Policy Framework Configuration Guide - Juniper Networks

CHAPTER 6
Extended Actions Configuration
This chapter provides information about the following routing policy actions configuration
tasks:
• Prepending AS Numbers to BGP AS Paths on page 135
• Adding AS Numbers to BGP AS Paths on page 136
• Using Routing Policies to Damp BGP Route Flapping on page 137
• Overview of Per-Packet Load Balancing on page 142
• Configuring Per-Packet Load Balancing on page 143
• Configuring Load Balancing Based on MPLS Labels on page 146
• Configuring Load Balancing for Ethernet Pseudowires on page 148
• Configuring Load Balancing Based on MAC Addresses on page 149
• Configuring VPLS Load Balancing Based on IP and MPLS Information on page 150
• Configuring VPLS Load Balancing on MX Series Ethernet Services Routers on page 151
• Example: Configuring Multicast Load Balancing over Aggregated Ethernet
Links on page 152
Prepending AS Numbers to BGP AS Paths
You can prepend one or more autonomous system (AS) numbers at the beginning of an
AS path. The AS numbers are added at the beginning of the path after the actual AS
number from which the route originates has been added to the path. Prepending an AS
path makes a shorter AS path look longer and therefore less preferable to BGP.
In Junos OS Release 9.1 and later, you can specify 4-byte AS numbers as defined in
RFC 4893, BGP Support for Four-octet AS Number Space, as well as the 2-byte AS numbers
that are supported in earlier releases of the Junos OS. In plain-number format, you can
configure a value in the range from 1 through 4,294,967,295. For more information about
configuring AS numbers, see the Junos OS Routing Protocols Configuration Guide.
If you have a router that does not support 4-byte AS numbers in the AS path, the
prependend AS number displayed in the AS path is the AS_TRANS number, AS 23456.
To display the route details, use the show route command. For more information, see
Prepending 4-Byte AS Numbers in an AS Path in the Using 4-Byte Autonomous System
Numbers in BGP Networks Technology Overview .
Copyright © 2010, Juniper Networks, Inc.
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