troubleshooting reverse DNS

["Jeremy C. Reed" <reed@wcug.wwu.edu>]

For some reason the reverse (in-addr.arpa) mapping of an IP doesn't
always work.

dig -x 209.102.25.210

This usually returns SERVFAIL (or NXDOMAIN).

So I was guessing that it wasn't set up.

But I started at the beginning. The root-servers point to arin.net's
servers. Then arin.net's servers point to Savvis.net's two nameservers. (I
checked all of arin's servers.)

Then both of these two savvis.net server's point to the ISP's two servers.
And they both have a PTR record for the IP.

For example:

dig -x 209.102.25.210 @b.root-servers.net
dig -x 209.102.25.210 @GINSENG.ARIN.NET
dig -x 209.102.25.210 @NS2.SAVVIS.NET.
dig -x 209.102.25.210 @ns1.gnrac.net. # successfully gives PTR

So it looks like it is setup correctly.

dig -x 209.102.25.210 # reports SERVFAIL

I can't figure out where the problem is. I have tried it on three
different hosts (on three different networks) and I can't get the PTR
record without specifically asking the authoritative server. (I don't
notice that problem for other IPs I have tried.)

(I don't think it is a cache problem, because it was setup months ago --
and I noticed this over a month ago.)

Can anyone notice what is wrong with this?

Also, how can I use dig or another tool that will automatically show the
recursive steps (i.e. show the requests and each server it asks) that it
does when doing a lookup?

Thanks,

  Jeremy C. Reed