> 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
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.