Date: Fri, 6 Sep 2002 11:10:03 -0700 (PDT) From: Jeff Behl <jeff@expertcity.com> To: freebsd-bugs@FreeBSD.org Subject: Re: kern/42137: Path MTU broken - initial too-large packet continuously resent Message-ID: <200209061810.g86IA3RY002791@freefall.freebsd.org>
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The following reply was made to PR kern/42137; it has been noted by GNATS. From: Jeff Behl <jeff@expertcity.com> To: Martin Kaeske <Martin.Kaeske@Stud.TU-Ilmenau.DE> Cc: freebsd-gnats-submit@FreeBSD.org, Steve Francis <sfrancis@expertcity.com> Subject: Re: kern/42137: Path MTU broken - initial too-large packet continuously resent Date: Fri, 06 Sep 2002 11:07:02 -0700 Actually, it would be our layer two load balancer that is not re-writing the icmps from the router correctly. I was using ethereal to do a inspection of the packets but it doesn't seem to show the sequence number in the tcp header in the icmp. Thanks! I knew it had something to do with this blasted load balancer. This is a foundery serveriron for all who might be interested But in any case, it still doesn't seem to be a 'good idea' for the stack to transmit packets (and keep re-transmitting them) that are above the MTU that it has for a certain host, does it? or is this the only way it makes sense as it would be inefficient to have TCP re-check the MTU on every re-transmitted packet? I'm certaintly no expert in this area... thanks again. Jeff Martin Kaeske wrote: > Hi Jeff, > Thanks for the tcpdump, i think i was able to identify the problem. > As i wrote in the PR tcp_ctlinput() is responsible for calling tcp_mtudisc > but tcp_ctlinput() does not only check src/dst-port it also examines wether > the tcp-sequence number (found in the ICMP-response) is between snd_una (send > unacknowledged) and snd_max (highest number sent). I found out that the > ICMP-responses doesn't contain the correct seq. number, the first two bytes > are correct but the last two aren't. > > So i think it is a router problem (as it was in my case ;). > > HTH > Martin > To Unsubscribe: send mail to majordomo@FreeBSD.org with "unsubscribe freebsd-bugs" in the body of the message
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