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9.2 | ![]() |
Basic BGP Operation | |
9.2.6 | ![]() |
Path attributes |
Much of the work in configuring BGP focuses on path attributes. Each
route has its own set of defined attributes that can include path
information, route preference, next hop, and aggregation information.
Administrators use these values to enforce routing policy. Based on
attribute values, BGP can be configured to filter routing information,
prefer certain paths, or otherwise customize its behavior. Many of
these attributes and policy configurations are explored later in this
module, in the section "The BGP Routing Process".
Every update message has a variable length sequence of path attributes in the form <attribute type, attribute length, attribute value>. Because path attributes will be used extensively when configuring routing policy, note that not all vendor implementations of BGP recognize the same attributes. The following are the four different attribute types:
Each individual attribute is identified by its type and attribute
code. Figure
Several of these attributes are discussed later in this module. Attributes 11, 12, and 13 are not implemented by Cisco because they do not add functionality and will not be covered.
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