BGP NEIGHBOR STATES
BGP varieties unicast-based connection to every of its BGP-speaking friends. BGP it makes use of TCP port 179 as its underlying supply mechanism. BGP establishes a neighbour adjacency with different BGP routers earlier than they change any routing data.
Not like different routing protocols, nevertheless, BGP doesn’t use broadcast or multicast to “uncover” different BGP neighbours.
Associated Article – BGP Native Choice
When BGP is configured with a neighbour IP tackle, it goes via a collection of phases earlier than it reaches the specified Established state. Per RFC 1771, BGP goes via the next phases of a neighbor relationship –
- IDLE State: verifying path to the neighbor
BGP refuses all incoming connections. No BGP sources are allotted in idle state, and no incoming BGP connections are allowed.
- Join State:
BGP waits for a TCP connection to be accomplished. If profitable, the BGP state machine strikes into the OpenSent state after sending the OPEN message to the peer. Failure on this state might end in both going into Energetic state or Join state, or reverting again to Idle state, relying on the failure causes.
Associated – BGP Interview Questions
- Energetic State: (Trying connectivity to neighbor)
On this state, a TCP connection is initiated to determine a BGP peer relationship. If profitable, BGP sends its OPEN message to the peer and strikes to OpenSent state. Failure may end up in going to the Energetic or Idle states.
- OpenSent State: (Open message despatched to neighbor)
After sending an OPEN message to the peer, BGP waits on this state for the OPEN reply.
If a profitable reply is available in, the BGP state strikes to OpenConfirm and a keepalive is shipped to the peer. Failure may end up in sending the BGP state again to Idle or Energetic.
- OpenConfirm State: (Neighbor replied with open message)
The BGP state machine is one step away from reaching its closing state (Established).BGP waits on this state for keepalives from the peer. If profitable, the state strikes to Established; in any other case, the state strikes again to Idle based mostly on the errors.
Associated – BGP Confederation
- Established State: (Connection between neighbors established)
That is the state during which BGP can change data between the friends. The data might be up to date, keepalives, or notification.
