communicate between route domains

Route domains are virtual routing instances. If you want to cross from one to the other, you're going to have to leave the F5 on an interface in the originating route domain, and re-enter the F5 on an interface in the destination route domain. This might be an external router, firewall, etc, but it won't be an iRule.

Route domains are virtual routing instances. If you want to cross from one to the other, you're going to have to leave the F5 on an interface in the originating route domain, and re-enter the F5 on an interface in the destination route domain. This might be an external router, firewall, etc, but it won't be an iRule.

Forwarding of traffic between route domains is by default enabled between route domains in a parent-child relationship only. (That is, traffic received in a child route domain can be forwarded to a parent route domain and the reverse.)

Consequently, by default, the BIG-IP system does not load balance traffic arriving in route domain 1 to servers in any other route domain, except for the parent route domain.

https://support.f5.com/kb/en-us/products/big-ip_ltm/manuals/product/tmos-ip-routing-administration-11-2-0/2.html

As ekaleido explained, you might need a next-hop for communicating between route domains if there is no parent-child relationship.

-Jinshu

The problem is solved. Triggered by your answers to route outside the F5, I just used:

server.company.nl {
    node ip-address port }

Thanks for your help.