Equipment (Modems,Gateways)

Replacing SMC gateway with SB6121

I find the business class SMC gateway to be a pile of junk. The Comcast custom software load is crippled from the full functionality of the device, the periodic password resets are unacceptable and the interface is awful. I'd like to switch to an SB6121 so I can use my own proper firewall (Juniper SRX210), which is what I used when I had residential service.


My contract includes modem rental. Can I purchase my own SB6121 and get that montly rental charge off my bill? If not, will Comcast provide an SB6121 to me?


Also, if I switch to the SB6121, will my support SLAs change? The reason I was given for having the SMC device foisted upon me during service signup was because it allegedly gives support better diagnostic tools so they don't have to roll a truck as often.

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New Member

Re: Replacing SMC gateway with SB6121

I did that myself. The gateway is a pile of junk and having a double NAT on my network was causing chaos. They allowed me to swap to the SB6121 and they did remove the modem rental fee when they did so. It took some work in doing so, but they did let me.

Community Manager
Community Manager

Re: Replacing SMC gateway with SB6121

Hello ducksauz,


Welcome to the forum.

SB6121 is on the approved modem list.

If you prefer to use your own purchased modem, I suggest the following:


After purchasing your SB6121 get the MAC address of the modem and go to the nearest Comcast service center in your area. (Link), with your current Comcast modem/router to return it.

Inform the technician that you want to use your modem and provide them with the SB6121's information.

They will update your account to your request. 

Please keep your receipt and call back to verify your request after few business days.


Alternatively you can contact our technical support line at 1-800-391-3000 and request for a change of service to use your modem.


Thank You



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