BGP: Difference between revisions
→MED vs Local Preference vs Weight
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;Multi-Exit Discriminator
* The MED is an optional attribute that comes in handy when there are multiple entrance paths to an AS.
* The
* The MED is passed between the two autonomous systems, but the value is not passed to any other ASs.
* The path with the lowest MED is the preferred path.
* This attribute is only used to influence entry INTO the AS.
;Local Preference
*LOCAL_PREF is a well-known attribute that is also used when multiple paths between autonomous systems exist.▼
*The LOCAL_PREF attribute is just that… local and exclusive to the AS.▼
*Routers within the local AS are told what path to use to exit that AS.▼
*The local preference value is passed only among iBGP peers, and this value never leaves the local AS.▼
▲* LOCAL_PREF is a well-known attribute that is also used when multiple paths between autonomous systems exist.
▲* The LOCAL_PREF attribute is just that… local and exclusive to the AS.
*Weight is configured for Outgoing direction:▼
▲* Routers within the local AS are told what path to use to exit that AS.
[R1]-------[R2]▼
▲* The local preference value is passed only among iBGP peers, and this value never leaves the local AS.
|▼
|--------[R3]▼
If you want R1 to prefer R3, Configure more weight on R1▼
Configured on Per-Neighbor basis.▼
* Local Preference is configured in Incoming direction.
;Weight:
Cisco Proprietary▼
▲* Weight is configured for Outgoing direction:
▲ [R1]-------[R2]
▲ |
▲ |--------[R3]
;Example Scenario:
<--AS3--> <--AS100-->
|------[R2]--------[R4]
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|------[R3]--------[R5]
* Weight R1 to R2 or R3:
|------>
* Local Preference R2 to R1 or R3 to R1:
<------|
* MED R4 to R2 or R5 to R3:
|--------->
| |||