Date: Wed, 26 Aug 1998 16:22:35 +0200 (METDST) From: hm@hcs.de (Hellmuth Michaelis) To: freebsd-net@FreeBSD.ORG (FreeBSD Networking) Subject: TCP checksum errors resulting from IP addr change Message-ID: <m0zBgT5-0000fAC@hcswork.hcs.de>
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I'm trying to debug a strange effect occuring on a sync PPP ISDN interface
which is used to connect to a Cisco 1003.
To get an address dynamically from the remote side, the local PPP inter-
face (on 2.2.5-RELEASE) is set up with:
ifconfig isppp0 link1 0.0.0.0 192.76.124.10 netmask 0xffffffff debug
Now i telnet to 192.76.124.10 and the link gets established but the telnet
session doesn't.
I looked at the traces and noticed the very first IP packet going out with
source address 0.0.0.0 to the Cisco - i removed that in the driver but still
the telnet session is not established. (btw. only the first session is not
established, if i terminate the first telnet and restart it on the open link,
it works immediately; but i want the first to work ...).
I enabled TCP debugging on the Cisco, and for all the packets from this
first telnet session it says "TCP checksum error".
So i think, IP address 0.0.0.0 is used for checksum calculation of the TCP
packets for this forst session, but the "real" IP address of the interface
changes to 192.something after the first packet and the TCP checksum is
somehow not recalculated causing checksum errors on the remote side.
Has anyone a hint or an idea how to solve this ?
hellmuth
--
Hellmuth Michaelis Tel +49 40 559747-70
HCS Hanseatischer Computerservice GmbH Fax +49 40 559747-77
Oldesloer Strasse 97-99 Mail hm [at] hcs.de
22457 Hamburg WWW http://www.hcs.de
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