BGP attributes

Each route in a BGP network has a set of attributes associated with it. These attributes define the route, and are modified as required along the route.

BGP can work well with mostly default settings, but if you are going to change settings you need to understand the roles of each attribute and how they affect those settings.


AS_PATH	A list of ASes a route has passed through. See “AS_PATH”.
MULTI_EXIT_DESC (MED)	Which router to use to exit an AS with more than one external connection. See “MULTI_EXIT_DESC (MED)”.
COMMUNITY	Used to apply attributes to a group of routes. See “COMMUNITY”.
NEXT_HOP	Where the IP packets should be forwarded to, like a gateway in static routing. See “NEXT_HOP”.
ATOMIC_AGGREGATE	Used when routes have been summarized to tell downstream routers not to de-aggregate the route. See “ATOMIC_AGGREGATE”.
ORIGIN	Used to determine if the route is from the local AS or not. See“ORIGIN”.
LOCAL_PREF	Used only within an AS to select the best route to a location (like MED)


	Inbound policies on FortiGate units can change the NEXT-HOP,LOCAL-PREF, MED and AS-PATH attributes of an internal BGP (iBGP) route for its local route selection purposes. However, outbound policies on the unit cannot affect these attributes.