Re: ip default-network [7:16507]
It's not dynamic. I can't ship that router out with the same config to anyplace in the world. Using a default network, you can. It will come up, peer, get it's routing table, and send it's default stuff towards "home". Let's say for instance that you have a large core network. You want all traffic that isn't in the routing table to not go to Null0, but you want it to flow down to this core and let the core deal with it. You may want this for a number of reasons, most obviously if you default route to the Internet, but also if you are running multiple routing protocols and not redistributing between all of them. You can then set a loopback on all the core routers on say '192.168.200.0' network. Then on all your routers you deply, you set the ip default-network to 192.168.200.0. Now no matter where you drop that router, if it's got a routing table, and that table knows at least one person that can get to 192.168.200.0, then you're set. No more configuration. Let's also say that edge router has an isdn dial backup. If your primary goes down, and the other comes up, when the new routes flow in, it will take the new interface with the new next hop to the core automatically - no route changes. The new routes will just get tagged as default candidates and away it goes. -me Rick Foster wrote: > How is this different from configuring two different default routes for the > same network > e.g. > ip route 10.0.0.0 255.0.0.0 202.33.22.11 > ip route 10.0.0.0 255.0.0.0 203.44.33.22 > ip route 10.0.0.0 255.0.0.0 204.55.44.33 > > Regards ... Message Posted at: http://www.groupstudy.com/form/read.php?f=7&i=16574&t=16507 -- FAQ, list archives, and subscription info: http://www.groupstudy.com/list/cisco.html Report misconduct and Nondisclosure violations to [EMAIL PROTECTED]
Re: ip default-network [7:16507]
How is this different from configuring two different default routes for the same network e.g. ip route 10.0.0.0 255.0.0.0 202.33.22.11 ip route 10.0.0.0 255.0.0.0 203.44.33.22 ip route 10.0.0.0 255.0.0.0 204.55.44.33 Regards ... Message Posted at: http://www.groupstudy.com/form/read.php?f=7&i=16566&t=16507 -- FAQ, list archives, and subscription info: http://www.groupstudy.com/list/cisco.html Report misconduct and Nondisclosure violations to [EMAIL PROTECTED]
Re: ip default-network [7:16507]
Excellent find !! I never heard or seen that explained so succinctly. Good Post, Tony M. #6172 > Rich, > Try this brief lab example I got from the CCO. I think this will clear it > up > for you: > 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 > S198.10.1.0 [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 > C161.44.192.0 is directly connected, Ethernet0 > S161.44.0.0 255.255.0.0 [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 > S171.70.0.0 255.255.0.0 [1/0] via 171.70.24.0 > S171.70.24.0 255.255.255.0 [1/0] via 131.108.99.2 > 131.108.0.0 255.255.255.0 is subnetted, 1 subnets > C131.108.99.0 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 >
Re: ip default-network [7:16507]
Hi Richard, Some good CCO links have already been posted. I just wanted to add a quick point. This command is useful as a tool for providing a semi dynamic default route. For example, if you are connected to two upstream networks which both offer you routes toward a destination, say 10/8 for example, you can use this command to ensure that your routers chose a default route toward the most functional of the two. For example, with normal static routes, the route remains active so long as the immediate connectivity toward the next hop is alive and well. Hence, should the next hop router have a failure on one of its' upstream links, or should any other upstream routers beyond it fail, you routers will still consider the route active and thus send traffic toward a likely black hole. By using ip default network pointed towards 10/8, which you know is an upstream network, you can protect yourself against any failures that deter you from reaching that network since those failures will cause the faulty network to cease advertising 10/8 to you. In my example, if the active next-hop for 10/8 becomes unable to deliver traffic there, your routers will dynamic change default toward your alternate path. Hope that helps some :) Pete *** REPLY SEPARATOR *** On 8/19/2001 at 5:36 PM richard dumoulin wrote: >Would anybody be so kind to explain me how the hell is this command >working? >The more I read about it the more I get confused. > >Regards. Message Posted at: http://www.groupstudy.com/form/read.php?f=7&i=16509&t=16507 -- FAQ, list archives, and subscription info: http://www.groupstudy.com/list/cisco.html Report misconduct and Nondisclosure violations to [EMAIL PROTECTED]
Re: ip default-network [7:16507]
In a message dated 8/19/01 4:37:05 PM Central Daylight Time, [EMAIL PROTECTED] writes: << Subj: ip default-network [7:16507] Date: 8/19/01 4:37:05 PM Central Daylight Time From: [EMAIL PROTECTED] (richard dumoulin) Sender:[EMAIL PROTECTED] Reply-to: [EMAIL PROTECTED] (richard dumoulin) To:[EMAIL PROTECTED] Rich, Try this brief lab example I got from the CCO. I think this will clear it up for you: 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 S198.10.1.0 [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 C161.44.192.0 is directly connected, Ethernet0 S161.44.0.0 255.255.0.0 [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 S171.70.0.0 255.255.0.0 [1/0] via 171.70.24.0 S171.70.24.0 255.255.255.0 [1/0] via 131.108.99.2 131.108.0.0 255.255.255.0 is subnetted, 1 subnets C131.108.99.0 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
