BGP Local preference (Local_Pref) Path attribute gives the router inside a single autonomous system a value that they can set per-route and advertise to all iBGP routers inside the autonomous system, so that all routers in the autonomous system agree about which routers is the best exit point for packet destined for that prefix.





lets see the configuration:-









Topology:





















Goal:

configure the topology as per the diagram.

configure iBGP and eBGP peering using directly connected interfaces.

advertise all the networks as per the topology.

configure router 1 exit point for autonomous system of 65111.

make sure router 2 reach all the network via router 1.





R1#show ip interface brief

Interface IP-Address OK? Method Status Protocol FastEthernet0/0 10.1.1.1 YES manual up up Serial3/0 1.1.1.1 YES manual up up Serial3/3 4.1.1.2 YES manual up up Loopback0 11.0.0.1 YES manual up up Loopback1 11.0.1.1 YES manual up up Loopback2 11.0.2.1 YES manual up up Loopback3 11.0.3.1 YES manual up up





R2#show ip interface brief Interface IP-Address OK? Method Status Protocol FastEthernet0/0 20.1.1.1 YES manual up up Serial3/0 1.1.1.2 YES manual up up Serial3/1 2.1.1.1 YES manual up up Loopback0 12.0.0.1 YES manual up up Loopback1 12.0.1.1 YES manual up up Loopback2 12.0.2.1 YES manual up up Loopback3 12.0.3.1 YES manual up up





R3#show ip interface brief Interface IP-Address OK? Method Status Protocol FastEthernet0/0 30.1.1.1 YES manual up up Serial3/1 2.1.1.2 YES manual up up Serial3/2 3.1.1.1 YES manual up up Loopback0 13.0.0.1 YES manual up up Loopback1 13.0.1.1 YES manual up up Loopback2 13.0.2.1 YES manual up up Loopback3 13.0.3.1 YES manual up up







R4#show ip interface brief Interface IP-Address OK? Method Status Protocol FastEthernet0/0 40.1.1.1 YES manual up up Serial3/2 3.1.1.2 YES manual up up Serial3/3 4.1.1.1 YES manual up up Loopback0 14.0.0.1 YES manual up up Loopback1 14.0.1.1 YES manual up up Loopback2 14.0.2.1 YES manual up up Loopback3 14.0.3.1 YES manual up up







R1(config)#router bgp 65111 R1(config-router)#neighbor 1.1.1.2 remote-as 65111 R1(config-router)#neighbor 4.1.1.1 remote-as 65444 R1(config-router)#neighbor 1.1.1.2 next-hop-self R1(config-router)#network 10.0.0.0 R1(config-router)#network 1.0.0.0 R1(config-router)#network 4.0.0.0 R1(config-router)#network 11.0.0.0 mask 255.255.255.0 R1(config-router)#no auto-summary R1(config-router)#no synchronization







R2(config)#router bgp 65111 R2(config-router)#neighbor 1.1.1.1 remote-as 65111 R2(config-router)#neighbor 2.1.1.2 remote-as 65333 R2(config-router)#neighbor 1.1.1.1 next-hop-self R2(config-router)#network 20.0.0. R2(config-router)#network 20.0.0.0 R2(config-router)#network 2.0.0.0 R2(config-router)#network 1.0.0.0 R2(config-router)#network 12.0.0.0 mask 255.255.255.0 R2(config-router)#no auto-summary R2(config-router)#no synchronization







R3(config)#router bgp 65333

R3(config-router)#neighbor 2.1.1.1 remote-as 65111 R3(config-router)#neighbor 3.1.1.2 remote-as 65444 R3(config-router)#network 30.0.0.0 R3(config-router)#network 3.0.0.0 R3(config-router)#network 2.0.0.0 R3(config-router)#network 13.0.0.0 mask 255.255.255.0 R3(config-router)#no synchronization R3(config-router)#no auto-summary







R4(config)#router bgp 65444 R4(config-router)#neighbor 3.1.1.1 remote-as 65333 R4(config-router)#neighbor 4.1.1.2 remote-as 65111 R4(config-router)#network 40.0.0.0 R4(config-router)#network 4.0.0.0 R4(config-router)#network 14.0.0.0 mask 255.255.255.0 R4(config-router)#network 3.0.0.0 R4(config-router)#no synchronization R4(config-router)#no auto-summary







R1#show ip bgp BGP table version is 14, local router ID is 11.0.3.1 Status codes: s suppressed, d damped, h history, * valid, > best, i - internal, r RIB-failure, S Stale, m multipath, b backup-path, f RT-Filter, x best-external, a additional-path, c RIB-compressed, Origin codes: i - IGP, e - EGP, ? - incomplete RPKI validation codes: V valid, I invalid, N Not found



Network Next Hop Metric LocPrf Weight Path * i 1.0.0.0 1.1.1.2 0 100 0 i *> 0.0.0.0 0 32768 i *>i 2.0.0.0 1.1.1.2 0 100 0 i *> 3.0.0.0 4.1.1.1 0 0 65444 i * i 1.1.1.2 0 100 0 65333 i * 4.0.0.0 4.1.1.1 0 0 65444 i *> 0.0.0.0 0 32768 i *> 10.0.0.0 0.0.0.0 0 32768 i *> 11.0.0.0/24 0.0.0.0 0 32768 i *>i 12.0.0.0/24 1.1.1.2 0 100 0 i * 13.0.0.0/24 4.1.1.1 0 65444 65333 i *>i 1.1.1.2 0 100 0 65333 i *> 14.0.0.0/24 4.1.1.1 0 0 65444 i *>i 20.0.0.0 1.1.1.2 0 100 0 i * 30.0.0.0 4.1.1.1 0 65444 65333 i Network Next Hop Metric LocPrf Weight Path *>i 1.1.1.2 0 100 0 65333 i *> 40.0.0.0 4.1.1.1 0 0 65444 i







R2#show ip bgp BGP table version is 14, local router ID is 12.0.3.1 Status codes: s suppressed, d damped, h history, * valid, > best, i - internal, r RIB-failure, S Stale, m multipath, b backup-path, f RT-Filter, x best-external, a additional-path, c RIB-compressed, Origin codes: i - IGP, e - EGP, ? - incomplete RPKI validation codes: V valid, I invalid, N Not found

Network Next Hop Metric LocPrf Weight Path *> 1.0.0.0 0.0.0.0 0 32768 i * i 1.1.1.1 0 100 0 i * 2.0.0.0 2.1.1.2 0 0 65333 i *> 0.0.0.0 0 32768 i * i 3.0.0.0 1.1.1.1 0 100 0 65444 i *> 2.1.1.2 0 0 65333 i *>i 4.0.0.0 1.1.1.1 0 100 0 i *>i 10.0.0.0 1.1.1.1 0 100 0 i *>i 11.0.0.0/24 1.1.1.1 0 100 0 i *> 12.0.0.0/24 0.0.0.0 0 32768 i *> 13.0.0.0/24 2.1.1.2 0 0 65333 i * 14.0.0.0/24 2.1.1.2 0 65333 65444 i *>i 1.1.1.1 0 100 0 65444 i *> 20.0.0.0 0.0.0.0 0 32768 i Network Next Hop Metric LocPrf Weight Path *> 30.0.0.0 2.1.1.2 0 0 65333 i * 40.0.0.0 2.1.1.2 0 65333 65444 i *>i 1.1.1.1 0 100 0 65444 i











R1#show ip route bgp Codes: L - local, C - connected, S - static, R - RIP, M - mobile, B - BGP D - EIGRP, EX - EIGRP external, O - OSPF, IA - OSPF inter area N1 - OSPF NSSA external type 1, N2 - OSPF NSSA external type 2 E1 - OSPF external type 1, E2 - OSPF external type 2 i - IS-IS, su - IS-IS summary, L1 - IS-IS level-1, L2 - IS-IS level-2 ia - IS-IS inter area, * - candidate default, U - per-user static route o - ODR, P - periodic downloaded static route, H - NHRP, l - LISP + - replicated route, % - next hop override

Gateway of last resort is not set



B 2.0.0.0/8 [200/0] via 1.1.1.2, 00:36:56 B 3.0.0.0/8 [20/0] via 4.1.1.1, 00:32:47 12.0.0.0/24 is subnetted, 1 subnets B 12.0.0.0 [200/0] via 1.1.1.2, 00:36:43 13.0.0.0/24 is subnetted, 1 subnets B 13.0.0.0 [200/0] via 1.1.1.2, 00:34:45 14.0.0.0/24 is subnetted, 1 subnets B 14.0.0.0 [20/0] via 4.1.1.1, 00:33:18 B 20.0.0.0/8 [200/0] via 1.1.1.2, 00:36:56 B 30.0.0.0/8 [200/0] via 1.1.1.2, 00:35:16 B 40.0.0.0/8 [20/0] via 4.1.1.1, 00:33:48











R1#traceroute 13.0.0.1 Type escape sequence to abort. Tracing the route to 13.0.0.1 VRF info: (vrf in name/id, vrf out name/id) 1 1.1.1.2 32 msec 36 msec 8 msec 2 2.1.1.2 36 msec 64 msec 64 msec

R1#traceroute 30.1.1.1 Type escape sequence to abort. Tracing the route to 30.1.1.1 VRF info: (vrf in name/id, vrf out name/id) 1 1.1.1.2 12 msec 60 msec 24 msec 2 2.1.1.2 44 msec 52 msec 60 msec





R2#traceroute 13.0.0.1 Type escape sequence to abort. Tracing the route to 13.0.0.1 VRF info: (vrf in name/id, vrf out name/id) 1 2.1.1.2 288 msec 60 msec 28 msec

R2#traceroute 30.1.1.1 Type escape sequence to abort. Tracing the route to 30.1.1.1 VRF info: (vrf in name/id, vrf out name/id) 1 2.1.1.2 76 msec 72 msec 60 msec







(To reach 30.1.1.1, 13.0.0.1 network router 1 and router 2 using 2.1.1.2 path because it has less numbers of autonomous system. but as per our requirement we need router use 4.1.1.1 interface to reach all the networks, to manipulate the path we use local_pref)





R1(config)#router bgp 65111 R1(config-router)#bgp default local-preference 5000 R1(config-router)#end

R1#clear ip bgp * soft





R1#traceroute 30.1.1.1 Type escape sequence to abort. Tracing the route to 30.1.1.1 VRF info: (vrf in name/id, vrf out name/id) 1 4.1.1.1 8 msec 52 msec 28 msec 2 3.1.1.1 [AS 65444] 80 msec 40 msec 64 msec

R1#traceroute 13.0.0.1 Type escape sequence to abort. Tracing the route to 13.0.0.1 VRF info: (vrf in name/id, vrf out name/id) 1 4.1.1.1 24 msec 60 msec 68 msec 2 3.1.1.1 [AS 65444] 112 msec 72 msec 52 msec







R2#traceroute 30.1.1.1 Type escape sequence to abort. Tracing the route to 30.1.1.1 VRF info: (vrf in name/id, vrf out name/id) 1 1.1.1.1 4 msec 44 msec 28 msec 2 4.1.1.1 36 msec 60 msec 8 msec 3 3.1.1.1 [AS 65444] 60 msec 52 msec 44 msec



R2#traceroute 13.0.0.1 Type escape sequence to abort. Tracing the route to 13.0.0.1 VRF info: (vrf in name/id, vrf out name/id) 1 1.1.1.1 8 msec 28 msec 36 msec 2 4.1.1.1 64 msec 116 msec 64 msec 3 3.1.1.1 [AS 65444] 72 msec 72 msec 52 msec





R1#show ip bgp BGP table version is 21, local router ID is 11.0.3.1 Status codes: s suppressed, d damped, h history, * valid, > best, i - internal, r RIB-failure, S Stale, m multipath, b backup-path, f RT-Filter, x best-external, a additional-path, c RIB-compressed, Origin codes: i - IGP, e - EGP, ? - incomplete RPKI validation codes: V valid, I invalid, N Not found

Network Next Hop Metric LocPrf Weight Path * i 1.0.0.0 1.1.1.2 0 100 0 i *> 0.0.0.0 0 32768 i *>i 2.0.0.0 1.1.1.2 0 100 0 i *> 3.0.0.0 4.1.1.1 0 0 65444 i * 4.0.0.0 4.1.1.1 0 0 65444 i *> 0.0.0.0 0 32768 i *> 10.0.0.0 0.0.0.0 0 32768 i *> 11.0.0.0/24 0.0.0.0 0 32768 i *>i 12.0.0.0/24 1.1.1.2 0 100 0 i *> 13.0.0.0/24 4.1.1.1 0 65444 65333 i *> 14.0.0.0/24 4.1.1.1 0 0 65444 i *>i 20.0.0.0 1.1.1.2 0 100 0 i *> 30.0.0.0 4.1.1.1 0 65444 65333 i *> 40.0.0.0 4.1.1.1 0 0 65444 i









R2#show ip bgp BGP table version is 22, local router ID is 12.0.3.1 Status codes: s suppressed, d damped, h history, * valid, > best, i - internal, r RIB-failure, S Stale, m multipath, b backup-path, f RT-Filter, x best-external, a additional-path, c RIB-compressed, Origin codes: i - IGP, e - EGP, ? - incomplete RPKI validation codes: V valid, I invalid, N Not found



Network Next Hop Metric LocPrf Weight Path *> 1.0.0.0 0.0.0.0 0 32768 i * i 1.1.1.1 0 5000 0 i * 2.0.0.0 2.1.1.2 0 0 65333 i *> 0.0.0.0 0 32768 i *>i 3.0.0.0 1.1.1.1 0 5000 0 65444 i * 2.1.1.2 0 0 65333 i *>i 4.0.0.0 1.1.1.1 0 5000 0 i *>i 10.0.0.0 1.1.1.1 0 5000 0 i *>i 11.0.0.0/24 1.1.1.1 0 5000 0 i *> 12.0.0.0/24 0.0.0.0 0 32768 i *>i 13.0.0.0/24 1.1.1.1 0 5000 0 65444 65333 i * 2.1.1.2 0 0 65333 i * 14.0.0.0/24 2.1.1.2 0 65333 65444 i *>i 1.1.1.1 0 5000 0 65444 i Network Next Hop Metric LocPrf Weight Path *> 20.0.0.0 0.0.0.0 0 32768 i *>i 30.0.0.0 1.1.1.1 0 5000 0 65444 65333 i * 2.1.1.2 0 0 65333 i * 40.0.0.0 2.1.1.2 0 65333 65444 i *>i 1.1.1.1 0 5000 0 65444 i







R2#show ip bgp 30.1.1.1 BGP routing table entry for 30.0.0.0/8, version 17 Paths: (2 available, best #1, table default) Advertised to update-groups: 3 Refresh Epoch 2 65444 65333 1.1.1.1 from 1.1.1.1 (11.0.3.1) Origin IGP, metric 0, localpref 5000, valid, internal, best rx pathid: 0, tx pathid: 0x0 Refresh Epoch 1 65333 2.1.1.2 from 2.1.1.2 (13.0.3.1) Origin IGP, metric 0, localpref 100, valid, external rx pathid: 0, tx pathid: 0







(you can also use route map for particular routes. comment below for route map)