BGP MED Use Case

[Ganesh Devarshetty]

Can i use MED in above case to influence inbound traffic.R1 & R2 are advertising same prefixes to three different ISPs.Outbound traffic is influence by local preference.

[MHM Cisco World]

This all your topolgy? 

If yes then there is one link between each AS so no need MED at all.

MHM

[Ganesh Devarshetty]

Remember, MED is relevant when comparing routes from the same AS. If you want to consider MED across different ASes, use the always-compare-med command.

[MHM Cisco World]

That true if AS-z and AS-B advertise same prefix 

Then R4 and R5 can push MED to R1 

And R1 can config to use MED to prefer path to AS-Z or AS-B

But the topology ypu share NOT mention that both AS z and b advertise or interconnect 

That why my answer is no need.

And it true you need 

Med always-compare 

Since the R1 recieve MED from two different AS

MHM

[M02@rt37]

Hello @Ganesh Devarshetty 

Assuming ISP provide R1 and R2 are connected to ISP providers, using AS path prepending can effectively influence inbound traffic in your network setup.

By artificially lengthening the AS path attribute in BGP advertisements, you can make certain routes less attractive to your ISPs, thereby directing traffic to preferred entry points. For instance, if you want R1 to handle more traffic, you would prepend additional AS numbers to the advertisements from R2, making its path seem longer and less favorable. This method can help balance the load between R1 and R2 without upgrading your links. 

The AS path is one of the BGP attributes, it's a well-known mandatory attribute which means that it's included with all prefixes that are advertised through BGP. When a BGP router advertises a prefix, it will include its own AS number to the left of the AS path attribute.

[Ganesh Devarshetty]

Remember, MED is relevant when comparing routes from the same AS. If you want to consider MED across different ASes, use the always-compare-med command. Pls confirm