A Cisco router can use the BGP weight, in that router to influence that one router’s choice of outbound route. To do so, when a router receives a BGP update, that router can set the weight either selectively, per route, using route map or for all routes learned competing routes, choosing the route with the bigger weight.











configure the topology as per the diagram.

configure the basic iBGP and EBGP peering using directly connected interfaces.

advertise all the interfaces as per the topology

configure the next-hop address should be the next router address

configure router 4 to prefer exit path via router1 to reach all the networks.







R1#show ip interface brief

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





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







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





R4#show ip interface brief Interface IP-Address OK? Method Status Protocol FastEthernet0/0 40.1.1.1 YES NVRAM up up Serial3/2 3.1.1.2 YES NVRAM up up Serial3/3 4.1.1.1 YES NVRAM up up Loopback0 14.0.0.1 YES NVRAM up up Loopback1 14.0.1.1 YES NVRAM up up Loopback2 14.0.2.1 YES NVRAM up up Loopback3 14.0.3.1 YES NVRAM 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 20.0.0.0 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 summary BGP router identifier 11.0.3.1, local AS number 65111 Neighbor V AS MsgRcvd MsgSent TblVer InQ OutQ Up/Down State/PfxRcd 1.1.1.2 4 65111 14 13 14 0 0 00:06:21 7 4.1.1.1 4 65444 14 9 14 0 0 00:02:07 7









R2#show ip bgp summary BGP router identifier 12.0.3.1, local AS number 65111 Neighbor V AS MsgRcvd MsgSent TblVer InQ OutQ Up/Down State/PfxRcd 1.1.1.1 4 65111 13 14 14 0 0 00:06:56 7 2.1.1.2 4 65333 11 12 14 0 0 00:04:29 6





R3#show ip bgp summary BGP router identifier 13.0.3.1, local AS number 65333 Neighbor V AS MsgRcvd MsgSent TblVer InQ OutQ Up/Down State/PfxRcd 2.1.1.1 4 65111 13 12 14 0 0 00:05:27 9 3.1.1.2 4 65444 11 14 14 0 0 00:03:59 9







R4#show ip bgp summary BGP router identifier 14.0.3.1, local AS number 65444 Neighbor V AS MsgRcvd MsgSent TblVer InQ OutQ Up/Down State/PfxRcd 3.1.1.1 4 65333 14 12 21 0 0 00:04:25 10 4.1.1.2 4 65111 11 16 21 0 0 00:04:05 9





R4#sh ip bgp BGP table version is 21, local router ID is 14.0.3.1 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 4.1.1.2 0 0 65111 i * 3.1.1.1 0 65333 65111 i * 2.0.0.0 4.1.1.2 0 65111 i *> 3.1.1.1 0 0 65333 i *> 3.0.0.0 0.0.0.0 0 32768 i * 3.1.1.1 0 0 65333 i *> 4.0.0.0 0.0.0.0 0 32768 i * 4.1.1.2 0 0 65111 i * 3.1.1.1 0 65333 65111 i *> 10.0.0.0 4.1.1.2 0 0 65111 i * 3.1.1.1 0 65333 65111 i *> 11.0.0.0/24 4.1.1.2 0 0 65111 i * 3.1.1.1 0 65333 65111 i *> 12.0.0.0/24 4.1.1.2 0 65111 i Network Next Hop Metric LocPrf Weight Path * 3.1.1.1 0 65333 65111 i * 13.0.0.0/24 4.1.1.2 0 65111 65333 i *> 3.1.1.1 0 0 65333 i *> 14.0.0.0/24 0.0.0.0 0 32768 i *> 20.0.0.0 4.1.1.2 0 65111 i * 3.1.1.1 0 65333 65111 i * 30.0.0.0 4.1.1.2 0 65111 65333 i *> 3.1.1.1 0 0 65333 i *> 40.0.0.0 0.0.0.0 0 32768 i









R4#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 3.1.1.1 168 msec 60 msec 24 msec





To reach the 30.1.1.1 router 4 by default using 3.1.1.1 interface because it has less numbers of AS.

but we want to router 4 go via 4.1.1.1 interface to reach all the networks.





R4(config)#router bgp 65444 R4(config-router)#neighbor 4.1.1.2 weight 20000 R4(config-router)#end

R4#clear ip bgp * soft

R4#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 4.1.1.2 8 msec 56 msec 4 msec 2 1.1.1.2 [AS 65111] 52 msec 40 msec 36 msec 3 2.1.1.2 [AS 65111] 52 msec 40 msec 64 msec



R4#show ip bgp 30.1.1.1 BGP routing table entry for 30.0.0.0/8, version 22 Paths: (2 available, best #1, table default) Advertised to update-groups: 1 Refresh Epoch 2 65111 65333 4.1.1.2 from 4.1.1.2 (11.0.3.1) Origin IGP, localpref 100, weight 20000 , valid, external, best rx pathid: 0, tx pathid: 0x0 Refresh Epoch 3 65333 3.1.1.1 from 3.1.1.1 (13.0.3.1) Origin IGP, metric 0, localpref 100, valid, external rx pathid: 0, tx pathid: 0

R4#show ip bgp R4#show ip bgp BGP table version is 29, local router ID is 14.0.3.1 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 4.1.1.2 0 20000 65111 i * 3.1.1.1 0 65333 65111 i *> 2.0.0.0 4.1.1.2 20000 65111 i * 3.1.1.1 0 0 65333 i *> 3.0.0.0 0.0.0.0 0 32768 i * 3.1.1.1 0 0 65333 i *> 4.0.0.0 0.0.0.0 0 32768 i * 4.1.1.2 0 20000 65111 i * 3.1.1.1 0 65333 65111 i *> 10.0.0.0 4.1.1.2 0 20000 65111 i * 3.1.1.1 0 65333 65111 i *> 11.0.0.0/24 4.1.1.2 0 20000 65111 i * 3.1.1.1 0 65333 65111 i *> 12.0.0.0/24 4.1.1.2 20000 65111 i Network Next Hop Metric LocPrf Weight Path * 3.1.1.1 0 65333 65111 i *> 13.0.0.0/24 4.1.1.2 20000 65111 65333 i * 3.1.1.1 0 0 65333 i *> 14.0.0.0/24 0.0.0.0 0 32768 i *> 20.0.0.0 4.1.1.2 20000 65111 i * 3.1.1.1 0 65333 65111 i *> 30.0.0.0 4.1.1.2 20000 65111 65333 i * 3.1.1.1 0 0 65333 i *> 40.0.0.0 0.0.0.0 0 32768 i











Weight is cisco proprietary attribute, weight tells how to exit the autonomous system. Path with the highest weight is more desirable range is 0 through 65,535, by default 0 for learned routes, 32,768 for locally injected routes. weight is partial attribute, set on inbound route update.lets see the configuration:-Topology:-GOAL: