[lug] two NIC's but only one for Internet access

Carl Wagner carl.wagner at verbalworld.com
Wed Sep 29 09:42:13 MDT 2010


Thomas,

Are you using DHCP for eth1?

You may be losing your routing.


Before bringing up eth1 do
netstat -rn

You should have something like:
Destination Gateway Genmask Flags MSS Window irtt Iface
0.0.0.0 192.168.0.1 0.0.0.0 UG 0 0 0 eth0
(with a few other lines, the gateway address may be different, but look 
for the one that has 0.0.0.0 for the destination)

Then bring up eth1, enter the above command again and see if your 
default router points to your local lan.
If this is the case you need to fix your DHCP server, use static IP for 
eth1, or possibly do static routing.

Can you ping an external IP when eth1 is up?
ping 72.246.164.112
(one of Redhat's web servers)

If this is the case you might be losing your DNS entry by being 
overwritten by the DHCP server.


Carl.




Thomas DiGennaro wrote:
>
> I have several computers running Ubuntu 9 or 10, and they each have 
> two network cards.
>
> One card is connected to my router (and cable modem) for access to the 
> Internet.
>
> One card is connected to another router, for use only as a LAN for 
> development embedded systems.
>
> How do I configure the network so that only one card (say “eth0”) is 
> used for Internet access?
>
> I find that when I connect “eth1” to its router, Internet access 
> disappears since I suspect that eth1 is being used, but it’s not 
> connected to the Internet of course.
>
> Thanks.
>
> Oz DiGennaro
> "No reason to be alarmed, though. The NSA claims that this is just 
> research."
>
>
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>
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