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[lwip-devel] [patch #7837] Default TCP_MSS to 1220 if LWIP_IPV6 support

From: Ivan Delamer
Subject: [lwip-devel] [patch #7837] Default TCP_MSS to 1220 if LWIP_IPV6 support is enabled
Date: Tue, 28 Aug 2012 19:30:00 +0000
User-agent: Mozilla/5.0 (Windows NT 6.1; rv:14.0) Gecko/20100101 Firefox/14.0.1

Follow-up Comment #1, patch #7837 (project lwip):

This is an interesting patch. It's true that for IPv6 there should ideally be
a minimum MSS of 1220. In general, this will be a bit larger (e.g. for
Ethernet it will be around 1400). Personally I set this value in lwipopts.h to
match the smallest netif MTU I'll be using.

I'm not sure what kind of memory implications changing this default brings,
and if it is 100% safe (I'm not saying it's not safe, I just don't know yet).
Obviously if we have IPv6 then we should be able to accomodate 1220 whether
the TCP session is over v4 or v6. So from an MTU point of view it should be a
safe change.

But I guess this will increase the minimum memory requirement for a default
environment. And I don't know if this would break a system which does not set
its own TCP_MSS (relying on default) and does not increase the memory

Any other opinions?


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