[CentOS] Help with iptables rule for blocking UDP port 53

Sean Carolan scarolan at gmail.com
Tue Jul 15 16:15:31 UTC 2008


I would like to block all DNS queries that come from one particular ip
address.  I used TCPdump to verify that the queries were in fact,
coming from this IP:

[scarolan at server:~]$ sudo tcpdump -n udp port 53 and src 10.100.1.1
tcpdump: listening on eth0
11:12:17.162100 10.100.1.1.19233 > 10.100.1.61.domain:  14270+ A?
server.domain.com. (32) (DF)

Could someone help with the proper syntax for an IPtables rule to
block port 53 udp traffic from this IP?  I tried this rule but it
doesn't work:

-A RH-Firewall-1-INPUT -s 10.100.1.1 -m udp -p udp --dport 53 -j REJECT



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