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I'm running ISC DHCP deamon on centOS and want to block unwanted(by clients MAC address) discovery messages before they reach dhcpd.

how can I do this with iptables or anything else?

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The Linux netfilter firewall has the ability to match on MAC address and then simply filter the DHCP protocol (UDP port 67,68) messages:

/sbin/iptables -I INPUT -m mac --mac-source 00:11:22:33:44:55 -p udp --sport 67:68 --dport 67:68  -j DROP

Although a better alternative is probably to configure your DHCP server to ignore requests from certain MAC addresses as described in this Q&A

| improve this answer | |
  • can I match wildcard mac 11:22:33:* ? – misha Oct 20 '17 at 14:36
  • I think the required form is xx:xx:xx:xx:xx:xx but I don't know if xx:xx:xx:*:*:* works. Why don't you go and test that? – HBruijn Oct 20 '17 at 14:56
  • still getting discovery messages after adding following rule : sbin/iptables -I INPUT -m mac --mac-source 00:11:22:33:44:55 -j DROP – misha Oct 23 '17 at 12:13
  • You did replace the sample MAC address with the actual MAC you're trying to block, right? – HBruijn Oct 23 '17 at 12:19
  • yes I did.I found that all the requests are from same mac addr(GW dhcp server is using) so, inspecting just layer 2 mac will not help. it needs to inspect dhcp message headers. – misha Oct 23 '17 at 12:27

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