BGP Inbound Influence

[Sagar Purohit]

Hi

I am aware that we can influence inbound routes via 2 attributes that is:

AsPath and MED. 

Can you guys explain what would one choose and why.

Thanks,

Sagar

[nkarthikeyan]

Hi,

Yes, as you said you can use as-path prepend and MED to control the inbound traffic.... I prefered to use MED, since it doesn't makes any change in your BGP path and it is just the attribute value, whichever is lower MED value then it is prefered to recieve the certain routes......

When you use as-path prepend you will see the repeated as-number in BGP path, which might be confusing sometimes to do with the troubleshooting.... but as-path is something very simple....

http://ciscodreamer.blogspot.com/2009/10/bgp-med.html

http://ciscodreamer.blogspot.com/2009/07/bgp-as-path-prepending.html

You can go through the above blogs and see which once you feel comfortable to use in your network.

Regards

Karthik

[Sagar Purohit]

MED only works well when both the remote end routers are in same AS but still if the remote end routers ( consider ISP) has configured local prefer then MED is useless.

what if the both remote end router are in different AS configuring med won't make any difference.

Hence configuring As path would make influence the path appropriately.

Above is my understanding

I am basically looking for the detailed picture, what exactly should be done when configuring two edge routers with two different ISPs, how to influence inbound routes.

will configuring med beneficial here as we are not aware how ISP routers are configured to choose the best path

[nkarthikeyan]

Hi Sagar,

Yes.If the route is already influenced by ISP, then as you said it is not worth to use it....  But always you should be having a control with your ISP route settings.... you can get them to customize your internet /wan traffic on how you want....

Let me check and try to find the architectural diagram to explain it.... and update here

Regards

Karthik

[Sagar Purohit]

Thanks Karthik! An Architectural diagram would be very useful. Please update once you found it

Thanks,

Sagar