From owner-freebsd-hackers Fri Aug 28 01:03:02 1998 Return-Path: Received: (from majordom@localhost) by hub.freebsd.org (8.8.8/8.8.8) id BAA13988 for freebsd-hackers-outgoing; Fri, 28 Aug 1998 01:03:02 -0700 (PDT) (envelope-from owner-freebsd-hackers@FreeBSD.ORG) Received: from mail.ppp.net (mail.ppp.net [194.64.12.35]) by hub.freebsd.org (8.8.8/8.8.8) with ESMTP id BAA13953 for ; Fri, 28 Aug 1998 01:02:55 -0700 (PDT) (envelope-from ernie!bert.kts.org!hm@ppp.net) Received: from casparc.ppp.net (casparc2.ppp.net [194.64.12.42]) by mail.ppp.net (8.8.8/8.8.8) with SMTP id KAA04373 for ; Fri, 28 Aug 1998 10:02:01 +0200 Received: from ernie by casparc.ppp.net with uucp (Smail3.1.28.1 #1) id m0zCJTt-002ZjZC; Fri, 28 Aug 98 10:02 MET DST Received: from bert.kts.org(really [194.55.156.2]) by ernie.kts.org via sendmail with smtp id for ; Fri, 28 Aug 1998 09:22:42 +0200 (CEST) (Smail-3.2.0.91 1997-Jan-14 #3 built 1998-Feb-14) Received: by bert.kts.org via sendmail with stdio id for freebsd-hackers@freebsd.org; Fri, 28 Aug 1998 09:22:43 +0200 (CEST) (Smail-3.2.0.94 1997-Apr-22 #2 built 1998-Aug-25) Message-Id: From: hm@kts.org (Hellmuth Michaelis) Subject: TCP checksum errors resulting from IP addr change To: freebsd-hackers@FreeBSD.ORG (FreeBSD Hackers) Date: Fri, 28 Aug 1998 09:22:43 +0200 (CEST) Organization: Kitchen Table Systems Reply-To: hm@kts.org X-Mailer: ELM [version 2.4ME+ PL40 (25)] MIME-Version: 1.0 Content-Type: text/plain; charset=US-ASCII Content-Transfer-Encoding: 7bit Sender: owner-freebsd-hackers@FreeBSD.ORG Precedence: bulk X-Loop: FreeBSD.ORG Hi, I've posted this to -net without a reaction. Any reaction is welcome since i totally ran out of ideas: I'm trying to debug a strange effect occuring on a sync PPP ISDN interface which is used to connect to a Cisco 1003 (on 192.76.124.10). 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 (Is this correct ?). Is there a way to inform the TCP layer to recalculate checksums or to get the new IP address from the interface ? Do i have to recalculate the checksums for this session in the driver ? Has anyone another 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 To Unsubscribe: send mail to majordomo@FreeBSD.org with "unsubscribe freebsd-net" in the body of the message -- Hellmuth Michaelis hm@kts.org Hamburg, Europe A duck is like a bicycle because they both have two wheels except the duck (terry@cs.weber.edu) To Unsubscribe: send mail to majordomo@FreeBSD.org with "unsubscribe freebsd-hackers" in the body of the message