OSPF協(xié)議中cost值的計算

1、ospf協(xié)議中cost值的計算在ospf協(xié)議屮每個接口根據(jù)其速率不同，都有一個默認的公式計算的cost 值，ospf協(xié)議采用cost值來決定到達tl的地的最佳路徑，如果存在多條到達h 的地的路徑，優(yōu)先選用cost值最低的路徑。cost值的計算是沿fl的地途中所有 轉(zhuǎn)發(fā)數(shù)據(jù)的接口的cost值的總和，下血通過實驗來驗證一下。如下拓撲圖：1729.1 oj/24vlanl:172.19.10.254/24pcipc2192.168.2.0/2419268.1.0.24在rt11上的路由表如下:rt1l#sh ip routecodes: c - connected, s - static, r -

2、rip, m - mobile, b - bgpd - etgrp, ex - etgrp external, 0 - ospf, ta - ospf inter arean1 - ospf nssa external type 1, n2 - ospf nssa external type 2el - ospf external type 1, e2 - ospf external type 2i - is-is, su - is-is summary, li - is-is level-1, l2 - is-is level-2ia - is-is inter area, * - cand

3、idate default, u - per-user static routeo 一 odr, p - periodic downloaded static routegateway of last resort is not set172.19.0. 0/24 is subnetted, 1 subnets0172. 19. 10. 0 110/3 via 10. 1. 1. 6, 00:00:12, fastethernet2/010.0.0.0/30 is subnetted, 2 subnets010. 3.3.4 110/2 via 10. 1. 1.6, 00:00:12, fa

4、stethernet2/0c10.1.1.4 is directly connected, fastethernet2/0c192. 168. 1. 0/24 is directly connected, fastethernet0/0c192. 168.2. 0/24 is directly connected, fastetherneto/1在這臺路由器上到達172. 19. 10. 0的度量值為3,計算方式為：rt11的數(shù)據(jù)轉(zhuǎn)發(fā)接口 f2/0的cost值“1” +rt12的數(shù)據(jù)轉(zhuǎn)發(fā)接口 f2/0的 cost 值 “"+sw2 的目標接口 vlanl 的 cost 值 “ 1&q

5、uot;二3。為了證明，將rt12的數(shù)據(jù)流入接口 f0/0的cost值改為50,數(shù)據(jù)轉(zhuǎn)發(fā)接口 f2/0的cost值改為60, sw2的vlanl的cost改為70,再來看看路由表： rtll#sh ip routecodes: c - connected, s - static, r - rip, m - mobi.le, b - bgp d - eigrp, ex - eigrp external, 0 - ospf, ia - ospf inter arean1 - ospf nssa external type 1, n2 - ospf nssa external type 2el -

6、ospf external type 1, e2 - ospf external type 2i - 1s-is, su - 1s-is summary, li - 1s-1s level-1, l2 - 1s-1s level-2ia - is-is inter area, * - candidate default, u - per-user static routeo 一 odr, p 一 periodic downloaded static routegateway of last resort is not set172.19.0. 0/24 is subnetted, 1 subn

7、ets0172. 19. 10.0 110/131 via 10. 1. 1.6, 00:00:00, fastethernet2/010. 0. 0. 0/30 is subnetted, 2 subnets010. 3. 3. 4 110/61 via 10. 1. 1.6, 00:00:00, fastethernet2/0c10. 1. 1. 4 is directly conncctcd, fastethernet2/0c192. 168. 1. 0/24 is directly connected, fastethernet0/0c192. 168.2.0/24 is direct

8、ly connected, fastetherneto/1這時到達172. 19. 10. 0的度量值為131 t,由1+60+70計算得來,rt12上 的數(shù)據(jù)流入接口 f0/0的cost值沒有參與計算。那么再看從sw1上的路由表：sw2#sh ip routecodes: c - connected, s - static, r - rip, m - mobile, b - bgpd - eigrp, ex - eigrp external, 0 - ospf, ia - ospf inter arean1 - ospf nssa external type 1, n2 - ospf nss

9、a external type 2el - ospf external type 1, e2 - ospf external type 2 i - is-is, su - is-is summary, li - is-is level-1, l2 - is-is level-2 ia - ts-is inter area, * 一 candidate default, u 一 per-user staticrouteo - odr, p - periodic downloaded static routegateway of last resort is not set172. 19. 0.

10、0/24 is subnetted, 1 subnetsc172. 19. 10. 0 is directly connected, vlanl10.0.0.0/30 is subnetted, 2 subnetsc10. 3. 3. 4 is directly connected, vian2010.1.1.4 110/51 via 10. 3. 3.5, 00:00:00, vlan20192. 168. 1. 0/24 110/52 via 10. 3. 3.5, 00:00:00, vlan20192. 168.2.0/24 110/52 via 10. 3. 3.5, 00:00:0

11、0, vlan2從這個路曲表上就更加驗證了 ospf協(xié)議中度量值的計算，從swl到192. 16& 1.0的度量值計算為：swl的數(shù)據(jù)轉(zhuǎn)發(fā)接口 vlan2的cost值“1” +rt12的數(shù)據(jù)轉(zhuǎn)發(fā)接口 f0/0的cost 值 “50” +rt11 的目的接口的 cost 值 =52那么針對重發(fā)布的路由的度量值又是如何計算的呢，在rt11上將兩個直連網(wǎng)絡(luò)192. 168. 1. 0和192. 168. 2. 0改為重發(fā)布：配置命令：access-list 10 permit 192.168.1. 0access-list 20 permit 192. 168. 2. 0 route-map

12、 setmetric permit 10match ip address 10set metric 5iroute-map setmetric permit 20match ip address 20set metric 20 router ospf 100log-adjacency-changcsredistribute connected subnets toutemap setmetrie這樣就將192. 168. 1.0的度量值改為t 5, 192. 168. 2.0的度量值改為了 20,在rtl2和sw1上查看路由表:rt12#sh ip routecodes: c - connec

13、ted, s - static, r - rip, m - mobile, b - bgpd - eigrp, ex - eigrp external, 0 - ospf, ia - ospf inter arean1 - ospf nssa external type 1, n2 - ospf nssa external type 2el - ospf external type 1, e2 - ospf external type 2i - is-is, su - is-is summary, li - is-is level-1, l2 - is-is level-2ia 一 ts_ts

14、 inter area, * 一 candidate defauu 一 peruser staticrouteo 一 odr, p - periodic downloaded static routegateway of last resort is not set172. 19.0.0/24 is subnetted, 1 subnets172.19.10.0 110/130 via 10.3.3.6, 00:04:0& fastethernet2/010. 0-0. 0/30 issubnetted, 2 subnets10. 3.3.4 isdirectly cormcctcd,

15、 fastethcrnet2/010. 1. 1.4 isdirectly connected， fastethernet0/0e2192. 168. 1. 0/24110/5 via 10. 1.1.5, 00:04:0& fastetherneto/oe2192. 168.2. 0/24110/20 via 10. 1.1.5,00:04:08, fastetherneto/0sw2#ship routecodes:c 一 connected, s 一 static, r -rip,m - mobile, b - bgpd - e1grp, ex - e1grp external,

16、ospf，1a - ospf inter arean1 - ospf nssa external type 1,n2 - ospf nssa external type 2routeel - ospf external type 1, e2 - ospf externali 一 is-is, su 一 ists summary, li 一 is-is level-1,ici 一 is-is in ter area, * 一 cam di date defau lt，utype 2l2 - is-is level-2一 per-user statico 一 odr, p - periodic downloaded static routegateway of last resort is not set172. 19. 0. 0/24 is subnetted, 1 subnetsc172. 19.10.0 is directly connected, vlanl10.0. 0. 0/30 is subnetted, 2 subnetsc10. 3.3.4 is directly connected, vian2010.1.1.4 110/51 via 10. 3. 3.5, 00:04:32, v