Frequently Asked Questions

Q— Does BGP send periodic updates like RIP?

A— No. BGP exchanges routing information once, when the BGP session is being established. After that, only network changes are exchanged between BGP peers.

Q— Does the BGP session become "established" after all the routing updates have been exchanged between BGP neighbors?

A— No. It is the other way around. No routing exchange can take effect until both BGP neighbors agree on all parameters and the session becomes established.

Q— Is the Network Layer Reachability Information (NLRI) the actual BGP routing update?

A— No. The NLRI is one of the elements that is carried in a BGP UPDATE message. Other elements are the attributes and the unreachable networks.

Q— You talk about authentication as an example of the BGP optional parameters. How important is authentication?

A— Authentication is a means to validate the BGP peer. This is to prevent hackers from assuming the identity of one of your peers and feeding you wrong routing information. With authentication, both peers validate the connection via password mechanisms.

Q— Where does BGP carry information about AS numbers?

A— AS numbers are listed as part of the AS_PATH attribute carried in the UPDATE message.

Q— Is BGP connection symmetrical, or does it utilize a master/slave relationship?

A— The BGP protocol has no master and slave roles. At the transport layer, the connection is always initiated by one side and appears as a client (with the source TCP port number greater than 2048) that connects to a server (port 179), but it does not have any influence at the protocol level.

Q— The link to my provider has a firewall. What must be done in order for BGP to work?

A— The firewall must be configured to allow a TCP connection to port 179 in at least one direction (from the provider to you, or from you to the provider). Use caution, because some providers use passive BGP mode (their router does not attempt to establish the BGP connection).

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