Re: DNS ACL ?

["Stephen J. Smoogen" <smooge () gmail com>]

On 11/11/05, John Hally <JHally () epnet com> wrote:
> Hello All,
>
> I need a sanity check regarding DNS ACLs.  For external facing DNS servers
> you need to allow only udp/53 inbound, correct?  I know tcp/53 is used for
> zone transfers and requests/replies greater than a certain size, but they
> shouldn't typically happen for general dns queries correct?

I think that the backbone DNS servers and certain upstream DNS servers
require TCP, and if for some reason a query can not fit into a single
UDP packet it will switch to TCP.

So if you do not have insane hostnames or extra info (long TXT
sections etc), then TCP would not be needed to the world.. locking it
down so that it only talks to known upstream boxes would probably be
correct.

--
Stephen J Smoogen.
CSIRT/Linux System Administrator

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