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Debian bug tracking system administrator (administrator, Debian Bugs database) -------------------------------------- Received: (at submit) by bugs.debian.org; 11 Oct 1996 17:52:33 +0000 Received: (qmail 17499 invoked from smtpd); 11 Oct 1996 17:52:30 -0000 Received: from chiark.eng.cam.ac.uk (HELO chiark.greenend.org.uk) ([EMAIL PROTECTED]) by master.debian.org with SMTP; 11 Oct 1996 17:52:29 -0000 Received: by chiark.greenend.org.uk id m0vBlbR-0004OIC (Debian /\oo/\ Smail3.1.29.1 #29.35); Fri, 11 Oct 96 18:42 BST Message-Id: <[EMAIL PROTECTED]> Date: Fri, 11 Oct 96 18:42 BST From: Ian Jackson <[EMAIL PROTECTED]> To: Debian bugs submission address <[EMAIL PROTECTED]> Subject: XDMCP problem with multihomed X servers (design error?) Package: xbase Version: 3.1.2-9 I have an X server running on a machine with two different network interfaces (ethernet and ppp) onto separate networks. I've been trying to get that X server to talk to an xdm on one of those networks (ppp), by using X -query <name-of-xdm-host>. This appears to work correctly (XDMCP UDP packets are exchanged) until xdm tries to make an actual X connection to the X server. It seems that xdm has synthesised a DISPLAY value containing the hostname of the X server's ethernet interface, by doing a reverse lookup of an IP address provided by the X server (both the X server and xdm have access to name/address mappings for all the interfaces involved, all of which have distinct canonical names and reverse map correctly). Examining the source code I can see that XDMCP has a facility for the X server to tell its address to xdm, other than by having xdm examine the IP headers on the (UDP) XDMCP query. This message has room for several addresses in different address families (connection types in X speak). I presume that this facility is there so that an X server which supports several different connection types can advertise them all, and xdm can pick the right one. However: (a) the X server always advertises all of its IP interfaces in this message, in the order they were configured. (b) the function in xdm which is supposed to choose which entry from the table to pick always returns 0, so that the first entry is always used. In my situation this causes xdm to try to make an X connection to the X server's ethernet interface, which doesn't work (because the two networks are partitioned). There appear to be no options to X or xdm which help the situation. Interestingly, the X server does have access to a more appropriate address: when it does XDMCP it uses a UDP socket to send packets to the xdm's ppp interface and the kernel does select an appropriate source address: the X server's ppp interface. I've managed to find a workaround: using LD_PRELOAD to override ioctl so that SIOCGIFCONFIG (used by the X server to find which interfaces are available) doesn't return the ethernet interface at all. However this is a horrible hack. I'm not entirely sure, but I think that the right fix is something like the following: * xdm should have a way to configure `preferred' addresses, much as named does for returning RRs. * xdm should try all the addresses it has been given in order, and its timeout for going on to the next one should be shorter than the X server's timeout for giving up on the XDMCP session. * xdm should disregard addresses with connection types it doesn't understand (at the moment it doesn't appear to do this). * X should make sure that the local address of the UDP port it's using to communicate with xdm is first on the list of addresses it advertises. * X should have an option to specify which local address to use. An alternative strategy would be: * X should only advertise one address with each connection type. * If it has many possible addresses to choose from X should try doing a session with each. * X should try the local address it is using for its XDMCP session first. * X should have a way to specify an order for the interfaces it advertises; there needs to be a default (which just overrides the list from SIOCGIFCONFIG) and an overriding version (which can override the local end of the XDMCP session too). * xdm should skip down the list of addresses until it finds a type it supports. (Currently I believe it will fail if the first connection type advertised is not supported.) What the strategy should be will need to be decided globally, perhaps by fiat by the X consortium if there is no obvious right answer to those who know this area better than I do. Ian. PS: I'm using the xdm from Debian's xbase 3.1.2-9 and the XF86_S3 from 3.1.2-5. --------------------------------------- Received: (at 4757-done) by bugs.debian.org; 31 Dec 2002 00:23:48 +0000 >From [EMAIL PROTECTED] Mon Dec 30 18:23:40 2002 Return-path: <[EMAIL PROTECTED]> Received: from (hotmail.com) [62.76.154.4] ([/rF3519XNSsRl4yY/QNs3zjw+C5/CLgF]) by master.debian.org with smtp (Exim 3.12 1 (Debian)) id 18TAAL-0003Ua-00; Mon, 30 Dec 2002 18:21:53 -0600 Received: from 202.230.53.204 ([202.230.53.204]) by webmail.halftomorrow.com with smtp; Mon, 30 Dec 2002 05:24:54 +0500 Received: from [13.163.173.238] by snmp.otwaloow.com with NNFMP; Mon, 30 Dec 2002 10:20:02 +0800 Received: from group21.345mail.com ([127.38.70.163]) by relay.2yahoo.com with local; Mon, 30 Dec 2002 18:15:10 +0600 Reply-To: <[EMAIL PROTECTED]> Message-ID: <000801b2ac66$ebd23088$4488682a@aftrseof> From: <[EMAIL PROTECTED]> To: Wannabe Subject: Watch what we do together.. Date: Mon, 30 Dec 2002 18:56:22 +0500 MIME-Version: 1.0 Content-Type: text/plain; charset="us-ascii" Content-Transfer-Encoding: 8bit X-Priority: 3 X-MSMail-Priority: Normal X-Mailer: Microsoft Outlook, Build 10.0.2627 Importance: Normal Delivered-To: [EMAIL PROTECTED] X-Spam-Status: No, hits=4.0 required=5.0 tests=FORGED_HOTMAIL_RCVD,FROM_ENDS_IN_NUMS,INVALID_MSGID, MISSING_MIMEOLE,NO_REAL_NAME,SPAM_PHRASE_00_01, SUBJ_ENDS_IN_SPACE,TO_MALFORMED version=2.41 X-Spam-Level: **** Hi,.. Please, please write again, hope you still have my email, to make things worse I am not sure about yours either, anyway you can always catch me on http://www.singlers.com/index_vip.html Hope to see you very, very soon. Kisses and more :) Dealy -- To UNSUBSCRIBE, email to [EMAIL PROTECTED] with a subject of "unsubscribe". Trouble? Contact [EMAIL PROTECTED]