[techtalk] Default Deny

Jamie Walker jj.walker at auckland.ac.nz
Fri Jan 28 08:32:07 EST 2000

Subba Rao wrote:

> I cannot go out to the Web nor resolve any DNS names. Mail will not go out.
> My system does have a small DNS which forwards requests to my ISP's nameserver.
> Nothing really works.


>         ipchains -A input -i ppp0 -p UDP -s I.S.P.NS -d $LOCALIP 53 -j ACCEPT
>         ipchains -A input -i ppp0 -p UDP -s I.S.P.NS1 -d $LOCALIP 53 -j ACCEPT

These two rules are both assuming that DNS requests are going out with a
source port of 53. Quite often nowadays DNS uses non-privileged source
ports (ie, not < 1024) so this might be what's breaking DNS. If DNS is
broken, that probably doesn't help web or mail traffic. :-/

Work: jj.walker at auckland.ac.nz	Home: jamiew at clear.net.nz
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