firewall config....what to open....tcp or udp port 53?

Saad Kadhi bsdguy at
Wed Oct 23 07:19:25 UTC 2002

On Wed, Oct 23, 2002 at 10:11:18AM +0800, Elias wrote:
> Hi guys,
> DNS queries are done via UDP port 53 only right? I want to completely block all zone transfer request, so can I block tcp port 53 on my firewall? Or do i still need to open that port? Thanks.

DNS queries are mostly done via UDP. However, when the DNS msg is too big to fit
in a UDP packet, DNS will use TCP for queries. So I'd keep tcp/53 open as well
unless 100% sure all DNS msgs will fit into a UDP packet.

IMHO, Restricting zone xfers should not be done at the firewall but rather at the
named level by using 'allow-transfer' substatements and eventually combining
this with TSIG keys.

Saad Kadhi -- [saad at] [bsdguy at]
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