Making a BGP route less attractive by repeating ASNs to lengthen its AS path, steering traffic towards a different site or path.
Also called autonomous system path.
Read more: Microsoft Learn
In the Ultra Transcenders books
Each book explains AS-path prepending in context, with comparison tables and the common traps.
Terms in this definition
- BGP
Dynamic routing protocol used with both ExpressRoute and VPN connections. On ExpressRoute private peering it is the only way to exchange routes, including a 0.0.0.0/0 default route for forced tunnelling.
- AS path
BGP attribute recording each ASN a route has passed through. Routes with shorter paths usually win, so adding extra ASNs makes one look less attractive.
- LSDOU
The sequence in which Group Policy is processed: the local policy first, followed by site, domain and organisational unit policies. The nearest, last-processed setting takes effect unless Enforced or Block Inheritance alters that.
- PATH
Parent-child hierarchies in DAX rely on this function. For each row it builds one delimited text value listing the IDs of the row's ancestors, top level first and ending with the row's own ID, which PATHITEM, PATHLENGTH and friends can then pick apart.