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Cisco Bug: CSCvs59641 - EIGRP inserting /32 route from LISP redistribution even when ARP is removed, causing loop

Last Modified

May 23, 2020

Products (1)

  • Cisco Nexus 7000 Series Switches

Known Affected Releases


Description (partial)

We have 2 N7K (N7K-Agg1 & N7K-Agg2) routers configured as EIGRP stub to reduce the query domain. The ASA is not a stub. Thus, in the setup, we see that when we lose x.x.x.x/32 (which are LISP redistributed routes) on N7K-Agg2. N7K-Agg2 only sends a unicast QUERY to ASA (Firewall) and not to N7K-Agg1 (which is a stub). This is because here there are mixed peers (stubbed and non-stubbed) on an interface, EIGRP sends UNICAST QUERY only to non-stubbed PEER. This means ASA receives a UNICAST QUERY and N7K-Agg1 does not receive the QUERY. The same happens on N7K-Agg1.
When LISP routes are withdrawn from RIB of N7K-Agg2, EIGRP topology has an alternate path via N7K Agg1. Since the query is suppressed when DUAL is initiated for x.x.x.x/32, the alternate path which is via N7k Agg1 gets installed into the RIB.
Similarly, it happens for N7k-Agg1 and it ends up pointing to each other resulting in a routing loop.

As mentioned in Nexus config guide

When using EIGRP stub routing, you need to configure the distribution and remote routers to use EIGRP and configure only the remote router as a stub.
Also, as mentioned in IOS documentation regarding stub functionality,

+ LISP learns dynamic EID routes from ARP for directly connected servers.

+ Further LISP routes (/32) getting redistributed into EIGRP. 

+ N7K-Agg1 & N7K-Agg2 routers configured as EIGRP stub to reduce the query domain.

+ Each VRF on the N7K-Agg switch has 2 Eigrp neighbors: 
   ASA FW as a non-stubbed peer
   and peer N7K-Agg switch as a stubbed peer.

+ EIGRP sends UNICAST QUERY only to non-stubbed PEER which is ASA, on the other hand, peer N7K-Agg does not receive the QUERY since it is configured as a stubbed peer.
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