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OK, after asking my last question, I've done some digging and I think I've figured out how everything works, but there are some things about glue records I haven't quite figured out.

If a resolver tries to resolve ourdomain.com, at some point it will query a gTLD server, which will return some NS records. In our case, the result should look like this:

% dig +norecurse ourdomain.com @a.gtld-servers.net

;; AUTHORITY SECTION:
ourdomain.com.             172800  IN      NS      ns1.the-isp.net.
ourdomain.com.             172800  IN      NS      our-server.ourdomain.com.

;; ADDITIONAL SECTION:
ns1.the-isp.net.           172800  IN      A       nnn.nnn.nnn.nnn
our-server.ourdomain.com.  172800  IN      A       mmm.mmm.mmm.mmm

I gather that there are glue records on each gTLD server that associate the two name servers with the IP addresses.

  1. Do the glue records have TTL's? (Is that what the 172800 is in the ADDITIONAL SECTION?)
  2. If so, what happens when the glue record expires? Suppose the glue record for our-server.ourdomain.com expires. Would the gTLD server then do a lookup on that name to find the IP address (which, in this case, would have to go through ns1.the-isp.net, I think)? If that query results in a different IP address, does the glue record then get changed? If that isn't how it works, then do glue records have to be changed manually, or is there some other mechanism that would cause it to change?
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ajb
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1 Answers1

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Your glue records within the .com TLD will not expire, at least not so long as you are paying your bills. The .com name servers are authoritative for that zone.

The TTL value doesn't really matter to the zones that are authoritative, the TTL is a value that is passed along to other clients, and resolving DNS servers to inform them how long they are permitted to cache a particular record.

So if you happened to be using Google 8.8.8.8 as your resolver, when Google looked up your GLUE records from the .com servers it would only keep them with in the Google cache for no longer then ammount of time described by the TTL. After that it would perform the lookup again.

Zoredache
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