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BPG Common Header
Originator ID and Cluster List Both the ORIGINATOR_ID (Type
Code 9) and CLUSTER_LIST (Type Code 10) optional non-transitive
attributes are used to support the route-reflector feature used to scale
iBGP meshes. These attributes are detailed in BGPv2 and are not covered
in this book. The ORIGINATOR_ID is four octets long, and a
CLUSTER_LIST attribute can vary in length in multiples of four octets.
The ORIGINATOR_ID attribute is used to identify the router that orig-
inated a particular route into an iBGP mesh. This way, if an iBGP router
learns of a route again, it will know the source of the original routing
information and not re-advertise this information to those peers that have
already been sent the routing information.
The CLUSTER_LIST attribute is used to detect updates that are looping
inside the cluster. This way, if a route has already been advertised to a
cluster, the advertisement message will be rejected.
Route reflectors and iBGP meshes will be covered in detail in Chapter 9.
Multiprotocol Reachable NLRI The MP_REACH_NLRI (Type
Code 14) attribute is used in the Multiprotocol Extensions for BGP. This
attribute identifies a newly reachable route in a particular address family
other than global IP version 4. This attribute is not covered in this book.
Multiprotocol Unreachable NLRI The MP_UNREACH_NLRI (Type
Code 15) attribute is carried in a BGP UPDATE message for which the
ORIGIN and AS_PATH attributes pertain to the native IPv4 BGP com-
munications that carry the message. The Type Code of 15 identifies a
route that has been withdrawn. This attribute is not covered in this book.
Type Code 11 (Destination Preference) is defined by MCI. Type Code 12
(Advertiser) and Type Code 13 (RCID_PATH) are both defined by Baynet. Type
Code 255 is reserved for development. These type codes will not be covered
in this book.
Copyright ©2001 SYBEX , Inc., Alameda, CA