Query source port 53

[Barry Margolin]

In article <bmeic1$esj$1 at sf1.isc.org>, Bragi Baldursson <bb at simi.is> wrote:
>I have been looking over the RFCs and the threads about the issue of using
>source port 53 for querying and it seems to me
>that the standard is to use port 53 as the query source port.

This was the behavior of BIND 4, but AFAIK it's not specified in any
standard.  And BIND 8 changed the default behavior -- it now selects an
ephemeral source port.

>In a GPRS network environment we have typically 2 DNS servers.   Each of
>these servers refer to a root
>server who resides in a GRX environment to get info for resolving.
>
>Now I have been having a problem with a particular GPRS operator that he
>will not allow my DNS to query
>his DNSs using source port 53.   My DNSs have always used source port 53
>for querying so I was quite
>taken aback by this.   His argument was that you are not allowed to use
>port 53 as a source port for DNS
>but you should use any port number > 1023.
>
>Due to this they close their firewall for all DNS queries coming from
>source port 53.    Is this correct?

I don't think there's any standard restriction on the source port.  And
since BIND 4 always uses port 53, he's blocking any access to his DNS from
sites that use old software.

-- 
Barry Margolin, barry.margolin at level3.com
Level(3), Woburn, MA
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