discussion: Enabling IPv6 on Cisco 6500/7600 breaks IPv4 Internet connectivity

Ranganath Hande rangha at microsoft.com
Mon Jun 25 19:14:19 CEST 2012

Looks like there is some discussion going on related to - Enabling IPv6 on Cisco 6500/7600 breaks IPv4 Internet connectivity. This issue is interesting. Here is some more info...:)

It is fairly common for RP utilization to go up initially when either v4 or v6 internet BGP peer comes up first time--due to large number of BGP prefixes that router has to process. In case of v6,  impact is more visible as resource utilization is 4 times higher. Possible solutions are --

*         FIB/TCAM scaling (mls cef max-routes)

*         Limiting/filtering BGP learned prefixes  (For IPv6 - limit to /32 or /48)

*         Avoid using VRF for full internet route table as VRFs have lower default resource  allocations than global table and cannot scale much. In case full IPv6 internet routes are needed downstream and you have MPLS backbone, use 6PE for internet routes and 6VPE for IPv6 MPLS VPNs.

*         If full internet route table is not really needed -- negotiate with upstream ISP to send only 'default+backbone or customer' routes.

*         Shop for bigger router periodically as Internet route table grows --costs more as it needs more money.

Thank you,


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