6to4 relay on IOS <-> CEF switching?

Gert Doering gert at space.net
Thu Oct 9 11:37:28 CEST 2008

Hi Folks,

we've just moved our 6to4 relay to a new router (well, it's still an old
router, but a dedicated machine to that purpose).

It's a 3640 with 12.3(22) on it, and "bog standard" 6to4 relay config:

interface Tunnel2002
 description 6to4 relay - RFC 3056 (sp1)
 no ip address
 no ip redirects
 load-interval 30
 ipv6 address 2002:C195:2CD0::1/128
 tunnel source
 tunnel mode ipv6ip 6to4
ipv6 route 2002::/16 Tunnel2002

... and it's working well, that is, packets move back and forth and
the latency is good.

What I'm unhappy about is the CPU load - these packets are not CEF switched
("show int switching" etc), and as such, measly 15 Mbit/s create 99% CPU 

There is no fragmentation going on, so it seems to be more a matter of 
"CEF not supporting 6to4 in 12.3".

Before I start upgrading things (adding RAM etc) - what are your experiences
with 6to4 relays on IOS?  Which combination of hardware and software are
you using, and does it properly CEF switch these packets?

So far, I have received comments about 12.2SB, which seems to do CEF
switching on egress but not on ingress (!?), and 12.4 on 2800, which
seems to do both directions.

(Just for the records: we're offering native IPv6 to all our customers, and
we're not announcing the relay to "the world" - so something that can 
do 20-30 mbit/s is perfectly fine for our needs, as in 'the occasional
customer that has never considered IPv6 but 6to4 just happened to his
machine by virtue of a MacOS device nearby')

Gert Doering
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