[Madlug] odd CentOS5 networking behavior

[Darrick Hartman]

Travis Sobeck wrote:
> or I just don't know nearly as much as I think I do.  When I try to ping 
> a server (and I've seen this on a couple with the same set-up) or ssh 
> (any protocol really) that has 2 Nics and 2 separate IP address on 2 
> separate subnets, all the packets go to only One Nic (also happens to be 
> the nic with the default route. eth0).  I checked this by running 
> tcpdump on both interfaces and no matter wich interface I ping all the 
> packets go to one interface.  Neither interface is in promisc mode.  
> Below is a simple sketch of the path to each interface.
> 
> pc --> routerA --> routerB --> SwitchA --> Server (eth0)
> 
> pc --> routerA --> routerB --> SwitchA --> loadbalancer/Router --> 
> SwitchB -->  Server (eth1)
> 
> It's not really causing any issues specifically, it just doesn't seem 
> like eth0 should be accepting packets for eth1 nor being delivered there 
> in the first place.
> Any thoughts?
> Thanks

Look at the man page for ping and look at the -I option.

 From the server, 'ping -I eth1 google.com' should pass traffic out 
through eth1 to google.

iftop is also a good tool to use to watch traffic on an interface.