Module 3

1

CCNA3
–

module 3 EIGRP

2

EIGRP


Cisco proprietary, released in 1994


Based on IGRP


EIGRP is an
advanced distance
-
vector

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


Supports VLSM and CIDR


Allows for multiple routed protocols

3

EIGRP


Uses Hello protocols to create and maintain neighbor
relationships and to determine when a link is down.
(Like link
-
state)


Every 5 seconds, with a hold timer of 15 seconds


Links less than T1 speed, Hellos are every 60
seconds, hold timer of 180 seconds


Partial routing updates in response to topology
changes


When a change in topology occurs, EIGRP does not
flood updates like link
-
state protocols, but
immediately

sends those changes to its neighbors.

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

4

EIGRP Benefits


Rapid Convergence
–

DUAL routing algorithm


Efficient use of bandwidth


partial, bounded updates
–

only sent to routers
that need the information & not entire routing
table


small “Hello” packets to keep in touch with other
routers
–

minimal use of bandwidth


Supports VLSM and CIDR


Multiple network
-
layer support (multiprotocol)


IP, IPX, and AppleTalk

5

EIGRP and IGRP


Automatically

redistributes when using same AS
number.


Topology example….

6

Metric calculation: IGRP/EIGRP

(with the following default constant values):

Constant Value

K1



1

K2



0

K3 1

K4



0

K5



0

Notes



k2

metric effects
LOAD



k4

and
k5

effects
RELIABILITY


metric

= [K1 *
bandwidth

+ ((K2 *
bandwidth
) / (256 *
load
)) +
(K3 *
delay
)] * [K5/(
reliability

+ K4)]

7

Metric Calculation

Simplify the previous equation by
applying the default constants
…

8

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


bandwidth


delay


load


reliability


By default, EIGRP uses only:


Bandwidth (carrying capacity)


Delay (end
-
to
-
end travel time)

Metric Calculation

9

If these are the default:


bandwidth (default)


delay (default)


When are these used?


load


reliability


Use
show interface

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

Metric Calculation

10

Metric 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>

11

Bandwidth


Expressed in
kilobits

(
show interface
)


This is a
static number

and used for metric
calculations only.


Does not necessarily reflect the actual bandwidth of
the link.


You can adjust the bandwidth metric on an interface
using what command?


What command restores the interface bandwidth to
the original default?


The default values:


What is the default bandwidth of serial interfaces on
CISCO routers?

Metric Calculation
–

Bandwidth

12

Delay


Like bandwidth, delay it is a
static number
.


Expressed in
microseconds
,
millionths of a
second



(Uses the Greek letter mu with an S,

S, NOT “ms”
which is millisecond or
thousandths of a second
)


The default values:


What is the default delay of a Cisco serial interface?



IGRP/EIGRP metric uses the
sum of all of the
delays

of all of the outbound interfaces to the
destination network.

Metric Calculation
–

Delay

13

Changing the delay informational parameter:

The delay can be changed using:


Router(config
-
if)#
delay

tens
-
of
-

S



(microseconds)



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


Router(config
-
if)#
delay

3000


To restore the 20,000 microsecond default value:


Router(config
-
if)#
no delay

Metric Calculation
–

Delay

14

IGRP vs EIGRP Metric Calculation

The difference
:


IGRP metric is 24 bits long


EIGRP metric is 32 bits long


EIGRP metric is 256 times greater for the
same route


EIGRP allows for finer comparison of
potential routes

15

IGRP vs EIGRP Metric Calculation

IGRP


bandwidth = (10,000,000
÷

bandwidth
)


delay =
delay
÷

10


EIGRP


bandwidth = (10,000,000
÷

bandwidth
) * 256


delay = (
delay
÷

10) * 256


Note: The reference
-
bandwidth


For both IGRP and EIGRP: 10
7
,
(10,000,000/bandwidth), whereas


with OSPF it
was 10
8
(100,000,000/bandwidth)

16

Metrics
–

HOP COUNT


EIGRP also imposes a maximum hop count
of 224


IGRP maximum hop count of 255


RIP maximum hop count of 15

17

EIGRP Configuration

RTA(config)#
router eigrp
AS

RTA(config
-
router)#
network
network

RTA(config
-
router)#
eigrp

log
-
neighbor
-
changes

RTA(config
-
if)#
bandwidth

kilobits

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.

Enables logging of neighbor adjacency
changes to monitor stability & help
detect problems

CISCO recommends this command.

EIGRP assumes default if not set.

If the link is slower, router might not
converge, routing updates may be lost,
or suboptimal path selection may result.

18

EIGRP tables


Neighbor


Topology


Routing

19

EIGRP Neighbor tables


Lists adjacent routers


One table for each routed protocol that
EIGRP supports


RTX#
show ip eigrp neighbors

IP
-
EIGRP neighbors for process 1

H Address Interface Hold Uptime SRTT RTO Q Seq


(sec) (ms) Cnt Num

1 10.2.0.2 Se1 12 00:27:39 333 1998 0 10

0 10.1.0.1 Se0 14 01:17:14 40 240 0 27

20

EIGRP Neighbor tables


Fields in neighbor table:


Neighbor address (Address)


Hold time (Hold Uptime)


Smooth round
-
trip timer (SRTT)


Queue count (Q Cnt)


Sequence number (Seq No)


21

DUAL
–

calculating best paths


When the hold time expires, DUAL is informed of
the topology change and must recalculate the
new topology.




DUAL (Diffusing Update Algorithm)
–

allows
routers involved in a topology change to
synchronize at the same time, while not
involving routers that are unaffected by the
change (distance
-
vector algorithm)


22

EIGRP Topology tables


Contains all of the EIGRP routing tables in the
autonomous system


DUAL combines information supplied by
neighbor and topology tables and calculates
the lowest cost routes to each destination.


EIGRP routers track changes and switch to
alternate routes when necessary


DUAL places this primary route, or
successor
route
, information in the routing table


23

EIGRP Topology tables

Topology tables includes:


Feasible distance (FD)
–

lowest calculated metric to
each destination.


Route source (via xxx.xxx.xxx.xxx)
–

ID of router that
originally advertised route


Reported distance (RD)
–

distance that an adjacent
neighbor reports to specific destination


Interface information
–

interface through which the
destination is reachable


Route status
–



passive (P)
–

route is stable and ready for use


Active (A)
–

route is in the process of being recomputed by
DUAL

24

EIGRP Topology tables

RTX#
show ip eigrp topology

IP
-
EIGRP Topology Table for process 100


Codes: P
-

Passive, A
-

Active, U
-

Update, Q
-

Query, R
-

Reply, r
-

Reply status


P 200.10.3.0/24, 1 successors, FD is 2169856


via Connected, Serial1


via Redistributed (2169856/
0
)

P 200.10.4.0/24, 1 successors, FD is 2169856


via Connected, Serial0

RD

25

EIGRP Topology tables

Successor
–

route that is selected as the primary
route to use to reach a destination.


DUAL identifies and places route in routing table


There can be up to
four

successor routes for any
particular route.


Copy of successor is also placed in topology table


EIGRP sorts the topology table so that the
successor routes are at the top, followed by the
feasible successors. Bottom of list may include
routes that DUAL believes to be loops.

26

EIGRP Topology tables

Feasible Successor
–

backup route


Identified at same time as successor but kept only
in the topology table


May have multiple feasible successors but not
mandatory to have any


They are neighbors that are downstream (closer
to the destination)


Must have lower advertised cost (RD) than
existing successor’s FD


If feasible successor not identified,
active status

placed on route and query packets sent to all
neighbors to recompute topology.

27

Successor & Feasible Successor

28

Recomputation of Routes


If route becomes unavailable and DUAL
cannot find feasible successor.


Neighbor routers are compelled to answer
query for a loop
-
free path.


If neighbor has no route, it responds so.


Excess computation = network instability


To prevent convergence problems, DUAL
always tries to find a feasible successor before
resorting to recomputation

29

Recomputation of Routes


Stuck in Active

routers
–



one or more routers don’t respond to query
(180 seconds) then routes placed in stuck in
active state


EIGRP then clears its table of neighbors
that did not respond

30

Route Tagging


Routing Table
–



Internal routes


routes originating
within

the EIGRP AS


External routes


routes originating
outside

the EIGRP AS


31

Routing Table & Tagging

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



External EIGRP routes are redistributed from IGRP networks

32

RTA#
show ip route

<output omitted>

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


External EIGRP routes are redistributed from IGRP networks

RTC#
show ip route

<output omitted>

C 192.168.1.0 is directly connected, Serial0

I

10.1.0.0 [100/10476] via 192.168.1.1, 00:00:04, Serial0

I

172.16.0.0 [100/10476] via 192.168.1.1, 00:00:04, Serial0

RTC only sees

IGRP routes

192.168.1.0

was redistributed

from IGRP

33

Hellos & RTP


Hello Packets


Sent every 5 seconds (high
-
bandwidth links)
and every 60 seconds by default (low
-
bandwidth links)


As long as routers receive hello packets
–

route in
passive

state


Reliable Transport Protocol (RTP)


Layer 4 protocol


Guarantees delivery of packets


Allows EIGRP to multicast and unicast to
different peers simultaneously

34

DUAL FSM


DUAL Finite
-
State Machine (DUAL FSM)


Full name of DUAL technology


Tracks routes advertised by neighbors and
uses composite metric to compare them


Guarantees each path is loop
-
free


Inserts lowest
-
cost paths (successor routes)
into routing table


Neighbor & Topology tables supply DUAL with
route information to make decisions quickly

35

DUAL FSM

FD is not mandatory

2 < 3

36

EIGRP Packets

•
Hello Packets

•
5 second updates (T1/Point
-
to
-
Point link)

•
Multicast on IP address
224.0.0.10

•
Hold Time =
3 times the Hello interval



(15 seconds)

•
Neighbor routers hello and dead intervals
do not

need to match with EIGRP (unlike
OSPF)

37

EIGRP Packets

•
Acknowledgement

•
Used by RTP to signal reliable exchange of information

•
Hello packet without data; unicast to specific host


•
Update

•
Discovery of new neighbor

•
EIGRP router sends unicast to neighbor so that it can
add to its topology table

•
EIGRP router send multicast to all neighbors if topology
change occurs

38

EIGRP Packets

•
Query & Reply

•
Query
-

Used to obtain specific information from one or
all of its neighbors (multicast or unicast)

•
Reply
–

response to query (unicast)

•
Used, for example, if DUAL places a route in active
state and multicasts neighbors, searching for successor

39

EIGRP Route Summarization


EIGRP automatically summarizes routes at the
classful

boundary

This may not be preferable, especially if using
VLSM

To disable auto
-
summarization:

Router(config
-
router)#
no auto
-
summary

Manual Summarization command:

Router(config
-
if)#
ip summary
-
address
eigrp
AS ip
-
address subnet
-
mask
administrative distance

(configured on a per-interface basis)
40

EIGRP Route Summarization


41

Verifying EIGRP


Show ip eigrp neighbors


Show ip eigrp interfaces


Show ip eigrp topology


Show ip eigrp topology all
-
links


Show ip eigrp traffic
AS


Debug eigrp fsm


Debug eigrp packets

42

RIP, IGRP, & OSPF
Troubleshooting


Show & debug commands


Debug ip rip


Debug ip igrp events


Debug ip igrp transactions


Debug ip ospf events


Show ip route


Show running
-
config


Show ip protocols


show ip ospf neighbor