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Cisco Bug: CSCuk45735 - Enabling CEFv6 breaks IPv6 tunnels

Last Modified

Feb 03, 2017

Products (1)

  • Cisco IOS

Known Affected Releases

12.2(17.10)SWB5 12.2(18)S3 12.2(19.7)SPI4i 12.2S 12.2SPI4

Description (partial)

Symptoms: For all IPv6 tunnel modes (that is, 6to4, auto, Intra-Site Automatic 
Tunnel Addressing Protocol [ISATAP], or manual) connectivity to endpoint 
destinations that are reachable via the tunnel may fail, preventing any 
traffic from being forwarded.

In addition, when packets that exceed the IPv6 maximum transmission unit (MTU) 
of the tunnel are forwarded to the tunnel headend router, the headend router 
may fail to send a "packet too big" Internet Control Message Protocol for IPv6 
(ICMPv6) message to the source address of the packet.

Conditions: These symptoms are observed on a Cisco router only when Cisco 
Express Forwarding version 6 (CEFv6) is enabled.
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  • Status
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