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North American Network Operators Group Date Prev | Date Next | Date Index | Thread Index | Author Index | Historical Re: should TCPs do MTU black hole detection?
Unfortunately, the MTU problem can be caused by the client's network admin as well as by the ISP; it's very difficult to explain what's wrong, for this admins, and MTU discovery is not the part of traditional IP approach. This means that black-hole detection whould be implemented anyway to prevent lost of connectivity which we have sometimes nopw when some MS-based server or crlient refuse to allow ip fragmentation. On Thu, 18 Nov 1999, Vern Paxson wrote: > Date: Thu, 18 Nov 1999 14:40:01 PST > From: Vern Paxson <[email protected]> > To: [email protected] > Subject: should TCPs do MTU black hole detection? > > > The IETF's tcp-impl (TCP implementation) working group has a draft document > discussing problems with path MTU discovery: > > http://www.ietf.org/internet-drafts/draft-ietf-tcpimpl-pmtud-02.txt > > The main issue we're trying to decide is whether the draft should advocate > "black hole detection". That is, when a TCP is doing PMTU discovery, but > somewhere the necessary ICMPs are either not being generated or are being > filtered out before the TCP receives them, the TCP notices that it's losing > multiple packets of the same size, so it then tries sending smaller segments, > even though it hasn't received a "Datagram Too Big" ICMP. > > The plus of black hole detection is that it can work around a sometimes very > hard to debug problem. The minus is that it masks problems that should > instead be fixed. > > To help resolve this issue, I'm wondering whether the ISP community has a > clear preference for either yes-do-detection or no-we-want-the-problems-fixed. > Comments appreciated. > > Thanks, > > Vern > > Aleksei Roudnev, Network Operations Center, Relcom, Moscow (+7 095) 194-19-95 (Network Operations Center Hot Line),(+7 095) 230-41-41, N 13729 (pager) (+7 095) 196-72-12 (Support), (+7 095) 194-33-28 (Fax)
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