2nd default gateway

Hi All,

I have Linux machine with 2 ethernet cards in different segments. Like 10.2.1.1 and 192.168.1.1 Do i need 2 default gateways in routing table? Please, give me an example when it may happen.

Zaphod
thanks in advance

To my understanding no, that won't work since the default gw is a match anything solution. Thus if you put two default gws into your routing table the second one will never be looked at (if sorting stays the same).

HTH

Carsten

No, you cannot have two default gateways. Your default gateway is the interface and next hop address you use to get to any net you do not have a explicit routing table entry for. What you will do depends on your exact network layout. For instance, probably the most common case for having two networks in linux is when acting as a gateway for a local subnet. In that case you will have routes to two networks and one default gateway.

[root@localhost ~]# route -n
Kernel IP routing table

Destination     Gateway         Genmask         Flags Metric Ref    Use Iface
192.168.100.0   0.0.0.0         255.255.255.0   U     0      0        0 eth1
10.1.1.0     0.0.0.0         255.255.255.0   U     0      0        0 eth0
0.0.0.0         10.1.1.1     0.0.0.0         UG    0      0        0 eth0

[root@localhost ~]#

In this case, I am acting as the gateway for the 192.168.100.0/24 subnet. I also have the 10.1.1.0/24 subnet, which is my route to the larger world. My next hop to the rest of the world (in this case, my default gateway) is 10.1.1.1.

That is just one possible use case. Yours may differ. If we had more information about your particular case we may be able to help a little more.

-Philip