BGP path selection with as-path

[wfqk]

 Hi, Please see picture attached. both R1 and R2 are in one AS of ISP, and both R3 and R4 are in one AS of company. R1 sends out routes with shorter AS as primary path, and R2 sends routes with longer AS as backup. In the company side, routes need to send back. so the company have to send out routes through R4 as primary and R3 as backup, right? otherwise inbound and outbound route would be in different path or asysmetric, right? Thank you

[Reza Sharifi]

otherwise inbound and outbound route would be in different path or asysmetric, right?

Asymmetric routing works for some application and not so much for others.  That said, I like for traffic to take the same path both inbound and outbound. It makes it so much easier for troubleshooting.

HTH

[wfqk]

Thanks for your reply. I agree with you. Voice packet should go symetric path. so it is better for us to send routes out on R4 by AS number as primary path. therefore, we need to send route out on R4, and R4 is primary path and R3 as backup path in order to consistent with R1 as primary path on ISP side, Do you  think so? 

[Reza Sharifi · Accepted solution]

Hi,

Yes, correct.  I like for the path to be deterministic. If you have enough bandwidth for each circuit, active/standby works well. So, for your scenario, if you want r4 to be the active device for outbound traffic, you can setup hsrp between r4 and r3 and make r4 active and r3 standby.

HTH

[wfqk]

Thank you Reza, it is very good explanation.