ACLs and HSRP, BGP, OSPF, VRRP, GLBP...
Here’s a handy list of ACL entries to allow your devices to speak routing protocols, availability protocols, and some other stuff. We’ll assume you have ACL 101 applied to your Ethernet inbound; your Ethernet has an IP of 192.168.0.1.
* BGP : Runs on TCP/179 between