TWC Business Class (5 static IP) & 2 3750e stacked switches

[bradley]

I am extremely new to networking and I am trying to setup the network in our new warehouse.  I am going to include my topology, but here is what I am hoping to achieve.  We have internet coming in through TWC business class modem/router and 1 line terminating at the switch stack (2 catalyst 3750e: WS-C3750E-48PD-S) port gig1/0/1.  I have created 3 VLANS (2- SERVERS, 3 - USERS, 4 - WIFI).  All the servers will connect directly to VLAN 2 ports, all user computers to VLAN 3 ports, and WIFI access points to VLAN 4 ports.  My question is: Is it possible to have this 1 line terminating at the switch stack support 3 different external static IP addresses, 1 for each VLAN?  How would I setup the switch & modem/router to support this?  I've spent the past few days researching and working on this with little success.  Please let me know if any more information is needed.

[Richard Burts]

We do not have quite enough information to be able to really answer your question. Am I correct that what you refer to as the router/modem is TWC equipment which they configure and control? Do you know whether the line coming from them to your switch is a standard Ethernet (single untagged vlan) or is a trunk with multiple vlans?

If the line is a trunk then you might have an option to associate a vlan with a public IP. Otherwise you will have to find a different way to associate a public IP with each vlan.

The biggest issue that you will face is the necessity to provide Network Address Translation. Since TWC is providing you with public addresses it seems likely that they expect all traffic coming from your network (which uses private IP addressing) to be translated into public IP. The last time I checked the 3750 does not support NAT. You will either need to get TWC to accept traffic with private addressing and to do the translation or you will need to invest in some additional router which can do the address translation.

HTH

Rick

[bradley]

Hello Richard,

Unfortunately, I'm not in front of the equipment right now.  Can we assume it is a trunk for this problem?  Also, they offer a LAN setting called RoutedWithNAT from their equipment.  It originally was setup with RoutedWithoutNAT, but I've been messing with it and currently have it set to RoutedWithNAT.  Right now I have a single line coming into gig1/0/1 set to the first static IP and the switch has internet.  Also, the VLAN connected device's can reach the switch and vice-versa.  How would one go about using more than 1 static IP from a single terminating line into the switch stack?  Whatever you need, please let me know.  I have a hard deadline this week.  Worst case scenario, I fall back to the single static IP for all VLAN's until I can get a better solution, but I really don't want to be forced to do that yet.

[Richard Burts]

It is not clear to me what the TWC device would do in RoutedWithNAT mode. The name sort of suggests that it would perform NAT at least for devices in the connected vlan. Do you have any information from TWC that clarifies what is done in RoutedWithNAT mode?

 Your post says that the switch has access to Internet, which is a good start. It is not clear whether any devices in your network connected to the switch have access to Internet. Can you clarify this?

For your situation to work it would be necessary either to find a way to get the TWC device to perform NAT for multiple subnets in your network, or to obtain some device that would do NAT for you. Once we know which device will be doing NAT we can address how to support multiple public IPs.

HTH

Rick

[bradley]

So I went out and bought a Linksys LRT224 Router to handle NAT between switch stack & TWC modem.  I added the VLANs to the router and the static IP to WAN1.  I then setup all VLANs to be used though LAN1 in the router as Tagged.  Now I need to know how to configure gig1/0/1 which is the terminating line from the router.  I tried a trunk port with dot1q encapsulation since the router is using 802.1Q and gave all VLANs access.  I also tried no switchport with the router default IP.  No more internet on the switch.  Whatever information is needed can be supplied.  Thank you again.

[Richard Burts]

Having a router should be helpful. I am not familiar with the Linksys LRT224 and so will not have any specific advice for that device. But in general I would expect the router to be able to perform NAT for your multiple vlans/subnets. I can not speak to whether this router would be able to use different Public IP for each of your subnets.

Perhaps we should start with basic functionality and after that is working we can get more complex. Am I correct in understanding that your new router is connected to TWC on a standard Ethernet connection (not trunk) and uses one of your Public IP on that interface?

The next thing to consider is how the new router connects to your switch. Note that this is influenced by how you choose to do inter vlan routing. You might choose to do the inter vlan routing on your 3750 switches (which I would probably recommend) or you might choose to do inter vlan routing on the Linksys. If inter vlan routing is to be done on the 3750 then the connection of switch to Linksys would be a standard Ethernet (not trunk) on the Linksys and an access port (not trunk) on the 3750. The Linksys would need to have routes for each of your subnets with the 3750 interface as the next hop. The 3750 would have routes for each of your subnets as connected routes and would need a default route with the Linksys as the next hop. If you choose to do inter vlan routing on the Linksys then the connection of switch to Linksys would be a trunk which would carry all of the vlans to the Linksys. The Linksys would need to have an IP in each of the vlans to be able to do routing between the vlans. And in either case the Linksys would need to perform NAT for traffic coming from the switch and going to the outside. I suggest that you start by working with a single vlan/subnet on the switch and get that one working with Linksys. After you get the first one working successfully then you can work with the other vlans.

HTH

Rick