EIGRP backup - PtP

bmauro

Hey guys - actually have a real life senario I'm trying to work out.

We have a remote site that is currently on dial-backup using EIGRP. I was looking at the T1 when I notice that the EIGRP neighbor-relationship was bouncing everyonce and a while. I turned on some debugs and waited for the relationship to drop again.

Once it did I noticed that the remote site holding time expired first:

Jan 9 11:12:45 EST: %DUAL-5-NBRCHANGE: IP-EIGRP(0) 10: Neighbor 192.168.254.1 (Async0/1/0) is down: holding time expired
Jan 9 11:12:45 EST: EIGRP: Sending HELLO on Async0/1/0
Jan 9 11:12:45 EST: AS 10, Flags 0x0, Seq 0/0 idbQ 1/0 iidbQ un/rely 0/0

And then on the RAS a few seconds later:

Jan 9 11:12:49 EST: %DUAL-5-NBRCHANGE: IP-EIGRP(0) 10: Neighbor 192.168.254.51 (Async1/53) is down: holding time expired

So just by looking at the timestamps I'm assuming that the last hello that the remote site received was approximately at 11:12:30, and the last hello the RAS received was at 11:12:34.

Now my first question is how to "fix" the constant flapping. I'm assuming that hellos packets are being either dropped or lost not 100% sure on verifing this part:

Async0/1/0 is up, line protocol is up
Input queue: 1/75/0/0 (size/max/drops/flushes); Total output drops: 26
Queueing strategy: weighted fair
Output queue: 0/1000/64/26 (size/max total/threshold/drops)


I would think that upping the hold timer to a higher value than 15 seconds on both sides of the link would fix the issue of the relationship dropping.

Hows that sound?? Any other ideas? Now the link is going down and coming back up almost immediately so I doubt anyone is even noticing the drop .

kafifi13

How many times a day do you think this is happening? Constantaly? Does this happen daily?

bmauro

This is a backup link, so I can't say this is everyday, but...



Jan 9 11:59:19 EST: %DUAL-5-NBRCHANGE: IP-EIGRP(0) 10: Neighbor 192.168.254.1 (Async0/1/0) is down: Interface Goodbye received
Jan 9 11:59:19 EST: %DUAL-5-NBRCHANGE: IP-EIGRP(0) 10: Neighbor 192.168.254.1 (Async0/1/0) is up: new adjacency
Jan 9 11:59:19 EST: %DUAL-5-NBRCHANGE: IP-EIGRP(0) 10: Neighbor 192.168.254.1 (Async0/1/0) is down: peer restarted
Jan 9 11:59:19 EST: %DUAL-5-NBRCHANGE: IP-EIGRP(0) 10: Neighbor 192.168.254.1 (Async0/1/0) is up: new adjacency
Jan 9 12:20:58 EST: %DUAL-5-NBRCHANGE: IP-EIGRP(0) 10: Neighbor 192.168.254.1 (Async0/1/0) is down: holding time expired
Jan 9 12:21:12 EST: %DUAL-5-NBRCHANGE: IP-EIGRP(0) 10: Neighbor 192.168.254.1 (Async0/1/0) is up: new adjacency
Jan 9 12:21:12 EST: %DUAL-5-NBRCHANGE: IP-EIGRP(0) 10: Neighbor 192.168.254.1 (Async0/1/0) is down: Interface Goodbye received
Jan 9 12:21:12 EST: %DUAL-5-NBRCHANGE: IP-EIGRP(0) 10: Neighbor 192.168.254.1 (Async0/1/0) is up: new adjacency
Jan 9 12:21:13 EST: %DUAL-5-NBRCHANGE: IP-EIGRP(0) 10: Neighbor 192.168.254.1 (Async0/1/0) is down: peer restarted
Jan 9 12:21:13 EST: %DUAL-5-NBRCHANGE: IP-EIGRP(0) 10: Neighbor 192.168.254.1 (Async0/1/0) is up: new adjacency
Jan 9 12:23:16 EST: %DUAL-5-NBRCHANGE: IP-EIGRP(0) 10: Neighbor 192.168.254.1 (Async0/1/0) is down: holding time expired
Jan 9 12:23:23 EST: %DUAL-5-NBRCHANGE: IP-EIGRP(0) 10: Neighbor 192.168.254.1 (Async0/1/0) is up: new adjacency
Jan 9 12:23:23 EST: %DUAL-5-NBRCHANGE: IP-EIGRP(0) 10: Neighbor 192.168.254.1 (Async0/1/0) is down: Interface Goodbye received
Jan 9 12:23:23 EST: %DUAL-5-NBRCHANGE: IP-EIGRP(0) 10: Neighbor 192.168.254.1 (Async0/1/0) is up: new adjacency
Jan 9 12:23:24 EST: %DUAL-5-NBRCHANGE: IP-EIGRP(0) 10: Neighbor 192.168.254.1 (Async0/1/0) is down: peer restarted
Jan 9 12:23:24 EST: %DUAL-5-NBRCHANGE: IP-EIGRP(0) 10: Neighbor 192.168.254.1 (Async0/1/0) is up: new adjacency
Jan 9 12:26:26 EST: %DUAL-5-NBRCHANGE: IP-EIGRP(0) 10: Neighbor 192.168.254.1 (Async0/1/0) is down: holding time expired
Jan 9 12:26:43 EST: %DUAL-5-NBRCHANGE: IP-EIGRP(0) 10: Neighbor 192.168.254.1 (Async0/1/0) is up: new adjacency
Jan 9 12:26:43 EST: %DUAL-5-NBRCHANGE: IP-EIGRP(0) 10: Neighbor 192.168.254.1 (Async0/1/0) is down: Interface Goodbye received
Jan 9 12:26:43 EST: %DUAL-5-NBRCHANGE: IP-EIGRP(0) 10: Neighbor 192.168.254.1 (Async0/1/0) is up: new adjacency
Jan 9 12:26:43 EST: %DUAL-5-NBRCHANGE: IP-EIGRP(0) 10: Neighbor 192.168.254.1 (Async0/1/0) is down: peer restarted
Jan 9 12:26:43 EST: %DUAL-5-NBRCHANGE: IP-EIGRP(0) 10: Neighbor 192.168.254.1 (Async0/1/0) is up: new adjacency
Jan 9 12:29:13 EST: %DUAL-5-NBRCHANGE: IP-EIGRP(0) 10: Neighbor 192.168.254.1 (Async0/1/0) is down: holding time expired
Jan 9 12:29:38 EST: %DUAL-5-NBRCHANGE: IP-EIGRP(0) 10: Neighbor 192.168.254.1 (Async0/1/0) is up: new adjacency
Jan 9 12:29:39 EST: %DUAL-5-NBRCHANGE: IP-EIGRP(0) 10: Neighbor 192.168.254.1 (Async0/1/0) is down: Interface Goodbye received
Jan 9 12:29:39 EST: %DUAL-5-NBRCHANGE: IP-EIGRP(0) 10: Neighbor 192.168.254.1 (Async0/1/0) is up: new adjacency
Jan 9 12:29:39 EST: %DUAL-5-NBRCHANGE: IP-EIGRP(0) 10: Neighbor 192.168.254.1 (Async0/1/0) is down: peer restarted
Jan 9 12:29:39 EST: %DUAL-5-NBRCHANGE: IP-EIGRP(0) 10: Neighbor 192.168.254.1 (Async0/1/0) is up: new adjacency
Jan 9 12:39:07 EST: %DUAL-5-NBRCHANGE: IP-EIGRP(0) 10: Neighbor 192.168.254.1 (Async0/1/0) is down: holding time expired
Jan 9 12:39:22 EST: %DUAL-5-NBRCHANGE: IP-EIGRP(0) 10: Neighbor 192.168.254.1 (Async0/1/0) is up: new adjacency
Jan 9 12:39:22 EST: %DUAL-5-NBRCHANGE: IP-EIGRP(0) 10: Neighbor 192.168.254.1 (Async0/1/0) is down: Interface Goodbye received
Jan 9 12:39:22 EST: %DUAL-5-NBRCHANGE: IP-EIGRP(0) 10: Neighbor 192.168.254.1 (Async0/1/0) is up: new adjacency
Jan 9 12:39:22 EST: %DUAL-5-NBRCHANGE: IP-EIGRP(0) 10: Neighbor 192.168.254.1 (Async0/1/0) is down: peer restarted
Jan 9 12:39:22 EST: %DUAL-5-NBRCHANGE: IP-EIGRP(0) 10: Neighbor 192.168.254.1 (Async0/1/0) is up: new adjacency


From the logs you can see that there isn't a set amount of time the relationship stays up. Sometimes its up for 20-30 mins, other times only 3-5 mins. And like I said before, the adjancey is flapping so quickly that it really isn't affecting the site and I highly doubt its even noitced.

dtlokee

Is this a demand dial connection? If it is try a debug dialer.

bmauro

Kinda moot point now - T1 was restored. But it still interests me.. so ...


dtlokee - I wish I would have thought about that, but the one reason I didnt look at debugging the dialer was that the ppp connection was stable, and I believe the connection time was over 4 hours. Then again I've never done a debug dialer, so I can't even really say what information I would see. I didn't see any errors on the async, so at this point I was making an educated guess on the lost hello packets.

I did get the green light (production environment) to bump up the hold timer on both sides from 15 seconds to 60 seconds. Once that was done the neighbor relationship stayed up until the circuit was restored (well over 1 hour).

So at this point I'm more interested in the "theory" side of this issue, to make sure I was looking at the right areas (hello and dead timers) and that in this type of situation this is the course that should be taken.

dtlokee

Is it possible the bandwidth was set differently on both sides ?(remember how EIGRP will determin the hello and dead timers will be determined by the link bandwidth)

bmauro

dtlokee - thanks for the reply.

Thought of that and checked - bandwidth was set to "MTU 1500 bytes, BW 115 Kbit, DLY 100000 usec," on both sides.

But correct me if I'm wrong - EIGRP hello and dead timers for multiaccess links AND P-t-P links are 5 seconds and 15 seconds respectively.

Multipoint links are tied to bandwitdth, with 1.544 and slower having the timers set to 60 and 180, and 1.544+ links being once again set to 5 and 15.

So in this case the PtP analog line would have been set for 5 and 15 seconds no matter what the bandwidth was set to.

And please please please correct me if I'm wrong