enabling IPv6 on Cisco 6500 breaks IPv4 Internet connectivity.

Jon Harald Bøvre jon at bovre.no
Fri Jun 1 07:14:50 CEST 2012

Could it be anything related to 'mls cef maximum-routes'?


Sent from my iPad

On 1. juni 2012, at 02:46, Jim Trotz <jtrotz at gmail.com> wrote:

> 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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