dns query id not changing

phn at icke-reklam.ipsec.nu phn at icke-reklam.ipsec.nu
Fri Dec 17 07:13:38 UTC 2004

Adam Denenberg <straightflush at gmail.com> wrote:
> Well the issue is that that same "tuple" is coming in as the firewall
> is tearing down the connection.  The firewall needs about 60ms for the
> connection to expire according to Cisco.

> I agree that there is definitely an issue with the firewall, but it
> was also my understadning  the resolver used random query IDs for each
> request.  Out of nowhere, the resolver appears to re-use a query ID
> that it just used in a very short span (20ms) and it confuses the
> firewall b/c the firewall has not torn down the previous connection. 
> Shouldnt this behavior be somewhat consistent?

> We have an application (pam_ldap) that needs to make 3 or 4 DNS
> requests. The 3rd dns request is _always_ using the same ID as the 2nd
> DNS request and occurs in about 10ms before the firewall has torn down
> the original connection and thus causes a timeout (the FW drops it).

>  I guess what i am trying to figure out is why the behavior of the
> resolver for creating a query ID is not consistent.  It should either
> reuse the same one, or create totally random ones.  It is doing a
> little bit of both and thus breaking the app.

As this id os a 16-bit value it will be reused fast.

Do as others suggested, fix the pix! Change vendor if needed.

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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