[CentOS] Dual personality Server (network pass through)

Mon Jun 14 23:13:07 UTC 2010
Alan Hodgson <ahodgson at simkin.ca>

On Monday, June 14, 2010, Robert Arkiletian <robark at gmail.com> wrote:
> I have 3 nics in a NATed gateway file server. Two nics (eth1, eth2)
> Is it possible to disable the NATing, nfs, dhcp and just somehow
> bridge the external WAN nic to the internal ones such that it's just a
> pass through? Basically having the server behave like a switch?
> Allowing the internal systems to join the network on the WAN. I know
> how to disable NAT, nfs and dhcp but not how to configure the nics.
> 

You do this by creating a bridge.

The Red Hat/CentOS way is to create emptyish interface files like:

# cat /etc/sysconfig/network-scripts/ifcfg-eth0
DEVICE=eth0
BOOTPROTO=none
BRIDGE=br0
ONBOOT=YES

# cat /etc/sysconfig/network-scripts/ifcfg-eth1
DEVICE=eth1
BOOTPROTO=none
BRIDGE=br0
ONBOOT=YES

And then a bridge interface file:

# cat /etc/sysconfig/network-scripts/ifcfg-br0 
DEVICE=br0
TYPE=Bridge
ONBOOT=yes
STP=on
IPADDR=system.ip.address.here
NETMASK=your.dotted.quad.mask

Obviously, adjust as needed to match your actual hardware, etc.

This can of course also be scripted using the actual networking commands, 
that I don't recall offhand.

-- 
"No animals were harmed in the recording of this episode. We tried but that 
damn monkey was just too fast."