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Slow speeds on MB8600 vs Leased (DPC3941T & SB6120)

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Just replaced my old SB6120 (leased) with a MB8600 and am getting much slower speeds. Running speed tests (Ookla, Xfinity's and DSLReports) was only giving me between 30-60Mbps (tried each port on the modem). I'm on the Blast Pro 200 tier, so the number should be around 200Mbps.The speed tests were run with a direct connection to the modem (I additionally tried 2 different ethernet cables for good measure). 

 

The SB6120 was able to get 130Mbps. I measured right before I switched.

 

The MB8600 lists the configuration file as: d11_m_mb8600_blastpro_c01.cm. I'm guessing this is the right one, although I don't know for sure.

 

An Xfinity tech came out the other day, did some tweaks to the cable lines, which didn't seem to noticably improve anything. He suggested we try an Xfinity cable modem, the DPC3941T instead, which oddly enough was able to get around 200Mbps.

 

I recently tried several other modems (Arris SB8200, Arris SB6183 & Netgear CM400), all with very similar results (only 30-60Mbps).

 

I don't want to lease a modem any longer, yet no modem I purchase seems to be working well. Any ideas on what's going on?

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Ok, just purchased a different modem and subsequently activated it (Netgear CM1000). The problem continues as it also gets only 30-60Mbps as opposed to 200Mbps per the Blast Pro 200 tier. See attached connection info, and speed tests (sensitive info blacked out).

 

How is it possible that every modem I purchase only gets 30-60Mbps (MB8600, Arris SB8200, Arris SB6183 & Netgear CM400), while the Xfinity leased modems do far better? The DPC3941T gets 200Mpbs, while the SB6120 (end of life modem) is capable of getting 130Mbps. I have a hard time believing 5 different store bought modems have defective hardware.

 

What in the world is going on here!?!?

 

 

 

 

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Posted by
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The config file on the MB8600 looked to be correct. What equipment shows on your account? Trying so many modems may have somehow confused the system. Saw your post on DSL Reports too, maybe try posting on Comcast Direct over there...?

https://www.dslreports.com/forum/comcastdirect

 

Posted by
Official Employee

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Hello @Septimous. If you are still experiencing slow speeds on your new modem, I can help. Please send me a private message and include your full name, service address, and account number so I can assist you. 




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