BGP Basics: BGP Packet types

BGP Packet Types 
Border gateway Protocol

Today we are going to talk about BGP packet types. Most of you already knew but we still going to discuss for the students who are just started studying BGP in details.

BGP: Border Gateway Protocol
BGP is external gateway protocol to exchange the routes between the two organizations having different AS(autonomous systems) numbers. The connection is setup up with the setting up the peers between the two organizations.

Fig 1.1- BGP Sample Topology

BGP Packet Types
Below are the four types of BGP packet types

  • Open
  • Keepalive
  • Update
  • Notification

Packet Type 1: Open
Open packet type is used to establish BGP adjacencies and is also used to negotiation of session capabilities. The hold time is 180 seconds.

Packet type open contains
Contains Router-ID, BGP Version, ASN of originating router, hold time, BGP identifier and other optional capabilities

Packet Type 2: Keepalive
Keepalive as you know used to check that BGP neighbors are still active. Keepalive is send to peer after every 60 Seconds.

Packet Type 3: Update
Update packet type actually tells that new and updated advertises feasible routes and it replaces previously advertised routes.

Packet type Update contains
Packet Type Update includes Network Layer Reachability Information (NLRI), such as prefix and path attributes. (Used to reset hold timers on BGP neighbors).

Packet Type 4: Notification
Notification is sent to the BGP network whenever an error is detected like Hold timer expired, neighbor capabilities changing or a BGP session reset is requested.