Disable Accepting Packets Routed Between Local Interfaces

Description

To set the runtime status of the net.ipv4.conf.all.accept_local kernel parameter, run the following command:

$ sudo sysctl -w net.ipv4.conf.all.accept_local=0

To make sure that the setting is persistent, add the following line to a file in the directory /etc/sysctl.d:

net.ipv4.conf.all.accept_local = 0

Rationale

Configure net.ipv4.conf.all.accept_local=0 to consider as invalid the packets received from outside whose source is the 127.0.0.0/8 address block. In combination with suitable routing, this can be used to direct packets between two local interfaces over the wire and have them accepted properly.