Posts tagged dhcp

firewall: block DHCP traffic

posted on 2016-02-20 23:29:26

To block DHCP reqests as well as responses, block:

src port range 67 to 68
dst port range 67 to 68

Why?

[ jl@jl ~ ] 23:31:06 $ \grep -e '\s67/' -e '\s68/' /etc/services 
bootps          67/tcp                          # BOOTP server
bootps          67/udp
bootpc          68/tcp          dhcpc           # BOOTP client
bootpc          68/udp          dhcpc

Which means port 67->68 are DHCP responses, whereas 68->67 are DHCP requests.

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