EIGRP

1
EIGRP

• CCNP1 version 3.1
• Chapter 5

2
Table of Contents

• Basics of EIGRP
• EIGRP Terminology
• EIGRP Operation
• EIGRP Configuration
• Monitoring EIGRP

3

• Basics of EIGRP

4
EIGRP Overview

• Enhanced version of Ciscos proprietary IGRP
• Uses a more granular version of IGRPs metrics
  (32 bits v. 24 bits)
• Has faster convergence than any other IGP
• Is scalable because of VLSM and route
  summarization
• Supports multiple routed protocols through
  protocol-dependant modules
• Is technically an advance distance-vector routing
  protocol
• Uses partial updates
• Hello packets for neighbor discovery

5
EIGRP Metrics

• EIGRP scales IGRPs metrics by a factor of 256
• IGRP metric 24 bits EIGRP metric 32 bits
• Bandwidth and Delay are equally weighted
• Reliability, Load, and MTU are off by default
• Hop count limited to 224 (IGRPs limit is 255)

6
EIGRP Tables

• Like OSPF, EIGRP maintains three unique tables to
  assist in routing traffic.
• Neighbor Table
• Topology Table
• Routing Table
• EIGRP maintains one table of each for each routed
  protocol configured on the router.
• For example, if a router was configured with IP,
  IPX and AppleTalk, EIGRP would maintain
• 3 Neighbor Tables
• 3 Topology Tables
• 3 Routing Tables

7
Neighbor Table

• Use the show ip eigrp neighbors command to view
  the table.
• Similar to OSPFs Adjacencies database
• Contains a list of all neighbors discovered
  through hellos
• Maintains hello and holdtime intervals on each
  neighbor
• Maintains information required by RTP (discussed
  later)
• SRTTSmooth Round-trip Timer avg. time it takes
  to send and then receive a reply from that
  neighbor
• RTORetransmission Timeout how long to wait
  without receiving an acknowledgement to a
  reliably sent packet

Routershow ip eigrp neighbors IP-EIGRP neighbors
for process 100 H Address
Interface Hold Uptime SRTT RTO Q Seq

(sec)
(ms) Cnt Num 0 192.168.224.2
Se0 13 000128 930 5000 0
30 1 192.168.208.2 Se1 11
000220 35 1140 0 21
8
Topology Table

• Use the show ip eigrp topology all-links
  command to view the table.
• Similar to OSPFs Link-State (Topology) database
  
• Contains all learned routes from its neighbors
  all information necessary to calculate distance
  vector to all reachable destinations
• FDFeasible Distance lowest calculated metric to
  reach a destination as opposed to
• RDReported Distance or Advertised Distance
  distance to the destination reported by the
  neighbor.

9
Routing Table

• Use the show ip route command to view table
• Like all routing protocols, EIGRP maintains a
  routing table with
• Best routes to destination networks
• Maintains up to four equal-cost routes for each
  destination
• Unequal-cost routes can be installed if the
  variance command has been configured

10

• EIGRP Terminology

11
EIGRP Concepts Terminology

• Successor
• The best/lowest cost route to the destination is
  installed in the routing table.
• Multiple successors can be installed for load
  balancing
• Feasible Successor
• A next-hop alternative route to the destination
  is kept in the topology table, ready to be
  installed if the successor fails
• Feasible successors are only in the topology table

12
EIGRP Concepts Terminology

• Active State
• During route recomputation, routes lost due to a
  successors failure are said to be in the active
  state.
• The active state ends when the route is restored
  or removed.
• Passive State
• Installed routes that are not in the process of
  being recomputed are said to be in the passive
  state.

13
EIGRP Concepts Terminology

• Diffusing Update Algorithm (DUAL)
• EIGRPs route computation engine guarantees a
  loop-free topology.
• calculates EIGRPs metric and installs successors
  in the routing table feasible successors in the
  topology table
• Route Evaluation
• Occurs when the topology changes DUAL evaluates
  the topology table, searching for feasible
  successors and immediately installing them, if
  found no recomputation is necessary.

14
EIGRP Concepts Terminology

• Route Recomputation
• DUAL begins recomputing if no feasible successors
  are found queries neighbors for alternative
  routes process ends when all neighbors have
  replied and DUAL either installs successor or
  removes route from the topology and routing
  tables.
• Protocol Dependant Modules (PDM)
• EIGRPs scalable and adaptable feature because of
  its modularity.
• Theoretically, EIGRP does not have to be
  completely rewritten to route IPv6just add a new
  PDM.

15
EIGRP Packet Types

• Hello Packets
• Unreliable multicast to 224.0.0.10 to discover
  and maintain neighbors contains the routers
  neighbor table
• Default hello interval depends on the bandwidth
• 1.544 Mbps 60 sec. hello interval (180
  holdtime)
• gt 1.544 Mbps 5 sec. hello interval (15
  holdtime)
• Update Packets
• Sent reliably, there are 2 types
• Unicast to new neighbor discover contains
  routing table
• Multicast to all neighbors when topology changes

16
EIGRP Packet Types

• Query Reply Packets
• Queries are multicast reliably during route
  recomputation, querying neighbors for a new
  successor to a lost route
• Neighbors unicast a reply to the query whether or
  not they have a route.
• Acknowledgement Packets
• Dataless packet that acknowledges the receipt
  of a packet sent reliably

17
Reliable Transport Protocol

• RTP is EIGRPs flexible protocol used to
  transport message types through a network
• Since EIGRP is protocol independent, it has to
  have its own connection-oriented and
  connectionless services
• RTP allows unicasting and multicasting reliable
  and unreliable packets to peers simultaneously
• RTP maintains a transmission list in the neighbor
  table with sequence numbers to determine when a
  required acknowledgement has been received.
• Works much like TCPs Positive Acknowledgement
  with Retransmission

18

• EIGRP Operation

19
The EIGRP Process

• EIGRP operation is completed in five stages
• Building neighbor relationships (1)
• Discovering routes (1)
• Choosing the best routes (2)
• Maintaining routes (2)
• Removing routes
• These stages do not necessarily occur sequentially

20
Building Neighbor Relationships

• Neighbor relationships are established through
  the use of Hello packets
• A new router configured with EIGRP will multicast
  hello packets to directly connected routers
• The receiving routers will reply if the new
  router is
• Configured with EIGRP
• In same AS
• Using the same metric weights

21
Discovering Routes

• While neighbor relationships are established, the
  following steps occur
• The new router multicast hellos to 224.0.0.10
• Directly connected routers respond with a unicast
  update packet containing all the routes in their
  routing table
• The new router replies to all neighbors with a
  unicast Ack packet and places the contents of the
  updates in its topology table
• The new router then unicast update packets to all
  neighbors with the contents of its topology table
  (this is how its neighbors learn about the
  routers uniquely configured networks such as a
  new LAN)
• Neighbors reply to the new routers update with
  an Ack packet.

22
Building/Discovering Example

• C comes online and multicasts hellos to A B.
• A B unicast an update packet containing routing
  table contents
• C replies to unicast updates with Ack packet and
  builds topology table
• C unicasts updates to A B with contents of
  topology table (includes Cs new LAN)
• A B reply with an Ack packet.

23
Choosing the Best Routes

• After a new router has received all the updates
  from directly connected neighbors, it can
  calculate its DUAL.
• 1st - the metric for each route in the topology
  table is calculated using the following formula
• Metric 256(10,000,000/min. bandwidth) sum of
  delays
• 2nd - the route with the lowest cost is
  designated the successor and is installed (max 4
  equal costs) in the routing table.
• DUAL looks for feasible successors. An FS must
  have a lower feasible distance to the destination
  than the installed routes feasible distance.
• All FS are maintained in the topology table so
  DUAL can install them immediately if the
  successor fails.

24
Maintaining Routes

• As new routers come online and old routes fail,
  EIGRP quickly and efficiently handles these
  situations with little or no downtime.
• As new routers come online, their hello packets
  and the ensuing update process has a domino
  effect on the network.
• All routers in the AS almost instantaneously
  converge on the routers new networks.
• Maintaining routes also means informing directly
  connected neighbors when another neighbor stops
  sending hello packets at the required interval.

25
Removing Routes

• When a route fails (a directly connected neighbor
  is no longer sending hellos), the detecting
  routers DUAL
• Enters the route evaluation phase.
• Is there a feasible successor in the topology
  table? If so, immediately install it, begin
  routing to the alternative path, and update
  neighbors about the alternative.
• If no feasible successor exists, enter route
  recomputation

26
Removing Routes

• If necessary, enter the route recomputation
  phase.
• Query neighbors for a alternative route
• If neighbor has a feasible successor, it will
  send it to the router
• If it does not have one, it will query all its
  directly connected neighbors, thus flooding the
  AS with the query until an alternate route is or
  is not found.
• Once the router has received replies from all
  queried neighbors, it can then recalculate the
  best route.
• If a new alternative is found, it will be
  installed in the routing table.
• If no new alternative is found, the old route is
  removed.

27
EIGRP Convergence Summary

• Router detects link failure enters route
  evaluation
• Feasible successors are promoted to successors
• Successors are installed in the routing table
  immediately
• All neighbors are updated about the new alternate
  route
• If no feasible successors, router enters route
  recomputation
• Queries are flooded throughout the AS in search
  of an alternate
• All routers reply whether they have an
  alternative or not
• Originating router waits for all replies before
  either
• Removing the queried network for its topology and
  routing tables or
• Adding an alternative path for the queried
  network in its tables
• If a query receives no response, the route
  becomes stuck-in-active

28
EIGRP Convergence Summary

• The router has now converged and will now work to
  converge the entire internetwork by
• Generating an update and multicasting it out all
  interfaces
• Update contains info. on what paths the router
  has added/removed from its topology and routing
  tables
• Each receiving router will replay with an Ack
  packet and modify tables accordingly
• The EIGRP internetwork has now converged.

29

• Perform Labs as needed please.

30
EIGRP Configuration
31
Basic Configuration

• Similar to IGRP, EIGRP is started with the
  following commands
• Router(config)router eigrp AS_number
• Router(config-router)network network-number
• A router running both IGRP and EIGRP with the
  same AS number will automatically redistribute
  from one routing process into the other
• EIGRP routes redistributed into IGRP are denoted
  with an I in the routing table.
• IGRP routes redistributed into EIGRP are denoted
  with an D EX in the routing table.

32
Basic Configuration

• For interfaces whose actual bandwidth is
  different than EIGRPs defaults, use the
  following command.
• Router(config-if)bandwidth kilobits
• For example, a serial link defaults to T1 speeds
  or 1544 kbps. If the contracted speed is ½ a T1
  or 768 kbps
• Router(config-if)bandwidth 768

33
Route Summarization

• EIGRP recognizes two types of summary routing
• Automatic route summarization
• Manual route summarization
• Automatic Summarization (on by default in EIGRP)
• Works the same as IGRP and RIP
• Summarizes routes on the classful boundary does
  not advertise subnets subnets must be
  contiguous.
• For example
• Subnets 172.16.16.0/20, 172.16.32.0/20, and
  172.16.48.0/20 would be automatically summarized
  as 172.16.0.0/16
• Automatic summarization has its benefits
• Conserves resources across classful boundaries in
  networks with proper IP addressing design.

34
Manual Summarization

• Automatic summarization must be turned off.
• in the routing process for EIGRP
• Router(config-router)no auto-summary
• To configure a classless summary route
• Subnets must be contiguous!!
• Use the following command on the interface that
  will advertise the summary
• Router(config-if)ip summary-address eigrp
  AS-number ip-address mask

35
Manual Summarization Example

• On Router B, you would summarize routes
  advertised to A as follows
• !Start the routing process disable automatic
  summarization
• RTB(config)router eigrp 100
• RTB(config-router)network 190.1.1.0
• RTB(config-router)network 190.1.2.0
• RTB(config-router)network 190.1.3.0
• RTB(config-router)no auto-summary
• !Then on the interface, summarize the subnets
  advertised to A
• RTB(config-router)interface e0
• RTB(config-if)ip address 10.2.50.1 255.255.255.0
• RTB(config-if)ip summary-address eigrp 100
  190.1.0.0 255.255.252.0

36
Manual Summarization Example

• Router Bs topology table would show all the
  specific routes as well as the summary
• RTBshow ip eigrp topology
• IP-EIGRP Topology Table for process 1
• (output omitted)
• P 190.1.1.0/24, 1 successors, FD is 10511872
• via Connected, Serial1
• P 190.1.0.0/22, 1 successors, FD is 10511872
• via Summary (10511872/0), Null0
• P 190.1.3.0/24, 1 successors, FD is 10639872
• via 190.1.1.1 (10639872/128256), Serial1
• P 190.1.2.0/24, 1 successors, FD is 10537472
• via 190.1.1.1 (10639872/128256), Serail1

37
Manual Summarization Example

• Router As topology table would show only the
  summary route
• Any packet destined for a network that is part of
  the 190.1.0.0/22 summary would be sent to Router
  B.
• RTAshow ip eigrp topology
• IP-EIGRP Topology Table for process 1
• (output omitted)
• P 190.1.0.0/22, 1 successors, FD is 11023872
• via 10.2.50.1 (11023872/10511872), Serial0

38
Bandwidth Optimization

• By default, EIGRP will only consume up to 50 of
  a links configured bandwidth.
• Why would you want to change the default setting?
• A network apps require minimum bandwidth at all
  times.
• traffic will require a certain level of bandwidth
  availability.
• Note Changing EIGRPs bandwidth percentage has
  no effect on user traffic.
• Two commands to configure EIGRP traffic
  percentage.
• bandwidth
• ip bandwidth-percent eigrp

39
bandwidth Configuration

• Router(config-if)bandwidth bandwidth
• Whatever value is specified with the bandwidth
  command, EIGRP always takes 50 of it (by
  default).
• Remember The bandwidth command is only used by
  routing protocolsit has no effect on user
  traffic when the protocol is EIGRP. The router
  does not use this command for any other purpose.
• For example, you have a 128kbps link and you only
  want EIGRP to use 16kbps.
• Router(config-if)bandwidth 32
• EIGRP will use, at most, 50 of the configured
  bandwidth
• User traffic will still be allowed to use at
  least 112kbps (128-16)

40
bandwidth-percent Configuration

• The second way to modify how much bandwidth EIGRP
  uses is to use the following command
• Router(config-if)ip bandwidth-percent eigrp
  AS-number percent
• Used to specify a different percentage than 50
  of the configured bandwidth.
• IE you have a 64kbps link and the bandwidth has
  been set to 32kbps for metric calculation
  purposes.
• EIGRP needs to use 32kbps of the links 64kbps
  speed.
• Router(config)int s0
• Router(config-if)bandwidth 32
• Router(config-if)ip bandwidth-percent eigrp 123
  100

41
NBMA Configurations

• NBMA Configuration Guidelines
• EIGRP should not exceed the CIR of the hubs
  serial line (also called the access line).
• called oversubscribing the link
• Aggregate traffic of all links to the hub should
  not exceed the hubs access line speed.
• Bandwidth on virtual circuits must be the same in
  both directions.

42
Point-to-Point NBMA

• Each spoke router has a virtual circuit to the
  hub with a CIR of 256kbps.
• This is an oversubscribed situation.
• Why would you want to oversubscribe the spoke
  routers?
• Allows up to 256kbps per spoke when traffic from
  other spokes is light.

• Solution
• Configure the 10 subifs with bandwith of 154kbps
  so EIGRP will only use 50 of the subif when the
  NBMA is saturated with user traffic.

43
Point-to-Point Configurations

• Hub_Router(config)interface serial 0
• Hub_Router(config-if)encapsulation frame-relay
• Hub_Router(config-if)int serial0.1
  point-to-point
• Hub_Router(config-subif)bandwidth 154
• Hub_Router(config-subif)int serial0.2
  point-to-point
• Hub_Router(config-subif)bandwidth 154
• . . .
• Hub_Router(config-subif)int serial0.10
  point-to-point
• Hub_Router(config-subif)bandwidth 154

44
Multipoint EIGRP

• In point-to-multipoint configurations...
• If the CIR of each Spoke Router is the same, set
  the access lines bandwidth to the sum of the
  CIRs
• If the CIR of the Spoke Routers are different,
  which is the usual case, either...
• Take the lowest CIR and multiply it by the number
  of virtual circuits. This causes higher bandwidth
  links to be underutilized.
• Preferred Hybrid Solution Use subinterfaces and
  configure like bandwidth virtual circuits on the
  same subinterface.

45

• Monitoring EIGRP

46
Monitoring EIGRP