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Old 6th November 2008
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anomie anomie is offline
Join Date: Apr 2008
Location: Texas
Posts: 445
Default Two NICs on same subnet

I have a Red Hat Enterprise Linux 4.7 server with two ethernet NICs on the same subnet. (Note that Linux names ethernet cards eth0, eth1,... ethn.)

# ifconfig | egrep 'eth|inet'
eth0      Link encap:Ethernet  HWaddr 00:22:19:04:EA:7A  
          inet addr:  Bcast:  Mask:
eth3      Link encap:Ethernet  HWaddr 00:15:17:8C:7C:D1  
          inet addr:  Bcast:  Mask:
eth0 ( has sshd listening on tcp port 22. eth3 ( has httpd listening on tcp port 443.

# netstat -ltn
Active Internet connections (only servers)
Proto Recv-Q Send-Q Local Address               Foreign Address             State      
tcp        0      0   *                   LISTEN          
tcp        0      0  *                   LISTEN
I'm noticing some odd behavior: my host-level firewall logging shows that sometimes traffic to is coming in on eth3, but other times traffic to is coming in on eth0.

Here is my routing table:

# netstat -rn
Kernel IP routing table
Destination     Gateway         Genmask         Flags   MSS Window  irtt Iface U         0 0          0 eth0 U         0 0          0 eth3     U         0 0          0 eth3         UG        0 0          0 eth0
I suspect the behavior I'm seeing could be solved by a routing table entry, but I am not confident that I know exactly what that entry should be. I'm willing to experiment a bit (while physically on site, in case I break the networking), but could someone speak to whether this makes sense and/or whether I appear to be barking up the right tree?
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