[c-nsp] IPv6 in IP overhead and ip tcp adjust-mss

Tom Storey tom at snnap.net
Wed Mar 19 09:27:17 EDT 2008


IPv6 headers are 40 bytes, twice that of IPv4.

Add 20 bytes for TCP headers, just as you would with IPv4, which gives  
you 60 bytes total for TCP/IPv6.

If using PPPoE you'd probably want an MSS of 1432 for IPv6.

However, IPv4 headers can vary in length to greater than 20 bytes,  
but, IPv6 has a fixed IP header length so it should be predictable.  
Unless youre doing something fancy, 1452 should suffice for IPv4 in  
most deployments (at least going by experience).

Tom

On 19/03/2008, at 8:45 PM, Kevin Barrass wrote:

>
> Hi
>
> I'm playing with a IPv6 tunnel broker on my home ADSL/Cisco 1701 for
> testing as we are deploying IPv6 at work over a long period.
> On my ADSL router I have ip tcp adjust-mss 1452 to account for the ppp
> over atm encapsulation overhead im assuming 1452 is correct as ive had
> varying recommendations. Does anyone know what the overhead for IPv6  
> in
> IP is as I would like to adjust the MSS on traffic over the IPv6  
> tunnel.
>
> Kind Regards
>
> Kev
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