Date: Tue, 22 Apr 2003 21:22:24 +0400 (MSD) From: Maxim Konovalov <maxim@macomnet.ru> To: Don Lewis <truckman@freebsd.org> Cc: freebsd-net@freebsd.org Subject: Re: IP fragmentation disagreement between current and stable Message-ID: <20030422211839.D75980@news1.macomnet.ru> In-Reply-To: <200304221712.h3MHCTXB027263@gw.catspoiler.org> References: <200304221712.h3MHCTXB027263@gw.catspoiler.org>
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On 10:12-0700, Apr 22, 2003, Don Lewis wrote:
> On 22 Apr, To: freebsd-net@freebsd.org wrote:
>
> > # ping -c 1 -s 3176 192.168.101.3
>
> > If I increase the packet size by any multiple of 1480 bytes (which
> > results in the same final fragment size), I see the same symptoms.
> > Interestingly, I don't see any problems if I decrease the packet size by
> > 1480 bytes to 1696, everything works just fine.
>
> I explored the vicinity of 3176 and found that 3174 works, 3175 through
> 3177 don't work, and 3178 works. I'm smelling a packet length
> calculation error. In the case of a 3176 byte ping, the final fragment
> will contain 222 bytes of data. With a 14 byte Ethernet header and a 20
> byte IP header, that just fits into one 256 byte mbuf. I wonder if
> there is a divide by 4 to calculate the number of words, and the
> remainder is being discarded instead of being rounded up? And why does
> this problem only occur if there are three or more fragments?
>
> Could this be a driver problem instead of a problem in the stack itself?
> Both ends are fxp cards.
can't reproduce with ref5.freebsd.org:
stable# ping -c 1 -s 3176 ref5.freebsd.org
PING ref5.freebsd.org (216.136.204.102): 3176 data bytes
3184 bytes from 216.136.204.102: icmp_seq=0 ttl=46 time=194.385 ms
ref5$ netstat -s -p ip | grep frag
7496159 fragments received
0 fragments dropped (dup or out of space)
0 fragments dropped after timeout
38994 output datagrams fragmented
231719 fragments created
0 datagrams that can't be fragmented
ref5$ netstat -s -p ip | grep frag
7496162 fragments received
0 fragments dropped (dup or out of space)
0 fragments dropped after timeout
38995 output datagrams fragmented
231722 fragments created
0 datagrams that can't be fragmented
It got three fragments, defragmented them, sent icmp echo reply in
three fragments.
--
Maxim Konovalov, maxim@macomnet.ru, maxim@FreeBSD.org
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