enabling IPv6 on Cisco 6500 breaks IPv4 Internet connectivity.

Jim Trotz jtrotz at gmail.com
Fri Jun 1 02:46:40 CEST 2012

We have a pair of Cat6500s with sup720XL supervisors running 12.2(33)SXJ1
IOS that are configured as enterprise Edge routers. These routers have a
VRF for Internet "outside" connections and the global table is used for
"Inside" connections. The outside VRF has full BGP routing tables with 406K
V4 routes.

Cisco ASAs are connected on ports associated each routing table. Named mode
EIGRP is used for IGP both inside and in the external VRF to communicate
with our 2 Internet Hub routers (also 6500s, dual stacked, working fine).

The problem we have is that when we try to configure IPV6 on the edge
routers we loose the ability to pass IPv4 traffic as soon as the "ipv6
unicast routing" command is entered - no IPV6 addresses have been applied
at that point, no interfaces enabled for IPv6 and no ipv6 routing
configured either.

Cisco TAC seems to be stumped. The logs don't show anything, Eigrp & BGP
neighbors stay up and the CPU rises to 99% utilization.

The odd thing is that when we apply the "ipv6 unicast routing" command to
the other router it works fine. The only thing we could think of thats
different between the two is the "broken" router's ASA firewall is in
active state and the "good" router's ASA is in standby. We plan to fail
them over to see if thats really the difference.

I have tried duplicating the problem in the lab without luck so far.

Has anyone had a similar problem or have any suggestions?
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