Re: draft-wbeebee-ipv6-cpe-router-04 comments

[Mikael Abrahamsson <swmike@swm.pp.se>]

On Sun, 5 Apr 2009, Mag Pat wrote:

Hi,

I know I am a bit late, but I read thru the 
http://tools.ietf.org/html/draft-ietf-v6ops-ipv6-cpe-router-00
and I have a question:

In section:

8.5. 6to4 Automated Tunneling (MEDIUM)/Dual-Stack Lite (DEV)/ISATAP (MEDIUM)

Would it make sense to put in a recommendation about doing MSS-adjust for 
packets traversing v6-in-v4 tunnels? I'm personally doing this today to 
avoid MTU related problems, and I think it's a better way than doing 
tunnel packet fragmentation (which is problematic as for instance our 6to4 
gateway has 4470 MTU on its core facing interfaces so any 1500 byte IPv6 
packet will be over 1500 when encapsulated in ipv6-in-ip, and then there 
might be a v4 packet fragmentation problem on the way to the tunnel 
endpoint and the packet might be dropped).

Setting MSS to 1350 (or other value substantially lower than what is 
required to pass unfragmented thru ip-in-ip tunnels) avoids this 
fragmentation problem. It doesn't fix UDP of course, but it would avoid 
performance and functionality problems in TCP (which in my experience make 
up the majority of Internet traffic).

--
Mikael Abrahamsson    email: swmike@swm.pp.se