What is benefit of allocating ASN to edge routers and not Ip addresses ? I mean we could have given these edge routers unique public ip addresses too ?

  • 4
    I believe you are misinterpreting the article. All Internet devices have IP addresses -- that's how they communicate. AS Numbers are also used in the context of BGP protocol.
    – Ron Trunk
    Aug 21, 2019 at 11:52
  • 3
    AS numbers are used by BGP, a routing protocol. Routing protocols do not route packets, they exchange routing information; packets are still routed by IP address.
    – Ron Maupin
    Aug 21, 2019 at 13:07
  • Thnx @RonMaupin and Ron Trunk. Please some one among you combine both comments and write as answer so that I can accept it
    – Number945
    Aug 21, 2019 at 13:11
  • The answer provided by @Zac67 actually does that, and you should accept it.
    – Ron Maupin
    Aug 21, 2019 at 13:14

2 Answers 2


ASN numbers are assigned to corporate entities and don't ever change. IP routes are advertised under an ASN and can change at any time. Of course, devices participating in BGP require public IP addresses.


Edge routers do have IP addresses, in-fact they will nearly always have multiple IP addresses.

The design of internet routing is designed to maintain a separation between "Internal" and "external" routing and hence simplify the overall routing problem. The "Path" information in BGP only indicates the list of independent networks that the traffic passes through not the precise links it uses within those networks.

AS numbers are used to identify the independent networks in a path, both for troubleshooting purposes and to prevent the inadvertent formation of routing loops.

Decoupling internal and external routing is important because it reduces the "blast radius" of most network changes, both short and long term. In the short term it means that a path change within an ISP, say because of a link going down does not affect the routes that are propagated to other ISPs. In the long term, it means that an ISP can freely design their internal network without worrying that the perceived number of hops or the internal weights assigned to those routes within their network will affect routing preferences of devices in other networks.

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