EIGRP – Enhanced Internal Gateway Routing Protocol

EIGRP – Enhanced Internal Gateway Routing Protocol.

This Blog post is more of notes for myself, and information for others related to EIGRP features.

Capabilities and other Attributes.

Default times and numbers to remember.

Active queries -> 3 minutes.

Hello packets -> 5 seconds.

Default Hold timer – > 180 Seconds

Multicast address – >

Port – > 88

Fast convergance

EIGRP Default Metric(K Values) – > K1 and K3 = 1 (Bandwith and delay)

Internal Administrative Distance – > 90

External Administrative Distance – > 170

Cisco Proprietary

Features of EIGRP

Advanced Distance Vector

Partial / triggered updates based up its neighbors

Multiple network layer support – v6/v4 IPX apple talk

VLSM support

Dual Algorithm

Route Summarization by default

RTP – > uses RTP

EIGRP keeps different tables each EIGRP router has the following tables.

EIGRP Neighbor Table – > Includes the neighbors…. Next hop router / Interface

EIGRP Topology Table – > Learns routes from each EIGRP Neighbor

EIGRP IP routing Table – > Lists only the best routes using EIGRP

Different type of EIGRP Packets..

Hello – > packets used for neighborhood discovery

Update – > When a change is made from neighbor to neighbor it send a update packet

Query – > when a router does not have a Feasible successor and needs a backup route

Reply – > a packet is sent when replying to a Query

ACK – > Unicast packets sent as to acknowledge reply

EIGRP Neighbor forming process

Hello packet is sent out of an interface

Hello packet is received interface

Router A Sends complete topology table

Router B sends ACK then sends its Topology table

Then Router A sends ACK that it got the table.

EIGRP uses K Values for its metric.

How EIGRP Does metric Calculation In K Values….



Reliability – based on keepalives.


MTU(not by default but can be configured to use)

How to change K Values?

# router eigrp [as]

# metric weights 0 1 1 1 1 0

So if I wanted to go about changing my K value to 3x as much for bandwith I would do the following…

# metric weights 0 3 1 1 1 0

How to check K values?

Sh Ip proto

EIGRP uses to ways of calculating its Metric, Advertised Distance and Feasible Distance

Using our Topology table to compare

Advertised Distance – > Host ———-10 cost———Router———-20cost——-Router

Feasible distance – > 30 cost

Feasible distance – > cost from you

Advertised distance – > distance from your neighbor to path. Hence why it is called Advertised distance, the router is advertising that distance from it.

Successor – > Best route to a path.

Feasible Successor – > backup path to the best path

EIGRP Supports several types of routes – > internal , external, summary.

WAN EIGRP with Frame Relay

Make sure to disable split horizon..

No ip split-horizon eigrp 110

It will then resync the neighbor after a No split-horizon, after sending a Graceful shutdown.

Make sure with even point to point to turn off auto summary especially if the following happens.

( A———FR Cloud—————–Router B(

Any maybe some other 192.168.2-3 etc. Each one will do its classful summarization only… so we have to turn no auto summary on.

How to pass off a Static route from Router 1 to everything else??

R1 has a static route in its routing table for example…

S via

Do the following.

Router eigrp 110


To make EIGRP Point to a default route..

Ip default-network

After doing this in the routing table should show the following at the bottom.


This will NOT set the gateway of last resort

But it is the default route.

But in the neighbors it will set

D* to all other routers.

But on all other routers it will show as the gateway of last resort.

The default network command HAS to be classful.

How to summarize ONLY summary route to send to other routers..

Config t

R1#ip summary-address Eigrp 110 for example will only send – > 192168.3.0

How to use unequal load cost Balancing…

By default Does not do it..

have to use the variance command..


Config t

Router eirgrp 10

variance 2

Variance 2 will make it load balance over paths that are twice as bad for the distance…. It will also increase the metrix x2. Same goes with Variance 3 will be 3x as bad.

Also keep in Mind with Bandwith EIGRP uses 50% of a links bandwith..

So if I had 500k over one line it only uses 250k… and if it has 2 sub interfaces..


S0/0.1 – > 125

S0/0.2 – > 125k

Ip-bandwith percent eigrp 110 50 – > increases it 50%

By default EIGRP will use only half of the bandwith available on that interface.

So for example…

Ip bandwith-percent eigrp 100 200…. Makes that interfaces bandwith x200 in AS 100

EIGRP Authentication.

Supports both simple password authentication and MD5 Authentication.

Simple – Password is on each router and sent in clear text.

MD5 – > Crypto authentication. Each router has a key, configured on each one. Key password and Key ID

EIGRP uses Keychains…

Specific keys with different dates and times.

How to set it up..

Config t

Key chain NameofChain

R1(config-keychain)Key 1

R1(Config-key-keychain)key-string Password(this is the password for the key)

R1(Config-keychain-key)Accept-lifetime 00:00:00 1 jan 2010(starts) 00:00:00 1 Feb 2010

Then after enter should do send-life time same thing.

Shows up in the running config.

After you have to do the following….

Go to the interface and start the authentication.

Ip authentication mode eigrp 110 Md5


Ip authentication key-chain eigrp 110 NameofPassword

Queries / Stuck inactive.

Queries happen When a route has no feasible successor, when that route goes down a query is sent via the multi cast address.. after the query is sent the only way for that route to go back to passive is if a ACK is sent back….

You can change the time for a Router to go active for Default is 3 minutes.

Timers active-time (minutes) or Disabled

When stuck in active / queries keep in mind the neighbor adjacency is reset for the neighbors who do not reply to the quire packets… the reasons why a ACK is not sent back…

Router is too busy CPU load.

Link is no good

Failure to cause traffic to flow in one direction.

Ways to fix queries or help them?

  1. multiple areas… a query stops at the Border router.
  2. Router Summerization

Router summerazation seems to work best…. For example… if Router A does the following..

Ip summary-address eigrp

Its only routes are in the classful so it only sends routes – >

So what happens here if something else goes down a Router will reply back that it does not have it..

So what will happen is that router that sent the summary address says he has – > 4.0..

So if 1.0 goes down it will send the Query message, and each router that Knows only those summary routes are there on that Router they will send a message back simply saying NO

The goal here is to not have that route in the routers ip route, that way it will tell it it does not have it it is unreachable when querying

  1. Limiting Query Range using a Stub…

The way this works is if we have a default route….

So a network of EIGRP routers.. and there is a default route outside to the AS, this will block that default route from possibly being queried.

To configure a router as a stub router the following must happen…

Eigrp stub (Receive-only| connected| static|summary|redistributed|)

So for example/

Router Eigrp 110


Eigrp stub

^^^^ Will summarize only Connected / Summary routes to the internal network.

Eigrp stub receive-only – > will make it a passive interface.. will only receive updates but not send any.

Eigrp Static – > will only advertise static routes on the stub network. But it has to be redistributed.

Graceful Shutdown..

Reasons for a graceful shutdown….. it will tell the other router it is going to shutdown, otherwise it would have to wait for its hold timer then start the convergence process… this will start a shutdown,

For some Ungodly unknown reason, Graceful shutdown sets K values to 255, then it sends a Good bye message….???? Wtf? Y I dunno?

Has to be IOS 12.3

SIA – query

SIA – Reply

^^^ Also referred to as active process enhancement feature.

The reason for the SIA reply / query is so the routers keep the relationship… so if router A is asking for the query response/ack and does not receive it SIA reply will be sent.

Limiting the amount of queries also called Queries also called Query scoping..

Useful EIGRP Commands

Sh Ip route

Gateway of last resort is not set

D [90/156160] via, 00:01:11, FastEthernet0/0 is subnetted, 1 subnets

SH ip route Eigrp

r2#Sh ip route eigrp

D [90/156160] via, 00:02:23, FastEthernet0/0

SH ip Protocols

r2#Sh ip protocols

Routing Protocol is “eigrp 1 ”

Outgoing update filter list for all interfaces is not set

Incoming update filter list for all interfaces is not set

Default networks flagged in outgoing updates

Default networks accepted from incoming updates

EIGRP metric weight K1=1, K2=0, K3=1, K4=0, K5=0

EIGRP maximum hopcount 100

EIGRP maximum metric variance 1

Redistributing: eigrp 1

Automatic network summarization is in effect

Automatic address summarization:

Maximum path: 4

Routing for Networks:

Routing Information Sources:

Gateway Distance Last Update 90 1138468

Distance: internal 90 external 170

Show IP eigrp topology

r2#sh ip eigrp topology

IP-EIGRP Topology Table for AS 1

Codes: P – Passive, A – Active, U – Update, Q – Query, R – Reply,

r – Reply status

P, 1 successors, FD is 28160

via Connected, FastEthernet0/0

P, 1 successors, FD is 156160

via (156160/128256), FastEthernet0/0

Show IP eigrp Traffic

r2#Sh ip eigrp traffic

IP-EIGRP Traffic Statistics for process 1

Hellos sent/received: 75/71

Updates sent/received: 5/1

Queries sent/received: 0/0

Replies sent/received: 0/0

Acks sent/received: 1/2

Input queue high water mark 1, 0 drops

SIA-Queries sent/received: 0/0

SIA-Replies sent/received: 0/0

Running config If EIGRP is present

router eigrp 1




SH IP eigrp Interface

r2#sh ip eigrp int

IP-EIGRP interfaces for process 1

Xmit Queue Mean Pacing Time Multicast Pending

Interface Peers Un/Reliable SRTT Un/Reliable Flow Timer Routes

Fa0/0 1 0/0 1236 0/10 0 0

SH Ip eigrp Traffic

r2#sh ip eigrp traffic

IP-EIGRP Traffic Statistics for process 1

Hellos sent/received: 60/20

Updates sent/received: 3/4

Queries sent/received: 0/0

Replies sent/received: 0/0

Acks sent/received: 4/1

Input queue high water mark 1, 0 drops

SIA-Queries sent/received: 0/0

SIA-Replies sent/received: 0/0

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  • Dan  On December 22, 2010 at 1:43 pm

    Nice blog. One bit of info that may need updating is your statement about EIGRP using UDP port 88. Eigrp is not a UDP protocol. EIGRP is IP protocol 88 (next header field in the IP header).

    Good luck on your journey!

  • danielhertzberg  On December 22, 2010 at 1:47 pm

    You know, I might have put that there by accident. Very true, sometimes I think some things carried over from RIP… but good call.

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