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Q&A What is Border Gateway Protocol (BGP) keepalive and hold time expired messages, and what is the default value?

Question

What is a Border Gateway Protocol (BGP) keepalive and hold time expired message and what are default values used?

 

Environment

  • Silverline
    • DDoS
      • Routed

 

Answer

  • The BGP speaker calculates the value of the Hold Timer by using the smaller of its configured Hold Time and the Hold Time received in an OPEN message. 
  • The default value for the hold time suggested in the BGP specification (RFC 4271) is 90 seconds, and keepalives should be sent at intervals of one third the hold time (30 seconds). However, Cisco and other vendors default to 180 and 60 seconds. If the Hold Time is set for zero, no keepalive messages are sent between the BGP neighbors.
  • This calculated value indicates the maximum number of seconds that may elapse between the receipt of successive KEEPALIVE and/or UPDATE messages from the sender.
  • Border Gateway Protocol (BGP) does not rely on the TCP connection state to ensure that the neighboring adjacencies are still established.

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