It reminds me how inter AS connection should be trusted one another. They just advertises same prefix with more specific subnets. According to the BGP role, longest matched subnet would be preferred.
On Sunday, 24 February 2008, Pakistan Telecom (AS17557) started an unauthorised announcement of the prefix 208.65.153.0/24. One of Pakistan Telecom’s upstream providers, PCCW Global (AS3491) forwarded this announcement to the rest of the Internet, which resulted in the hijacking of YouTube traffic on a global scale.
In this report we show how the events were seen by RIPE NCC’s Routing Information Service (RIS) and how, in general, one can use the RIS tools to obtain hard data on network events.
Event Timeline
- Before, during and after Sunday, 24 February 2008: AS36561 (YouTube) announces 208.65.152.0/22. Note that AS36561 also announces other prefixes, but they are not involved in the event.
- Sunday, 24 February 2008, 18:47 (UTC): AS17557 (Pakistan Telecom) starts announcing 208.65.153.0/24. AS3491 (PCCW Global) propagates the announcement. Routers around the world receive the announcement, and YouTube traffic is redirected to Pakistan.
- Sunday, 24 February 2008, 20:07 (UTC): AS36561 (YouTube) starts announcing 208.65.153.0/24. With two identical prefixes in the routing system, BGP policy rules, such as preferring the shortest AS path, determine which route is chosen. This means that AS17557 (Pakistan Telecom) continues to attract some of YouTube’s traffic.
- Sunday, 24 February 2008, 20:18 (UTC): AS36561 (YouTube) starts announcing 208.65.153.128/25 and 208.65.153.0/25. Because of the longest prefix match rule, every router that receives these announcements will send the traffic to YouTube.
- Sunday, 24 February 2008, 20:51 (UTC): All prefix announcements, including the hijacked /24 which was originated by AS17557 (Pakistan Telecom) via AS3491 (PCCW Global), are seen prepended by another 17557. The longer AS path means that more routers prefer the announcement originated by YouTube.
- Sunday, 24 February 2008, 21:01 (UTC): AS3491 (PCCW Global) withdraws all prefixes originated by AS17557 (Pakistan Telecom), thus stopping the hijack of 208.65.153.0/24. Note that AS17557 was not completely disconnected by AS3491. Prefixes originated by other Pakistani ASs were still announced by AS17557 through AS3491.
See the complete analysis here
