usingroutemapstomanipulatebasicbgppaths.ppt

Implementing BGP Using Route Maps to Manipulate Basic BGP Paths BGP Is Designed to Implement Policy Routing Changing BGP Local Preference For All Routes Local Preference Case Study Router C BGP Table with Default Settings Route Map for Router A Router C BGP Table with Local Preference Learned Changing BGP MED for All Routes BGP Using Route Maps and the MED Route Map for Router A Route Map for Router B MED Learned by Router Z Summary The BGP local preference attribute can be changed to manipulate the best-path decision process, either for all routes or for selected routes using route maps. Higher local preference values are preferred. Local preference is used only between IBGP speakers within the same AS. The MED values can be changed to manipulate packets returning to an AS, either for all routes or for selected routes, using route maps. ?????? Lower MED values are preferred. The MED is sent to EBGP neighbors; those routers propagate the MED within their AS. The routers within the AS use the MED but do not pass it on to the next AS. Routers in a typical enterprise BGP implementation multihome to two ISPs and pass default routes to other routers within the enterprise. BGP is designed for manipulating routing paths. bgp default local-preference value Router(config-router)# This command changes the default local preference value. All routes advertised to an IBGP neighbor have the local preference set to the value specified. Local preference is used in these ways: Within an AS between IBGP speakers To determine the best path to exit theAS to reach an outside network Set to 100 by default; higher values preferred What is the best path for router C to 65003, 65004, and 65005? RouterC# show ip bgp BGP table version is 7, local router ID is 3.3.3.3 Status codes: s suppressed, d damped, h history, * valid, best, i - internal, r RIB-failure, S Stale Origin codes: i - IGP, e - EGP, ? - incomplete Network Next Hop Metric LocPrf Weight Path * i172.16.0.0