Date: Thu, 29 Nov 2001 20:00:03 -0800 (PST) From: Igor M Podlesny <poige@morning.ru> To: freebsd-bugs@FreeBSD.org Subject: Re[2]: misc/31575: wrong src ip address for some ICMPs Message-ID: <200111300400.fAU403m50997@freefall.freebsd.org>
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The following reply was made to PR misc/31575; it has been noted by GNATS. From: Igor M Podlesny <poige@morning.ru> To: Ruslan Ermilov <ru@FreeBSD.org> Cc: bug-followup@FreeBSD.org, freebsd-hackers@FreeBSD.org Subject: Re[2]: misc/31575: wrong src ip address for some ICMPs Date: Fri, 30 Nov 2001 11:01:56 +0700 > On Sun, Oct 28, 2001 at 08:10:25PM -0800, Igor M Podlesny wrote: hm.. it seems somebody has multiplied my timezone by -1 ;-) >> >> You might observe this bug doing traceroute while standing behind >> a GW's interface with several IP-addresses (aliases). In this case >> you always got ICMP.TIMXCEED (time exceeded) coming from IP-address >> which is usually the first on the interface, even if your box is >> not using this IP-address as its next-hop. Despite of the code >> selecting right IP-address for this purpose is working well it's >> being confused by wrong argument it is being given. This patch >> (http://www.morning.ru/~poige/patchzone/ip_icmp.c.diff) fixes namely >> this problem. >> > Let me see if I took you correctly. Suppose you have a gateway, GW: > rl0: flags=8843<UP,BROADCAST,RUNNING,SIMPLEX,MULTICAST> mtu 1500 > inet 192.168.4.115 netmask 0xffffff00 broadcast 192.168.4.255 > inet 192.168.4.200 netmask 0xffffffff broadcast 192.168.4.200 > And another host H on the network has the following routing table > entry: > 10 192.168.4.200 UGSc 0 16030 fxp0 > And you are complaining that when H sends an IP packet to the 10 > network, with TTL <= 1, gateway replies with an ICMP time exceeded > from 192.168.4.115 instead of expected 192.168.4.200, like this: > traceroute to 10.0.0.1 (10.0.0.1), 1 hops max, 40 byte packets > 1 192.168.4.115 0.448 ms > Right? But if that's the case (and I just checked for sure that > your patch doesn't make any difference), the GW doesn't know > which of the 192.168.4.115 or 192.168.4.220 addresses have been > used by H, because they both map to the same MAC address on H, > and the MAC address is what's used when forwarding: > ? (192.168.4.115) at 0:c0:df:3:2d:79 on fxp0 [ethernet] > ? (192.168.4.200) at 0:c0:df:3:2d:79 on fxp0 [ethernet] >> >How-To-Repeat: >> You should have several ip-address on interface of NEXT-HOP router >> running FreeBSD, then invoke traceroute some.where. >> > Yeah, that's exactly how I did it, and didn't notice any > difference after applying your patch... Ruslan, sorry, I'm very busy for an unpredictable amount of time, cause I'm a system administrator of ISP and recently I got a bunch of deeds to do, so I can't respond to your analyze shown before in all its details... and (sorry for that) I don't feel that it is really needed -- I changed the code in ip_icmp.c because I saw myself how really were routers acting before and after applying the patch. In addition, I suggest you to look at this http://www.sigmasoft.com/~openbsd/archive/openbsd-bugs/200110/msg00146.html P.S. The description of bug once more: [router] | X---->|backbone|--> | | Yip1----|the same media|------[some another ip-network] |ip2----|the same media|------|some box| Here is "router" with FreeBSD (OpenBSD, and, probably *BSD) and "Some box" doing traceroute to (for e.g.) a host which is _reachable_ _via_ _backbone_. X, Y -- NICs. Y has several IPs, making several ip-networks on "the same media". The problem: traceroute being run on "somebox" will hear respond from "router" coming from Y.ip1 address which isn't on its (somebox) IP-network. (well, I deem icmp.echoreply isn't alone in this.) And this happens because wrong IP-addr is passed to ifaof_ifpforaddr(). My patch fixes namely this problem -- I have worked out and applied it and I believe I know what I'm talking about. Look at it, and you'll realize what I mean... You may ask me for details, but, please, don't make different situations asking me how does it correlate with -- damn lack of time... -- Igor mailto:poige@morning.ru http://morning.ru/~poige To Unsubscribe: send mail to majordomo@FreeBSD.org with "unsubscribe freebsd-bugs" in the body of the message
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