



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.



Local preference (Local_Pref) is the second BGP attribute.

We can use the local preference to choose the outbound external BGP path.

Local preference is sent to all internal BGP (iBGP) routers in our autonomous system.

Local preference (Local_Pref) is not exchanged between external BGP routers.

It’s a well-known and discretionary BGP attribute.

Default value is 100.

The path with the highest local preference is desirable









TASK: To reach 50.1.1.1, 15.0.0.1 network router 2 and router 3 using 3.1.1.2 path ( AS 65144) because it has less numbers of autonomous system. but as per our requirement we need router use 1.1.1.1 interface to reach all the networks, to manipulate the path we use local_pref 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 2 exit point for autonomous system of 65123.

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





ROUTER-1(config)#Interface fastethernet 0/0 ROUTER-1(config-if)#Ip address 10.1.1.1 255.0.0.0 ROUTER-1(config-if)#No shutdown ROUTER-1(config-if)#No keepalive ROUTER-1(config-if)#Exit

ROUTER-1(config)#Interface serial 3/0 ROUTER-1(config-if)#Ip address 1.1.1.1 255.0.0.0 ROUTER-1(config-if)#No shutdown

ROUTER-1(config-if)#Exit ROUTER-1(config)#Interface serial 3/3 ROUTER-1(config-if)#Ip address 4.4.4.2 255.0.0.0 ROUTER-1(config-if)#No shutdown ROUTER-1(config-if)#Exit

ROUTER-1(config)#Interface loopback 0 ROUTER-1(config-if)#Ip address 11.0.0.1 255.255.255.0 ROUTER-1(config-if)#Exit









ROUTER-2(config)#Interface fastethernet 0/0

ROUTER-2(config-if)#Ip address 20.1.1.1 255.0.0.0 ROUTER-2(config-if)#No shutdown ROUTER-2(config-if)#No keepalive ROUTER-2(config-if)#Exit

ROUTER-2(config)#Interface serial 3/0 ROUTER-2(config-if)#Ip address 1.1.1.2 255.0.0.0 ROUTER-2(config-if)#No shutdown ROUTER-2(config-if)#Exit

ROUTER-2(config)#Interface serial 3/1 ROUTER-2(config-if)#Ip address 2.2.2.1 255.0.0.0 ROUTER-2(config-if)#No shutdown ROUTER-2(config-if)#Exit

ROUTER-2(config)#Interface loopback 1 ROUTER-2(config-if)#Ip address 12.0.1.1 255.255.255.0 ROUTER-2(config-if)#Exit









ROUTER-3(config)#Interface fastethernet 0/0

ROUTER-3(config-if)#Ip address 30.1.1.1 255.0.0.0 ROUTER-3(config-if)#No shutdown ROUTER-3(config-if)#No keepalive ROUTER-3(config-if)#Exit

ROUTER-3(config)#Interface serial 3/1 ROUTER-3(config-if)#Ip address 2.2.2.2 255.0.0.0 ROUTER-3(config-if)#No shutdown ROUTER-3(config-if)#Exit

ROUTER-3(config)#Interface serial 3/2 ROUTER-3(config-if)#Ip address 3.3.3.1 255.0.0.0 ROUTER-3(config-if)#No shutdown ROUTER-3(config-if)#Exit ROUTER-3(config)#

ROUTER-3(config)#Interface loopback 0 ROUTER-3(config-if)#Ip address 13.0.0.1 255.255.255.0 ROUTER-3(config-if)#Exit









ROUTER-4(config)#Interface fastethernet 0/0

ROUTER-4(config-if)#Ip address 40.1.1.1 255.0.0.0 ROUTER-4(config-if)#No shutdown ROUTER-4(config-if)#No keepalive ROUTER-4(config-if)#Exit

ROUTER-4(config)#Interface serial 3/2 ROUTER-4(config-if)#Ip address 3.3.3.2 255.0.0.0 ROUTER-4(config-if)#No shutdown ROUTER-4(config-if)#Exit

ROUTER-4(config)#Interface serial 3/4 ROUTER-4(config-if)#Ip address 5.5.5.2 255.0.0.0 ROUTER-4(config-if)#No shutdown ROUTER-4(config-if)#Exit

ROUTER-4(config)#Interface serial 3/3 ROUTER-4(config-if)#Ip address 4.4.4.1 255.0.0.0 ROUTER-4(config-if)#No shutdown ROUTER-4(config-if)#Exit









ROUTER-5(config)#Interface fastethernet 0/0 ROUTER-5(config-if)#Ip address 50.1.1.1 255.0.0.0 ROUTER-5(config-if)#No shutdown ROUTER-5(config-if)#No keepalive ROUTER-5(config-if)#Exit

ROUTER-5(config)#Interface serial 3/4 ROUTER-5(config-if)#Ip address 5.5.5.1 255.0.0.0 ROUTER-5(config-if)#No shutdown ROUTER-5(config-if)#Exit

ROUTER-5(config)#Interface loopback 0 ROUTER-5(config-if)#Ip address 15.0.0.1 255.255.255.0 ROUTER-5(config-if)#Exit









ROUTER-1(config)#router bgp 65111 ROUTER-1(config-router)#neighbor 1.1.1.2 remote-as 65123 ROUTER-1(config-router)#neighbor 1.1.1.2 remote-as 65144 ROUTER-1(config-router)#neighbor 4.4.4.1 remote-as 65144 ROUTER-1(config-router)#network 10.0.0.0 ROUTER-1(config-router)#network 1.0.0.0 ROUTER-1(config-router)#network 4.0.0.0 ROUTER-1(config-router)#network 11.0.0.0 mask 255.255.255.0 ROUTER-1(config-router)#no auto-summary ROUTER-1(config-router)#no synchronization ROUTER-1(config-router)#exit



*Nov 30 00:55:16.523: %BGP-5-ADJCHANGE: neighbor 1.1.1.2 Up



ROUTER-2(config)#router bgp 65123

ROUTER-2(config-router)#neighbor 1.1.1.1 remote-as 65111 ROUTER-2(config-router)#neighbor 1.1.1.1 remote-as 6511 ROUTER-2(config-router)#neighbor 2.2.2.2 remote-as 65123 ROUTER-2(config-router)#network 20.1.1.1 ROUTER-2(config-router)#network 2.1.1.1 ROUTER-2(config-router)#network 1.1.1.1 ROUTER-2(config-router)#network 12.0.0.0 mask 255.255.255.0 ROUTER-2(config-router)#no auto-summary ROUTER-2(config-router)#no synchronization ROUTER-2(config-router)#exit





ROUTER-2(config)#router bgp 65123 ROUTER-2(config-router)#neighbor 2.2.2.2 next-hop-self ROUTER-2(config-router)#exit

ROUTER-2(config)#do clear ip bgp * soft









*Nov 30 00:59:19.611: %BGP-5-ADJCHANGE: neighbor 1.1.1.1 Up









ROUTER-3(config)#router bgp 65123 ROUTER-3(config-router)#neighbor 2.2.2.1 remote-as 65123 ROUTER-3(config-router)#neighbor 2.2.2.1 remote-as 65144 ROUTER-3(config-router)#neighbor 3.3.3.2 remote-as 65144 ROUTER-3(config-router)#network 2.0.0.0 ROUTER-3(config-router)#network 3.0.0.0 ROUTER-3(config-router)#network 30.0.0.0 ROUTER-3(config-router)#network 13.0.0.0 mask 255.255.255.0 ROUTER-3(config-router)#no auto-summary ROUTER-3(config-router)#no synchronization ROUTER-3(config-router)#exit

*Nov 30 01:10:34.847: %BGP-5-ADJCHANGE: neighbor 3.3.3.2 Up



ROUTER-3(config)#router bgp 65123 ROUTER-3(config-router)#neighbor 2.2.2.1 next-hop-self ROUTER-3(config-router)#exit





*Nov 30 01:08:47.059: %BGP-5-ADJCHANGE: neighbor 2.2.2.1 Up





ROUTER-4(config)#router bgp 65144 ROUTER-4(config-router)#neighbor 3.3.3.1 remote-as 65123 ROUTER-4(config-router)#neighbor 4.4.4.2 remote-as 65111 ROUTER-4(config-router)#neighbor 5.5.5.1 remote-as 65155 ROUTER-4(config-router)#network 40.0.0.0 ROUTER-4(config-router)#network 4.0.0.0 ROUTER-4(config-router)#network 5.0.0.0 ROUTER-4(config-router)#network 3.0.0.0 ROUTER-4(config-router)#network 14.0.0.0 mask 255.255.255.0 ROUTER-4(config-router)#no auto-summary ROUTER-4(config-router)#no synchronization ROUTER-4(config-router)#exit

*Nov 30 01:17:25.667: %BGP-5-ADJCHANGE: neighbor 5.5.5.1 Up

*Nov 30 01:10:34.827: %BGP-5-ADJCHANGE: neighbor 3.3.3.1 Up

*Nov 30 01:10:54.627: %BGP-5-ADJCHANGE: neighbor 4.4.4.2 Up



ROUTER-5(config)#router bgp 65155 ROUTER-5(config-router)#neighbor 5.5.5.2 remote-as 65144 ROUTER-5(config-router)#network 50.0.0 ROUTER-5(config-router)#network 50.0.0.0 ROUTER-5(config-router)#network 5.0.0.0 ROUTER-5(config-router)#network 15.0.0.0 mask 255.255.255.0 ROUTER-5(config-router)#no auto-summary ROUTER-5(config-router)#no synchronization ROUTER-5(config-router)#exit





*Nov 30 01:17:24.823: %BGP-5-ADJCHANGE: neighbor 5.5.5.2 Up





ROUTER-1#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 [20/0] via 1.1.1.2, 00:33:49 B 3.0.0.0/8 [20/0] via 1.1.1.2, 00:33:19 B 5.0.0.0/8 [20/0] via 4.4.4.1, 00:30:49 13.0.0.0/24 is subnetted, 1 subnets B 13.0.0.0 [20/0] via 1.1.1.2, 00:33:19 14.0.0.0/24 is subnetted, 1 subnets B 14.0.0.0 [20/0] via 4.4.4.1, 00:30:49 15.0.0.0/24 is subnetted, 1 subnets B 15.0.0.0 [20/0] via 4.4.4.1, 00:25:00 B 20.0.0.0/8 [20/0] via 1.1.1.2, 00:07:25 B 30.0.0.0/8 [20/0] via 1.1.1.2, 00:09:46 B 40.0.0.0/8 [20/0] via 4.4.4.1, 00:31:20 B 50.0.0.0/8 [20/0] via 4.4.4.1, 00:25:00









ROUTER-2#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 3.0.0.0/8 [200/0] via 2.2.2.2, 00:33:53 B 4.0.0.0/8 [20/0] via 1.1.1.1, 00:43:44 B 5.0.0.0/8 [200/0] via 2.2.2.2, 00:23:08 B 10.0.0.0/8 [20/0] via 1.1.1.1, 00:43:44 11.0.0.0/24 is subnetted, 1 subnets B 11.0.0.0 [20/0] via 1.1.1.1, 00:43:44 13.0.0.0/24 is subnetted, 1 subnets B 13.0.0.0 [200/0] via 2.2.2.2, 00:33:40 14.0.0.0/24 is subnetted, 1 subnets B 14.0.0.0 [200/0] via 2.2.2.2, 00:23:08 15.0.0.0/24 is subnetted, 1 subnets B 15.0.0.0 [200/0] via 2.2.2.2, 00:23:08 B 30.0.0.0/8 [200/0] via 2.2.2.2, 00:09:55 B 40.0.0.0/8 [200/0] via 2.2.2.2, 00:23:08 B 50.0.0.0/8 [200/0] via 2.2.2.2, 00:23:08









ROUTER-3#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 1.0.0.0/8 [200/0] via 2.2.2.1, 00:24:04 B 4.0.0.0/8 [20/0] via 3.3.3.2, 00:31:33 B 5.0.0.0/8 [20/0] via 3.3.3.2, 00:31:03 B 10.0.0.0/8 [200/0] via 2.2.2.1, 00:24:04 11.0.0.0/24 is subnetted, 1 subnets B 11.0.0.0 [200/0] via 2.2.2.1, 00:24:04 14.0.0.0/24 is subnetted, 1 subnets B 14.0.0.0 [20/0] via 3.3.3.2, 00:31:03 15.0.0.0/24 is subnetted, 1 subnets B 15.0.0.0 [20/0] via 3.3.3.2, 00:25:13 B 20.0.0.0/8 [200/0] via 2.2.2.1, 00:07:39 B 40.0.0.0/8 [20/0] via 3.3.3.2, 00:31:33 B 50.0.0.0/8 [20/0] via 3.3.3.2, 00:25:13













ROUTER-4# 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 1.0.0.0/8 [20/0] via 4.4.4.2, 00:32:18 B 2.0.0.0/8 [20/0] via 3.3.3.1, 00:32:38 B 10.0.0.0/8 [20/0] via 4.4.4.2, 00:32:18 11.0.0.0/24 is subnetted, 1 subnets B 11.0.0.0 [20/0] via 4.4.4.2, 00:32:18 13.0.0.0/24 is subnetted, 1 subnets B 13.0.0.0 [20/0] via 3.3.3.1, 00:32:38 15.0.0.0/24 is subnetted, 1 subnets B 15.0.0.0 [20/0] via 5.5.5.1, 00:25:16 B 20.0.0.0/8 [20/0] via 3.3.3.1, 00:07:41 B 30.0.0.0/8 [20/0] via 3.3.3.1, 00:10:03 B 50.0.0.0/8 [20/0] via 5.5.5.1, 00:25:16









ROUTER-5#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 1.0.0.0/8 [20/0] via 5.5.5.2, 00:25:51 B 2.0.0.0/8 [20/0] via 5.5.5.2, 00:25:51 B 3.0.0.0/8 [20/0] via 5.5.5.2, 00:25:51 B 4.0.0.0/8 [20/0] via 5.5.5.2, 00:25:51 B 10.0.0.0/8 [20/0] via 5.5.5.2, 00:25:51 11.0.0.0/24 is subnetted, 1 subnets B 11.0.0.0 [20/0] via 5.5.5.2, 00:25:51 13.0.0.0/24 is subnetted, 1 subnets B 13.0.0.0 [20/0] via 5.5.5.2, 00:25:51 14.0.0.0/24 is subnetted, 1 subnets B 14.0.0.0 [20/0] via 5.5.5.2, 00:25:51 B 20.0.0.0/8 [20/0] via 5.5.5.2, 00:07:15 B 30.0.0.0/8 [20/0] via 5.5.5.2, 00:10:07 B 40.0.0.0/8 [20/0] via 5.5.5.2, 00:25:51

ROUTER-2#show ip bgp BGP table version is 22, local router ID is 12.0.1.1 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 r> 1.0.0.0 1.1.1.1 0 0 65111 i r>i 2.0.0.0 2.2.2.2 0 100 0 i *>i 3.0.0.0 2.2.2.2 0 100 0 i * i 4.0.0.0 2.2.2.2 0 100 0 65144 i *> 1.1.1.1 0 0 65111 i * 5.0.0.0 1.1.1.1 0 65111 65144 i *>i 2.2.2.2 0 100 0 65144 i *> 10.0.0.0 1.1.1.1 0 0 65111 i *> 11.0.0.0/24 1.1.1.1 0 0 65111 i *>i 13.0.0.0/24 2.2.2.2 0 100 0 i * 14.0.0.0/24 1.1.1.1 0 65111 65144 i *>i 2.2.2.2 0 100 0 65144 i *>i 15.0.0.0/24 2.2.2.2 0 100 0 65144 65155 i * 1.1.1.1 0 65111 65144 65155 i Network Next Hop Metric LocPrf Weight Path *> 20.0.0.0 0.0.0.0 0 32768 i *>i 30.0.0.0 2.2.2.2 0 100 0 i * 40.0.0.0 1.1.1.1 0 65111 65144 i *>i 2.2.2.2 0 100 0 65144 i *>i 50.0.0.0 2.2.2.2 0 100 0 65144 65155 i * 1.1.1.1 0 65111 65144 65155 i





ROUTER-2#traceroute 50.1.1.1 Type escape sequence to abort. Tracing the route to 50.1.1.1 VRF info: (vrf in name/id, vrf out name/id) 1 2.2.2.2 140 msec 76 msec 100 msec 2 3.3.3.2 128 msec 136 msec 200 msec 3 5.5.5.1 [AS 65144] 300 msec 252 msec 172 msec









( configuring local pref on router 2 )





ROUTER-2(config)#router bgp 65123 ROUTER-2(config-router)#b gp default local-preference 5000 ROUTER-2(config-router)#exit ROUTER-2(config)#do clear ip bgp * soft ROUTER-2(config)#end





ROUTER-2#traceroute 50.1.1.1 Type escape sequence to abort. Tracing the route to 50.1.1.1 VRF info: (vrf in name/id, vrf out name/id) 1 1.1.1.1 [AS 65111] 48 msec 48 msec 100 msec 2 4.4.4.1 [AS 65111] 116 msec 128 msec 128 msec 3 5.5.5.1 [AS 65144] 200 msec 180 msec 248 msec







ROUTER-2#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 3.0.0.0/8 [200/0] via 2.2.2.2, 00:03:05 B 4.0.0.0/8 [20/0] via 1.1.1.1, 00:03:05 B 5.0.0.0/8 [20/0] via 1.1.1.1, 00:03:05 B 10.0.0.0/8 [20/0] via 1.1.1.1, 01:00:29 11.0.0.0/24 is subnetted, 1 subnets B 11.0.0.0 [20/0] via 1.1.1.1, 01:00:29 13.0.0.0/24 is subnetted, 1 subnets B 13.0.0.0 [200/0] via 2.2.2.2, 00:03:05 14.0.0.0/24 is subnetted, 1 subnets B 14.0.0.0 [20/0] via 1.1.1.1, 00:03:05 15.0.0.0/24 is subnetted, 1 subnets B 15.0.0.0 [20/0] via 1.1.1.1, 00:03:05 B 30.0.0.0/8 [200/0] via 2.2.2.2, 00:03:05 B 40.0.0.0/8 [20/0] via 1.1.1.1, 00:03:05 B 50.0.0.0/8 [20/0] via 1.1.1.1, 00:03:05









