IPv6 neighbour discovery problem on Cisco 7609

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Nov 24th, 2009
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I have 2 VLAN's(3586 & 2021) configured with both IPv4 and IPv6 on Cisco 7609 Router. Please refer output of show-running-config command.


3586 - 2001:1234:5678:dcba:ffff:ffff:ffff:ffc0/125

2021 - 2001:1234:5678:AAAA::1/64


The client desktop PC belongs to VLAN 2021 and is configured with IP 2001:1234:5678:aaaa:a:e400:1113:7a35 and link local address fe80::222:19ff:fe19:82de. The server(Solaris based) is configured with IP 2001:1234:5678:dcba:ffff:ffff:ffff:ffc3.IPMP(IP multipathing) is configured on the Solaris server to have redundancy incase of a interface failure. When  a failover of network interface is done from one interface to another on the server, Neighbour advertisement messages are sent from the Server to the router. But the MAC table on the router is not geeting updated with the link layer address of the new interface.



Before Failover:

Cisco_7609-1#show ipv6 neighbors
IPv6 Address                              Age Link-layer Addr State Interface
FE80::214:4FFF:FE42:91A9                  106 0014.4f42.5d09  STALE Vl3506
FE80::214:4FFF:FE42:91AB                  106 0014.4f42.5d0b  STALE Vl3511
FE80::222:19FF:FE19:82DE                    0 0022.1919.82de  DELAY Vl2021
FE80::221:28FF:FE41:63DC                    0 0021.2841.63dc  STALE Vl3586
2001:1234:5678:AAAA:A:E400:1113:7A35        0 0022.1919.82de  STALE Vl2021
2001:1234:5678:DCBA:FFFF:FFFF:FFFF:FFC3     0 0021.2841.63dc  STALE Vl3586
.


After Failover:

Cisco_7609-1#show ipv6 neighbors
IPv6 Address                              Age Link-layer Addr State Interface
FE80::214:4FFF:FE42:91A9                  115 0014.4f42.5d09  STALE Vl3506
FE80::214:4FFF:FE42:91AB                  115 0014.4f42.5d0b  STALE Vl3511
FE80::222:19FF:FE19:82DE                    0 0022.1919.82de  DELAY Vl2021
FE80::221:28FF:FE41:63DC                    2 0021.2841.63dc  STALE Vl3586
2001:1234:5678:AAAA:A:E400:1113:7A35        9 0022.1919.82de  STALE Vl2021
2001:1234:5678:DCBA:FFFF:FFFF:FFFF:FFC3     9 0021.2841.63dc  STALE Vl3586


Due to this, the server is no longer accessbile from the client. Even a basic ping to the IP 2001:1234:5678:DCBA:FFFF:FFFF:FFFF:FFC3 fails!


Is there any special configuration required on the router for this to work? Do let me know if you need further details.


Thanks.

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Nagendra Kumar ... Wed, 11/25/2009 - 21:41
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Hi,


As per RFC, when an IPv6 node sends NA, it can set Override bit which will tell the receiving node to override the link layer address. So if the router receives the Neighbor Advertisement with "Override" bit set, it will update the cache accordingly.


Check if the server is sending NA with Override bit set.


HTH,

Nagendra

sudhir_shet Thu, 11/26/2009 - 23:33
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Hi,


Thanks for the reply. I checked the server is send NA with Override bit set to the FF02::1 multicast address with the new link layer address(please refer row no. 57 & 58 in the attached wireshark trace.). But the link layer address of the new interface is not getting updated in L3 neighbours table. What could be the reason for this?


Thanks for your help,


Regards,

Sudhir.

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