When studying for your BSCI communicating for the CCNP, you intend your prototypal discernment of BGP. One of the field differences between BGP and the added protocols you've unnatural to fellow is that BGP uses attributes to exposit paths, and to impact the activity of digit line over the other.
In this liberated tutorial, we're feat to verify a countenance at the Local Preference concept and study it to the Cisco-proprietary BGP concept weight.
The Local Preference (LOCALPREF) concept is utilised to impact how reciprocation module line from digit Autonomous System (AS) to added when binary paths exist. For example, if AS 100 has digit assorted paths to a instruction meshwork in AS 200, the LOCALPREF concept crapper be utilised to impact the line selection.
The field disagreement between the Weight and LOCALPREF attributes is that when the LOCALPREF concept is changed, that modify is echolike throughout the AS. The newborn LOCALPREF continuance module be advertised to every added routers in the AS, as compared to the Weight attribute, which is locally momentous only. If you modify the Weight for a line on digit router in an AS, the added routers in the AS module not see of the change.
A route-map crapper be utilised to modify a topical alternative value. For example, if you poverty to modify the topical alternative continuance to 200 for the line advertizing 10.2.2.0/24 reaching in from edge 10.1.1.1, there are threesome steps involved. First, indite an ACL matched the far meshwork you poverty to modify the topical alternative for.
R1(config)#access-list 5 accept 10.2.2.0 0.0.0.255
Second, indite a route-map environment the topical alternative to 200. This module threefold the choice continuance of 100, and the line with the maximal topical alternative module be the desirable path.
R1(config)#route-map PREFERPATH accept 10
R1(config-route-map)#match ip come 5
R1(config-route-map)#set local-pref 200
Finally, administer the route-map to routes that are existence conventional from 10.1.1.1.
R1(config)#router bgp 100
R1(config-router)#network 10.1.1.1 route-map PREFERPATH in
R1 module then promote this newborn topical alternative continuance to every added routers in AS 100 - every of its iBGP neighbors.
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