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
- Establishing a Peer Relationship Between a 4-Byte Capable Router and a 2-Byte Capable Router Using a 4-Byte AS Number
- 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
Juniper Networks Implementation of 4-Byte Autonomous System Numbers
Junos OS Release 9.1 and later supports 4-byte AS numbers.
If your network is currently using 2-byte AS numbers, you are not required to get new 4-byte AS numbers. The 2-byte AS number range is a subset of the 4-byte AS number range. A Juniper networks router that supports 4-byte AS numbers simply prepends a string of zeros in front of the 2-byte AS number. For example, the 2-byte AS number 65000 becomes the 4-byte AS number 00000.65000.
If your Juniper Networks router supports 4-byte AS numbers and has a peer relationship with a router that does not support 4-byte AS numbers, the following sequence takes place in the adjacent RIB-in routing table after the router that supports 4-byte AS numbers advertises this capability to the new peer:
- The router that supports 4-byte AS numbers receives an advertisement from the peer that supports only 2-byte AS numbers.
- On the router that supports 4-byte AS numbers, the 2-byte AS path is converted into the 4-byte AS number by prepending a string of zeros in front of the 2-byte AS number.
- If a 4-byte AS number is also present in the path, it is merged with the 2-byte AS numbers in the path.
- If the AGGREGATOR and AS4_AGGREGATOR attributes are present, these attributes are also merged.
If your Juniper Networks router supports 4-byte AS numbers and has a peer relationship with a router that does not support 4-byte AS numbers, the following sequence takes place in the adjacent RIB-out routing table:
- Update message are reformatted before being sent to the router that does not support 4-byte AS numbers.
- The router that supports 4-byte AS numbers sends the 4-byte AS number in the AS4_PATH attribute.
- The AS_PATH attribute is also sent. It is encoded with the 2-byte AS numbers. Mappable 4-byte AS numbers, below 64537, are sent as 2-byte AS numbers. Non-mappable 4-byte AS numbers, above 64536, are represented by the well-known 2-byte AS number, AS 23456.
- A single peer group is used for the routers that support 4-byte AS numbers and the routers that support only 2-byte AS numbers.
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
- Establishing a Peer Relationship Between a 4-Byte Capable Router and a 2-Byte Capable Router Using a 4-Byte AS Number
- 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: 2012-11-14
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
- Establishing a Peer Relationship Between a 4-Byte Capable Router and a 2-Byte Capable Router Using a 4-Byte AS Number
- 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
