topic Re: DMZ public IP? in Network Security

DMZ public IP?

ryancolson — Mon, 11 Mar 2019 15:36:46 GMT

I have seen postings, and heard of cases where people actually assign public IPs to servers sitting in a DMZ behind a firewall. My question is, if you only have one IP block(say a /29), how can you do this? I understand if you either 1-1 NAT or PAT from outside to DMZ, but how can you have an actual public IP on a server behind the DMZ on the ASA, on the same subnet as the outside interface?

Re: DMZ public IP?

Jon Marshall — Tue, 26 May 2009 19:27:04 GMT

Charles

"how can you have an actual public IP on a server behind the DMZ on the ASA, on the same subnet as the outside interface?"

You can't unless you run the firewall in transparent mode. When people use public IP's in the DMZ they generally have a separate subnet for the DMZ.

Note you could split your /29 into 2 /30's but you would only 2 addresses then in each subnet.

Jon

Re: DMZ public IP?

ryancolson — Tue, 26 May 2009 19:34:28 GMT

so when people put the actual public IP on a server in the DMZ, the DMZ is generlaly outside the firewall?

Re: DMZ public IP?

Jon Marshall — Tue, 26 May 2009 19:37:54 GMT

Not necessarily. They might well have a different subnet for the DMZ ie.

195.17.17.0 255.255.255.252 could be used for the outside.

Your ISP then allocates you another range -

195.18.18.0 255.255.255.248

so you could then use this subnet for your DMZ.

But if your ISP only allocates you

195.18.18.0 255.255.255.248

you can't have 195.18.18.x address on both the outside interface and on the DMZ.

Jon

Re: DMZ public IP?

ryancolson — Tue, 26 May 2009 19:41:32 GMT

thats pretty much what i thought. thanks a bunch!

Re: DMZ public IP?

darkbeatzz — Wed, 27 May 2009 08:46:15 GMT

You can have servers in your network with a public IP from your range but they would be patched directly to your outside switch