BGP Weight Attribute


(Mani A) #1

The BGP Weight is a Cisco-proprietary Path attribute. The BGP RFC does not define it and other vendors have not defined it either! So I was wondering if there is any specific BGP scenario that path selection is only doable using Weight and no other attributes such as LOCAL_PREF or MED can be used!

I have a feeling that Weight attribute is redundant and the user can use other standard path attributes (MED, LOCAL_PREF, etc.) to manipulate the BGP path selection. Is that right?


(Lazaros Agapides) #2

Hello Mani

You are correct that the weight attribute is Cisco proprietary. It is true that you can indeed bring about the same results using just MED, LOCAL_PREF etc. So why introduce the weight attribute?

Well, the major difference between the Weight attribute and all others is that it is completely local to the router and its value is never transmitted to any neighbours, unlike MED, LOCAL_PREF, AS Path length, origin code and others. This means that you are able to adjust the path selection of the specific router with the addition of a single attribute that takes precedence above all others. This essentially provides a greater granularity of path selection with a very simple implementation.

Sure you could achieve the same thing use only the non-proprietary attributes, but the most important thing that the Weight attribute provides is a powerful and simple way to affect path selection.

I hope this has been helpful!

Laz