nanog mailing list archives
Re: I-D on operational MTU/fragmentation issues in tunneling
From: Iljitsch van Beijnum <iljitsch () muada com>
Date: Wed, 13 Oct 2004 13:17:06 +0200
On 11-okt-04, at 10:12, Pekka Savola wrote:
The document is about to be IETF Last Called for Informational RFC, but prior to that, I'd like to solicit comments/feedback/review from the people here because I'm 100% sure a lot of people have been faced with these issues (we certainly have..).
Well, tunnels suck. No news there. It is interesting to note that at least one implementation provides a special knob to fragment the inner packet prior to encapsulation even if the DF bit has been set -- this is non-compliant behaviour, but possibly has been required in certain tightly controlled passive monitoring scenarios. Such a setup wouldn't work for packets which have already been fragmented if they needed to be fragmented again, though. Why would it be impossible to refragment fragments???I have a setup with dial-up over L2TP that doesn't support an MTU bigger than 576 (which is completely unnecessary of course, but try telling the people at the other end of the L2TP thingy that) so I clear the DF bit for all incoming packets that have to go through the PPP/L2TP tunnel. Works like a charm. (Surprisingly, all users seem to have systems that are capable of reassembling 1.5 kB packets now.)
But I don't understand why anyone would want to use tunnels in the backbone. That's what VLANs are for. And if you don't use ether, you aren't bound by yester-millennium's 1500 byte MTU anyway.
In IPv6 there is the interesting problem that there are already many tunnels all over the place that often have a 1280 byte MTU, so tunneling over that can't be done because of the mandatory minimum MTU of 1280 bytes.
Current thread:
- I-D on operational MTU/fragmentation issues in tunneling Pekka Savola (Oct 11)
- Re: I-D on operational MTU/fragmentation issues in tunneling Iljitsch van Beijnum (Oct 13)
- Re: I-D on operational MTU/fragmentation issues in tunneling Pekka Savola (Oct 14)
- Re: I-D on operational MTU/fragmentation issues in tunneling Sabri Berisha (Oct 14)
- Re: I-D on operational MTU/fragmentation issues in tunneling Joe Maimon (Oct 14)
- Re: I-D on operational MTU/fragmentation issues in tunneling Sam Stickland (Oct 19)
- Re: I-D on operational MTU/fragmentation issues in tunneling Joe Maimon (Oct 19)
- Re: I-D on operational MTU/fragmentation issues in tunneling Joe Maimon (Oct 14)
- Re: I-D on operational MTU/fragmentation issues in tunneling Mikael Abrahamsson (Oct 14)
- Re: I-D on operational MTU/fragmentation issues in tunneling Andre Oppermann (Oct 14)
- Re: I-D on operational MTU/fragmentation issues in tunneling Sabri Berisha (Oct 15)
- Re: I-D on operational MTU/fragmentation issues in tunneling Iljitsch van Beijnum (Oct 13)
- <Possible follow-ups>
- Re: I-D on operational MTU/fragmentation issues in tunneling Joe Maimon (Oct 15)