修改默认路由

wangxiaoguang

当主机受到ICMP重定向差错数据报文时会修改路由表中的默认路由还是保持默认路由不变再增加一个路由表项？

hjp0021

应该是默认路由不变化，再增加一条往目的地的最优化路由。

hjp0021

具体请看CISCO的解释。
ICMP redirect messages are used by routers to notify the hosts on the data link that a better route is available for a particular destination.

For example, the two routers R1 and R2 are connected to the same Ethernet segment as Host H. The default gateway for Host H is configured to use router R1. Host H sends a packet to router R1 to reach the destination on Remote Branch office Host 10.1.1.1. Router R1, after it consults its routing table, finds that the next-hop to reach Host 10.1.1.1 is router R2. Now router R1 must forward the packet out the same Ethernet interface on which it was received. Router R1 forwards the packet to router R2 and also sends an ICMP redirect message to Host H. This informs the host that the best route to reach Host 10.1.1.1 is by way of router R2. Host H then forwards all the subsequent packets destined for Host 10.1.1.1 to router R2.

1. This debug message shows router R1, as in the network diagram, sending an ICMP redirect message to Host H (172.16.1.1).
   
2. 
   
3. R1#
   
4. debug ip icmp
   
5. 
   
6. 
   
7. ICMP packet debugging is on
   
8. 
   
9. *Mar 18 06:28:54: ICMP:redirect sent to 172.16.1.1 for dest 10.1.1.1, use gw 172.16.1.200
   
10. 
    
11. R1#
    
12. Router R1 (172.16.1.100) sends a redirect to Host H (172.16.1.1) to use router R2 (172.16.1.200) as the gateway to reach the destination 10.1.1.1.

复制代码

ssffzz1

不会修改默认路由，并且添加的是主机路由。