Cisco 837 VLAN / Multinet

Posted on 2004-08-26
Last Modified: 2008-01-09

I have a Cisco 837 with IOS acting as an ADSL router on a single LAN at the moment. The router has a 4 port hub built in as you probably know.

I've been reading a little about VLANs and multinetting and wondered if I could use this to my advantage in the following scenario:

- LAN 1 - main LAN for internal business use
- LAN 2 - proposed test LAN


- VPN between LAN 1 and LAN 2 using the 837's ports
- Each nework must be completely separate (different subnets) and no machines should be able to see each other unless the VPN is up
- I use NAT on the 837 for getting to LAN 1 VPN Server (Windows 2003 Server) from the Internet. Can I set up a second VPN server operating on a different port on LAN 2 using NAT on the 837?

The purpose of the exercise is to avoid doubling up on routers and phone lines / ADSL fees if possible.


Question by:WebAdviser
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Expert Comment

ID: 11904149
If it really has a 4-port HUB built in, then it can't do this.  If it's a 4-port SWITCH, then you've got some possibility.

I'm not sure what you have in mind for VPN.  VPNs are typically host-to-host, host-to-router, or router-to-router.  With only one router, router-to-router makes no sense....


Author Comment

ID: 11904608
The 837 has a 4 port switch. LAN 1 is for internal use and LAN 2 is for testing (including VPNs).

The bottom line is do I need 2 lots of hardware and ADSL lines to achieve what I am looking to do?


Assisted Solution

diegogalletti earned 250 total points
ID: 11929405
Let me know if I understand correcly:

You would like to have two separate subnet VLAN (like two network offices) that share the Router and the two subnet must be separate by VLAN ?

The cisco 837 is unable to work with VLAN.
If you need to use VLAN you have to use another product like Cisco 1760 Router.

I've all this two product and make it only with the 1760! The inferface of 1760 can be declared with different VLAN and address.

Let me know.


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Author Comment

ID: 11929520
Thanks for your comments diegogalletti.

I didn't think the 837 coped with VLANs and I'd been looking at the 1760 so your confirmationis much appreciated.

One question: I think I've seen some switches which support VLAN. Could these be used with the 837 somehow?



Accepted Solution

stealth188 earned 250 total points
ID: 11934768
Unfortunately no.  The conceptual probelm that you are facing is this: each VLAN has to have a default gateway to get to the rest of the network.  The default gateway functionality is provided by a router.  The router has interfaces, and in the situation that you describe you would need at least two interfaces, one for VLAN A and one for VLAN B.  The interfaces can be either physical ethernet ports (read plug a cable in) or as you alluded to above some higher end switches can create VLANs and perform the routing function which allows hosts on both VLANs to communicate.  You would either need to buy a 1760 and a switch that supports VLANs or keep you 837 and buy a switch that supports VLANs and layer 3 functionality.  You can look at a 3550 as an example of the types of features available.  Depending on the size of your network and needs it may be way overkill though.

Author Comment

ID: 11934807
Thanks for all your comments - much appreciated!


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