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routing to dsl modem

Unanswered Question
svermill Fri, 10/19/2001 - 10:22
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Do you have both routers on the same shared segment or do you have hosts on the 1602 that need to hit the dlink via some router-to-router interconnection?

And are you running any kind of routing protocols on either of the routers?

svermill Mon, 10/22/2001 - 12:39
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OK. So you have other subnets on the 1603 that need to route to the DLink. Probably the easiest way in a simple network is to define a default route. In config mode:

ip route {outgoing interface | ip of DLink}

Enable IP classless if not on by default.

I'm still not certain that I fully visualize all of your network. If there are other routers between your 1603 and the subnets that need this route, all devices need a default route pointing to the next upstream interface or IP along the path to the DLink (if you are running a routing protocol it should distribute the default for you).

In this way, all traffic that is destined for anything unknown to the 1603 gets sent to the DLink. There are a couple of other ways to go about it, depending on your situation. I don't have much DSL experience outside of a classroom environment so you will have to take this with a grain of salt. Do all of your clients have a specific default gateway that is either the IP of the DLink or some box sitting at your ISP? If so, you can just build static routes to that box instead of an all-encompassing default route:

ip route {IP of default gateway} {mask of default gateway} {outgoing interface | ip of DLink or next upstream device}

I think that you could alternatively implement policy routing. It is more involved than the methods I have described, but it may be necessary if there is some level of complexity to your network that isn't apparent from your brief description.

Finally, if applicable, don't forget to add NAT statements for the subnets that will be using this default route/static route/policy routing.

svermill Thu, 10/25/2001 - 14:14
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Glad to hear it worked out. As for IP classless vs. no IP classless, it usually will work either way in a small network using private address space. Here is the deal (as I undertand it):

When using default routes (without IP classless), the router will only forward a packet to the default route if it knows nothing about that network. If a packet shows up that belongs to a subnet of a network to which the router has a route, it will look to forward the packet to that network. If it doesn't have that particular subnet in the table, it discards the packet. IP classless tells the router to disregard class and to use the best match in the entire (classless) routing table (to include if necessary). So if it has subnets of network, but not, say, specifically, it will forward the packet to the default.

I probably wasn't very clear on that but the bottom line is that it shouldn't matter in your case. It is just regarded as good practice to do IP classless with default routes.



nareshm Mon, 10/22/2001 - 12:56
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this sounds straight forward you need a default route, which would route all address to the dsl router. for example >>>>>>> dsl router enet interface


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