In my experience you need the following. I'm being really explicit here in case your additional poller is in a DMZ or across any kind of firewall. If it's just another poller in the core, you probably don't need to worry about some of these.
Addt'l Poller <--> Orion Platform: icmp
Addt'l Polller --> Primary Poller: TCP 80
Addt'l Polller --> Addt'l web server (if you have it): TCP 80
Addt'l Poller <--> Orion Platform: TCP 17777 (SW Information Service)
Addt'l Poller <--> Orion Platform: TCP 17778 (the other SW Information Service)
Addt'l Poller --> SQL Server: TCP 1433 (SQL Server Communication)
..OR whatever port you have your SQL server on.
I did NOT need to open this port:
Addt'l Poller --> Orion Platform: TCP 1801 (MSMQ) Not sure if this is needed or not?
Also note that if your DBA's (like mine) do NOT open ports by default, but instead used named instances, you will NEED to have a port set up if you are going through a firewall.
Finally, make sure that the communications between your additional poller and the targets is opened up. That means everything you will use to monitor has to be opened. it can be opened one way - meaning that the poller will always initiate the communication and the server will respond - presuming you don't actively PROHIBIT that return traffic in your firewall rules.
- icmp
- SNMP poll (UDP 161)
- RPC (TCP 139, 443, and a mess of others I can't think of right now)
- WMI (all ports over 1024)
Hope that helps.
- Leon