Nameserver IDs

phn at phn at
Mon Jan 5 20:13:16 UTC 2004

Gisle Vanem <giva at> wrote:
> I have some question regarding a ill-behaving DNS-server. It is
> part of a cheap little router. I don't even know the manufacturer of it.
> It seems to only handle 1 request at a time because the ID of the 
> last reply isn't the ID of the associated query sent.

> My DNS-client compares the ID in the responses with what it sent. 
> When no match, it returns empty.

> What happens between DNS Client <-> Server:
> C -> S, Query, ident _26241_
> C -> S  host1, Query, ident 31436  (retry)
>   client gives up and does a new lookup

> C -> S, Query, ident 58361
> S -> C, Reply, ident _26241_

> Although the 2nd lookup seems okay, it's ID is not what I'd expect.
> (the ID is from the 1st lookup). And since it's not received on the same
> socket, it's thrown away and the ID-cache is cleared.

> I didn't find a definitive answer in the RFCs to support such behaviour.
> Reading RFC-1035, sec 7.3 I give the idea that comparing ID is 
> recommended, but how does other stack and DNS-clients handle this? 
> I assume they use some heuristics to sort out the correct response.
> --gv

Matching ID of responses is essential. The above mentioned box is broken
and should be replaced.

Peter Håkanson         
        IPSec  Sverige      ( At Gothenburg Riverside )
           Sorry about my e-mail address, but i'm trying to keep spam out,
	   remove "icke-reklam" if you feel for mailing me. Thanx.

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