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My Xfinity Gigabit Gateway and my Router.

New Poster

My Xfinity Gigabit Gateway and my Router.

I've been going bonkers with this thing , since I got it.  I've reset and updated the gateway, multiple times.  I have also updated the firmware and reset my ASUS RT-AC5300 multiple times.  If I hardwire into the Xfinity gateway, no issues, but as soon as the ASUS is added, it drops speeds to around 92.Mbps Down and 45Mbps Up.  Ive ran new patch cables and everything.  Can anyone assist with this?  I also read that the chipset in the Xfinity Gigabit Gateway is/may be the cause.


I also tried putting the Gateway in Bridge Mode, jsu tto eliminate the WiFi.  Still, same issue when hardwired and WiFi.

Diamond Problem Solver

Re: My Xfinity Gigabit Gateway and my Router.

Do you have any QOS features enabled in the 5300 ? If so, disable it / them. 


Just for info purposes, if you are hanging a stand-alone / separate router off of the gateway device, and the gateway is not in *bridge mode*, you are cascading 2 routing devices which results in an undesirable "double NAT" condition on your home network.

Google "double NAT" for info about its potential pitfalls.


You really should keep it into bridge mode and use only the 5300 for your home networking / WiFi.

New Poster

Re: My Xfinity Gigabit Gateway and my Router.

I believe I solved the issue.  So here is the solution:

If you have Gigabit service, you must use the SAME type of wire to all devices (hardwire).  I had a mix of cat5, cat5e, and cat6.  Why these devices would not exceed over 100Mbps, does not make sense.  Cat5 and above can transmit between 1Gb-5Gb and sometimes 7Gb-10Gb.  I ran a cat5e line from the Xfinity gateway to my Asus 5300.  This gave me the correct hardline speeds (between 800Mbps and 1Gb).  However, I had to bridge connect the Xfinity gateway in order to make things stay current (this also diabled wifi on the gateway).  I only use hardlines and wifi from my Asus 5300.  Things seem to be working fine now, but I'm pretty mad that I had to change all of the wire I previously ran in my house.  Even being a cable guy for 10+ years, I have never come across a product with such issues.  The need for only "1" type of wire system in a home, is pretty rediculous.  Not for anything, but the Gb gateway needs this bug fixed.  Only accepting cat5e as its only true transmission wire is terrible.  I mean, cat6 transmits at a higer speed than cat5e just off of an extra twist and braid, yet it doesn't work on this service.  I'm now out of pocket over $150 in running new lines in my house.  I don't see any credits from Xfinity (Comcast) heading my way any time soon for this.

*** Word of caution to those getting this service.  It is a great service, once you get it up ad running.  However, if you dont acquire the correct wire system, which is not provided or disclosed ANYWHERE by Xfinity, you will be putting some money out of pocket. (1 line from the gateway to a PC is the only thing provided during installation) ***


Re: My Xfinity Gigabit Gateway and my Router.

@PhillyFire10 wrote:


If you have Gigabit service, you must use the SAME type of wire to all devices (hardwire). 

That is absolutely not true


I have a mix of CAT 5, CAT 5E, CAT 6, and even a CAT 7, an ARRIS SB8200 modem, and an ASUS RT-AC88U router with 8 LAN ports. 


The CAT 5 is connected to my Philips Hue bridge.

THe CAT 5e cables connect my modem to the router's WAN port, then the LAN Ports of my router to my QNAP-TS231 NAS (two cables link aggregation),  and my VIzio M55-C2 TV.

The CAT 6 cables connect my Apple TV 4k and my XBox One S to my router.

The CAT 7 cable connects my 2015 27" iMac to my router.


Aside from the Hue and the TV, all devices have Gigabit Ethernet. 


I have no trouble getting full gigabit speed on my other Ethernet devices.


The router is smart enough to auto negotiate the speed between the various devices on my network, and I don't see why your AC5300 shouldn't have been able to either. 


Plus, I didn't have any problems with internet speeds when I had my XB6 gateway in Bridge Mode, before I had the SB8200.


Whatever your problems were, they were not caused by some incompatibility with ethernet cables.



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New Poster

Re: My Xfinity Gigabit Gateway and my Router.

Most likely, its an internal issue with the Gigabit Gateway from Xfinity.  It's also new to this area, and I'm sure the bugs have not been worked out yet.  My personal equipment has no issues, from my router forward.  Whatever is behind the router, is the issue.