Comcast Router and VLANs

[Terp84Alum]

I have another customer again in the restaurant/bar business. We are installing Comcast business class double or triple play (data, voice, video). The modem/router they provide is the SMC SMCDG3-CCR. Like my other installs, the network will consist of a private subnet and a public subnet along with VOIP. This is my first time with VOIP. Up to now, I've been using 2 routers to separate the subnets primarily because I have not full grasped the correct procedures and hardware to establish VLANs. The router isn't bad so I'm thinking of using a managed switch to establish VLANs.

I'd like to set up VLANs for VOIP, Public WiFi, and Private Network. All three would share the Comcast internet service. I believe the way to share the internet is to have one port that is shared by all VLANs and then simply plug the run from the router to that port. I thought I read where it was recommended to set up a VLAN for the switch management but that's a little over my head.

So, what I'm hoping is that Cisco makes a basic managed switch that's "dumbed down" a little so it can be configured kind of like the Linksys stuff via a browser and graphic interface instead of code. Kind of like this http://ui.linksys.com/files/SRW2024P/1.0.3/home/home_smb.htm

THOUGHTS.


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[Tom Watts]

Hi Terp,

I am reviewing the admin guide for the modem. This seems to be a very basic unit. From the looks of it this box supports 1 ip address field and 1 dhcp scope.

The challenge will be with this unit is how do you want to manage traffic. This will dictate the quality of the switch you buy as well. Since the SMC box supports only 1 DHCP scope, do you plan to have an external DHCP server? If not, do you plan to use static IP addresses for all vlans except one of them?

I suspect your voice vlan can easily live without DHCP since the phones shouldn't be changed anyway. I also suspect your private network should have static IP addresses for accountability and could live without a DHCP server provided there are not new devices being introduced and removed.

A public network would obviously need a DHCP server since guests shouldn't be expected to configure their network cards to match your network.

The next challenge will be getting the 3 vlans on to the internet. The reason this is a challenge is because the SMC box does not appear to support multiple subnet functions or a vlan function. In order to make 3 vlans be able to access the internet while the router does not understand the subnets would be through static routes and a layer 3 switch.

Here is an example of a RV082 router and a SG300 to make a vlan-unaware router have the internet connectivity work for a discontiguous network.

https://supportforums.cisco.com/thread/2123434

The realistic requirement using this SMC box is using a SX300 switch in layer 3 mode. Create 3 vlans. Assign IP addresses to each VLAN and then create static routes on the SMC box to point to the IP addresses of your VLANS. The limitation you will have is DHCP without an external server.

To get a feel of a SX300 series model please look here-

https://www.cisco.com/assets/sol/sb/Nikola_GUI/SG_300-28P_v1_1/config/home.htm

-Tom
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[Terp84Alum]

Thanks Tom.  Like my customer's other facility, the POS system (private) uses static IP. VOIP is a first for me.  Public would require DHCP.  I also need wireless.  The reason I started this thread in the SWITCH area is because apparently Comcast will not allow you to put their router in bridge mode.  They claim they cannot do any remote troubleshooting.  Ideally, if I could just use the Comcast equipment for the modem, I assume I could then move to one of the RV wireless routers and be done.  Perhaps another Comcast business customer will chime in with their experience but scanning DSL Reports forum, it looks like Comcast is pretty strict about how you use the SMC equipment.

The problem I see, would be if I need DHCP on the private wireless side.  I thought the idea of a managed switch was the ability to have mutliple DHCP.  Am I wrong?  I just don't want to go down the path of using multiple routers like I am at the other facilities, although I'm only using 1 DHCP.

Another thing that I'm not clear on with respect to VLANs was that I thought in researching, it said each VLAN had to be on it's own switch.  That will not be practical for me as the facility is old and I have to consolidate network runs in a couple separate places.  I would have a switch in each consolidation area and then go from the switch back to the router.

Continuing, I thought I read where to enable the separate VLANs to access the internet, you would set up a VLAN just for the internet and have all the other VLANs "belong" to that port.  Then you just plut the SMC into that port.  Unfortunately, I didn't bookmark the articles I'm referring to so I may have misunderstood.

So should I try to pursue trying to use the SMC modem/router as just a modem and by a router with the ability to have multiple DHCP with an integrated managed switch or use the SMC as delivered and get a managed swich?

Thanks again for your help.

Ken

[Tom Watts]

Hi Terp,

For ease of deployment and management I always feel it is better to have a router that compliments the switch.

When you are using a router that does not support vlans, subinterfaces, multiple subnet functions, etc, it makes separating traffic somewhat difficult. The reason being, if the router does not support any features, the only way to accomplish multiple subnets/vlans is with another layer 3 device and using static routes on the router to tell those subnets how to route to the correct place.  This is also why routing protocols were invented.

For ease of management and equipment overhead, I think it is also agreeable that it is very nice to have a router that will support vlan dhcp. Reason being, setting up a DHCP server or maintaing the extra equipment just for this functionality seems impractical for a basic deployment.

-Tom
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[Terp84Alum]

So given that you would recommend...

Thanks Tom.

Ken

[Terp84Alum]

Below is a crude drawing of my infrastructure.  It's very similar to my other locations primarily because I cater to the restaurant business.  Up to now, I've simply been using 2 cheap routers to create 2 subnets.  I'd like to step up in this new facility to some better suited equipment. My dilemma as explained above is that this is an old building so home runs to a single location is not possible.  The term "CONS" means consolidation. I basically have 3 consolidation points.  In these locations will be runs from PC workstations and IP cameras.  On the public side, the BOILER CONS exists as well as the 3 WAPs and the hardwired jacks.

What I don't understand with respect to VLANs and managed switches is will every switch in the footprint need to be a managed switch.  I guess I thought if I used port based VLANs in the router/switch, anything I plugged into that port (another basic switch) would by default be in that VLAN.  I'm not sure I want to purchase 4 managed switches along with a router with a managed switch.  That's getting pretty expensive and I'd probably go back to the 2 subnet solution.

Thanks for your help.

Ken

[Tom Watts]

Terp, cool drawing. That looks pretty good.

You are right if you use a port base vlan, whatever connecting to the manage switchport will only be that vlan member.

So if you have your main switch at BAR CONS with a vlan 10 untagged connecting to an unmanaged switch at OFFICE CONS the OFFICE CONS will be only vlan 10 subnet member.

The real concern isn't necessarily the lay out. The concern is the manage switch interacting to the router. Which is where my original post expresses concerns.

If you have some generic router box that does not support vlans, subinterfaces, etc then the manage switch must be a layer 3 device. When this happens, the generic router box will require a static route to be pointed at the manage switch's vlan interfaces to allow all other vlans to get out to the internet.

If you have a router that supports vlans like a RV180 or RV220 then its just as simple as to create the vlan ID, verify the DHCP scope then assign a trunk link with all vlans assigned to the link on the manage switch side and router side.

-Tom
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[Terp84Alum]

Thanks Tom.  Comcast told me we could buy a Motorola Sufrboard modem or I could disable DHCP and firewall in the SMC.  I would then buy a RV router.  I'd like the wireless version but only if I could assign the wireless to the public VLAN only.  Is that a capability of the RV?  What are the primary differences between the 180 and 220?

So if I purchase a RV180 or 220, I can basically use the SF100D in each of the 4 locations that I show SWITCH?  I only have one internet connection, problem?  Lastly, since there are no permanent PCs on the PUBLIC side, how do I manage the APs?

Thanks again.

Ken