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I have an Airport Extreme Base Station (7.6.1) which has a public ip address on the WAN side. I have many hosts on the LAN side. I would like to configure the AEBS such that pings sent from the Internet are returned by a specific host (or not if the host is down). I have a static ip set up on the LAN side (192.168.15.2), but since icmp ping does not use a specific port (tcp or udp) I do not know how to configure port mappings. Can anyone please direct me?

Put another way, when I ping public ip, say 64.99.80.29, I want the AEBS to pass the ping through to a given host on my LAN. Is there a way to do this?

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There is no way to do that, what exactly are you trying to accomplish? – Gerry May 23 '12 at 0:09
Sounds like whatever it is will require an open router running Tomato or DD-WRT. – NReilingh May 23 '12 at 3:29
I have an machine at that location that I would like to ping from the internet to verify that the machine is up and connected to the internet. I'd run a script to alert me if it's not up. The machine is actually an ATM that I have little to no control of, but it does respond to pings on the LAN. – Scott May 23 '12 at 3:30

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You can make this host the default host in your AEBS settings, also known as the DMZ host.

Note however that everything that isn't mapped otherwise will be routed to that host, effectively making that host public from the internet. This might make this host more vulnerable for break-in attempts, be sure to lock all services down properly, and consider putting on a firewall.

Depending on your version of the Airport Utility client, you'll find the setting here:

AirPort Utility 6:

AirPort Utility 6 - Default Host

AirPort Utility 5.6:

AirPort Utility 5.6 - Default Host

Overall, I wouldn't recommend this approach because of the security risks on the one hand, on the other hand it doesn't look like a very reliable approach. If the host doesn't respond to pings there's no reason the host can't still be up, and if it does respond, are you sure it is the host responding, and not for example the router after a config reset?

I'd consider polling a dedicated service like httpd which you run on the host and you forward properly from the AEBS. You could run it on a non-standard port as well. With some scripting you could also return a whole lot more detailed information about the availability of the host and it's services.

Edit:

Since you mentioned the host in question is an ATM, I'd be even less inclined to make it the DMZ host. Consider polling it from another host on the local network and notifying you from there.

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I do not want to make the host the default host the default host. As for pinging from the local network, I could do that, but it does not guarantee that the host (atm) is available from the internet. – Scott May 23 '12 at 10:33
@Scott, there are no other alternatives as for pinging it on the local network from the internet. – Gerry May 23 '12 at 10:49

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