Lab Select Path 9-10
Platform:cisco iou
实验目的：理解BGP第九，第十选路原则。
9、如果配置了“maximum-path N”。而且从同一个AS的对等体收到多条外部路由，侧可以将N条路由加入到路由表中，使EBGP负载分担。
10、EBGP路径优先于最老的路由。
先看看第十条原则：
Step 1、配置各台路由器的IP地址，并且使用Ping命令确认各路由器的直连口的互通性。
Step 2、R2，R3，R4上运行ISIS，以及在其之间运行IBGP；R1和R2，R1和R3之间运行EBGP。
R1--------------------------------------------------------
router bgp 1
no synchronization
bgp router-id 1.1.1.1
bgp log-neighbor-changes
network 1.1.1.1 mask 255.255.255.255
neighbor 12.1.1.2 remote-as 234
neighbor 13.1.1.3 remote-as 234
no auto-summary
--------------------------------------------------------
R2--------------------------------------------------------
router isis
net 49.0001.2222.2222.2222.00
!
router bgp 234
no synchronization
bgp router-id 2.2.2.2
bgp log-neighbor-changes
neighbor 3.3.3.3 remote-as 234
neighbor 3.3.3.3 update-source Loopback0
neighbor 3.3.3.3 next-hop-self
neighbor 4.4.4.4 remote-as 234
neighbor 4.4.4.4 update-source Loopback0
neighbor 4.4.4.4 next-hop-self
neighbor 12.1.1.1 remote-as 1
no auto-summary
interface Loopback0
ip address 2.2.2.2 255.255.255.255
ip router isis
interface Serial0/1
ip address 24.1.1.2 255.255.255.0
ip router isis
-------------------------------------------------------------
R3------------------------------------------------------------
router isis
net 49.0001.3333.3333.3333.00
!
router bgp 234
no synchronization
bgp router-id 3.3.3.3
bgp log-neighbor-changes
neighbor 2.2.2.2 remote-as 234
neighbor 2.2.2.2 update-source Loopback0
neighbor 2.2.2.2 next-hop-self
neighbor 4.4.4.4 remote-as 234
neighbor 4.4.4.4 update-source Loopback0
neighbor 4.4.4.4 next-hop-self
neighbor 13.1.1.1 remote-as 1
no auto-summary
interface Loopback0
ip address 3.3.3.3 255.255.255.255
ip router isis
interface Serial0/1
ip address 34.1.1.3 255.255.255.0
ip router isis
----------------------------------------------------------------
R4---------------------------------------------------------------
router isis
net 49.0001.4444.4444.4444.00
!
router bgp 234
no synchronization
bgp router-id 4.4.4.4
bgp log-neighbor-changes
network 4.4.4.4 mask 255.255.255.255
neighbor 2.2.2.2 remote-as 234
neighbor 2.2.2.2 update-source Loopback0
neighbor 2.2.2.2 next-hop-self
neighbor 3.3.3.3 remote-as 234
neighbor 3.3.3.3 update-source Loopback0
neighbor 3.3.3.3 next-hop-self
no auto-summary
interface Loopback0
ip address 4.4.4.4 255.255.255.255
ip router isis
!
interface Serial0/0
ip address 34.1.1.4 255.255.255.0
ip router isis
interface Serial0/1
ip address 24.1.1.4 255.255.255.0
ip router isis
------------------------------------------------------------------
Step 3、在R1上sh ip bgp 观察去R4的路由。
R1#sh ip bgp
BGP table version is 3, 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
Origin codes: i - IGP, e - EGP, ? - incomplete
Network Next Hop Metric LocPrf Weight Path
*> 1.1.1.1/32 0.0.0.0 0 32768 i
* 4.4.4.4/32 13.1.1.3 0 234 i
*> 12.1.1.2 0 234 i
R1#sh ip bgp su
BGP router identifier 1.1.1.1, local AS number 1
BGP table version is 3, main routing table version 3
2 network entries using 202 bytes of memory
3 path entries using 144 bytes of memory
2 BGP path attribute entries using 120 bytes of memory
1 BGP AS-PATH entries using 24 bytes of memory
0 BGP route-map cache entries using 0 bytes of memory
0 BGP filter-list cache entries using 0 bytes of memory
BGP using 490 total bytes of memory
BGP activity 2/0 prefixes, 3/0 paths, scan interval 60 secs
Neighbor V AS MsgRcvd MsgSent TblVer InQ OutQ Up/Down State/PfxRcd
12.1.1.2 4 234 8 8 3 0 0 00:03:38 1
13.1.1.3 4 234 6 7 3 0 0 00:01:28 1
R1(config-router)#maximum-paths 2
R1#sh ip route
Codes: 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
Gateway of last resort is not set
1.0.0.0/32 is subnetted, 1 subnets
C 1.1.1.1 is directly connected, Loopback0
4.0.0.0/32 is subnetted, 1 subnets
B 4.4.4.4 [20/0] via 13.1.1.3, 00:00:10
[20/0] via 12.1.1.2, 00:00:10
12.0.0.0/24 is subnetted, 1 subnets
C 12.1.1.0 is directly connected, Serial0/0
13.0.0.0/24 is subnetted, 1 subnets
C 13.1.1.0 is directly connected, Serial0/1