BGP CHAPTER 13 - Understanding BGP Attributes

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