Avaya Configuring IP Services Instrukcja Użytkownika Strona 207

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Configuring BGP Services
5-3
BGP features include
TCP support
The neighbors communicate over a reliable transport layer connection —TCP
— so that BGP can assume that its communication with other BGP routers is
reliable. This eliminates the need to implement the update, retransmission,
acknowledgment, and sequencing that are necessary with EGP.
Multiple path elimination
A BGP speaker can announce only routes that it actually uses. Therefore, a
border router that learns multiple paths to an external destination must choose
only one of those routes for further advertisement into the AS or to other BGP
peers.
Authentication
BGP provides support for multiple authentication schemes. A scheme is
identified in the Open message, and each subsequent message on that TCP
connection must contain a marker field that complies with the scheme.
However, only the default authentication scheme (none) has been developed
at this time.
AS Path attribute
Each BGP route contains a list of the autonomous systems that it has
traversed. This allows a BGP speaker to eliminate looped routes. If a BGP
speaker sees its own AS listed in a route, then there is a loop, and the route is
not used.
Routing policy support
Each routing update contains information on which hop-by-hop policies can
be applied. For example, policies can be defined based on the information
contained in a route’s AS path attribute. BGP can favor routes based on AS
count, or the presence of a certain AS in the path. Conversely, it can also avoid
routes that contain a certain AS in the path or that originate in a certain AS.
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