Date: Wed, 8 Aug 2001 19:19:04 +0200 From: Jeroen Ruigrok/Asmodai <asmodai@wxs.nl> To: Mike Tancsa <mike@sentex.net> Cc: freebsd-net@freebsd.org Subject: Re: gif MTU of 1280 ? Message-ID: <20010808191904.R2937@daemon.ninth-circle.org> In-Reply-To: <5.1.0.14.0.20010808121005.04473600@marble.sentex.ca> References: <5.1.0.14.0.20010808101139.0277e010@marble.sentex.ca> <5.1.0.14.0.20010808101139.0277e010@marble.sentex.ca> <5.1.0.14.0.20010808121005.04473600@marble.sentex.ca>
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-On [20010808 18:51], Mike Tancsa (mike@sentex.net) wrote: > >Thanks for the clarification. I just had a read of the man pages as well >and there is mention of that too. I guess the question I am left with is >that can I safely set the MTU to 1500 if I am using it to tunnel IPV4 >traffic only, and in another case, IPV4 and IPSEC traffic. When using 1280 >in a strict tunnel mode, I have problems with large packets from certain >sites. Broken PMTU somewhere ? Not sure, but setting the MTU to 1500 >seemed to fix it. What I understand is that using a MTU of 1280 guarantees no IPv6 fragmentation since it is the minimum supported. Of course, if a link cannot accomodate the MTU it must fragment at a layer below the IPv6 layer, but it will not be fragmented on the IPv6 layer itself. Of course, like the RFC says: "[...]; it is recommended that they be configured with an MTU of 1500 octets or greater, to accommodate possible encapsulations (i.e., tunneling) without incurring IPv6-layer fragmentation." So it seems that the IPv6 fragmenting is causing problems of some sort. My best guess at least. :) -- Jeroen Ruigrok van der Werven/Asmodai asmodai@[wxs.nl|freebsd.org|xmach.org] Documentation nutter/C-rated Coder, finger asmodai@ninth-circle.dnsalias.net http://www.freebsd.org/doc/en_US.ISO8859-1/books/developers-handbook/ Teaching should be such that what is offered is perceived as a valuable gift and not as a hard duty... To Unsubscribe: send mail to majordomo@FreeBSD.org with "unsubscribe freebsd-net" in the body of the message
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