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Frequent Contributor

bgp bestpath as-path multipath-relax

Hello Guys

 

 

what the below hidden command does exactly ? how it works

 

bgp bestpath as-path multipath-relax

 

 

Thanks

 

 

9 REPLIES 9
Cisco Employee

Re: bgp bestpath as-path multipath-relax

Hi Ibrahim,

 

By default, IOS does not allow you to load balance between multiple paths received from different AS numbers. This commands changes this default behavior. I have seen some customers using it to load balance between two default routes (0/0) received from two upstream ISPs.

 

Regards,

Harold Ritter
Sr. Technical Leader
CCIE 4168 (R&S, SP)
harold@cisco.com
México móvil: +52 1 55 8312 4915
Cisco México
Paseo de la Reforma 222
Piso 19
Cuauhtémoc, Juárez
Ciudad de México, 06600
México
Frequent Contributor

Re: bgp bestpath as-path multipath-relax

Hello Harold

 

 

this is to load share out bound traffic no inbound , is that true

 

 

thanks

 

 

 

VIP Expert

Re: bgp bestpath as-path multipath-relax

Correct.
Beginner

Re: bgp bestpath as-path multipath-relax

If it is doing only to outbound traffic, Then what is the process to do for incoming traffic? 


@Joseph W. Doherty wrote:
Correct.

 

VIP Expert

Re: bgp bestpath as-path multipath-relax

That's often can become rather involved, i.e. discussions with your providers. Sometimes it might be as simple as how you advertise certain prefixes with AS prepends or, for complex, you might have community strings that trigger certain routing polices on your provider's equipment.
Beginner

Re: bgp bestpath as-path multipath-relax

Hi Harold Ritter,

Thank You for your reply, I am studying for CCIE R&S lab, i have created a big network in my own lab, where i faced this issue, Can you please suggest the solutions, I will be very thankful to your.

Please suggest the solution.

Regards
Siba
Beginner

Re: bgp bestpath as-path multipath-relax

Hi Harold Ritter,

If it is doing only to outbound traffic, Then what is the process to do for incoming traffic?

Regards
Siba
Beginner

Re: bgp bestpath as-path multipath-relax

Hi Ibrahim 

 

This is also applicable in case of DC fabric, ( leaf spine architecture ). 

In case one have different AS number at Spine and Leaf layer, even when you have multipath ; add path features enabled. Only one path is installed in routing table. As the router sees the AS - Path different on the 2 routes recieved ( Spine 1 & Spine 2 ) 

To enable BGP to install multiple path, all values must be equal. ( including AS path / length  ) so if we have 2 different AS path, it does not consider them equal 

 

This command allows BGP to deviate from standard rules, and install both prefixes even when they are received from different AS path 

 

Hope that helps 

VIP Advocate

Re: bgp bestpath as-path multipath-relax

Hi,

By default, there is no load balancing in IOS with BGP but this command will enable the Load balancing between two different routes.

 

https://ccieblog.co.uk/bgp/bgp-unequal-load-cost-sharing

Regards,
Deepak Kumar,
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