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Re: Domain names for ISP infrastructure links
From: Rob Liebschutz <rob () rjl com>
Date: Tue, 7 Jan 97 16:10:32 PST

I'm puzzled. Connections go from router to router. How does it help to say
routerb-x-y-z-routerc.blah.net 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 :)


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.


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