Extreme Networks ExtremeWare XOS 11.1, Руководство пользователя

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Exterior Gateway Routing Protocols
ExtremeWare XOS 11.1 Concepts Guide
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Overview
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 AS is a set of routers that are under a single technical administration. This set of routers uses a
different routing protocol, for example Open Shortest Path First (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 ASs) on behalf of all of the intra-routers.
BGP can be used as an exterior gateway protocol (referred to as EBGP), or it can be used within an AS
as an interior gateway protocol (referred to as IBGP).
BGP Attributes
The following BGP attributes are supported by the switch:
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Origin—Defines the origin of the route. Possible values are Interior Gateway Protocol (IGP), Exterior
Gateway Protocol (EGP), and incomplete.
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AS_Path—The list of ASs that are traversed for this route.
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Next_hop—The IP address of the next hop BGP router to reach the destination listed in the NLRI
field.
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Multi_Exit_Discriminator—Used to select a particular border router in another AS when multiple
border routers exist.
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Local_Preference—Used to advertise this router’s degree of preference to other routers within the
AS.
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Atomic_aggregate—Indicates that the sending border router has used a route aggregate prefix in the
route update.
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Aggregator—Identifies the BGP router AS number and IP address that performed route aggregation.
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Community—Identifies a group of destinations that share one or more common attributes.
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Cluster_ID—Specifies a 4-byte field used by a route reflector to recognize updates from other route
reflectors in the same cluster.
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Originator_ID—Specifies the router ID of the originator of the route in the local AS.
BGP Communities
A BGP community is a group of BGP destinations that require common handling. ExtremeWare XOS
supports the following well-known BGP community attributes:
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no-export
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no-advertise
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no-export-subconfed