Subnet Routing

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Aug 14th, 2008
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I apologize if this topic has been discussed, or if it seems simple. I'm having a problem routing within my office LAN when using 2 different subnets. I have a single Cisco 2600 router that I want to use as a “router on a stick”, to route traffic between my two subnets. I've set this up before however for some reason it is not working this time.


Here is my network setup.

My new network is on the 10.16.0.0\13 network and the old network is on the 100.100.143.0\24 network. I need to support both until a particular software package is phased out. I want to setup my 2600 router to route packets to the other directly connected network without doing any major network restructuring.


I know this is a simple fix and a very simple process, as I've done it before, but for the life of me I simply can not remember what all I did. Any advice


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Richard Burts Thu, 08/14/2008 - 08:16
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William


In addition to wanting to see the config I believe that it would help us if you would tell us a bit more about your environment. You describe this as router on a stick which implies that both networks are connected through a switch and the switch connects to a single interface on your router. Is this the case?


HTH


Rick

willsadventures Thu, 08/14/2008 - 11:12
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You have the basic idea. Don't look to far into this, its really a simple config. There are a total of 15 computers in this location that all run off a small DHCP server. That's the “old network” the new network has all the wonderful things that a true network should (DHCP, DNS, IIS, DC, etc) running off two different servers. I need to move all the computers from the old network to the new. Problem is there are a few servers that I can not move because the software that they are running does not support the new subnet. So in a nut shell I need to move 15 PCs to the new subnet (10.16.0.0\13) from the old (100.100.143.0\24) while still allowing the PCs to access the old subnet.


For the meantime I have a single Catalyst 2960 (48port) and a HP 48 port switch. The Catalyst is running on the new network and the HP on the old. The Router in question has 2 NICs, one to each switch.


My config on the router is on a fresh slate (as I never saved before I unplugged it), however I had setup both interfaces with IPs and their mask, along with the IP Route command for both interfaces.

(IP ROUTE 10.16.0.0 255.248.0.0 100.100.143.0)

(IP ROUTE 100.100.143.0 255.255.255.0 10.16.0.0)


From a computer I have on the old network (my personal, 100.100.143.101) I can ping the 10.16.0.6 address (the F0/1 on my router) but I can not ping the 10.16.0.5 (DC server). The router of course can ping all addresses


Richard Burts Thu, 08/14/2008 - 12:54
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William


The additional information that you provided is helpful. For one thing if each network is on a separate switch and connected to a separate router port then it is not what most of us would call router on a stick. It is just straight basic routing with a unique subnet/network per router interface. And configuring the router interface addresses and masks, and making sure that ip routing is enabled (it is by default, and will not show up in the running config) is really about all that is required on the router. So I am guessing that the problem may not be a problem on the router.


I am a bit puzzled about the ip route statements in your post. The router should not need any ip route statements if it is just routing between connected interfaces. And the logic of the route statements seems wrong to me:

IP ROUTE 10.16.0.0 255.248.0.0 100.100.143.0

why would we go through 100.100.143.0 to get to 10.16.0.0? Or is this a route statement for some PC or server in the network?


From your description of your PC being able to ping the router interface of the other network I believe that your PC is behaving correctly. But when your PC is not able to ping the DC server at 10.16.0.5 I would guess that the config of the DC server does not have the default gateway correctly configured. When it was all one network there was not much need for a default gateway on the DC server and who knows what it was configured to (if it was even configured at all). Now it is important that the default gateway of the DC server (and all other devices still in that network) be the router interface 10.16.0.6. If you check the default gateway and configure it correctly I believe that you will have connectivity.


HTH


Rick

willsadventures Thu, 08/14/2008 - 14:50
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You were right. I did have a setting wrong on the DC. (wrong GW)


Well yeah my term of "router on a stick" is wrong for this example but the orginal config only has one switch with two VLANs. I'm going back to that when I get this network design figured out.


Thanks for your help

Richard Burts Thu, 08/14/2008 - 18:24
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William


I am glad that my suggestion did lead you to the solution of your problem. Thank you for posting back to the forum and indicating that your problem was solved and what the solution was. It makes the forum more useful when people can read about a problem and can read the suggestion that lead to a solution.


HTH


Rick

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