Actually the router understand layer 4 parameters like port numbers, but we call it layer 3 because its routing decision based on ip (layer 3), like switches we call it layer 2 devices because the switching decision based on layer 2 information
BGP works at the Application Layer hence it has a well-known port number 179 to identify which application should handle these packets. BGP uses TCP windowing technique for packet exchange.
Yes, Router does work at Layer3. The primary function of a Switch is to forward frames which is Layer 2 function, hence we call the switch as Layer 2. The primary function of the router is routing packets to destinations which is Layer 3 function, hence we call it Layer 3.
Just like other applications such as TFTP(port69), Telnet(port23), etc work on the router, BGP also works on the router.
We are pleased to announce availability of Beta software for 16.6.3. 16.6.3 will be the second rebuild on the 16.6 release train targeted towards Catalyst 9500/9400/9300/3850/3650 switching platforms. We are looking for early feedback from custome...