RIPversion1路由信息的通告与接收原则
如上图,配置如下
R1
en
conf t
host R1
int f0/0
ip add 172.16.2.1 255.255.255.0
no sh
int lo 1
ip add 172.16.1.1 255.255.255.0
int lo 2
ip add 172.16.10.1 255.255.255.128
int lo 3
ip add 140.1.1.1 255.255.255.0
exit
router rip
net 172.16.0.0
net 140.1.0.0
exit
end
R2
en
conf t
host R2
int f0/0
ip add 172.16.2.2 255.255.255.0
no sh
int lo 1
ip add 140.1.2.1 255.255.255.0
int lo 2
ip add 172.16.3.1 255.255.255.0
exit
router rip
net 140.1.0.0
net 172.16.0.0
end
debug ip rip
R1#sh ip route
Codes: C - connected, S - static, I - IGRP, 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, E - EGP
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
140.1.0.0/24 is subnetted, 1 subnets
C 140.1.1.0 is directly connected, Loopback3
172.16.0.0/16 is variably subnetted, 5 subnets, 3 masks
C 172.16.10.0/25 is directly connected, Loopback2
C 172.16.4.1/32 is directly connected, Loopback4
C 172.16.1.0/24 is directly connected, Loopback1
C 172.16.2.0/24 is directly connected, FastEthernet0/0
R 172.16.3.0/24 [120/1] via 172.16.2.2, 00:00:28, FastEthernet0/0
R1#
00:28:58: RIP: sending v1 update to 255.255.255.255 via FastEthernet0/0 (172.16.2.1)
00:28:58: RIP: build update entries
00:28:58: network 140.1.0.0 metric 1
00:28:58: subnet 172.16.1.0 metric 1
00:28:58: subnet 172.16.4.1 metric 1
00:28:58: RIP: sending v1 update to 255.255.255.255 via Loopback1 (172.16.1.1)
00:28:58: RIP: build update entries
00:28:58: network 140.1.0.0 metric 1
00:28:58: subnet 172.16.2.0 metric 1
00:28:58: subnet 172.16.3.0 metric 2
00:28:58: subnet 172.16.4.1 metric 1
00:28:58: RIP: sending v1 update to 255.255.255.255 via Loopback2 (172.16.10.1)
00:28:58: RIP: build update entries
00:28:58: network 140.1.0.0 metric 1
00:28:58: subnet 172.16.4.1 metric 1
00:28:58: RIP: sending v1 update to 255.255.255.255 via Loopback3 (140.1.1.1)
00:28:58: RIP: build update entries
00:28:58: network 172.16.0.0 metric 1
00:28:58: RIP: sending v1 update to 255.255.255.255 via Loopback4 (172.16.4.1)
00:28:58: RIP: build update entries
00:28:58: network 140.1.0.0 metric 1
R2>en
R2#sh ip route
Codes: C - connected, S - static, I - IGRP, 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, E - EGP
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
140.1.0.0/24 is subnetted, 1 subnets
C 140.1.2.0 is directly connected, Loopback1
172.16.0.0/16 is variably subnetted, 4 subnets, 2 masks
R 172.16.4.1/32 [120/1] via 172.16.2.1, 00:00:25, FastEthernet0/0
R 172.16.1.0/24 [120/1] via 172.16.2.1, 00:00:25, FastEthernet0/0
C 172.16.2.0/24 is directly connected, FastEthernet0/0
C 172.16.3.0/24 is directly connected, Loopback2
R2#
00:28:55: RIP: received v1 update from 172.16.2.1 on FastEthernet0/0
00:28:55: 140.1.0.0 in 1 hops
00:28:55: 172.16.1.0 in 1 hops
00:28:55: 172.16.4.1 in 1 hops
00:29:00: RIP: sending v1 update to 255.255.255.255 via FastEthernet0/0 (172.16.2.2)
00:29:00: RIP: build update entries
00:29:00: network 140.1.0.0 metric 1
00:29:00: subnet 172.16.3.0 metric 1
00:29:00: RIP: sending v1 update to 255.255.255.255 via Loopback1 (140.1.2.1)
00:29:00: RIP: build update entries
00:29:00: network 172.16.0.0 metric 1
00:29:00: RIP: sending v1 update to 255.255.255.255 via Loopback2 (172.16.3.1)
00:29:00: RIP: build update entries
00:29:00: network 140.1.0.0 metric 1
00:29:00: subnet 172.16.1.0 metric 2
00:29:00: subnet 172.16.2.0 metric 1
00:29:00: subnet 172.16.4.1 metric 2
有类路由协议发送原则:
1.比较需要通告的网络或子网地址和发送接口的网络或子网是否属于同一主网络
2.如果属于同一主网络,比较子网掩码是否一致,如果子网掩码一致则正确通告该网络或者子网;如果不一致,则忽略(除非该信息是一个主机路由)
3.如果不属于同一主网络,自动汇总成有类网络地址后发送
有类路由协议接收原则:
1.比较接收的网络或子网地址和接收接口的网络或者子网是否属于同一主网络
2.如果属于同一主网络,则接收该信息并赋予一个接口的子网掩码
3.如果不属于同一主网络,首先查看自己的路由表中是否存在任意一条子网路由属于该主网络,如果没有,接收该信息并赋予一个有类的掩码;如果有,则忽略该信息
R1的路由通告:
R1通告的主网络有二个140.1.0.0(140.1.1.0/24)和172.16.0.0(172.16.1.0/24,172.16.2.0/24,172.16.10.0/25,172.16.4.1/32),共五个子网.而通过f0/0发送给R2。所以发送接口的IP地址为172.16.2.0,掩码是24位,四个需要通告的子网是140.1.1.0/24、172.16.1.0/24、172.16.10.0/25、172.16.4.1/32。根据有类路由协议发送原则,每一条需要通告的网络或子网都要和发送接口的网络或子网进行比较。
1)140.1.1.0/24和发送接口IP地址172.16.2.1/24比较。二者不属于同一主网络,所以该路由在接口上汇总为140.1.0.0的有类地址后,发送。
2)172.16.1.0/24和发送接口IP地址172.16.2.1/24比较。二者属于同一主网络,然后需要比较子网掩码是否一致,掩码一致,所以该子网也正确通告。
3)172.16.4.1/32和发送接口IP地址172.16.2.1/24比较。二者属于同一主网络,然后需要比较子网掩码是否一致,这里掩码不一致,但该路由是一主机路由,所以该路由也正确通告。
4)172.16.10.0/24和发送接口IP地址172.16.2.1/24比较。二者属于同一主网络,然后需要比较子网掩码是否一致,但掩码不一致,所以该子网路由不能被正确通告。
5)/172.16.2.1/24是和R2直连路由,不需要通告。
综上所述:共有三条路由信息被通告。见R1的debug ip rip信息。
R2的路由信息接收:
由于R1在F0/0口共通告了三条子网路由信息,所以R2也在接口f0/0口接收到三条子网路由信息(见R2debug ip rip 绿色部分信息)。根据有类路由接收原则,接收到的子网信息要和接收端口进行比较。
1)140.1.0.0和接收接口比较,不属于同一主网络。根据接收原则,R2查找自己的路由表,看是否存在一条子网路由属于该主网络。由于路由表中存在
C 140.1.2.0 is directly connected, Loopback1
这一子网路由,所以140.1.0.0/24被忽略,不写入路由表。
2) 172.16.1.0和接收接口比较,由于属于同一主网络。根据接收原则,赋于172.16.1.0一个接口的24位掩码。将该路由信息写入路由表。
3) 172.16.4.1和接收接口比较,由于属于同一主网络。但由于该路由是一主机路由,将不被赋于接口的掩码。直接将该路由信息加上32位掩码写入路由表。