Nexus/ASR EIGRP Flapping

[cyanesh]

Hello everyone,

I have been having a problem with EIGRP neighbor adjacency between N56128's and ASR 4451X.  The dual 56128's have a vPC configured to a 2960x.  I have two routers that also plug into the 2960x.  A 2921 and a 4451x.  I configured EIGRP on the VLAN and network used to establish adjacency.  the N56128 will form an adjacency with the 2921 with no problems.  However, with the 4451X,  I get constant flapping.  The RTO is 5000 and the SRTT is 1ms.  The show eigrp neighbors detail on both the Nexus and 4451 shows waiting for INIT, waiting for ACK.  I pinged 224.0.0.10 on the N5k specifying interface and it was 0% dropped 1ms.  The 4451X was 0% dropped 1ms.  I would appreciate any help, and can post relevant interface configs.  The N5k is running 7.3.1, so route peering should be supported by Cisco(now) with the 5600.  And, it works just fine with the 2921.  The 4451X is running 14.4(3)S6a.  I attached a quick drawing of how the devices are connected, sorry for the quality. 

Thanks,

Chris

[Reza Sharifi]

Hi,

Do you have the same issue when the 5ks are not configure as vPC?

Also, can you post relevant config from the 5k, 2960x and the router?

HTH 

[cyanesh]

Reza,

Thanks for you response.  I have not tried without using a vPC.  I suppose I could take one of the N5k ports and make it routed.  I think that would probably work OK.  But, the vPC does work, the 2921 has no issues across the same vPC.  I really need it to work this way, at least for the foreseeable future.  The architecture was setup way before my time and we are locked into a few design items.  I attached a .txt of the config items and some outputs of show ip eigrp neighbors.  Thanks for taking a look. 

[Reza Sharifi]

Chris,

Thanks for posting the configs.

So, vlan 100 is used for peering between 2921, 4451 and nexus all in the same subnet?

Can you separate them by using one vlan/subnet to connect to the 2921 and a different vlan/subnet  to connect to 4451 and test?

HTH

[cyanesh]

Reza,

Thats correct, VLAN 100 and the /16 network that goes with it is used for route peering for both routers, in addition to other vendor equipment.  I would love to segment the VLANs and networks, but that just isn't possible currently.  Too many actors in play that are locked in by IP. 

[cyanesh]

After further troubleshooting(don't know why I didn't do this earlier)...I did a traceroute to the n5k switch.  And it looks like it is going to the other n5k first, then to the one in question.  Which should mean it is going across the vPC peer link, which then decrements the TTL.  So I turned on EIGRP for the second n5k switch and it formed an adjacency just fine.  However, it didn't form an adjacency with the 2921.  So the 2921 has the path just the opposite.  I could swear from the statement below, from the link below Cisco fixed this in 7.3 code, which I have 7.3.1(n1).  Am I reading this wrong?

L3 over vPC

Beginning with Cisco NX-OS Release 7.3(0)N1(1), a layer 3 device can form peering adjacency between both the vPC peers in a vPC domain. Traffic sent over the peer link will not have TTL decremented. The L3 device can form peering adjacency with both vPC peers. This enhancement is not applicable for vPC+ and is applicable only for unicast (not multicast).
Note that L3 over vPC+ is supported on Cisco Nexus 5600 switches from Cisco Nexus 7.0 release.

http://www.cisco.com/c/en/us/td/docs/switches/datacenter/nexus5600/sw/release/notes/7x/Nexus5600_Release_Notes_7x.html#pgfId-685944