routing traffice through one port and exit through another port

Ok we have a cisco 1841 router with 4 fast ethernet ports.  We have a flex t1 that everything come and goes through.  We want to add a cable modem and attach it to one of the other ethenet ports available and have all vpn traffics,and all internet traffics come and go through that port.  I have not been able to figure this out.  I know the easy way is to purchase another router and make all computer except mail servers gateway to point to the new router.  Just seems I should be able to accomplish this with a 4 port router..
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John MeggersNetwork ArchitectCommented:
Should be no problem. You want your default route to point out the cable modem interface and have only certain other traffic go over the T1 circuit.  You just need to identify what you want to go where and determine whether you can use a dynamic protocol or whether everything needs to be static routes.  The router will see all subnets configured on interfaces as being directly connected; what you need to tell the router about (or have it learn from a peer) is the subnets it doesn't know about.  The router will only send traffic out the default if it doesn't have a more specific entry for the subnet.

For the static route, where a.b.c.d is the next IP hop on the other end of the cable modem:

ip route a.b.c.d

The combination of the two entries means "any address"

For static routes on the other end of the T1, you get more specific than the used in the default route.  Where it gets a little tricky is the wildcard mask you have to use following the subnet.  The wildcard mask is important because it has to align with the remote subnet, and it's essentially the reverse of a subnet mask.  So for a /24 subnet, the statement looks like:

ip route a.b.c.d

Let me know if I've misunderstood anything....

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Don JohnstonInstructorCommented:
Is the T-1 also an internet connection or does it go to another location?
Qlemo"Batchelor", Developer and EE Topic AdvisorCommented:
This question has been classified as abandoned and is closed as part of the Cleanup Program. See the recommendation for more details.
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