8

Simple setup here. I have a machine with multiple network interfaces, two for example - eth0 and eth1.

eth0 has a static address and has a default gateway assigned. eth1 has a static address and will not have a gateway on that interface's network address range.

The Question

Do I need an entry in network configuration file (/etc/network/interfaces) for the gateway option on the interface that does not have a gateway on its network, eth1 in the above example?

Additional Questions

If I do something like:

gateway 127.0.0.1

Will this have adverse effects? Will this interface now have a way to reach a gateway or will using the loopback interface as a gateway have no effect (i.e. same as leaving the gateway option off entirely)?

Example config for discussion

/etc/network/interfaces

# The loopback network interface
auto lo
iface lo inet loopback

# Interface 1
allow-hotplug eth0
iface eth0 inet static
address 10.1.10.200
netmask 255.255.255.0
gateway 10.1.10.1

# Interface 2
allow-hotplug eth1
iface eth1 inet static
address 192.168.100.1
netmask 255.255.0.0
gateway 127.0.0.1     # This is the line in question
111---
  • 4,424
  • 3
  • 27
  • 50

1 Answers1

6

You do not need a gateway entry for any NIC that you don't want to use to reach a network not in its collision domain (192.168/16 in this case). You can just omit that line if you don't want a gateway for that NIC.

I'm not sure what will happen if you try to use loopback as a gateway, but I wouldn't expect it to be happy times.

Eric Renouf
  • 18,141
  • 4
  • 49
  • 65
  • I haven't tested but I would guess that trying to set 127.0.0.1 as a gateway for 192.168.100.1 will not work because they are in disjoint networks: 127/8 vs 192.168/16. – zwets Aug 19 '15 at 21:56