Extreme Networks ExtremeWare 7.5, Command Reference Manual

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ExtremeWare 7.5 Command Reference Guide 1845
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BGP Commands— “i” Series Switches
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Border Gateway Protocol (BGP) is an exterior routing protocol that was developed for use in TCP/IP
networks. The primary function of BGP is to allow different autonomous systems (ASs) to exchange
network reachability information.
An autonomous system is a set of routers that are under a single technical administration. This set of
routers uses a different routing protocol (such as OSPF) for intra-AS routing. One or more routers in the
AS are configured to be border routers, exchanging information with other border routers (in different
autonomous systems) on behalf of all of the intra-AS routers.
BGP can be used as an exterior gateway protocol (E-BGP), or it can be used within an AS as an interior
gateway protocol (I-BGP).
BGP Attributes
The following well-known BGP attributes are supported by the switch:
• Origin – Defines the origin of the route. Possible values are IGP, EGP, and incomplete.
• AS_Path – The list of ASs that are traversed for this route.
• Next_hop – The IP address of the next hop BGP router to reach the destination listed in the NLRI
field.
• Multi_Exit_Discriminator – Used to select a particular border router in another AS when multiple
border routers exist.
• Local_Preference – Used to advertise this router’s degree of preference to other routers within the
AS.
• Atomic_aggregate – Indicates that the sending border router is used a route aggregate prefix in the
route update.
• Aggregator – Identifies the BGP router AS number and IP address that performed route aggregation.
• Community – Identifies a group of destinations that share one or more common attributes.
• Cluster_ID – Specifies a 4 byte field used by a route reflector to recognize updates from other route
reflectors in the same cluster.