From owner-freebsd-stable Fri Aug 24 14:39:58 2001 Delivered-To: freebsd-stable@freebsd.org Received: from obsecurity.dyndns.org (adsl-63-207-60-54.dsl.lsan03.pacbell.net [63.207.60.54]) by hub.freebsd.org (Postfix) with ESMTP id 00ECE37B403 for ; Fri, 24 Aug 2001 14:39:53 -0700 (PDT) (envelope-from kris@obsecurity.org) Received: by obsecurity.dyndns.org (Postfix, from userid 1000) id 85BE966D1C; Fri, 24 Aug 2001 14:39:52 -0700 (PDT) Date: Fri, 24 Aug 2001 14:39:52 -0700 From: Kris Kennaway To: Steven Holmes Cc: freebsd-stable@FreeBSD.ORG Subject: Re: Weird networking problem Message-ID: <20010824143952.A83415@xor.obsecurity.org> References: Mime-Version: 1.0 Content-Type: multipart/signed; micalg=pgp-md5; protocol="application/pgp-signature"; boundary="BXVAT5kNtrzKuDFl" Content-Disposition: inline User-Agent: Mutt/1.2.5i In-Reply-To: ; from steg@pc1-east2-0-cust144.ren.cable.ntl.com on Fri, Aug 24, 2001 at 10:37:38PM +0100 Sender: owner-freebsd-stable@FreeBSD.ORG Precedence: bulk List-ID: List-Archive: (Web Archive) List-Help: (List Instructions) List-Subscribe: List-Unsubscribe: X-Loop: FreeBSD.ORG --BXVAT5kNtrzKuDFl Content-Type: text/plain; charset=us-ascii Content-Disposition: inline Content-Transfer-Encoding: quoted-printable On Fri, Aug 24, 2001 at 10:37:38PM +0100, Steven Holmes wrote: >=20 > While trying to access some websites, I discovered a strange > networking problem that I am unable to solve. >=20 > Some IPs I am unable to connect to using TCP. tcpdump shows the SYN > packets that I send to have a bad checksum (I have included a sample > tcpdump output below). However, these are the only packets that > tcpdump shows a problem for, and all my other packets seem to have > correct checksums. >=20 > I can access everything from my internal windows box, which I am > performing NAT for. I am running ipf and ipnat, and have tried > disabling both, but without any result. I have tried with > tcp_extensions both enabled and disabled, have tried a different > network card and have tried with numerous different clients (including > telnet), but the problem remains. >=20 > I get no response to my initial packet (The checksum is always bad), > and this is the only packet that is sent. I am on a cable modem. >=20 >=20 > Sample tcpdump output for accessing www.slashdot.org (a problem IP): >=20 > 22:15:24.687044 pc1-east2-0-cust144.ren.cable.ntl.com.1034 > > 64.28.67.150.http: S [bad tcp cksum fffe!] 1158842795:1158842795(0) > win 16384 (DF) (ttl 64, id 2222, len 44) How new is your kernel? Kris --BXVAT5kNtrzKuDFl Content-Type: application/pgp-signature Content-Disposition: inline -----BEGIN PGP SIGNATURE----- Version: GnuPG v1.0.6 (FreeBSD) Comment: For info see http://www.gnupg.org iD8DBQE7hsmoWry0BWjoQKURAlOqAKDtNriD5CbdIJikeBzp1ow6PvHcKQCg/o+U gD0RnSmvLJIvXVATqtzAoT0= =BPhL -----END PGP SIGNATURE----- --BXVAT5kNtrzKuDFl-- To Unsubscribe: send mail to majordomo@FreeBSD.org with "unsubscribe freebsd-stable" in the body of the message