Answer: 1。 ip default-gateway用與路由器不作路由時使用，這時路由器就只是一臺主 機好象Win95PC一樣需要配一個網關才能與外界通信。 假如 “no ip routing"則路由器就不作路由。這時你可以配bridge-group，把路 由表及里器當switch使。
2。 ip route 0.0.0.0 0.0.0.0 用于履行路由功能。假如ip routin g是enable的則ip default-gateway不起作用.
FW:區別在于，ip route本機生效，ip default-network可以影響整個路由協議域 http://www.cisco.com/en/US/customer...sHtml#ipnetwork FW:IntrodUCtion This Tech Note eXPlains how to configure a default route, or gateway of last resort, using the following IP commands: ip default-gateway, ip default-network, and ip route 0.0.0.0 0.0.0.0. Let's look at each of these commands in more detail. Before You Begin Conventions For more information on document conventions, see the Cisco Technical Tips Conventions.
PRerequisites There are no specific prerequisites for this document.
Components Used This document is not restricted to specific software and hardware versions.
The information presented in this document was created from devices in a specific lab environment. All of the devices used in this document started with a cleared (default) configuration. If you are working in a live network, ensure that you understand the potential impact of any command before using it.
ip default-gateway The ip default-gateway command differs from the other two commands in that it should only be used when ip routing is disabled on the Cisco router.
For instance, if the router is a host in the IP world, you can use this command to define a default gateway for it. You might also use this command when your low end Cisco router is in boot mode in order to TFTP a Cisco IOS® Software image to the router. In boot mode, the router doesn't have ip routing enabled.
ip default-network Unlike the ip default-gateway command, you can use ip default-network when ip routing is enabled on the Cisco router. When you configure ip default-network the router considers routes to that network for installation as the gateway of last resort on the router.
For every network configured with ip default-network, if a router has a route to that network, that route is flagged as a candidate default route. Let's look at the following routing table taken from a Cisco router:
2513#show 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 E1 - OSPF external type 1, E2 - OSPF external type 2, E - EGP i - IS-IS, L1 - IS-IS level-1, L2 - IS-IS level-2, * - candidate default Gateway of last resort is not set 161.44.0.0 255.255.255.0 is subnetted, 1 subnets C 161.44.192.0 is directly connected, Ethernet0 S 198.10.1.0 [1/0] via 161.44.192.2 131.108.0.0 255.255.255.0 is subnetted, 1 subnets C 131.108.99.0 is directly connected, TokenRing0
Note the static route to 198.10.1.0 via 161.44.192.2 and that the gateway of last resort isn't set. If we configure ip default-network 198.10.1.0, the routing table changes to the following:
2513#show 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 E1 - OSPF external type 1, E2 - OSPF external type 2, E - EGP i - IS-IS, L1 - IS-IS level-1, L2 - IS-IS level-2, * - candidate default
Gateway of last resort is 161.44.192.2 to network 198.10.1.0
161.44.0.0 255.255.255.0 is subnetted, 1 subnets C 161.44.192.0 is directly connected, Ethernet0 S 161.44.0.0 255.255.0.0 [1/0] via 161.44.192.0 S* 198.10.1.0 [1/0] via 161.44.192.2 131.108.0.0 255.255.255.0 is subnetted, 1 subnets C 131.108.99.0 is directly connected, TokenRing0 2513#show ip protocols 2513#
We can see the gateway of last resort has now been set as 161.44.192.2. This result is independent of any routing protocol, as shown by the show ip protocols command at the bottom of the output.
We can add another candidate default route simply by configuring another instance of ip default-network:
2513#config terminal Enter configuration commands, one per line. End with CNTL/Z. 2513(config)#ip route 171.70.24.0 255.255.255.0 131.108.99.2 2513(config)#ip default-network 171.70.24.0 2513(config)#^Z
2513#show 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 E1 - OSPF external type 1, E2 - OSPF external type 2, E - EGP i - IS-IS, L1 - IS-IS level-1, L2 - IS-IS level-2, * - candidate default
Gateway of last resort is 161.44.192.2 to network 198.10.1.0
161.44.0.0 255.255.255.0 is subnetted, 1 subnets C 161.44.192.0 is directly connected, Ethernet0 S 161.44.0.0 255.255.0.0 [1/0] via 161.44.192.0 S* 198.10.1.0 [1/0] via 161.44.192.2 171.70.0.0 is variably subnetted, 2 subnets, 2 masks S 171.70.0.0 255.255.0.0 [1/0] via 171.70.24.0 S 171.70.24.0 255.255.255.0 [1/0] via 131.108.99.2 131.108.0.0 255.255.255.0 is subnetted, 1 subnets C 131.108.99.0 is directly connected, TokenRing0
Flagging a Default Network Note: The ip default-network command is classful, which means if the router has a route to the subnet indicated by this command, it installs the route to the major net. At this point neither network has been flagged as the default network. The ip default-network command must be issued again, using the major net, in order to flag the candidate default route.
2513#config terminal Enter configuration commands, one per line. End with CNTL/Z. 2513(config)#ip default-network 171.70.0.0 2513(config)#^Z
2513#show 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 E1 - OSPF external type 1, E2 - OSPF external type 2, E - EGP i - IS-IS, L1 - IS-IS level-1, L2 - IS-IS level-2, * - candidate default
Gateway of last resort is 161.44.192.2 to network 198.10.1.0
161.44.0.0 255.255.255.0 is subnetted, 1 subnets C 161.44.192.0 is directly connected, Ethernet0 S 161.44.0.0 255.255.0.0 [1/0] via 161.44.192.0 S* 198.10.1.0 [1/0] via 161.44.192.2 171.70.0.0 is variab
