使用distribute list控制路由重分發

 

distribute list可以用來控制路由更新，它需要用到access list。一般情況下，access list並不能控制由路由器自己生成的數據流，但是如果將access list應用到distribute list，則可以用來允許、拒絕路由選擇更新。

下面是本實例用到的拓撲：

 

 

 

 

---

應用distribute list之前的路由器配置及路由表

R1#show run
!         
interface Ethernet1/0
 ip address 10.0.0.1 255.255.255.252
 duplex half
!   
interface Ethernet1/2
 ip address 10.1.0.1 255.255.0.0
 duplex half
!        
interface Ethernet1/3
 ip address 10.2.0.1 255.255.0.0
 duplex half
!        
interface Ethernet1/4
 ip address 10.3.0.1 255.255.0.0
 duplex half
!            
router rip
 version 2
 network 10.0.0.0
! 

 

R2#show run
!        
interface Ethernet1/0
 ip address 10.0.0.2 255.255.255.252
 duplex half
!        
interface Ethernet1/1
 ip address 10.0.0.9 255.255.255.252
 duplex half
!        
router ospf 1
 log-adjacency-changes
 redistribute rip subnets
 network 10.0.0.8 0.0.0.3 area 0
!        
router rip
 version 2
 redistribute ospf 1 metric 5
 network 10.0.0.0

 

R3#show run
!        
interface Ethernet1/0
 ip address 10.0.0.10 255.255.255.252
 duplex half
!        
interface Ethernet1/2
 ip address 10.8.0.1 255.255.0.0
 duplex half
!        
interface Ethernet1/3
 ip address 10.9.0.1 255.255.0.0
 duplex half
!        
interface Ethernet1/4
 ip address 10.10.0.1 255.255.0.0
 duplex half
!        
interface Ethernet1/5
 ip address 10.11.0.1 255.255.0.0
 duplex half
!        
router ospf 1
 log-adjacency-changes
 network 10.0.0.8 0.0.0.3 area 0
 network 10.8.0.0 0.3.255.255 area 0

配置後，我們分別查看三臺路由器的路由表：

R1#show ip route
Gateway of last resort is not set

     10.0.0.0/8 is variably subnetted, 9 subnets, 2 masks
R       10.10.0.0/16 [120/5] via 10.0.0.2, 00:00:20, Ethernet1/0
R       10.11.0.0/16 [120/5] via 10.0.0.2, 00:00:20, Ethernet1/0
R       10.8.0.0/16 [120/5] via 10.0.0.2, 00:00:20, Ethernet1/0
R       10.0.0.8/30 [120/1] via 10.0.0.2, 00:00:20, Ethernet1/0
R       10.9.0.0/16 [120/5] via 10.0.0.2, 00:00:20, Ethernet1/0
C       10.2.0.0/16 is directly connected, Ethernet1/3
C       10.3.0.0/16 is directly connected, Ethernet1/4
C       10.0.0.0/30 is directly connected, Ethernet1/0
C       10.1.0.0/16 is directly connected, Ethernet1/2

可以看到R1收到了5條從OSPF重分發過來的路由。

 

R2#show ip route
Gateway of last resort is not set

     10.0.0.0/8 is variably subnetted, 9 subnets, 2 masks
O       10.10.0.0/16 [110/20] via 10.0.0.10, 02:51:12, Ethernet1/1
O       10.11.0.0/16 [110/20] via 10.0.0.10, 02:51:12, Ethernet1/1
O       10.8.0.0/16 [110/20] via 10.0.0.10, 02:51:12, Ethernet1/1
C       10.0.0.8/30 is directly connected, Ethernet1/1
O       10.9.0.0/16 [110/20] via 10.0.0.10, 02:51:12, Ethernet1/1
R       10.2.0.0/16 [120/1] via 10.0.0.1, 00:00:04, Ethernet1/0
R       10.3.0.0/16 [120/1] via 10.0.0.1, 00:00:04, Ethernet1/0
C       10.0.0.0/30 is directly connected, Ethernet1/0
R       10.1.0.0/16 [120/1] via 10.0.0.1, 00:00:04, Ethernet1/0

R2收到4條OSPF路由和3條RIP路由。

 

R3#show ip route
Gateway of last resort is not set

     10.0.0.0/8 is variably subnetted, 9 subnets, 2 masks
C       10.10.0.0/16 is directly connected, Ethernet1/4
C       10.11.0.0/16 is directly connected, Ethernet1/5
C       10.8.0.0/16 is directly connected, Ethernet1/2
C       10.0.0.8/30 is directly connected, Ethernet1/0
C       10.9.0.0/16 is directly connected, Ethernet1/3
O E2    10.2.0.0/16 [110/20] via 10.0.0.9, 02:52:45, Ethernet1/0
O E2    10.3.0.0/16 [110/20] via 10.0.0.9, 02:52:45, Ethernet1/0
O E2    10.0.0.0/30 [110/20] via 10.0.0.9, 02:52:45, Ethernet1/0
O E2    10.1.0.0/16 [110/20] via 10.0.0.9, 02:52:45, Ethernet1/0

R3收到了4條從RIP重分發過來的路由，顯示爲2類外部路由。

 

---

 

應用distribute list之後的路由器配置及路由表

我們現在希望R2只將OSPF網絡的路由10.8.0.0重分發給RIP網絡，而其他網絡都不重分發；同時我們希望R2不要重分發來自RIP網絡的10.1.0.0給OSPF，而其他網絡則允許。

我們可以在R2上通過配置distribute list來達到這個目的。在配置distribute list之前，我們需要先配置access list：

access-list 1 permit 10.8.0.0
access-list 2 deny   10.1.0.0 0.0.255.255
access-list 2 permit any

然後我們將這兩個access list提供給distribute list使用，給它用作判斷條件。細心的朋友還會發現，我們在配置access list 2的時候使用了通配符，而配置access list 1的時候則沒有使用。實驗發現，如果access list 1配置成：access-list 1 permit 10.8.0.0 0.0.255.255，則distribute list不會對OSPF重分發到RIP的路由起任何過濾作用。

R2(config)#router ospf 1
R2(config-router)#distribute-list 2 out rip

這裏的2是上面配置的access list的號碼，這句話的意思是，將access list 2定義的篩選條件用來生成一個distribute list，後面的rip是指需要重分發到ospf的路由協議，out是指出口方向，注意我們是在ospf進程下配置的，所以這裏是將RIP重分發到OSPF，所以出口方向應該是向OSPF這一邊（也就是圖中向右的方向）。也即符合access list 2的路由更新會被重分發到OSPF，不符合的會丟棄。

R2(config-router)#router rip
R2(config-router)#distribute-list 1 out ospf

這句話的意思是對OSPF重分佈到RIP的路由更新應用access list。

我們再查看一下路由器R1和R3的路由表：

R1#show ip route
Gateway of last resort is not set

     10.0.0.0/8 is variably subnetted, 6 subnets, 2 masks
R       10.8.0.0/16 [120/5] via 10.0.0.2, 00:00:09, Ethernet1/0
R       10.0.0.8/30 [120/1] via 10.0.0.2, 00:00:09, Ethernet1/0
C       10.2.0.0/16 is directly connected, Ethernet1/3
C       10.3.0.0/16 is directly connected, Ethernet1/4
C       10.0.0.0/30 is directly connected, Ethernet1/0
C       10.1.0.0/16 is directly connected, Ethernet1/2

可以看到，除了10.8.0.0以及10.0.0.8之外，R2沒有將OSPF的其他路由重分發給RIP。我們同時看到，作爲直連網絡的10.8.0.0/30並不在限制的範圍之內。

R3#show ip route
Gateway of last resort is not set

     10.0.0.0/8 is variably subnetted, 8 subnets, 2 masks
C       10.10.0.0/16 is directly connected, Ethernet1/4
C       10.11.0.0/16 is directly connected, Ethernet1/5
C       10.8.0.0/16 is directly connected, Ethernet1/2
C       10.0.0.8/30 is directly connected, Ethernet1/0
C       10.9.0.0/16 is directly connected, Ethernet1/3
O E2    10.2.0.0/16 [110/20] via 10.0.0.9, 03:15:47, Ethernet1/0
O E2    10.3.0.0/16 [110/20] via 10.0.0.9, 03:15:47, Ethernet1/0
O E2    10.0.0.0/30 [110/20] via 10.0.0.9, 03:15:47, Ethernet1/0

可以看到這裏比原來少了10.1.0.0這條路由。