Re: Does redirect in PREROUTING require open port in INPUT?

[Antony Stone <Antony@Soft-Solutions.co.uk>]

On Saturday 27 March 2004 8:31 pm, forum@users.pc9.org wrote:

> My situation is, I run two different nameservers (one on udp 53 and another
> one on udp 5300). The one on the higher port is meant to be private and
> used only by permitted IPs.
>
> Currently, I am using the following with success:
> -----------------------
> iptables -P INPUT DROP
> iptables -A INPUT -i $EXTIF -p udp --dport 53 -j ACCEPT
> iptables -A INPUT -i $EXTIF -p udp --dport 5300 -j ACCEPT
>
> iptables -t nat -A PREROUTING -i $EXTIF -p udp --dport 53 -s 1.2.3.4 \
> 	-j REDIRECT --to-ports 5300
> -----------------------
>
> Works fine; only the IP 1.2.3.4 can access the private nameserver while all
> other public requests go to the default server on port 53. However I found
> that I needed to explicitly open up port 5300 on INPUT for this to work.
> While I could throw in an additional -s check in the INPUT rules, it seems
> like an ugly duplication if I have a large number of IPs.
>
> Is there a more elegant way to do this port redirection without opening up
> the private port to the world? i.e. somehow see that a REDIRECT happened,
> rather than a packet actually coming in with destination port 5300?

I would recommend the use of split DNS.

Do it at the application layer instead of the network layer, then everything 
works on port 53.

Regards,

Antony.

-- 
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If you want to be happy for a year, get married.
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