Here’s another BGP attributes which I’m going to explore. It’s called Local Preference which has the following characteristics:
1. Second BGP attributes
2. Local Preference is used to choose the outbound external BGP paths.
3. Local Preference can be sent in BGP updates among the BGP routers within an AS.
4. It has a default value of 100.
5. Local Preference is considered as Well-Known Descretionary BGP attributes which means that
this attribute must be recognized by all BGP routers but it’s an optional on BGP updates.
6. The BGP path with the HIGHEST Local preference is the preferred path.
Below is my topology for my lab…
Here is my complete working configurations for both the EBGP and IBGP:
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R1#sh run | sec bgp
ipv6 multicast rpf use-bgp router bgp 65001 bgp log-neighbor-changes network 1.1.1.0 mask 255.255.255.0 neighbor 172.16.12.2 remote-as 65002 neighbor 172.16.13.3 remote-as 65002 |
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R2#sh run | sec ospf
router ospf 1 network 2.2.2.2 0.0.0.0 area 0 network 172.16.24.0 0.0.0.255 area 0 R2#sh run | sec bgp
ipv6 multicast rpf use-bgp router bgp 65002 bgp log-neighbor-changes network 172.16.24.0 mask 255.255.255.0 neighbor 3.3.3.3 remote-as 65002 neighbor 3.3.3.3 update-source Loopback2 neighbor 4.4.4.4 remote-as 65002 neighbor 4.4.4.4 update-source Loopback2 neighbor 4.4.4.4 next-hop-self neighbor 172.16.12.1 remote-as 65001 |
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R3#sh run | sec ospf
router ospf 1 network 3.3.3.3 0.0.0.0 area 0 network 172.16.34.0 0.0.0.255 area 0 R3#sh run | sec bgp
ipv6 multicast rpf use-bgp router bgp 65002 bgp log-neighbor-changes neighbor 2.2.2.2 remote-as 65002 neighbor 2.2.2.2 update-source Loopback3 neighbor 4.4.4.4 remote-as 65002 neighbor 4.4.4.4 update-source Loopback3 neighbor 4.4.4.4 next-hop-self neighbor 172.16.13.1 remote-as 65001 R3# |
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R4#sh run | sec ospf
router ospf 1 network 4.4.4.4 0.0.0.0 area 0 network 172.16.24.0 0.0.0.255 area 0 network 172.16.34.0 0.0.0.255 area 0 R4#sh run | sec bgp
ipv6 multicast rpf use-bgp router bgp 65002 bgp log-neighbor-changes network 10.10.10.0 mask 255.255.255.0 neighbor 2.2.2.2 remote-as 65002 neighbor 2.2.2.2 update-source Loopback4 neighbor 3.3.3.3 remote-as 65002 neighbor 3.3.3.3 update-source Loopback4 |
Below are the BGP Database:
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R1#show ip bgp
BGP table version is 4, local router ID is 1.1.1.1 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 R2#show ip bgp
BGP table version is 8, local router ID is 2.2.2.2 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 R3#show ip bgp
BGP table version is 12, 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, 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 R4#show ip bgp
BGP table version is 4, local router ID is 10.10.10.10 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 You can see above on R4 BGP database that the Local Preference value is 100 (Default)…Why R2 was chosen because all other Attributes are the same and the last BGP attribute ( Router ID) determines the path…The Lowest the Router ID the better path..
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Here’s my traceroutes and ping to 1.1.1.1/24…
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R4#traceroute 1.1.1.1
Type escape sequence to abort. Tracing the route to 1.1.1.1 VRF info: (vrf in name/id, vrf out name/id) 1 172.16.24.2 56 msec 52 msec 56 msec 2 172.16.12.1 56 msec 52 msec 88 msec R4#ping 1.1.1.1 source 172.16.24.4
Type escape sequence to abort. Sending 5, 100-byte ICMP Echos to 1.1.1.1, timeout is 2 seconds: Packet sent with a source address of 172.16.24.4 !!!!! Success rate is 100 percent (5/5), round-trip min/avg/max = 72/89/120 ms R4# |
Look at R4…..R4 is taking R2 to reach 1.1.1.1/24…
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R4#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 1.0.0.0/24 is subnetted, 1 subnets |
Now, I want to used LOCAL PREFERENCE to influence R4 how it will reach 1.1.1.1/24…By this time, I want R4 to reach 1.1.1.1/24 via R3…
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We can used the command: bgp default local-preference
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R3(config)#router bgp 65002
R3(config-router)#bgp default ? inter-as-hybrid Configure Inter-AS Hybrid peer defaults ipv4-unicast Activate ipv4-unicast for a peer by default ipv6-nexthop Default IPv6 nexthop format local-preference local preference (higher=more preferred) route-target Control behavior based on Route-Target attributes R3(config-router)#bgp default local R3(config-router)#bgp default local-preference 101 |
Now, let’s check R4 BGP database.. I just increased the Local Pref value by 1….and now I have a path towards 1.1.1.1/24 via R3…
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R4#show ip bgp
BGP table version is 5, local router ID is 10.10.10.10 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 |
****************************END OF LAB*************************
NETWORK LESSON 
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