Asterisk routing/call forwarding

I’m a newbie to asterisk and I really need help to solve this issue.

I have 3 networks and 1 asterisk each:

Asterisk 1, Asterisk2 and Asterisk3. What I’m trying to do is to call from Asterisk 1 to Asterisk 3 , using Asterisk2 as Central to forward calls either from Asterisk1 to Asterisk 3 or vice versa.

Sip Extension: 1111 Iax Extension: 1122

Sip Extension: 2222 Iax Extension: 2233

Sip Extension: 3333 Iax Extension: 3344

I can already call from Asterisk1 to Asterisk 2 and vice versa, Asterisk2 to Asterisk3 and vice versa. But I don’t know how to forward call using Asterisk2 so that I can call from Asterisk1 to Asterisk 3.

BTW: I’m using web GUI for this configuration.

What if you use SIP Trunks between the routers and configure call routing rules acordingly?
I don’t know the details of your GUI, but I think this might be a good way to go about this setup.