Which ports to open when doing SQL Replication from a 2008R2 Cluster to a standalone SQL Server outside of your network

I have a SQL Server 2005 cluster with two nodes (active/passive). Here's the configuration :

Cluster name : MYCLUSTER .
Cluster IP : 123.123.0.10
Node 1 (active node) hostname : NODE1
Node 1 IP : 123.123.0.11
Node 2 (passive node) hostname : NODE2
Node 2 IP : 123.123.0.12
Instance Name: MYCLUSTER/MYINSTANCE
Instance IP: 123.123.0.13

I need to have my Network Folks open the Firewall to allow SQL Replication Traffic to a SQL Server outside of our Network.    We opened the Firewall using the IP of the SQL Instance (123.123.0.13) (TCP and port 1433)  but that did not do the trick.   Can someone tell me what IPs have to be opened at the Firewall to allow the Replication Traffic?