eigrp k values. good bye message

[sarahr202]

Hi every body

1 )Ley say we have two routers,R1 and R2, both running eigrp, with default k values.

R1-----------------R2

Assume neighbor relationship is formed.

Let say i change the k values on R1,  R1  sends the hello with different K values.

R2 receives the hello and  finds different k values.  Now assume  hold down timer is not expired on R2.  Now what will R2 do? will it drop the adjacency with R1 because it receives the hello with different values? or will R2 wait for hold down timer to expire and then drop neighbor relationship with R1 ?

2) Cisco introduced goodbye message which uses hello message with all k values equal to 255.

Let say we have two routers, R1 and R2.

R1 is running old ios which does not understand goodbye messages

R2 is running newer ios which understand  good bye message.

R1---------------------R2

Assume Neighbor relationship is established.

Let say due to some reason, eigrp has to send good bye message ( e.g  R2 is just configured with stub option, change summary address  etc).

When R1 receives the hello messages it finds all k values set to 255, it logs a messages  '"mismatch k values, hello received".  But Will R1 drop neighbor relationship  with R2? or R1 will wait for holddown timer to expire  before R1 can drop neighbor relationship with R2?

thanks and have nice weekend

[Reza Sharifi · Accepted solution]

Hi Sara,

When the peeing is formed between R1 and R2, if you change the metric on one of the routers, the peering goes down imediatly. So, there is no waiting for hold down to expire.

I tested it this with 2 routers

see bellow:

1-peering is formed and the 2 routers are peers

IP-EIGRP neighbors for process 1
H   Address                 Interface       Hold Uptime   SRTT   RTO  Q  Seq
                                            (sec)         (ms)       Cnt Num
0   172.17.1.1              Gi0/0             11 00:04:16 1472  5000  0  4
T-1(config-router)#

IP-EIGRP neighbors for process 1
H   Address                 Interface   Hold Uptime   SRTT   RTO  Q  Seq Type
                                        (sec)         (ms)       Cnt Num
0   172.17.1.2              Et0/0         14 00:04:00    1  3000  0  4  
r10#

as soon as I change the metric on one of the routers, you will see the peering go down right a way

T-1(config-router)# metric weights 0 2 0 1 0 0  
T-1(config-router)#
*May 21 19:49:55.148: %DUAL-5-NBRCHANGE: IP-EIGRP(0) 1: Neighbor 172.17.1.1 (GigabitEthernet0/0) is down: metric changed
*May 21 19:49:55.600: %DUAL-5-NBRCHANGE: IP-EIGRP(0) 1: Neighbor 172.17.1.1 (GigabitEthernet0/0) is down: K-value mismatch
*May 21 19:50:00.588: %DUAL-5-NBRCHANGE: IP-EIGRP(0) 1: Neighbor 172.17.1.1 (GigabitEthernet0/0) is down: K-value mismatch
*May 21 19:50:05.208: %DUAL-5-NBRCHANGE: IP-EIGRP(0) 1: Neighbor 172.17.1.1 (GigabitEthernet0/0) is down: K-value mismatch

as soon as I delete the metric the peering comes up

T-1(config-router)#no metric weights 0 2 0 1 0 0
*May 21 19:50:37.780: %DUAL-5-NBRCHANGE: IP-EIGRP(0) 1: Neighbor 172.17.1.1 (GigabitEthernet0/0) is up: new adjacency

http://www.cisco.com/en/US/docs/ios/12_2/ip/configuration/guide/1cfeigrp.html#wp1001020

HTH

Reza

[sarahr202]

Thanks Reza for your response

.In your  test, I assume you are running ios 12.3(1.4) or later release.  I observed the same behavior  in my lab. Let me elaborate on it

.R1----------------R2

Both are running ios 12.3 (1.4) and using default K values,  assume  neighbor relationship has already been established.Let say I changed the K values on R1

.Following will occur:

.1)  R1 compares   its configured  K values with k values just received in hello from R2. and decides it has to drop adjacency with R2.

2) R1 sends a Good bye message  to R2 and tears down the relationship with R2.

3) R2 receives the good bye message and and tears down its relationship with R1.In above case, this is the behavior exhibited by routers running ios which support good bye message.

  However we   can not be sure if the similar behavior will be exhibited by ios which does not support goodbye message.The  question we need to answer is Will a router running older ios than 12.3(1.4), will drop its already established neighbor relationship upon receiving a hello with different k values ?thanks and have a nice weekend.