no ip classless 在查找路由时仅查找主类及其子网的匹配路由,如主类存在但子网不匹配,则路由器认为路由不存在,也不会再使用默认路由.如主类不存在,则路由器还会使用默认路由. 而ip classless 在查找路由时直接查找路由标中的匹配路由,如匹配路由不存在,则路由器会使用默认路由.
路由器A配置如下:
interface Loopback0
ip address 10.1.1.1 255.255.255.0
!
interface Loopback1
ip address 10.2.1.1 255.255.255.0
!
interface f0/0
ip address 12.1.1.1 255.255.255.0
!
ip route 0.0.0.0 0.0.0.0 12.1.1.2
!
show ip route显示路由器A的路由如下:
Gateway of last resort is 12.1.1.2 to network 0.0.0.0
10.0.0.0/24 is subnetted, 2 subnets
C 10.2.1.0 is directly connected, Loopback1
C 10.1.1.0 is directly connected, Loopback0
12.0.0.0/24 is subnetted, 1 subnets
C 12.1.1.0 is directly connected, FastEthernet0/0
S* 0.0.0.0/0 [1/0] via 12.1.1.2
路由器B配置如下:
interface Loopback0
ip address 10.3.1.1 255.255.255.0
!
interface Loopback1
ip address 11.1.1.1 255.255.255.0
!
interface f0/0
ip address 12.1.1.2 255.255.255.0
测试一：
在路由器A上配置no ip classless,
ping 10.3.1.1结果如下:
Type escape sequence to abort.
Sending 5, 100-byte ICMP Echos to 10.3.1.1, timeout is 2
seconds:
.....
Success rate is 0 percent (0/5)
解释:主类(10.0.0.0)存在,但子网(10.3.0.0)不匹配,则路由器认为路不存在,也不会再使用默认路由.
测试二：
在路由器A上配置no ip classless,
ping 11.1.1.1结果如下:
Type escape sequence to abort.
Sending 5, 100-byte ICMP Echos to 11.1.1.1, timeout is 2 seconds:
!!!!!
Success rate is 100 percent (5/5), round-trip min/avg/max = 16/16/16 ms
解释:如主类(11.0.0.0)不存在,则路由器还会使用默认路由.
测试三：
在路由器A配置ip classless
ping 10.3.1.1结果如下:
Type escape sequence to abort.
Sending 5, 100-byte ICMP Echos to 10.3.1.1, timeout is 2 seconds:
!!!!!
Success rate is 100 percent (5/5), round-trip min/avg/max = 16/16/16 ms
ping 11.1.1.1结果如下:
Type escape sequence to abort.
Sending 5, 100-byte ICMP Echos to 11.1.1.1, timeout is 2 seconds:
!!!!!
Success rate is 100 percent (5/5), round-trip min/avg/max = 12/12/16 ms
解释:可以看到不论所查询路由的主类是否存在,路由器均使用了默认路由
