Connectivity Guide

Weight and local preference
The weight attribute is local to the router and does not advertise to neighboring routers. If the router learns about more than one route to
the same destination, the route with the highest weight is preferred. The route with the highest weight is installed in the IP routing table.
The local preference — LOCAL_PREF represents the degree of preference within the entire AS. The higher the number, the greater the
preference for the route.
LOCAL_PREF is one of the criteria that determines the best path — other criteria may impact selection, see Best path selection. Assume
that LOCAL_PREF is the only attribute applied and AS 100 has two possible paths to AS 200. Although the path through Router A is
shorter, the LOCAL_PREF settings have the preferred path going through Router B and AS 300. This advertises to all routers within AS
100, causing all BGP speakers to prefer the path through Router B.
Multiexit discriminators
If two autonomous systems connect in more than one place, use a multiexit discriminator (MED) to assign a preference to a preferred path.
MED is one of the criteria used to determine best path—other criteria may also impact selection.
One AS assigns the MED a value. Other AS uses that value to decide the preferred path. Assume that the MED is the only attribute applied
and there are two connections between AS 100 and AS 200. Each connection is a BGP session. AS 200 sets the MED for its Link 1 exit
point to 100 and the MED for its Link 2 exit point to 50. This sets up a path preference through Link 2. The MEDs advertise to AS 100
routers so they know which is the preferred path.
Layer 3
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