BGP Administrative Distance and BGP Path Attributes
BGP Administrative Distance
As you know routing protocols have Administrative Distance values for preferability.And different vendors have different AD values for the same routing protocols.This is also valid for BGP.
Some main vendors and BGP AD(Preference) Values are below:
In Cisco routers two AD values used for BGP. For the routes learned outside the AS (eBGP routes) this value is 20, while the AD for iBGP and locally-originated routes is 200.
In Juniper and Alcatel-Lucent routers the Administrative Distance phrase changes to Preference value.
In Juniper routers Junos OS uses the same preference value for both EBGP and IBGP. This value is 170. However, difference between vendors has no operational impact because Junos OS always prefers EBGP routes over IBGP routes.
Preference value is also 170 in Alcatel-Lucent routers.
BGP Path Attributes
BGP uses path attributes to determine the best path to a destination. And the BGP path attributes lesson, is the most important and common lesson in BGP. With BGP path attributes, network administrator can manage the traffic flow and determine where the traffic will flow.
BGP path attributes divide into two main class. These classes are Well-Known and Optional path attributes. These two are also divide two again. These four classes are: