Which layer of the OSI model does the BGP protocol run on?

Question

Options

• ASession layer
• BApplication layer
• CData link layer
• DNetwork layer

• A
  14% (7)
• B
  73% (37)
• C
  10% (5)
• D
  4% (2)

Explanation

BGP (Border Gateway Protocol) operates at the Application layer because it runs on top of TCP (port 179), and any protocol that uses TCP or UDP as its transport sits at Layer 7 in the OSI model. BGP's job is to exchange routing information between autonomous systems, which is an application-level function even though it influences how packets are routed. The Session layer (A) is a distractor because BGP does establish long-lived TCP sessions, but the Session layer refers to the OSI construct for managing sessions, not where BGP itself lives. The Data link layer (C) handles physical addressing between directly connected nodes (think MAC addresses and Ethernet frames), which has nothing to do with BGP's inter-domain routing role. The Network layer (D) is the most tempting wrong answer since BGP deals with routing, but Layer 3 is where IP packet forwarding happens -- BGP is the control-plane protocol that populates routing tables, not the layer that moves packets.

Memory tip: Ask yourself "does this protocol ride on top of TCP or UDP?" If yes, it belongs at the Application layer. BGP uses TCP port 179, so it is Application layer -- same logic applies to DNS (UDP 53), HTTP (TCP 80), and SMTP (TCP 25).

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