In all our previous post we have seen Concept and Configuration of BGP neighborship , Advertisement of networks in BGP , BGP Synchronization rule , Auto Summary etc.
From this post onwards we will start focusing on BGP Attributes and understand what exactly role does BGP Attributes play in BGP .
As we are aware that each routing protocol uses some metric for path selection
e.g. RIP uses Hop count , EIGPR uses a composite metric which includes Bandwidth and Delay (by default) , OSPF uses Cost i.e Bandwith to calculate the best route.
Similarly BGP also uses something known as "Attributes" to the find the best route to reach a destination.
It is very important to have good understanding of BGP Attributes before understanding BGP Path Selection Process.
There are 4 categories of BGP Attributes :-
1) Well Known Mandatory -
- Supported (Known/Understand) by all BGP Routers
- Must be present in BGP Update Message.
- AS Path, Origin ,Next Hop.
2) Well Known Discretionary -
- Supported (Known/Understand) by all BGP Routers.
- May or May not be present in BGP Update Message.
- Local Preference
3) Optional Transitive -
- May or May not be supported a BGP Routers.
- Passed on the other BGP Routers.
- Aggregator , Community.
4) Optional Non-Transitive-
- May or May not be supported by a BGP Routers.
- If not supported may ignore the update and may not pass on to the other BGP Routers.
- MED ,Router Cluster list , Router Originator List.
Hope you all like this post !!!
Thanks for Reading
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