Business Class Comcast Cable Modem is there a max that the device can handel?

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This might be an odd question but it related to an issue.

Does Comcast Business Modem have a maximum number of devices that can attach to it.

Ok here is the case. I have the very high speed Comcast Business internet service with a modem SMS modem DOCSIS 3.0

Of couse it has 4 ports for connecting devices on the back. But I have a total of about 20 computers behind the cable modem and about 20 VOIP phones (They are Hosted Voip so the pbx box is not in house).

Two switches make up my network and the modem is connected using one of the ports to one of the switches.

Both switches are gig switches.

All computer devices are plugged into one switch and voip phones are connected to another switch.

So there is one cable from the cable modem to one port on the switch.

Now there is basicly a total of 40 devices. Not much of a firewall but just keep this in mind. Trying to give you all an idea of what's behind the cable mode.

Aparently a tech from comcast one of there advance guys. The ones that the guys in the field correspond with.

Said this today. "Your customer has I see 40 devices connected" not sure what your going to tel him but modems really not design to have that many devices connected behind it. Its quite possiable that that might be part of the issue.

Now my question is this. Is this real? Can a cable modem really only support a certain number of devices behind it?

Oh by the way I'am on a 50 down and 5 up up plan.

Both the tech with me who is cool and very knowledgeable we both looked at each other and with puzzlement. His guy on the phone did have a point. Devices can be over loaded I guess.

I would like to hear others outtake on this.

Also if this is the case what are some of the solutions. NO I 'am not doing T1 or DSL

because the circut in my area are bad even the telephone guys said it wouldn't do any good.

SO my only chose for good internet is comcast

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Technically the builtin DHCP server on the device will issue 254 IP addresses. So, technically you can connect 254 devices. That is the limit. Is it a best practice to put that kind of load of this class of broadband modem? No.

that modem supports SNMP, you can ask what is the read-only community string (probably "public") and monitor modems performance and load by yourself.

Also the web interface of the modem will have some sort of monitoring info.


Comcast doesn't have much in there web interface for the customer to monitor.

254 yes but can the modem support that . see that sorta what I was getting at today. I have Dhcp done on my server but I have 40 devices communicating all through that gateway modem. apparently I am finding out that there may be a max that the modem itself can Handel before it starts dropping it's sync with Comcast make sence now?
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what is mode of the it routed or bridge..


I've got a client that has approx 65 users over 1 Comcast business connection without problems. However, as a standard practice, I always bridge the Comcast device to an internal router. This way you have more control over routing functions and also reduce load on the SMC gateway. Without contacting SMC Networks for technical info, there's really no way to tell the max it can handle.


I see thanks..

I will try that .. Any good suggestions for an inexpensive modem. I was kinda thinking this yeasterday. I have a good tech I've made friends with who was on the phone yesterday. Had his phone on speaker for when the guy said "looks like your customer has about 40 devices' and the modem may have issues with that many devices.

Anyway would the plan be a problem I'am on a 22 down and a 5 up. Should i bump it up? or do you think what I am on is ok.?

If I got a router I have 5 statics. Would I just bridge the connection from the comcast modem SMC to the router.

And I guess from what your saying the router would take the load of the 20 computers plus 20 voip phones. There for easing the load on the modem am I correct in saying this?

Cisco WRVS4400N Wireless-N Gigabit Security Router would work great for what you're doing. It's under $200 but offers a lot of functionality.

Talk to Comcast about your bandwidth usage to see if you're maxing it out or not. If you're not close to maxing it out, there's no need to up your bandwidth package.

Yes, have Comcast do the bridging unless you are familiar with the procedure on the SMC gateway.

Yes, the router would handle the load of the internal network and the SMC device would simple pass traffic inbound or outbound.


Those 20 voip phones I have are on a hosted voip solution with no pbx in house so they are consent communicating with their server which is outside of office.

Accually we have a 22 down and 5 up .. But are pulling much higher speeds even the Comcast guy said he wouldn't mess with the speed plan

We pull about 80 down and 5 up but thats using there comcast speed test site. Speak easy and speed test . net show average of 24 down and 4 up.

Internally we don't draw that much and never had issues with the voip phones. Clarity is perfect. We sorta thinking its a plant issue between the tech and me.

Seeing how the rest of the week turns out but that modem idea is something I thought about in the past.

Question though I would still be pumping 20 voip phone to a service hosted voip provider? from what your saying adding the router would still help in this case as far as traffic balancing?

The Cisco router does have QoS services which will help to prioritize traffic.


I guess thus reducing the load on the SMC?

going to see what the manufacture says on SMC



I looked up this router but I don't see where I can put in or assign the ip's I have 5 ps

that I do NAT with 1 to 1

Lan                                   WLAN

bab bab baaaa                      COMCAST STATIC IP PROVIDED 1

 bab bab baaaa                      COMCAST STATIC IP PROVIDED 2

 bab bab baaaa                      COMCAST STATIC IP PROVIDED 3

 bab bab baaaa                      COMCAST STATIC IP PROVIDED 4

 bab bab baaaa                      COMCAST STATIC IP PROVIDED 5
To assign a useable public IP to the router's WAN interface, login to the web administration page and navigate to Setup > WAN > Choose Static IP for Internet Connection Type.

This is not a multi-WAN (AKA dual-WAN) router. Thus, it does not provide WAN redundancy.

This router does not have one-to-one NAT capability.


what would be a low cost solution then so I can route my 5 statics I get from my ISP to internal computers servers
Cisco RV042 or Cisco RV082 - $200-$300 range.

Both have dual WAN and one-to-one NAT capabilities.


I want gig speeds and do not really need dual WLAN because I only want and need just comcast

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