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Notes:


Note that to distinguish between the parts of the AS_Path learned from external peers and the parts belonging to the current confederations, there are several types of path segments inside the AS_Path attribute.

Without confederations, two types of path segments can appear :
Value Segment Type

1 AS_SET: unordered set of ASs a route in the UPDATE message has traversed

2 AS_SEQUENCE: ordered set of ASs a route in the UPDATE message has traversed

Inside confederations, two additional path segment types are used :

3 AS_CONFED_SEQUENCE: ordered set of Member AS Numbers in the local confederation that the UPDATE message has traversed

4 AS_CONFED_SET: unordered set of Member AS Numbers in the local confederation that the UPDATE message has traversed

See
P. Traina, D. McPherson, J. Scudder, "Autonomous System Confederations for BGP", RFC 3065, February 2001.
for a detailed discussion of the processing of the two new path segments.