Here is the scenario,
ISP has 2 uplinks toward the upstream provider, The first link represent the Internet Gateway link (Main Internet GW), the Second link represent the National link for (National exchange).
The ISP has its own registered public AS number from RIPE. The upstream National provider has a private AS as its peering address with the ISP and its being removed when announcing thier Network to the National peers. The Upstream National provider also has its own Internet link (This link is being used for thier own usage not used to connect the ISP to the outside world). The ISP uses the second upstream Internet GW to announce it network and connect to the Internet.
The Upstream National provider has announces the ISP Network to the Internet by mistake (The link that is used for thier own purpose), The public AS of the ISP has been removed when thier Network announced to the Internet.
Now, The Outside world have 2 possible paths to reach the ISP Network, however, One of the paths is annoncing the Network without its registered Public AS.
The Second link (Main Internet GW link) is announcing the ISP Network with its associated Public registered AS number.
What happened is that the ISP Network has been down for a while, why?? The Internet has prefered the National link path to reach ISP Network because its the shortest AS path, although thier AS is not announced.
MY question: Since a border Router (BGP router) uses AS attributes to reach particulat destination , How is it going to ssure that a particular Network belong to a particular registere AS number? why the Second link is not considered although its announcing thier Public AS?