iptables and bootp

[Christoph Pleger]

Hello,

I'm using the following commands to drop all traffic to and from the
bootp-port of one of my machines:

iptables -I INPUT -i eth0 -p tcp --destination-port bootps -j DROP
iptables -I INPUT -i eth0 -p udp --destination-port bootps -j DROP
iptables -I OUTPUT -o eth0 -p tcp --source-port bootps -j DROP
iptables -I OUTPUT -o eth0 -p udp --source-port bootps -j DROP

But this machine gives a reply to another machine's bootp-request that
was created by the program "bootpc" (it is not possible that that answer
comes from another bootp-Server). Iptables-Statistics show that
UDP-packets to the bootps-port have been dropped, but obviously that has
not really happened (as shown by tcpdump). Dropped outgoing packets from
port bootps do not appear in the statistics. 

When I change the port number in the above commands (for example, to
20003), the packets are actually blocked.

Does somebody have any advice?

Kind regards
  Christoph Pleger
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