Basic Routing\Switching Problem

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Mar 13th, 2008
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Hi All.

I have a server with an IP of and I have a Cisco Catalyst 1900 switch with an IP of The server goes into the second port of the server.

Now, the first port of the server has a router attached to it with a default gateway of (Separate network)

What I want to do is be able to connect to the internet through my server as I cant currently do this.

Can anyone please help? I have attached a diagram to make it a bit easier to explain.


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Richard Burts Thu, 03/13/2008 - 09:34
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There are a few aspects of your situation that are not clear. You describe a router connected to the switch but are not clear whether this connection is a access port on the switch (an access port is in only a single VLAN) or is a trunk port (trunk ports can carry multiple VLANs). And it is not clear whether the switch is configured with all the ports in a single VLAN or if the switch is configured with multiple VLANs. And it is not clear whether the port that the server is in is the same VLAN as the port that the router is in.

If we knew these things we would be closer to being able to give a good answer to your question.



Ianwillo123 Thu, 03/13/2008 - 10:03
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Hi Rick.

Sorry, ill try and explain again.

Ok, I have a Server, a switch and a PC.

The Switch's IP is

The server's IP is (connected in port 2 of the router)

The PC picks up a DHCP. (connected in port 3 of the router)

All this works fine, I can access network resources etc fine.

Now, I have access to a router provided by an ISP which I can access the internet when directly connected to my server or PC. When I plug this router into port 1 of the switch I cannot access the internet on either the PC or Server.

However, the routers VLAN is 192.168.1, with the default gateway of

So what I need to do is to be able to access the internet from the pc or server, but I cannot have both switch and router on the same VLAN (for several reasons!)

How c an I get the internet on these machines?




Richard Burts Thu, 03/13/2008 - 10:22
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This explanation also leaves multiple points of confusion. It implies but never quites makes it plain that the router and the PC and server are in different VLANs. If you would explain clearly how the switch is configured and what ports are in what VLANs it would be very helpful.

This explanation does have this statement:

but I cannot have both switch and router on the same VLAN (for several reasons!)

if it is communicating what I think it is doing then I believe that the answer is that you will not be able to get Internet access from PC or server while connected to the switch.



pankaj_goyal Thu, 03/20/2008 - 23:57
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Hello there

The address range - is a private ip address range which you are using in your network. These addresses cannot be routed on network outside your private network. So to access internet, u have to convert these addresses to public ip address which is provided to you by your ISP.

When you directly connect a pc or server to your ISP, it takes the IP address provided by your ISP (dynamic/static). But when you are using both, your pc and server, you need to configure NAT on your router.

(ps: i am currently on a linux machine so cannot see your diagram. What i have posted is the general concept.)




narayana.yelakaturi Tue, 03/25/2008 - 18:59
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It seems the switch you have is a layer 2 switch.Since your server is in 1 subnet & router in other subnet, you're not able to reach the router & vice versa .So either you need to create 2 VLANs on the router or use a multilayer switch instead of layer 2 switch to do inter-VLAN routing.

I assume that the router is doing NAT to translate ur private IP to public b4 it sends the packet in to Internet.

Hope this helps

craig.burtenshaw Wed, 03/26/2008 - 18:35
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I believe you have to turn the router into a bridge.

I am experiencing the same issue, where I have a server, switch and Notebook. I configure the Ethernet port on the Server, Switch and Notebook to be in the same range.

I allow the Notebook's wireless port to get it's IP via DHCP from the router, I allow computers that are trying to use the Notebook to access the internet, but then it all stops.

I haven't tracked down how to turn my 2wire router into a bridge yet.


jaipal Sun, 04/06/2008 - 22:20
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Let me assume like this:

1. Router on 2.0 subnet, (connect to port1)VLAN1 and LAN on 1.0 subnet [VLAN2] throughout (port2 - 24)

2. So Ian needs the internet available on the LAN (traffic passing from VLAN1 to VLAN2.

If this is the scenario, your switch is 1900 series, you have to enable IP routing from VLAN1 to VLAN2.

a.forestal Mon, 04/07/2008 - 14:08
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hi there:

your issue is still mysterious. I've looked it over. You have a few options here:

1. Renumber your subnet to a subnet - of course either renumber the server or the Router's interface on that subnet

2. Keep everything as is, and configure sub-interfaces on the Router and assign each interface to and subnets, trunk that interface to your 1900 and you'll have a classic "ROAS" (Router on a stick) configuration. Of course creating separate vlans for hosts which will reside in these two subnets

Of Course, your server and PC (on the subnet will be able to access the internet, but will also, theoretically, be able to access hosts on the subnet. You did not make it clear whether there were any hosts on the subnet

Of course you can always create accesslists on the Router to prevent packets from routing between subnets...

After doing all that, the EASIEST thing to do is to renumber your entire network to use single subnet and have all traffic flow through the router.

Hope this helps


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