Enabling IPv6 on Cisco 6500 breaks IPv4 Internet connectivity.

Jim Trotz jtrotz at gmail.com
Sat Jun 23 23:50:24 CEST 2012

Final update:

   After much testing in the lab and working with Cisco TAC (almost no
   I have reached a conclusion about the problem - its a hardware

   Enabling IPV6 routing on a 6500 (with XL cards) and a full Internet
   table in a VRF exceeds the limits of SP processing, The SP goes to 99%
   utilization reconfiguring something but eventually recovers. In the lab
   this took almost 5 minutes!  In real life with many 10Gb interfaces
   - who knows!!

   The problem is that the router still passes enough traffic that EIGRP
and BGP stay
   up, but all user traffic is "black hole'd" due to the 1-10kbs effective

   It looks like this may be a one time event, but neither Cisco TAC or the
   could say for sure this wouldn't happen again under some kind of BGP flap
   of VRF reconfig.

   Our TCAM limit is 512K ipV4 routes now and we have 409K routes today.

   We will probably resort to filtering down the BGP learned routes to
100-200K  and
   then  default for everything else to our Internet routers and then go
   for a new router.

   The problem isn't noticeable until we have more than about 250K routes.

   There was no interest in redesigning the network to not use VRFs for the
   Internet table.

  Once IPV6 is enabled and all is stable we will probably go shopping for
new routers.

   Thanks again for everyone's suggestions, it helped us figure out the root
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