Which layer is BGP?

[lagapidis (Lazarus Agapidis)]

Hello Gareth

@rickyccnp is correct in that BGP uses TCP in order to operate and exchange information and thus it cannot be a Layer 3 protocol. However, BGP is actually considered an Application layer protocol. In the TCP/IP stack, any entity that functions above the Transport layer is considered an Application Layer protocol. BGP’s intelligence operates within a process in routing devices that sits on top of the Transport layer, and uses TCP to communicate its information between peers.

Take a look at this post for a bit more info:

BGP Communities Explained

Hello Mohamed Even though it is used to exchange routing and reachability information, which is a Layer 3 functionality, BGP itself does indeed operate at the Application layer. Because it uses TCP to actually exchange information, it is the Application layer entity of BGP that provides the data for the TCP segments. So BGP is indeed an Application layer protocol. Compare this with OPSF. It doesn’t use any functionalities above Layer 3, so OSPF is only a Layer 3 protocol. I hope this has b…

I hope this has been helpful!

Laz