dual nics and routes

[Gerald Combs]

On Wed, 10 Apr 2002, Lucas Peet wrote:

> Ok, I have one machine, with one nic connected to my cable  
> modem.  I brought an older machine back to life, and threw a  
> 2nd nic into my main machine to connect to the old one.   
> Main's eth1 IP is 10.0.0.1, Older's IP is 10.0.0.2.  Older  
> machine is running Win2K, Main running Linux.  Neither can  
> ping each other, and I think it's has something to do with  
> the routes.  
>   
> Here's my route table for Main:  
>  
> [root at riodo lib]# /sbin/route 
> Kernel IP routing table 
> Destination     Gateway         Genmask         Flags Metric 
> Ref    Use Iface 
> 172.16.118.0    *               255.255.255.0   U     0      
> 0        0 vmnet1 
> 10.0.0.0        *               255.255.255.0   U     0      
> 0        0 eth1 
> 172.16.234.0    *               255.255.255.0   U     0      
> 0        0 vmnet8 
> 65.30.112.0     *               255.255.240.0   U     0      
> 0        0 eth0 
> 127.0.0.0       *               255.0.0.0       U     0      
> 0        0 lo 
> default         mkc-65-30-112-1 0.0.0.0         UG    0      
> 0        0 eth0 
> [root at riodo lib]# 

Assuming that "eth1" is your inside interface, and "eth0" is your outside
interface, the routing table looks good.  To troubleshoot this, I'd do
the following:

  - Check your cabling.  If you're using a direct connection, make sure
    you're using a crossover cable.  If you're on a hub, make sure you're
    using straight-through cables, and that you're not using the hub's
    "uplink" port.  Either way make sure you have link lights on each
    port in the path. 

  - Run "ifconfig -a" on the Linux box.  Check to make sure eth0 is in an
    "UP" state, and that your netmask and broadcast address look good.

  - On the Windows box run "ipconfig/all" and do the same.

  - On the linux box scan the output of "dmesg" to make sure the
    interfaces came up correctly.

  - On each box run "arp -a".  If the other side doesn't show up in the
    arp table, you most likely have a connectivity problem.

  - Check the routing table on the Windows box.  Either "route print"
    or "netstat -nr" should work.

>  
>  
> Any ideas? 
>  
> -Lucas 
> 
> 
>