DHCP, cable modem, rfc1918
I setup a machine for my parents that is basically the gateway
system to the internet. It is connected on eth0 to a cable modem
using DHCP. The system has Shorewall installed.
Everything works, but I noticed an enormous amount of logging by
Shorewall concerning rfc1918 drops. Since I am not very familiar
with DHCP I have to make some assumptions.
Their isp uses 172.31.254.133 as DHCP server.
The cable modem has an address in the range of 10.144.xxx.xxx.
Again the setup has just worked, but I want to reduce the logging of
Shorewall to these "known" destinations.
Since I can imagine why a DHCP-client would like to talk to the
server I have allowed the server ips packets to pass.
But why is the modem talking to the dhcp-client (or I assume it is
trying to do that). Since the isp tells me that the modem ip is
dynamic, I will have to assume that just allowing one ip in the
10.144.xxx.xxx range is not enough.
Is it safe or recommended to open up a wide range of rfc1918 ips? I
could ofcourse also have the packets dropped silently, but now I
know about this, I am not sure that blocking traffic with regards to
DHCP is smart.
Bob
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