Mac – How does a router find the MAC address of next hop router

arpmac addressnetworking

I know that in an Ethernet LAN, the ARP protocol is used to get a MAC address from an IP address. How does my router get the MAC address of another router on an external network if ARP is not possible?

Best Answer

Why are you assuming ARP is not possible? ARP is the way its done. There is nothing special about your "internal network" vs an "external network", the same protocols are used on both.

Your router has a set of routes setup to route traffic to your internal network, but it also has a Default Gateway which points to a router in your ISP's network. Your router will use ARP to lookup the MAC address of that default gateway. Then that router will do the same to find its "next hop".