enabling IPv6 on Cisco 6500 breaks IPv4 Internet connectivity.

Jim Trotz jtrotz at gmail.com
Fri Jun 8 00:44:41 CEST 2012

By way of an update on the problem:

We have been able to recreate the problem in a network lab environment.

The router stops forwarding IPv4 traffic (ICMP still flows) whenever two
IPv6 configuration statements are entered. Traffic resumes after some time
(2-10 minutes).

Used separately, everything works fine. The commands are:     1) "ipv6
unicast-routing" and 2) adding "ipv6 address-family" to a VRF definition.

There is nothing in the router log indicating a problem, EIGRP and BGP
neighbors still remain connected (if BFD is not enabled), however the BGP
neighbors do fall off if the traffic is blocked for more than a few
minutes. Telnet sessions to the router still work. In the "live" routers
the CPU goes very high - this seems BGP related, but goes away.

We tried different versions of code and applying the commands in in
different sequences - same result.

Cisco TAC still has no suggestions.

I tried all of the CLI commands list members suggested (thanks for the
feedback!). It doesn't appear to be related to CEF or TCAM, the XL versions
of the DFCs all have 1GB of ram. The TCAM is configured for 512K IPV4
routes and 256K IPV6 routes. We currently have 408K IPV4 routes in our

We are planning on replacing these routers at some point - any suggestions?
We are a semi-small service provider; servicing Internet and enterprise
traffic for several hospital and University systems in the
Maryland/Washington DC area. I was considering the Cisco ASR9000 line - we
have mostly 10Gbs links to ISPs and the metro Ethernet WAN.  We need good
support for IPv6, MPLs and 100Gbs links - but not a super huge box like a
CRS, Juniper or Brocade?
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