Which BGP attribute is used first when determining the best path?

Origin is a well-known mandatory BGP attribute, but it is evaluated later in the best path selection process, after Weight, Local Preference, and AS Path length.

AS Path length is a well-known mandatory BGP attribute, used after Weight and Local Preference; a shorter AS path is generally preferred.

Local Preference is a well-known discretionary BGP attribute, evaluated after Weight but before AS Path length, influencing outbound traffic decisions within an AS.

The BGP best path selection algorithm on Cisco routers starts by evaluating the Weight attribute. Weight is a Cisco-proprietary attribute, local to the router, and is the highest-priority criterion in the BGP best path selection process, meaning a path with a higher weight is always preferred.