EIGRP非等成本的负载均衡

              ——验证新版本IOS的“四舍五入”改进

一、实验拓扑图：

二、实验目的：
       为了验证EIGRP在Cisco较新版本的IOS中，将链路开销的比值四舍五入的进行负载均衡传输，我们将链路的开销修改为1:1.65（其他也可以）。在R2的两个接口上采用访问控制链表的方式进行抓包验证，也可以通过在R1路由器上通过show ip route 2.2.2.2查看发包的顺序。
       实验还要验证一个细节：Cisco的不同版本的IOS对EIGRP关于非等开销的负载均衡处理方式是不同的。
三、具体配置：

R1

R2

! no ip cef ! interface Loopback0 ip address 1.1.1.1 255.255.255.0 ! interface FastEthernet0/0 ip address 20.0.0.1 255.255.255.0 delay 14262 duplex half ! interface Serial1/0 ip address 10.0.0.1 255.255.255.0 no ip route-cache serial restart-delay 0 …… ! router eigrp 10 variance 3 network 1.1.1.1 0.0.0.0 network 10.0.0.0 0.0.0.255 no auto-summary

! interface Loopback0 ip address 2.2.2.2 255.255.255.0 ! interface FastEthernet0/0 ip address 20.0.0.2 255.255.255.0 ip access-group 20 in delay 142620 duplex half ! interface Serial1/1 ip address 10.0.0.2 255.255.255.0 ip access-group 10 in serial restart-delay 0 ! router eigrp 10 variance 3 network 2.2.2.2 0.0.0.0 network 10.0.0.0 0.0.0.255 network 20.0.0.0 0.0.0.255 network 30.0.0.0 0.0.0.255 no auto-summary

       注意：在R1中红字标识的配置尤为重要，本人就是因为没有想起来这点，直接导致整整搞了将近5个小时的这个“可恶”的负载均衡，闲话不说，no ip cef
这个命令的作用是关闭路由器的快速转发功能，禁用CEF快速转发，也就是说，这个CEF中保存着和路由表一样的信息，当有包要发的时候路由器首先查询CEF缓存，如果有同样的条目，则根据转发记录直接转发，而并不通过路由器的路由表，所以也就代表着，如果不关闭这个CEF，包永远从一个端口转发，而达不到负载均衡的效果。切记。。。。。。

四、实验现象：
1．IOS版本7200 12.3 或者 12.2(T)

R1#sh ip rou Codes: C - connected, S - static, I - IGRP, R - RIP, M - mobile, B - BG 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, E - EGP i - IS-IS, 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 1.0.0.0/8 is variably subnetted, 2 subnets, 2 masks D 1.0.0.0/8 is a summary, 00:24:09, Null0 C 1.1.1.0/24 is directly connected, Loopback0 D 2.0.0.0/8 [90/2297856] via 10.0.0.2, 00:21:54, Serial1/0 [90/3810560] via 20.0.0.2, 00:21:54, Ethernet0/0 20.0.0.0/8 is variably subnetted, 2 subnets, 2 masks D 20.0.0.0/8 is a summary, 00:22:04, Null0 C 20.0.0.0/24 is directly connected, Ethernet0/0 10.0.0.0/8 is variably subnetted, 2 subnets, 2 masks D 10.0.0.0/8 is a summary, 00:21:54, Null0 C 10.0.0.0/24 is directly connected, Serial1/0

R1# sh ip ei to IP-EIGRP Topology Table for AS(10)/ID(1.1.1.1) Codes: P - Passive, A - Active, U - Update, Q - Query, R - Reply, r - reply Status, s - sia Status P 1.0.0.0/8, 1 successors, FD is 128256 via Summary (128256/0), Null0 P 1.1.1.0/24, 1 successors, FD is 128256 via Connected, Loopback0 P 2.0.0.0/8, 1 successors, FD is 409600 via 10.0.0.2 (2297856/128256), Serial1/0 via 20.0.0.2 (3810560/128256), Ethernet0/0 P 10.0.0.0/8, 1 successors, FD is 2169856 via Summary (2169856/0), Null0 P 10.0.0.0/24, 1 successors, FD is 2169856 via Connected, Serial1/0 P 20.0.0.0/8, 1 successors, FD is 2870016 via Summary (3682560/0), Null0 via 10.0.0.2 (2195456/281600), Serial1/0 P 20.0.0.0/24, 1 successors, FD is 3682560 via Connected, Ethernet0/0

R1#sh ip rou 2.2.2.2 Routing entry for 2.0.0.0/8 Known via "eigrp 10", distance 90, metric 2297856, type internal Redistributing via eigrp 10 Last update from 20.0.0.2 on Ethernet0/0, 00:22:29 ago Routing Descriptor Blocks: 10.0.0.2, from 10.0.0.2, 00:22:29 ago, via Serial1/0 Route metric is 2297856, traffic share count is 2 Total delay is 25000 microseconds, minimum bandwidth is 1544 Kbit Reliability 255/255, minimum MTU 1500 bytes Loading 1/255, Hops 1 * 20.0.0.2, from 20.0.0.2, 00:22:29 ago, via Ethernet0/0 Route metric is 3810560, traffic share count is 1 Total delay is 6000 microseconds, minimum bandwidth is 700 Kbit Reliability 255/255, minimum MTU 1500 bytes Loading 1/255, Hops 1

可以看到，同样的配置，到了这个版本的IOS下面就会被四舍五入为1:2


这次用IOS版本为12.4

R1#sh ip ei 10 to IP-EIGRP Topology Table for AS(10)/ID(1.1.1.1) Codes: P - Passive, A - Active, U - Update, Q - Query, R - Reply, r - reply Status, s - sia Status P 1.0.0.0/8, 1 successors, FD is 128256 via Summary (128256/0), Null0 P 1.1.1.0/24, 1 successors, FD is 128256 via Connected, Loopback0 P 2.0.0.0/8, 1 successors, FD is 156160 via 10.0.0.2 (2297856/128256), Serial1/0 via 20.0.0.2 (3787520/128256), FastEthernet0/0 P 10.0.0.0/8, 1 successors, FD is 2169856 via Summary (2169856/0), Null0 P 10.0.0.0/24, 1 successors, FD is 2169856 via Connected, Serial1/0 P 20.0.0.0/8, 1 successors, FD is 3557888 via Summary (3659520/0), Null0 via 10.0.0.2 (2172416/28160), Serial1/0 P 20.0.0.0/24, 1 successors, FD is 3659520 via Connected, FastEthernet0/0

R1#sh ip rou 2.2.2.2 Routing entry for 2.0.0.0/8 Known via "eigrp 10", distance 90, metric 2297856, type internal Redistributing via eigrp 10 Last update from 20.0.0.2 on FastEthernet0/0, 00:00:34 ago Routing Descriptor Blocks: * 20.0.0.2, from 20.0.0.2, 00:00:34 ago, via FastEthernet0/0 Route metric is 3787520, traffic share count is 73 Total delay is 5100 microseconds, minimum bandwidth is 700 Kbit Reliability 255/255, minimum MTU 1500 bytes Loading 1/255, Hops 1 10.0.0.2, from 10.0.0.2, 00:00:34 ago, via Serial1/0 Route metric is 2297856, traffic share count is 120 Total delay is 25000 microseconds, minimum bandwidth is 1544 Kbit Reliability 255/255, minimum MTU 1500 bytes Loading 1/255, Hops 1

！！注意：在12.4版本中这个比值不再四舍五入，但是否会无限制的扩大，我们可以设想，如果可以无限制的扩大，达到999：1000甚至更大，那么转发的方式是极不合理的，两条链路都会拥塞，我们改动一下Fa0/0口的带宽Bandwidth 为720（之前为700）。

R1#sh ip rou 2.2.2.2 Routing entry for 2.0.0.0/8 Known via "eigrp 10", distance 90, metric 2297856, type internal Redistributing via eigrp 10 Last update from 20.0.0.2 on FastEthernet0/0, 00:00:01 ago Routing Descriptor Blocks: * 20.0.0.2, from 20.0.0.2, 00:00:01 ago, via FastEthernet0/0 Route metric is 3685888, traffic share count is 5 Total delay is 5100 microseconds, minimum bandwidth is 720 Kbit Reliability 255/255, minimum MTU 1500 bytes Loading 1/255, Hops 1 10.0.0.2, from 10.0.0.2, 00:00:01 ago, via Serial1/0 Route metric is 2297856, traffic share count is 8 Total delay is 25000 microseconds, minimum bandwidth is 1544 Kbit Reliability 255/255, minimum MTU 1500 bytes Loading 1/255, Hops 1

可以很明显的看到，路由器对开销的比例做了处理，比12.2的版本更合理，将比值在更合理的范围内变得更加精细，是负载均衡更高效。。

路过就顶一下,看楼主那么努力在提供资料

挺好的哦，学习这样的教程也很实用的呢？呵呵谢谢了

汗，这个得好好的学习下，没怎么看懂呢，不知道该怎么办捏？？？