Extracting Vendor ATTR from Radius msg

We have some VENDOR attributes that we need to get from the RADIUS msg. We tried Radius:avp and it did not work.

 

 

If we use UDP:payload, how do we derive/calculate the offset to get to the VENDOR attribute section?

 

 

Since, we know the attribute name, is there someway to derive the offset from that?

 

 

Edit: We can find the value in the tcpdump of the Radius msg.

 

 

Thanks for any pointers.