Domain names for ISP infrastructure links

Rob Liebschutz rob at
Wed Jan 8 00:10:32 UTC 1997

> > > I'm puzzled. Connections go from router to router. How does it help to say
> > > when routerc will show up as the next hop in
> > > the traceroute?
> > 
> > I think it will help when routerc fails to show up as the next hop :)
> No.

Actually yes.  At first I had the same thought that you did, but
knowing which router the packet was supposed to have come from makes
it easy to tell from the output of a traceroute weather the routing
changed in the middle.  Having to use IP addresses to figure this out
is much more work.  On the other hand, I do question the idea of
trying to cram all this info into the the interface names in the DNS.

> Traceroute gives you the incoming interface on a router.  For a given
> incoming interface on a router there are multiple next hop routers
> (and multiple outgoing interfaces).
> Knowing that the outgoing interface that a packet came from on the
> previous hop router is not worth adding to the DNS.
> If this is a point-to-point link, as you seem to be assuming, then it
> should be subnetted as a /30 and you can thus subtract or add 1 to the
> IP address as appropriate to find the previous hop's outgoing
> interface, if that information is important to you.
> If it is a multiple-access link, then there is no chance of the
> incoming interface being specific to a particular previous hop anyway,
> so this scheme falls apart.
> --jhawk

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