Short for autonomous system number, which identifies a BGP routing domain. Azure VPN gateways use 65515 by default, a reserved value on-premises peers must avoid; Defender EASM also discovers ASNs as an internet asset type.
Also called autonomous system number.
Read more: Microsoft Learn
In the Ultra Transcenders books
Each book explains ASN 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.
- Geographic
A Traffic Manager routing method that picks the endpoint according to where the user is located geographically.
- Domain
A way of grouping workspaces by area of the business, in support of a data mesh approach. Items take on their workspace's domain, letting you filter the OneLake catalog by it, and certain tenant settings can be passed to domain admins; domains have no effect on access permissions.
- VPN
Traffic sent through an encrypted tunnel across a public network, as in a site-to-site connection to a VPN gateway in an Azure GatewaySubnet.
- Microsoft Defender External Attack Surface Management
Discovers the internet-facing assets an organisation owns, including domains, hosts, IPs, ASNs and certificates, and highlights their vulnerabilities. Defender for Cloud differs in assessing only the resources you connect to it.
Related terms
- Active-active VPN gateway
Configuration where tunnels run on both gateway instances, and each instance has a Standard static public IP of its own. Azure Route Server branch-to-branch transit needs this mode plus ASN 65515.
- 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.