The RIS and 4-byte Autonomous System Numbers

This information applies from 27 March 2007.

All RIS tools will accept and print 4-byte (32-bit) Autonomous System Numbers (ASNs), complying with the guidelines set out in the Internet Draft 'Canonical Textual Representation of 4-byte AS Numbers'.

As 4-byte ASNs may occur anywhere in the RIS (not only when you query for a 4-byte ASN) you will need to adjust any tools that read RIS data so that they can parse the new format.

Printing and Inputting ASNs

• Printing of an ASN up to and including 65535 is unchanged
• An ASN above 65535 will be printed as x.y, with x being the upper 16 bits and y being the lower 16 bits
• Input of an ASN up to and including 65535 may be done as either x or 0.x
• Input of an ASN above 65535 must be done as x.y (as noted above)

MyASN Alarms

Existing MyASN alarms will continue to work as before. However, when the first 4-byte ASN peering is set up, alarm notifications may contain a 4-byte ASN in the offending AS path.

If you have any tools that parse MyASN notifications, they will need to be able to parse the x.y format in AS paths.

Raw Data

The RIS raw data is written in the MRT format.

A new IETF draft has been published describing several changes to the MRT format, including changes for 4-byte ASNs.

The new draft describes three new MRT types:

• TABLE_DUMP_V2 to be used by RIS for all RIB dumps,
• BGP4MP_STATE_CHANGE_AS4, and
• BGP4MP_MESSAGE_AS4, which are used for updates.

Please note that a description of BGP4MP_STATE_CHANGE_AS4 is missing from the IETF draft. It is the same as BGP4MP_STATE_CHANGE except that the ASN field accommodates 4-byte ASNs.

A new version of libbgpdump has been published to support these new formats. The download includes the source code as well as several examples showing how to use the API.

We have also published example dumps of an RIB and a set of updates, which allow you to test your software.