22/09/2017
BGP AS Path
- Multiple path attributes to determine the best path for a certain prefix.
- When no path attributes are set, BGP uses the AS_PATH to determine the best route.
- Shortest AS path wins
- AS_SEQ is the component of the AS_PATH attribute.
- 10.10.10.0/24 20 10
- AS-SEQ (in order)
- 10.10.10.0/24 20 10
- With summarization:
- 10.10.0.0/16 20 10 { 1 2 5 4 3 }
- Prefix AS-PATH AS-SEQ { AS-SET }
- AS-SET are not in order
- Prevents Routing loops.
- If a BGP router received an update with it’s own AS#, it indicates a loop.
- If a BGP router received an update with it’s own AS#, it drops the route.
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