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From: heading@signal.dra.hmg.gb (Anthony Heading)
Newsgroups: comp.protocols.tcp-ip,comp.unix.bsd,comp.unix.ultrix
Subject: How do multi-homed hosts choose the interface?
Date: 24 Feb 1994 04:41:51 -0000
Organization: Defence Research Agency, UK
Lines: 30
Message-ID: <2khb6f$9fl@breeze.dra.hmg.gb>
NNTP-Posting-Host: breeze.dra.hmg.gb

Hello.
   I'm really puzzled by this. We have several hundred hosts on
a class B ethernet, and a few on a class C FDDI net, the routing
being done by one of two machines (an OSF/1 alpha and an Ultrix
DECstation) which have interfaces on both networks. The nameserver
has multiple A records for these machines - we hope to avoid 
giving different hostnames to the different interfaces.
  I want the two routing machines to use the FDDI network to
talk to each other, but they steadfastly refuse to use anything
but the ethernet. I've tried setting the interface metrics (which
doesn't work) and reversing the boot time configuration order in
the hope that this might reorder the routing table (without success
- netstat -r lists the class B network first always).
  Resorting to the obvious books, Comer vol.1 doesn't discuss
DNS style multiple addresses at all, and the 4.3BSD book claims
routing is a user-level process and the kernel doesn't try to
do anything smart. This makes me suspect that multiple A records
are used by trying each address in the gethostbyjingo() structure
in turn, but there seems to be no way of making the DNS server
impose order onto those addresses.

Any clues, speculation or even hard answers appreciated...

Thanks

Anthony
-- 

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AJR Heading, DRA UK