[wplug] Dual Ethernet Ports - One routing table

[Weber, Lawrence A]

I have the need to interface a Linux system to two separate subnets.  I
have run into a problem when one of the ports goes down due to either
being disconnected for a minute or due to no network traffic for
approximately 3 minutes.  When the port goes down it routes the
down-port's output to localhost.  When a valid message is then received
from a gateway, the system looks into the routing table and gets
confused because it finds two default gateways (one for each subnet).
The confusion occurs even though the default gateways are assigned to
individual interfaces (eth0 - eth1).  If it picks the wrong default
gateway, it cannot reach the gateway, so it assumes that the network is
still down and sends the response to itself.  There must be a timer
involved here too because after 4 to 5 minutes the interface
re-establishes itself and works fine.  As long as there is regular
traffic through the gateway the interface never goes down.
 
I have heard that there can be multiple routing tables, one for each
port and that a priority routing database is used to assign tables to
ports.  Has anyone had to implement multiple routing tables?  Does the
database need to know the subnet address for every message received
through its gateway?    
 
I really want to keep the configuration of this system as simple as
possible, as people who know less about networking than I do (if that is
possible) will have to set up the port parameters.  Ports will have
fixed address, no DHCP.
 
 
L. A. Weber
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