SUMMARY: gethostbyaddr() & multi-domained hosts...

From: Eric Berggren (eric@ee.pdx.edu)
Date: Fri Dec 31 1993 - 18:01:13 CST


> We have several multi-homed hosts with drops into other DNS domains. We
> presently have the reverse pointers setup so that the names reflect the
> domains in which that interface resides, however, this is creating a small
> mess for access lists and whatnot as we must be concerned over which of
> the interfaces is used to access a particular host and would like to
> have all revp's point to one single name.
> After modifying the PTR entry in one zone to a new name (but of another
> DNS domain name), normal DNS reverse queries succeed with the proper name,
> however, lookups using gethostbyaddr() now fails (tested with code).
>
> Example :

> ee.pdx.edu :
> ursula IN A 131.252.10.155
>
> BEFORE :
> 20.252.131.in-addr.arpa. :
> 155 IN PTR ursula-cs.cs.pdx.edu.
>
> AFTER :
> 20.252.131.in-addr.arpa. :
> 155 IN PTR ursula.ee.pdx.edu.

  I had neglected to add the other interface to the zone file, which
should have looked like :

  ee.pdx.edu:
         ursula IN A 131.252.10.155
                 IN A 131.252.20.155

  gethostbyaddr() under SunOS uses the algorithm below for the lookup :

        hp1 = gethostbyaddr(<addr>);
        hp2 = gethostbyname(hp1->h_name);

        if <addr> in hp2->h_addrlist
                return <hp>
        else
                syslog warning
                return NULL

  Thanks to : casper@fwi.uva.nl & Piete.Brooks@cl.cam.ac.uk .

-eric

-- 
  Eric Berggren             | "Parts of this product may be derived from
  Portland State University |  from UNIX and Berkeley 4.3 BSD systems..."
  eric@ee.pdx.edu           |                  -- Label on Solaris 2.x disk



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