User guide

13-2 E
XTREME
W
ARE
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OFTWARE
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SER
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UIDE
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XTERIOR
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ATEWAY
R
OUTING
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ROTOCOLS
O
VERVIEW
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 A
TTRIBUTES
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.