Preferred I over E & E over ?. It implies that the route was

injected into BGP as I (IGP), E (EGP) or ? (incomplete information).

Allows an AS to tell a

neighboring AS the best path to forward packets into the first AS. Lowest is

preferred.

Locally injected routes

(routes injected using network command) are better than iBGP/eBGP learned.

It is the number of ASNs in the AS Path. Lowest is preferred.

It is a numeric value set and communicated within a

single AS for the purpose of choosing best route for all routers in that AS to

reach a certain network. Highest is preferred

It is a numeric value set by a router when receiving updates to

influence the route for a prefix. It is not advertised to any BGP peers.

An Open message has been both sent to and received from the other

router. Next step is to receive a BGP Keepalive message (to confirm that all

neighbor-related parameters match) or a BGP Notification message (to learn that

there is some mismatch in neighbor parameters).

All neighbor parameters matched, the neighbor relationship has been

established and the peers can now exchange Update messages

BGP will try another TCP three-way handshake to establish a connection

with the remote BGP neighbor. If it is successful, it will move to the OpenSent

state.

The TCP connection exists, and a BGP Open message has been sent to the

peer, but the matching Open message has not yet been received from the other

router.

The BGP process is either administratively down or waiting for the the

next retry attempt.

The BGP process is waiting for the TCP connection to be completed. If it

is successful, it will continue to the OpenSent state. In case it fails, it

will continue to the Active state.

It is Used to report

BGP error. It results in a reset of neighbor relationship.

It is Sent periodically to maintain the neighbor relationship. If the

Keepalive message is not received within the negotiated Hold timer than BGP

neighborship will be turned down.

It exchanges Path Attributes and the associated prefix/length (NLRI)

that use those attributes.

It is Used to establish a neighbor relationship and exchange parameters,

including autonomous system number and authentication values.