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From: marka@syd.dms.CSIRO.AU (Mark Andrews)
Subject: Re: How do multi-homed hosts choose the interface?
Message-ID: <CLwuIM.344@syd.dms.CSIRO.AU>
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Nntp-Posting-Host: drugs.syd.dms.csiro.au
Organization: CSIRO Division of Mathematics and Statistics, Australia
References: <2khb6f$9fl@breeze.dra.hmg.gb>
Date: Mon, 28 Feb 1994 01:23:08 GMT
Lines: 43
In article <2khb6f$9fl@breeze.dra.hmg.gb> heading@signal.dra.hmg.gb (Anthony Heading) writes:
>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
>--
>
>------------------
>AJR Heading, DRA UK
BIND 4.9.2 includes code to sort answers to gethostbyname queries. This
is due for release RSN. In this case you would add the fddi network
before the enthernet network in resolv.conf of the two machines.
e.g. sortlist 130.155.160.0/255.255.240.0 130.155.0.
In this case subnet 160 is given preferance over the rest of 130.155 and
they are given preferance over the rest of the world. The sortlist
directive supports up to 10 {sub}networks.
Mark