Related Documentation
- M, MX, PTX, T Series
- 4-Byte Autonomous System Numbers Overview
- Configuring 4-Byte AS Numbers and BGP Extended Community Attributes
- Configuring 4-Byte Autonomous System Numbers
- Establishing a Peer Relationship Between a 4-Byte Capable Router and a 2-Byte Capable Router Using a 2-Byte AS Number
- Juniper Networks Implementation of 4-Byte Autonomous System Numbers
- Prepending 4-Byte AS Numbers in an AS Path
- Understanding 4-Byte AS Numbers and Route Distinguishers
- Understanding 4-Byte AS Numbers and Route Loop Detection
- Understanding a 4-Byte Capable Router AS Path Through a 2-Byte Capable Domain
Establishing a Peer Relationship Between a 4-Byte Capable Router and a 2-Byte Capable Router Using a 4-Byte AS Number
This section describes what happens when a router that supports 4-byte AS numbers establishes a peer relationship with a router that only supports 2-byte AS numbers if the first router is configured with an AS number outside the 2-byte AS number range.
In Figure 1, Router 2 is running Junos OS Release 9.2 that supports 4-byte AS numbers. Router 2 is configured to use a 4-byte AS number, AS 1000000. Router 3 is running Junos OS Release 8.5 that supports 2-byte AS numbers. Router 3 is configured with a 2-byte AS number, AS 60000.
Figure 1: 4-Byte Capable Router Having a Peer Relationship With a 2-Byte Capable Router Using a 4-Byte AS Number
You can configure a local AS number to be used only during the establishment of the BGP session with a BGP neighbor, but to be hidden in the AS path sent to external BGP peers. To configure the local AS number, include the local-as statement, specify the 2-byte AS number to use, 65530, and include the private option. With this configuration, only the global AS number, 1000000, is included in the AS path sent to external peers. The following example shows the relevant portion of the Router 1 configuration:
user@Router1# show configuration…
autonomous-system 1000000;
…
local-address 192.168.1.9;
export static-to-bgp;
neighbor 192.168.1.3 {
peer-as 60000;
local-as 65530 private;
}
The peer AS number on Router 3 should equal the local AS number on Router 1. The following example shows the relevant portion of the Router 3 configuration:
user@Router3# show configuration…
autonomous-system 60000;
…
local-address 192.168.1.3;
neighbor 192.168.1.9 {
peer-as 65530;
To verify that the AS path of route 22.1.2.3 contains AS 65530, use the show route command on Router 3. The following example shows that the BGP peer session is established and that the AS path of route 22.1.2.3 contains AS 65530:
user@Router3# show route 22.1.2.3...
22.1.2.3/32 *[BGP/170] 01:39:55, localpref 100, from 192.168.1.9
AS path: 65530 I
> via so-1/0/3.0
Related Documentation
- M, MX, PTX, T Series
- 4-Byte Autonomous System Numbers Overview
- Configuring 4-Byte AS Numbers and BGP Extended Community Attributes
- Configuring 4-Byte Autonomous System Numbers
- Establishing a Peer Relationship Between a 4-Byte Capable Router and a 2-Byte Capable Router Using a 2-Byte AS Number
- Juniper Networks Implementation of 4-Byte Autonomous System Numbers
- Prepending 4-Byte AS Numbers in an AS Path
- Understanding 4-Byte AS Numbers and Route Distinguishers
- Understanding 4-Byte AS Numbers and Route Loop Detection
- Understanding a 4-Byte Capable Router AS Path Through a 2-Byte Capable Domain
Published: 2013-02-08
Related Documentation
- M, MX, PTX, T Series
- 4-Byte Autonomous System Numbers Overview
- Configuring 4-Byte AS Numbers and BGP Extended Community Attributes
- Configuring 4-Byte Autonomous System Numbers
- Establishing a Peer Relationship Between a 4-Byte Capable Router and a 2-Byte Capable Router Using a 2-Byte AS Number
- Juniper Networks Implementation of 4-Byte Autonomous System Numbers
- Prepending 4-Byte AS Numbers in an AS Path
- Understanding 4-Byte AS Numbers and Route Distinguishers
- Understanding 4-Byte AS Numbers and Route Loop Detection
- Understanding a 4-Byte Capable Router AS Path Through a 2-Byte Capable Domain
