Date: Thu, 30 Jan 2003 10:03:55 -0500 (EST) From: Daniel Ellard <ellard@eecs.harvard.edu> To: freebsd-hackers@freebsd.org Cc: Audsin <dev.dhas@kcl.ac.uk> Subject: Re: Changing the Maximum Segment Size (MSS) of Kame MIP6 Free BSD4.4 Message-ID: <Pine.BSF.4.51.0301300944520.44006@bowser.eecs.harvard.edu>
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Terry Lambert <tlambert2@mindspring.com> wrote: > Audsin wrote: > > I am Dev, doing my research in Centre for Telecommunications Research, > > King's college London. My research project involves evaluating the > > performance of MIP6 TCP in the presence of fragmentation and without > > fragmentation. I am using Kame MIP6 for Free BSD 4.4 and have configured > > gif0 interface for ipv6ip tunnel. I wish to change the Maximum segment size > > of the TCP. Can you please help me , where i should change the MSS of the > > TCP. Can you tell me where the default size of the MSS mentioned? > > man ifconfig<cr> > /mtu<cr> The original question asked about the TCP MSS, not the MTU. Looking at ifconfig isn't going to help. I don't have the 4.4 source sitting around, but assuming that it hasn't changed much, in 4.6.2 you can find (or change) the defaults in /usr/src/sys/netinet/tcp.h. The default for TCP4 is 512, and 1024 for TCP6. You can get at them via sysctl (along with a lot of other TCP-related things): net.inet.tcp.mssdflt: 512 net.inet.tcp.v6mssdflt: 1024 Note that the actual MSS is negotiated; if both ends can't support the same value, the smaller is chosen. For MTUs, in case that's really what you meant, it's even more strict and depending on how the transport layer is implemented, it may be impossible (or reckless) to increase the MTU. For example, on ethernet many switches simply do not support an MTU larger than 1500. -Dan To Unsubscribe: send mail to majordomo@FreeBSD.org with "unsubscribe freebsd-hackers" in the body of the message
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