Hostgroup or service group?



I am currently monitoring 2 servers behind a netscreen firewall. The ip of the netscreen is on the outside. Since I have to do port redirection, the 2 servers and the netscreen as using the same “host”.

In other words, in the hostgroup, I have the services listed like so:

(in service detail)

Netscreen Netscreen Mem
Netscreen Sessions
Server 1 CPU
Server 1 HD
Server 1 Processor
Server 2 CPU
Server 2 HD
Server 2 Processor

the 2 servers I am watchin on the dmz and trusted side of the netscreen are and

I want to split them up in nagios via some sort of host group or service group. Which is best?

Any Advice?