BGP Cheatsheet
BGP Attributes
| Name | Description |
|---|---|
| 1. Origin | Must be supported and propagated |
| 2. AS Path | List of autonomous systems which the advertisement has traversed |
| 3. Next Hop | External peer in neighboring AS |
| 5. Local Preference | Metric for internal neighbors to reach external destinations (default 100) |
| 6. Atomic Aggregate | Includes ASes dropped due to aggregation |
| 7. Aggregator | ID and AS of summarizing router |
| 8. Community | Route tag |
| 9. MED | Metric for external neighbors to reach the local AS |
| 10. Originator ID | The originator of a reflected route |
| 11. Cluster ID | List of cluster IDs |
| 12. Weight | Cisco proprietary, not communicated to peers (default 0) |
BGP Path Selection
| Attribute | Description | Preference |
|---|---|---|
| 1. Weight | Administrative preference | Highest |
| 2. Local Preference | Communicated between peers within an AS | Highest |
| 3. Self-originated | Prefer locally originated paths | True |
| 4. AS Path | Minimize AS hops | Shortest |
| 5. Origin | Prefer IGP-learned routes over EGP | IGP |
Neighbor States
- Idle: Neighbor is not responding
- Active: Attempting to connect
- Established: Adjacency established
Troubleshooting
- show ip bgp: Displays BGP summary
- show ip route: Displays routing table
- clear ip bgp: Clears BGP sessions
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