Default Route question when there are two nic cards

[David G. Miller]

Jeff Vian <jvian10 at charter.net> wrote:

>If your system is acting as a gateway router for other systems on your
>local network there are different issues involving static routes.  For a
>workstation on 2 different networks, only one default gateway can be
>used.
>
This system is also my router.  eth0 (as per the annotations) has my 
public IP address and is my gateway to my ISP.  eth1 is the gateway for 
systems on my LAN.  That is, all of the systems on my LAN show a routing 
table that looks something like:

[dave at bend ~]# netstat -n -r
Kernel IP routing table
Destination     Gateway         Genmask         Flags   MSS Window  irtt 
Iface
169.254.0.0     0.0.0.0         255.255.0.0     U         0 0          0 
eth1
192.168.0.0     0.0.0.0         255.255.0.0     U         0 0          0 
eth1
0.0.0.0         192.168.255.254 0.0.0.0         UG        0 0          0 
eth1

I point people in this direction because their next question is usually, 
"How do I get the "other system" onto the internet?"  Also, only one 
default gateway ends up defined in the routing table.  The system does 
the right thing and uses the the default gateway specified for eth0 even 
though the gateway specified by eth1 comes "later:"

Kernel IP routing table
Destination     Gateway         Genmask         Flags   MSS Window  irtt 
Iface
72.19.169.0     0.0.0.0         255.255.255.0   U         0 0          0 
eth0
169.254.0.0     0.0.0.0         255.255.0.0     U         0 0          0 
eth1
192.168.0.0     0.0.0.0         255.255.0.0     U         0 0          0 
eth1
0.0.0.0         72.19.169.1     0.0.0.0         UG        0 0          0 
eth0

Cheers,
Dave

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