EIGRP authentication timers

[bapatsubodh]

Hello,

EIGRP key chain authentication is configured on R1 and R2.

Case 1.

there is no send and accept timers configured on any of the routers

Case 2. Send timer is configured on one router and Accept on another rouer

Case 3: Send timer  is configured on both routers but no accept timer configured on both routers

Case 4: Accept timer is configured on both routers but no send timer configured on both routers

In which cases EIGRP neighbor will be formed?  How router decide what key to send and what key should it accept?

Or any key that is "valid" at that time is accepted and alse used to send ?

Please share the experience!

Thx in advance!

Subodh

[John Blakley]

Subodh,

The default is send and accept with lifetime values. If you don't specify start and end times, the router will keep the key string as always valid. All of your cases should create an adjacency. The first key in the list is the one that's used, so if you have keys 1,2,3,4,5 with no send parameters changed, it will always use key 1. The keys have to match on both ends of the link though. If you have key 1 with the password of Cisco and key 5 on the other route with the password of Cisco, the adjacency will not form.

R2#sh key chain Cisco

Key-chain Cisco:

    key 1 -- text "Cisco"

        accept lifetime (always valid) - (always valid) [valid now]

        send lifetime (always valid) - (always valid) [valid now]

    key 5 -- text "Cisco2"

        accept lifetime (always valid) - (always valid) [valid now]

        send lifetime (always valid) - (always valid) [valid now]

R2#debug eigrp packet

Apr  2 14:16:23.603: EIGRP: received packet with MD5 authentication, key id = 1

After deleting key 1, my adjacencies were torn down and debug eigrp shows:

Apr  2 14:17:21.775: EIGRP: pkt authentication key id = 1, key not defined or not live

The last debug proves that the key numbers need to match on both ends. The router is receiving key id 1 from the other router, but key 1 doesn't exist on this router anymore after I deleted it.

HTH,

John

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