[rc445]

What do you mean "How can I find the port that packets pass through it?" . A firewall/router doesn't "accept" packets on a specific port. It routes (or doesn't route) all traffic based on rules.

The device will accept admin connections. Sometimes this is through a web UI or SSH. Sometimes, these devices wont accept admin connection through the LAN ports but will have a specific Management Port.
Most big organizations will segregate all their management traffic in a specific VLAN.