Create 2 Ethernet Networks DSL

April 17, 2009 at 13:04:51
Specs: Windows XP SP3
I'm trying to setup two seperate networks that can not communicate with each other, but both networks will need to be able to connect to the Internet. Currently my DSL provider only provides one public IP address.

Here's the concept in my head:

1. Connect a switch (s1) to the DSL Modem
2. From s1, connect two ethernet router (r1 and r2) with DHCP
3. Set r1 and r2 to give out different DHCP scopes (e.g. r1 will give out 192.168.1.x/24 and r2 will give out 192.168.2.x/24)

My question is will this work? If it does, can someone give me some suggestions on which router (model) should I get. And if there's any other setting I should be aware of.


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April 17, 2009 at 14:10:40
This is what you use a vlan for, you go,

modem ->router -> switch ->vlan -> pcs

You need a switch that suports vlans.

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April 17, 2009 at 15:03:31
Unfortunately, a switch that is VLAN capable is not the answer.

Even with an expensive managed VLAN capable L2 switch, you would still need a way to tell both VLAN's (ie: both subnets) how to get out onto the internet. This means a gateway, which would likely be a router. You could do this with an L3 switch but something tells me an L3, VLAN capable switch worth several thousand dollars might not be what you're looking for.

You should be able to do this with two SOHO routers. Have r1 be the one with the external connection. Daisychain r2 into r1 (ie: run a crossover cable from a LAN port on r1 into a LAN port on r2) and then configure them how you want them. Finally, you would have to establish a route from r1 to r2's gateway.

I can't say for sure you can do this as I've never tried to with a SOHO router. With a more expensive router, or even an L3 switch, you could do this quite easily. But, I see no reason why a SOHO router couldn't do it so you'd have to read the documentation to figure it out.

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April 17, 2009 at 15:28:39
You are mistaken.

If you connect to the internet by two connections, they will he able to connect to each other. It is called public IP's. Even if you use NAT to two private IP's you end up being visible to the web.

"Best Practices", Event viewer, host file, perfmon, antivirus, anti-spyware, Live CD's, backups, are in my top 10

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April 18, 2009 at 05:53:47
I don't get you Curt. He is planning on using 2 routers, so why not just use 1 x router and a vlan on the switch, hence you have your layer 2 switch and layer 3 router.

This would work, you don't need a layer 3 switch....

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April 18, 2009 at 05:56:17
Oops, my bad andynet. I reread your post just now and saw "router" which I had missed before. Please excuse me but you were correct. In my own defense, it was Friday afternoon and I was already thinking about all the chores my lovely wife had lined up for me this

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April 18, 2009 at 06:05:49

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April 22, 2009 at 12:07:10
I have connected a cisco slm2008 switch on the router, and configured 2 vlans 1 and 2.

Here's my configuration:

Port 1 ->router
vlan 1 has port 1-4
vlan 2 has port 1 and 5-8

I can connect to the internet with computers that are set on vlan 1, but I can't connect to the internet with computers that are on vlan2.

Can someone help me with this?

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April 22, 2009 at 12:38:47
Beacuse vlan 1 is a reserved default vlan that is open to all connections,your vlan 2 is an actual vlan, you then need to add trunking, (or vlan taggging) to beween the wan port (or gateway) route and the individual vlans.

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April 22, 2009 at 13:09:00
In other works the port that has the interntet connected to it has both vlans.

ports that have vlan1 deny vlan2
ports that have vlan2 deny vlan1

make sense?

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April 22, 2009 at 14:10:34
I have never worked with vlan before, so please bare with me.

How should I set it up so that both vlan gets Internet?

I have use the following setting but still cant get the networks connect to the Internet.

Port 1 is connected to a router and the router is connected to a dsl modem.

vlan 1 contains only port 1 and STP is enabled.

vlan 2 contains port 1 to 4

vlan 3 contains port 1 and 5 to 8

Please help.

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April 23, 2009 at 07:46:36
As has been said, you need to create a trunk port between the switch and router.

I'm not familiar with the model switch you're using but have worked extensively with 2900 XL, 2950, and the 3500. It's the same on all of them and I will go through the commands with you below.

Assuming the VLAN's are already configured and port 1 on the switch is connected to the router and the port on the router is already in trunk mode, and you are logged into the switch and already in privileged mode, you would:

# <- I will use this for my comments so you know it's not a
# command. I will use the short form of the commands
# and show the full command beside it in brackets

# go into global configuration mode
conf t (configure terminal)
# select the interface you wish to make a trunk
int fa0/1 (interface fa0/1)
# make the interface a trunk port
switchport mode trunk
# the above command makes port fa0/1 a trunk

By default with a Cisco switch, all VLAN's will be attached to a trunk port so in your present case, it will look as follows:

Port 1 = trunk
Base VLAN = 1
Allowed VLAN's = 1, 2, 3

Port 2 - 4
VLAN = 2

Port 5 - 8
VLAN = 3

No need to mention port 1 for VLAN's 2 and 3 because it's a trunk port and once you make it a trunk, by default all VLAN's are passed through it.

For VLAN's 2 and 3 to connect to the internet, you need routes in your router from their subnets to the VLAN 1 subnet and the gateway to the internet.

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