[Gllug] Routing and packetfiltering public IPs

[Dylan]

Hi All, 

I currently run a network comprising several desktop machines, a server 
and a gateway connected to the wild by ADSL. The fixed public IP is 
passed to the gateway's external interface by the ADSL router and the 
gateway does packet filtering, NAT, etc... The ADSL router will only 
connect to one machine when it is in bridging mode.

I'm looking to get an 8 IP block but I'm not at all clear as to how to 
configure the gateway for them. There are more machines on the internal 
network than available IP addresses (5 addresses, discounting the 
network address, broadcast and router, and eight machines.) I intend to 
assign the addresses to a DMZ mail and ftp server and the remaining 4 
to four of the desktop boxes.

So, any comments on the following options? I'm particularly interested 
to overcome NAT problems with applications like VoIP and IM etc. while 
creating the least complication for nfs and NIS.

A - All 5 boxes with public IPs connected to the router, with the 
gateway routing from the private IP network and NATing etc. This would 
mean configuring and maintaining the firewalls on each machine.

B - Having the gateway masquerade internal addresses such that 5 are 
associated with specific internal IPs and the other machines are NATed 
as usual.

C - Having the gateway filter all traffic, but pass on the public IPs to 
their destinations while NATing other machines. Maybe using IP aliases 
on the boxes with public IPs to place them on the private network.

Are there any other options? I've read through a pile of docs but at the 
moment it all seems a mush of info.

Cheers

Dylan
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