網(wǎng)絡(luò)ccna實(shí)驗(yàn)手冊(cè)互聯(lián)神州bsci30s06l

1、Implementing BGPUsing Route Maps to Manipulate Basic BGP PathsBGP is designed for manipulating routing paths.BGP Is Designed to Implement Policy RoutingChanging BGP Local Preference For All Routesbgp default local-preference valueRouter(config-router)#This command changes the default local preferenc

2、e 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 speakersTo determine the best path to exit theAS to reach an outside networkSet to 100 by default; higher values preferredWhat is th

3、e best path for router C to 65003, 65004, and 65005?Local Preference Case StudyRouter C BGP Table with Default SettingsRouterC# show ip bgpBGP table version is 7, local router ID is 3.3.3.3Status codes: s suppressed, d damped, h history, * valid, best, i - internal, r RIB-failure, S StaleOrigin code

4、s: i - IGP, e - EGP, ? - plete Network Next Hop Metric LocPrf Weight Path* i172.16.0.0 172.20.50.1 100 0 65005 65004 65003 i*i 192.168.28.1 100 0 65002 65003 i*i172.24.0.0 172.20.50.1 100 0 65005 i* i 192.168.28.1 100 0 65002 65003 65004 65005 i*i172.30.0.0 172.20.50.1 100 0 65005 65004 i* i 192.168

5、.28.1 100 0 65002 65003 65004iBy default, BGP selects the shortest AS path as the best () path.In AS 65001, the percentage of traffic going to 172.24.0.0 is 30%, 172.30.0.0 is 20%, and 172.16.0.0 is 10%.50% of all traffic will go to the next hop of 172.20.50.1 (AS 65005), and 10% of all traffic will

6、 go to the next hop of 192.168.28.1 (AS 65002).Make traffic to 172.30.0.0 select the next hop of 192.168.28.1 to achieve load sharing where both external links get approximately 30% of the load.Route Map for Router Arouter bgp 65001 neighbor 2.2.2.2 remote-as 65001neighbor 3.3.3.3 remote-as 65001nei

7、ghbor 2.2.2.2 remote-as 65001 update-source loopback0neighbor 3.3.3.3 remote-as 65001 update-source loopback0neighbor 192.168.28.1 remote-as 65002neighbor 192.168.28.1 route-map local_pref in!access-list 65 permit 172.30.0.0 0.0.255.255!route-map local_pref permit 10match ip address 65set local-pref

8、erence 400!route-map local_pref permit 20Router A configurationRouter C BGP Table with Local Preference LearnedRouterC# show ip bgpBGP table version is 7, local router ID is 3.3.3.3Status codes: s suppressed, d damped, h history, * valid, best, i - internal, r RIB-failure, S StaleOrigin codes: i - I

9、GP, e - EGP, ? - plete Network Next Hop Metric LocPrf Weight Path* i172.16.0.0 172.20.50.1 100 0 65005 65004 65003 i*i 192.168.28.1 100 0 65002 65003 i*i172.24.0.0 172.20.50.1 100 0 65005 i* i 192.168.28.1 100 0 65002 65003 65004 65005 i* i172.30.0.0 172.20.50.1 100 0 65005 65004 i*i 192.168.28.1 40

10、0 0 65002 65003 65004iBest () paths for networks 172.16.0.0/16 and 172.24.0.0/16 have not changed.Best () path for network 172.30.0.0 has changed to a new next hop of 192.168.28.1 because the next hop of 192.168.28.1 has a higher local preference, 400.In AS 65001, the percentage of traffic going to

11、172.24.0.0 is 30%, 172.30.0.0 is 20%, and 172.16.0.0 is 10%.30% of all traffic will go to the next hop of 172.20.50.1 (AS 65005), and 30% of all traffic will go tothe next hop of 192.168.28.1 (AS 65002).Changing BGP MED for All Routesdefault-metric numberRouter(config-router)#MED is considered the m

12、etric of BGP.All routes that are advertised to an EBGP neighbor are set to the value specified using this command.MED is used when multiple paths exist between two autonomous systems.A lower MED value is preferred. The default setting for Cisco is MED = 0.The metric is an optional, nontransitive att

13、ribute. Usually, MED is shared only between two autonomous systems that have multiple EBGP connections with each other.BGP Using Route Maps and the MEDRoute Map for Router ARouter As Configuration:router bgp 65001 neighbor 2.2.2.2 remote-as 65001neighbor 3.3.3.3 remote-as 65001neighbor 2.2.2.2 updat

14、e-source loopback0neighbor 3.3.3.3 update-source loopback0neighbor 192.168.28.1 remote-as 65004neighbor 192.168.28.1 route-map med_65004 out!access-list 66 permit 192.168.25.0.0 0.0.0.255access-list 66 permit 192.168.26.0.0 0.0.0.255 !route-map med_65004 permit 10match ip address 66set metric 100!ro

15、ute-map med_65004 permit 100set metric 200Route Map for Router BRouter Bs Configuration:router bgp 65001neighbor 1.1.1.1 remote-as 65001neighbor 3.3.3.3 remote-as 65001neighbor 1.1.1.1 update-source loopback0neighbor 3.3.3.3 update-source loopback0neighbor 172.20.50.1 remote-as 65004neighbor 172.20.

16、50.1 route-map med_65004 out!access-list 66 permit 192.168.24.0.0 0.0.0.255!route-map med_65004 permit 10match ip address 66set metric 100!route-map med_65004 permit 100set metric 200MED Learned by Router ZRouterZ# show ip bgpBGP table version is 7, local router ID is 122.30.1.1Status codes: s suppr

17、essed, d damped, h history, * valid, best, i - internal, r RIB-failure, S StaleOrigin codes: i - IGP, e - EGP, ? - plete Network Next Hop Metric LocPrf Weight Path*i192.168.24.0 172.20.50.2 100 100 0 65001 i* i 192.168.28.2 200 100 0 65001 i* i192.168.25.0 172.20.50.2 200 100 0 65001 i*i 192.168.28.

18、2 100 100 0 65001 i* i192.168.26.0 172.20.50.2 200 100 0 65001 i*i 192.168.28.2 100 100 0 65001 iExamine the networks that have been learned from AS 65001 on Router Z in AS 65004.For all networks: Weight is equal (0); local preference is equal (100); routes are not originated in this AS; AS path is

19、equal (65001); origin code is equal (i).192.168.24.0 has a lower metric (MED) through 172.20.50.2 (100) than 192.168.28.2 (200).192.168.25.0 has a lower metric (MED) through 192.168.28.2 (100) than 172.20.50.2 (200).192.168.26.0 has a lower metric (MED) through 192.168.28.2 (100) than 172.20.50.2 (200).BGP in an EnterpriseSummaryThe BGP local preference attribute can be changed to manipulate the best-path decision proc