What information is contained in an Open message?

• A. Version, My Autonomous System, Hold Time, Router ID and Optional Parameters such as Session Authentication
• B. NLRI, Withdrawn Routes
• C. Version, MD5 Checksum, Path Attributes
• D. Next Hop, AS Path, MED

Answer: (A)

In BGP, the Open message is used to establish the session and negotiate the basic parameters for communication. The essential pieces it carries are the protocol version, the sender’s Autonomous System number, the hold time (the maximum allowed time between messages before the session is considered down), and the router ID that uniquely identifies the speaker. It also includes a block of Optional Parameters, which can carry extra negotiation data such as capabilities or authentication options. This combination lets the two peers agree on who they are, how long they’ll wait between messages, and what capabilities they’ll use before any routes are exchanged.

Route information itself does not go in the Open message. The actual route announcements and withdrawals, along with their path attributes like Next Hop, AS Path, and MED, travel in Update messages. The MD5 or other session authentication mechanism is tied to the TCP layer, not the Open message, though Optional Parameters can carry additional negotiation data in some contexts.