (ms) (sec) (ms) CntCnt Num Num

0 0 192.168.0.1192.168.0.1 Se0 11 00:03:09 1138 5000 Se0 11 00:03:09 1138 5000 00 6 6

1 1 192.168.1.2192.168.1.2 Et0 12 00:34:46 4 200 Et0 12 00:34:46 4 200 00 4 4

Neighbor addressNeighbor address The network-layer address of the The network-layer address of the neighbor router(s).neighbor router(s).

Queue countQueue count The number of packets waiting in queue to The number of packets waiting in queue to be sent. If this value is constantly higher than zero, then be sent. If this value is constantly higher than zero, then there may be a congestion problem at the router. A zero there may be a congestion problem at the router. A zero means that there are no EIGRP packets in the queue.means that there are no EIGRP packets in the queue.

36

Neighbor Table includesNeighbor Table includesRouterC#RouterC#show ip eigrp neighborsshow ip eigrp neighborsIP-EIGRP neighbors for process 44IP-EIGRP neighbors for process 44H Address Interface H Address Interface HoldHold Uptime Uptime SRTTSRTT RTO Q Seq RTO Q Seq (sec)(sec) (ms)(ms) Cnt Num Cnt Num0 192.168.0.1 Se0 0 192.168.0.1 Se0 1111 00:03:09 00:03:09 11381138 5000 0 6 5000 0 61 192.168.1.2 Et0 1 192.168.1.2 Et0 1212 00:34:46 00:34:46 44 200 0 4 200 0 4

Smooth Round Trip Timer (SRTT)Smooth Round Trip Timer (SRTT) The average time it takes to send and The average time it takes to send and receive packets from a neighbor. receive packets from a neighbor.

This timer is used to determine the retransmit interval (RTO)This timer is used to determine the retransmit interval (RTO)

Hold TimeHold Time The interval to wait without receiving anything from a The interval to wait without receiving anything from a neighbor before considering the link unavailable. neighbor before considering the link unavailable.

Originally, the expected packet was a hello packet, but in current Cisco IOS Originally, the expected packet was a hello packet, but in current Cisco IOS software releases, software releases, any EIGRP packets received after the first hello will any EIGRP packets received after the first hello will reset the timerreset the timer..

37

EIGRP Topology TableEIGRP Topology Table Topology tableTopology table

– Each EIGRP router maintains a topology table for each configured Each EIGRP router maintains a topology table for each configured network protocol. network protocol.

– This table includes route entries for all destinations that the router This table includes route entries for all destinations that the router has learned. has learned.

– All learned routes to a destination are maintained in the topology All learned routes to a destination are maintained in the topology table. table.

EIGRP uses its EIGRP uses its topology tabletopology table to store all the information it needs to to store all the information it needs to calculate a set of distances and vectors to all reachable destinations.calculate a set of distances and vectors to all reachable destinations.

RouterB#show ip eigrp topology

IP-EIGRP Topology Table for process 44

Codes: P - Passive, A - Active, U - Update, Q - Query, R - Reply, r - Reply status

P 206.202.17.0/24, 1 successors, FD is 2195456

via 206.202.16.1 (2195456/2169856), Ethernet0

P 206.202.18.0/24, 2 successors, FD is 2198016

via 192.168.0.2 (2198016/284160), Serial0

via 206.202.16.1 (2198016/2172416), Ethernet0

More about this table later!

38

Topology TableTopology Table

Not only does the topology table track information Not only does the topology table track information regarding route states, but it can also record special regarding route states, but it can also record special information for external routes, including the administrator information for external routes, including the administrator tag.tag.

EIGRP classifies routes as either EIGRP classifies routes as either internalinternal or or externalexternal. .

EIGRP uses a process called route tagging to add special EIGRP uses a process called route tagging to add special tags to each route. tags to each route.

These tags identify a route as internal or external, and may These tags identify a route as internal or external, and may include other information as well.include other information as well.

39


All external routesAll external routes are included in the topology table, and are included in the topology table, and are tagged with the following information:are tagged with the following information:

The identification number (The identification number (router IDrouter ID) of the EIGRP ) of the EIGRP router that redistributed the route into the EIGRP networkrouter that redistributed the route into the EIGRP network– The EIGRP router ID is normally selected in the same manner as

Open Shortest Path First (OSPF)– Can also use: eigrp router-id <router-id>

The The AS numberAS number of the destination of the destination

The The protocolprotocol used in that external network used in that external network

The The cost or metriccost or metric received from that external protocol received from that external protocol

The configurable The configurable administrator tagadministrator tag

40

Topology TableTopology TableRTX#sh ip eigrp top 204.100.50.0RTX#sh ip eigrp top 204.100.50.0IP-EIGRP topology entry for 204.100.50.0/24IP-EIGRP topology entry for 204.100.50.0/24 State is Passive, Query origin flag is 1, 1 Successor(s), FD State is Passive, Query origin flag is 1, 1 Successor(s), FD

is 2297856is 2297856 Routing Descriptor Blocks:Routing Descriptor Blocks: 10.1.0.1 (Serial0), from 10.1.0.1, Send flag is 0x010.1.0.1 (Serial0), from 10.1.0.1, Send flag is 0x0 Composite metric is (2297856/128256), Route is ExternalComposite metric is (2297856/128256), Route is External Vector metric:Vector metric: Minimum bandwidth is 1544 KbitMinimum bandwidth is 1544 Kbit Total delay is 25000 microsecondsTotal delay is 25000 microseconds Reliability is 255/255Reliability is 255/255 Load is 1/255Load is 1/255 Minimum MTU is 1500Minimum MTU is 1500 Hop count is 1Hop count is 1 External data:External data: Originating router is 192.168.1.1Originating router is 192.168.1.1 AS number of route is 0AS number of route is 0 External protocol is Connected, external metric is 0External protocol is Connected, external metric is 0 Administrator tag is 0 (0x00000000)Administrator tag is 0 (0x00000000)

FD/RD

41


QuestionQuestion: Since EIGRP has a topology table, does this make it a link-: Since EIGRP has a topology table, does this make it a link-state routing protocol?state routing protocol?

AnswerAnswer: : No, the information in the topology table is No, the information in the topology table is notnot in the form of PDUs in the form of PDUs

describing the complete network topology. describing the complete network topology.

The EIGRP topology table contains information about paths through The EIGRP topology table contains information about paths through the router’s adjacent neighbors.the router’s adjacent neighbors.

Also, EIGRP does not perform shortest-path calculation by calculating Also, EIGRP does not perform shortest-path calculation by calculating the shortest-path tree, but instead uses the DUAL algorithm.the shortest-path tree, but instead uses the DUAL algorithm.

42

IP Routing TableIP Routing Table Routing tableRouting table

– EIGRP chooses the best (that is, successor) routes to a destination EIGRP chooses the best (that is, successor) routes to a destination from the topology table and places these routes in the routing from the topology table and places these routes in the routing table.table.

– Each EIGRP router maintains a topology table for each network Each EIGRP router maintains a topology table for each network protocol. protocol.

RouterB#show ip route

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 U - per-user static route

Gateway of last resort is not set

C 10.1.1.0 is directly connected, Serial0

D 172.16.0.0 [90/2681856] via 10.1.1.0, Serial0

D EX 192.168.1.0 [170/2681856] via 10.1.1.1, 00:00:04, Serial0

EIGRP displays both internal EIGRP routes and external EIGRP routes. External EIGRP routes are routes external to EIGRP (redistributed)

43

Routing TablesRouting Tables

The routing table contains the routes installed by DUAL as the best loop-free The routing table contains the routes installed by DUAL as the best loop-free paths to a given destination. paths to a given destination.

EIGRP will maintain up to four routes per destination. EIGRP will maintain up to four routes per destination.

These routes can be of equal, or unequal costThese routes can be of equal, or unequal cost (if using the (if using the variancevariance command). command).

44

EIGRP TerminologyEIGRP Terminology Successor – Successor – Current RouteCurrent Route

– A successor is a route selected as the primary A successor is a route selected as the primary route to use to reach a destination. route to use to reach a destination.

– Successors are the entries kept in the routing Successors are the entries kept in the routing table.table.

Feasible SuccessorFeasible Successor - - A backup routeA backup route– A feasible successor is a backup route. A feasible successor is a backup route. – These routes are selected at the same time the These routes are selected at the same time the

successors are identified, but they are kept in successors are identified, but they are kept in the topology table. the topology table.

– Multiple feasible successors for a destination Multiple feasible successors for a destination can be retained in the topology table. can be retained in the topology table.

45

Successors and Feasible SuccessorsSuccessors and Feasible Successors

RD=5

FD=15

Cost = 10

46

RD=5

RD=5

FD=15FD=15


10

10

47

FD=15FD=15

FD=20

RD=5

RD=5

RD=6


10

10

6

14

48

FD=15FD=15

FD=20

RD=5

RD=5

RD=6

Successors and Feasible SuccessorsI have a route

to Z with a metric of 25

RD=25

RTZ is not a feasible successor because its RD of 25 is greater than RTA’s current FD of 15

10

10

10

14

49

Feasible distance (FD)Feasible distance (FD) is the minimum distance (metric) along a path is the minimum distance (metric) along a path to a destination network.to a destination network.

Reported distance (RD)Reported distance (RD) is the distance (metric) towards a destination is the distance (metric) towards a destination as advertised by an upstream neighbor. Reported distance is the as advertised by an upstream neighbor. Reported distance is the distance reported in the queries, the replies and the updates.distance reported in the queries, the replies and the updates.

A neighbor meets the A neighbor meets the feasible condition(FC)feasible condition(FC) if the reported distance if the reported distance by the neighbor is smaller than the current feasible distance (FD) of by the neighbor is smaller than the current feasible distance (FD) of this router. "If a neighbors metric is less than mine, then I know this router. "If a neighbors metric is less than mine, then I know the neighbor doesn't have a loop going through me.“the neighbor doesn't have a loop going through me.“

50

A A feasible successorfeasible successor is a neighbor whose reported distance (RD) is is a neighbor whose reported distance (RD) is less than the current feasible distance (FD). less than the current feasible distance (FD). Feasible successor is Feasible successor is one who meets the feasible condition (FC)one who meets the feasible condition (FC)..

Your route (metric) to the network (RD to me) must be LESS than my Your route (metric) to the network (RD to me) must be LESS than my current route (my total metric) to that same network. If your route current route (my total metric) to that same network. If your route (metric) to the network (RD to me) is LESS than my current route (metric) to the network (RD to me) is LESS than my current route (my total metric), I will include you as a (my total metric), I will include you as a FEASIBLE FEASIBLE SUCCESSORSUCCESSOR..

If your route (metric) to the network (RD to me) is MORE than my If your route (metric) to the network (RD to me) is MORE than my current route (my total metric), I will current route (my total metric), I will NOTNOT include you as a include you as a FEASIBLE SUCCESSORFEASIBLE SUCCESSOR..

51

What if Successor fails?What if Successor fails?Feasible Successor exists:Feasible Successor exists: If current successor route fails, feasible successor becomes If current successor route fails, feasible successor becomes

the current successor, i.e. the current route.the current successor, i.e. the current route. Routing of packets continue with little delay.Routing of packets continue with little delay.

NoNo Feasible Successor exists: Feasible Successor exists:

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

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

Routing of packets continue but with more of a delay.Routing of packets continue but with more of a delay.

52

Convergence Using EIGRPConvergence Using EIGRP

FDDI R ing

Router A

Router H

Router B

Router D Router E Router F

Router C

Router G

(10)

(20)

(100)

(1)

(100)

(10)

(10)

172.30.1.0/24

Current Successor = 31 RD= 21, Rtr A FD = 31

Feasible Successor, FC: RD30 < FD31

NOT Feasible Successor, FC: RD220 not< FD31

FD to 172.30.1.0 is 31 via Router Y

RouterX

RouterY

RouterZ

RTY is successor with a computed cost of 31.RTY is successor with a computed cost of 31. ““31” is the Feasible Distance (FD).31” is the Feasible Distance (FD). RTX is a feasible successor because its RD is less than the FD.RTX is a feasible successor because its RD is less than the FD.

53


Since RTX is a feasible successor, it is installed in the routing table Since RTX is a feasible successor, it is installed in the routing table immediately (no recomputation).immediately (no recomputation).

It’s RD (30) is less than the FD (31).It’s RD (30) is less than the FD (31).

FDDI R ing

Router A

Router H

Router B


Router C

Router G

(10)

(20)

(100)

(1)

(100)

(10)

(10)

172.30.1.0/24





RouterX

RouterY

RouterZ

X

54


RTZ is not a feasible successor. RTZ is not a feasible successor. It’s RD (220) is greater than the FD (31) for 172.30.1.0/24. It’s RD (220) is greater than the FD (31) for 172.30.1.0/24. Before this route can be installed, the route to net 24 must be placed in Before this route can be installed, the route to net 24 must be placed in

the the active stateactive state and recomputed. and recomputed. Coming soon!Coming soon!

FDDI R ing

Router A

Router H

Router B


Router C

Router G

(10)

(20)

(100)

(1)

(100)

(10)

(10)

172.30.1.0/24





RouterX

RouterY

RouterZ

X

X

55

EIGRP Packet TypesEIGRP Packet Types

The five EIGRP packet types are:The five EIGRP packet types are: HelloHello AcknowledgementAcknowledgement Update (RTP)Update (RTP) Query (RTP)Query (RTP) Reply (RTP)Reply (RTP)

56

Hello packets to discover, verify, and rediscover neighbor routers. Hello packets to discover, verify, and rediscover neighbor routers. EIGRP routers send hellos at a fixed (and configurable) interval, EIGRP routers send hellos at a fixed (and configurable) interval,

called the called the hello intervalhello interval. . The default hello interval depends on the bandwidth of the interface. The default hello interval depends on the bandwidth of the interface.

– 5 seconds, hold time 15 seconds for T1 and faster5 seconds, hold time 15 seconds for T1 and faster– 60 seconds, hold time 180 seconds for slower than T160 seconds, hold time 180 seconds for slower than T1

EIGRP hello packets are multicast. EIGRP hello packets are multicast. On IP networks, EIGRP routers send hellos to the multicast IP address On IP networks, EIGRP routers send hellos to the multicast IP address

224.0.0.10224.0.0.10..

If a neighbor is not heard from for the duration of the If a neighbor is not heard from for the duration of the hold time (three hold time (three times hello interval)times hello interval), EIGRP considers that neighbor down, and , EIGRP considers that neighbor down, and DUAL must step in to reevaluate the routing table. DUAL must step in to reevaluate the routing table. – By default, the hold time is three times the hello interval, but an By default, the hold time is three times the hello interval, but an

administrator can configure both timers as desired. administrator can configure both timers as desired. Unlike OSPFUnlike OSPF routers, EIGRP routers do routers, EIGRP routers do notnot need to have the same need to have the same

hello intervals and hold down intervals.hello intervals and hold down intervals.

EIGRP Hello PacketsEIGRP Hello Packets

57

Acknowledgement PacketsAcknowledgement Packets

Acknowledgement packets, which are “data-less” hello packets, are Acknowledgement packets, which are “data-less” hello packets, are used to ensure reliable communication.used to ensure reliable communication.

– Unlike multicast hellos, acknowledgement packets are unicast. Unlike multicast hellos, acknowledgement packets are unicast.

– Acknowledgements can be made by piggybacking on other kinds Acknowledgements can be made by piggybacking on other kinds of EIGRP packets, such as reply packets.of EIGRP packets, such as reply packets.

58

Update PacketUpdate Packet Update packets are used when a router discovers a new neighbor. Update packets are used when a router discovers a new neighbor.

– An EIGRP sends unicast update packets to that new neighbor so An EIGRP sends unicast update packets to that new neighbor so that it can add to its topology table. that it can add to its topology table.

– More than one update packet may be needed to convey all of the More than one update packet may be needed to convey all of the topology information to the newly discovered neighbor.topology information to the newly discovered neighbor.

Update packets are also used when a router detects a topology change. Update packets are also used when a router detects a topology change. The EIGRP router sends a multicast update packet to all neighbors The EIGRP router sends a multicast update packet to all neighbors

alerting them to the change.alerting them to the change. All update packets are sent reliably. (All update packets are sent reliably. (RTPRTP)) EIGRP routers exchange routing information the same way as other EIGRP routers exchange routing information the same way as other

distance vector routing protocols, but do not send periodic updates.distance vector routing protocols, but do not send periodic updates. EIGRP updates are only sent when a network is added or removed EIGRP updates are only sent when a network is added or removed

from the topology database, when the successor for a given network from the topology database, when the successor for a given network changes, or when the locally used metric is updated.changes, or when the locally used metric is updated.

59

Query and Reply PacketsQuery and Reply Packets EIGRP routers use query packets whenever it needs specific EIGRP routers use query packets whenever it needs specific

information from one, or all, of its neighbors. information from one, or all, of its neighbors.

– A reply packet is used to respond to a query.A reply packet is used to respond to a query.

If an EIGRP router loses its successor and cannot find a feasible If an EIGRP router loses its successor and cannot find a feasible successor for a route, DUAL places the route in the active state. successor for a route, DUAL places the route in the active state.

– the router multicasts a query to all neighbors, searching for a successor to the destination network.

– Neighbors must send replies that either provide information on successors, or indicate that no successor information is available..

Queries can be multicast or unicastQueries can be multicast or unicast, while , while replies are always replies are always unicastunicast. .

Both packet types are sent reliably. (Both packet types are sent reliably. (RTPRTP))

60

A router views its feasible successors as neighbors that are downstream, A router views its feasible successors as neighbors that are downstream, or closer, to the destination than it is.or closer, to the destination than it is.

If something goes wrong with the successor, DUAL can quickly identify If something goes wrong with the successor, DUAL can quickly identify a feasible successor from the topology table, and install a new route to a feasible successor from the topology table, and install a new route to the destination. the destination.

If no feasible successors to the destination exist, DUAL places the route If no feasible successors to the destination exist, DUAL places the route in the active state. in the active state.

Entries in the topology table can be in one of two states: Entries in the topology table can be in one of two states: activeactive or or passivepassive. .

A A passive routepassive route is one that is stable and available for use. is one that is stable and available for use. An An active routeactive route is a route in the process of being recomputed by DUAL. is a route in the process of being recomputed by DUAL.

RecomputationRecomputation happens if a route becomes unavailable and DUAL happens if a route becomes unavailable and DUAL can’t find any feasible successors.can’t find any feasible successors.

Another route may exist, it is just that their Reported Distance was Another route may exist, it is just that their Reported Distance was greater than your Feasible Distance.greater than your Feasible Distance.


61

EIGRP ConfigurationEIGRP Configuration

RTA(config)#RTA(config)#

AS must be the same on all routers in the AS

If AS’s are identical on a router running both IGRP and EIGRP, routing tables are redistributed automatically.

router eigrp ASRTA(config-router)#network networkRTA(config-router)#network 1.0.0.0

IOS 12.0 added the stub command (separate line) for stub networks and allows for a wildcard mask in the network statement. Stub routers only announce their directly connected networks or static routes to the hub routers.

router(config-router)# eigrp stub

62

RTA(config)#RTA(config)#

Use the EIGRP network command as you would the IGRP or RIP network command.

router eigrp 123

RTA(config-router)#network 1.0.0.0

EIGRP ConfigurationEIGRP Configuration

63

EIGRP Route SummarizationEIGRP Route SummarizationOptional Interface Command:Optional Interface Command:

RTA(config-if)# RTA(config-if)# no auto-summaryno auto-summary

RTA(config-if)# RTA(config-if)# ip summary-address eigrpip summary-address eigrp autonomous-system-number ip-address maskautonomous-system-number ip-address mask

You can configure a summary aggregate address for a specified interface, RTA(config-if), or for all interfaces, RTA(config-router). (Same command.)

If any more specific routes are in the routing table, EIGRP will advertise the summary address out the interface with a metric equal to the minimum of all more specific routes.

64

Default behaviorDefault behavior

By default, EIGRP summarizes at classful network By default, EIGRP summarizes at classful network boundaries, like RIP.boundaries, like RIP.

Summarization can be disabled using: (RouterTwo)Summarization can be disabled using: (RouterTwo)

router eigrp 2000router eigrp 2000

no auto-summaryno auto-summary

172.16.0.0/16

172.16.1.0/24

172.16.3.0/24

172.16.2.0/24

172.16.0.0/16

65

ip summary-address (interface specific only) - choose your mask!ip summary-address (interface specific only) - choose your mask!

interface Serial0 interface Serial0

ip address 10.1.50.1 255.255.255.0 ip address 10.1.50.1 255.255.255.0

ip summary-address eigrp 2000 192.1.0.0 255.255.252.0ip summary-address eigrp 2000 192.1.0.0 255.255.252.0

router eigrp 2000router eigrp 2000

no auto-summaryno auto-summary

network ...network ...

192.1.1.0/24

192.1.2.0/24

192.1.3.0/24

192.1.0.0/18

66

EIGRP Variance CommandEIGRP Variance CommandOptional Interface Command:Optional Interface Command:

RTA(config-router)# RTA(config-router)# variance variance numbernumber

IGRP and EIGRP also support unequal cost path load balancing, which is known as variance.

The variance command instructs the router to include routes with a metric less than or equal to n times the minimum metric route for that destination, where n is the number specified by the variance command.

Note: If a path isn't a feasible successor, then it isn't used in load balancing.

67

Let's look at an example, there are three ways to get to Let's look at an example, there are three ways to get to Network X, from Router E: (Note: metrics incorrectly not Network X, from Router E: (Note: metrics incorrectly not including outgoing interface to Net X.)including outgoing interface to Net X.)

E-B-A with a metric of 30 E-B-A with a metric of 30

E-C-A with a metric of 20 E-C-A with a metric of 20 <<<-- Minimum Metric<<<-- Minimum Metric

E-D-A with a metric of 45E-D-A with a metric of 45

68

variance 2variance 2 This increases the minimum metric to 40 (2 * 20 = 40). This increases the minimum metric to 40 (2 * 20 = 40). EIGRP includes all the routes that have a metric less than or EIGRP includes all the routes that have a metric less than or

equal to 40, equal to 40, andand are feasible successors. are feasible successors. In the above configuration, EIGRP now uses two paths to get In the above configuration, EIGRP now uses two paths to get

to Network X, E-C-A and E-B-A, because both paths have a to Network X, E-C-A and E-B-A, because both paths have a metric under 40.metric under 40.

router eigrp 1

network x.x.x.x

variance 2

69

Two unequal-cost paths:Two unequal-cost paths:

E-B-A with a metric of 30 <<<-- Also below 2*20 E-B-A with a metric of 30 <<<-- Also below 2*20

E-C-A with a metric of 20 E-C-A with a metric of 20 <<<-- Minimum Metric<<<-- Minimum Metric

E-D-A with a metric of 45E-D-A with a metric of 45

EIGRP doesn't use path E-D-A because it has a metric of 45, EIGRP doesn't use path E-D-A because it has a metric of 45, andand it's not a it's not a feasible successor. Can have up to 6 unequal cost paths.feasible successor. Can have up to 6 unequal cost paths.

router eigrp 1

network x.x.x.x

variance 2

70

Redistribution b/t EIGRP & IGRPRedistribution b/t EIGRP & IGRP

Same AS numbersSame AS numbers

Router TwoRouter Two router eigrp 2000 router eigrp 2000 network 172.16.1.0network 172.16.1.0! ! router igrp 2000 router igrp 2000 network 10.0.0.0network 10.0.0.0

(automatic redistribution)(automatic redistribution)

Different AS numbers Router Two router eigrp 2000 redistribute igrp 1000 network 172.16.1.0! router igrp 1000 redistribute eigrp 2000 network 10.0.0.0

So what is the difference? We’ll see later when discussing Redistribution.

71

EIGRP and default routesEIGRP and default routes

There are three ways to inject a default route into There are three ways to inject a default route into EIGRP: EIGRP:

Redistribute a static routeRedistribute a static route IP default-networkIP default-network Summarize to 0.0.0.0/0Summarize to 0.0.0.0/0

72

Redistribute a static routeRedistribute a static route

Use the first method when you want to draw all traffic to unknown Use the first method when you want to draw all traffic to unknown destinations to a default route at the core of the network. destinations to a default route at the core of the network.

This method is effective for advertising connections to the Internet. This method is effective for advertising connections to the Internet. For example: For example:

Gateway RouterGateway Routerip route 0.0.0.0 0.0.0.0 x.x.x.x (next hop) ip route 0.0.0.0 0.0.0.0 x.x.x.x (next hop) ! ! router eigrp 100 router eigrp 100 redistribute staticredistribute static <text omitted><text omitted>


73

Ip default-networkIp default-network

Propagates a default route to other routers, but needs to have a route or Propagates a default route to other routers, but needs to have a route or default route out once the packets arrive.default route out once the packets arrive.

Gateway RouterGateway Router

router igrp 24router igrp 24

<text omitted><text omitted>

network 207.21.20.0network 207.21.20.0

ip route 0.0.0.0 0.0.0.0 207.21.20.1ip route 0.0.0.0 0.0.0.0 207.21.20.1

ip default-network 207.21.20.0ip default-network 207.21.20.0


74

Extra: Summarize to 0.0.0.0/0Extra: Summarize to 0.0.0.0/0

Summarizing to a default route is effective only when you want to Summarizing to a default route is effective only when you want to provide remote sites with a default route. provide remote sites with a default route.

Since summaries are configured per interface, you don't need to worry Since summaries are configured per interface, you don't need to worry about using distribute-lists or other mechanisms to prevent the default about using distribute-lists or other mechanisms to prevent the default route from being propagated toward the core of your network.route from being propagated toward the core of your network.

router eigrp 100 router eigrp 100 network 10.0.0.0 network 10.0.0.0 ! ! interface serial 0 interface serial 0 ip address 10.1.1.1 ip address 10.1.1.1 ip summary-address eigrp 100 0.0.0.0 0.0.0.0ip summary-address eigrp 100 0.0.0.0 0.0.0.0


Sem5 eigrp chp6

Technology

Transcript of Sem5 eigrp chp6