[176] in linux-net channel archive
Possible bug with ICMP redirects (in kernel 1.2.3)
daemon@ATHENA.MIT.EDU (Lutz Pressler)
Wed Apr 5 16:50:36 1995
Date: Wed, 5 Apr 1995 20:06:53 +0200 (MEZ)
From: Lutz Pressler <Lutz.Pressler@unix.med-stat.gwdg.de>
To: linux-net@vger.rutgers.edu
cc: Alan.Cox@linux.org, linux-kernel@vger.rutgers.edu
Hello Alan and all,
today I found out about what seems to be a bug in Linux sending ICMP
redirect messages. The setup is as follws, a bit complicated:
ppp1.subnet Linux 1.2.3, ppp-2.1.2b, dial-in modem(s)
ppp2.subnet Linux 1.2.3, ppp-2.1.2b, dial-in modem(s)
remote.subnet Linux 1.2.3, ppp-2.1.2b, modem, single host, sometimes
connected to subnet by PPP via ppp1.subnet, sometimes
via ppp2.subnet
gateway.subnet Wellfleet Router "Backbone Concentrator Node", conects subnet
to FDDI backbone etc.
some.distant.host running icmplog and admin sending log entry to me..
(thanks)
ppp1 and ppp2 using ProxyARP instead of some routing protocol (which isn't
feasable here) to ensure proper routing of incoming connections to remote.
Practically this is working, but not as intended:
The problem is, that gateway caches ARP table entries for quite a while.
So when remote makes a PPP connection via ppp2 after doing so via ppp1
some time before, gateway still sends incoming packets for remote to ppp1.
ppp1 is forwarding these to ppp2, so practically everything is working
as long as ppp1 is still up. BUT: as we found out today, ppp1 is sending
ICMP redirect messages to some.distant.host! That's the (modified) log entry
from some.distant.host:
Apr 5 13:38:45 some.distant.host icmplog: [03866]: msg from
ppp1.subnet [aa.bb.cc.dd], types=redirect, code=host,
gateway=remote.subnet [qq.rr.ss.tt]
I don't think, an ICMP redirect msg to a host many hops away is correct.
Shouldn't ppp1 send an ICMP redirect to gateway instead, and gateway
update it's ARP tables so further packets will go to ppp2 directly?
(I don't know what the Wellfleet router would do concening it's ARP
tables, because Linux doesn't seem to send redirects to it - instead
to the source host)
I'm no TCP/IP expert (haven't implemented the protocols or such..) -
so maybe I'm wrong and this is no Linux bug, but for me it seems to be one.
Thanks and have a nice day,
Lutz
--
Abteilung Medizinische Statistik Lutz Pre"sler
Universit"at G"ottingen (Systemverwaltung) privat:
Humboldtallee 32 Kreuzburger Str. 11
D-37073 G"ottingen D-37085 G"ottingen
Tel.: (+49[0]551) 39-4956 FAX: -4995 Tel.: (+49[0]551) 7700178
----> E-mail: Lutz.Pressler@Med-Stat.GWDG.DE / lpressl1@GWDG.DE <----
