New problem - not Activating w/ Centurylink VDSL, Zyxel C1000Z, and Netgear R7000 Nighthawk

Mentor

New problem - not Activating w/ Centurylink VDSL, Zyxel C1000Z, and Netgear R7000 Nighthawk

I've been using a Microcell for a few years already, most recently with a Netgear R7000 Nighthawk as the router, an Actiontec PK5000 DSL modem/router in bridge mode.  (Service was Centurylink, either ADSL or ADSL2 not sure).

Microcell -> Netgear R7000 -> Actiontec PK5000 in transparent bridge mode

 

 

This past week, Centurylink upgraded my internet speed and apparently put me on a VDSL (or VDSL2) circuit, and they sent me a new modem, a Zyxel C1000Z.  I need to use the new modem because my old modems are not compatible w/ VDSL.

 

I have not been able to get the Microcell to activate using the same exact configuration except for the modem:

Microcell ->  Netgear R7000 -> Zyxel C1000Z in transparent bridge mode.

 

I spent hours with this issue.  Everything else that I have works fine (other devices that set up DDNS or UPnP ports to the outside world, etc) , except for the Microcell.  I went and physically added port forwarding on the Microcell ports that I saw in Otto's guide and in the ATT instructions.  (123 UDP, 443 TCP, 500 UDP, 4500 UDP).

 

This works:    microcell -> Zyxel C1000Z in gateway/router mode, but that's not what I want.

 

I have temporarily established this setup, but again it's not what I was hoping for and since all of this used to work before with the older modem/DSL combo:

 

microcell -> Netgear R700 in AP mode -> Zyxel C1000Z as the gateway/router

(I didn't have to do any explicit port forwarding).

 

BTW, all of the scenarios listed above were connected as Modem LAN port to Router WAN port.

 

For reasons that I don't want to get into, I want to use the Netgear R7000 to do all my network processing, and just use the modem/gateway for DSL (i.e. bridged).

 

Does anyone have a similar configuration and did you get it to work?  Any other ideas?

 

Thanks in advance.

 

 

 

 

Message 1 of 30 (5,740 Views)
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Mentor

Re: New problem - not Activating w/ Centurylink VDSL, Zyxel C1000Z, and Netgear R7000 Nighthawk

[ Edited ]

Sorry for the delay in providing an update on this topic, but this may help others who have a problem with this configuration:  Centurylink VDSL circuit, Zyxel C1000Z, and Netgear R7000 Nighthawk.

After hours trying to adjust my network configuration etc, including using a temporary router, etc, etc. the temporary router by accident made me find this "fix".

 

What made the Microcell finally work in the configuration I wanted is a simple tweak in the router WAN config:  MTU set to 1480 instead of 1492, which is listed a requirement for the microcell.  Everything works.

 

So I have the Zycel C1000Z in bridge mode, the netgear R7000 performing all routing and switching functions, and the microcell connected to one of the wired ports of the R7000.  I didn't have to touch anything else on the defaults.

 

Cheers.

Message 16 of 30 (4,952 Views)
ACE - Master

Re: New problem - not Activating w/ Centurylink VDSL, Zyxel C1000Z, and Netgear R7000 Nighthawk

Glad to hear that it's working out for you now. It is sometimes very easy to miss a basic requirement especially when you are trying all kinds of troubleshooting methods.

___________________________________________________________

MicroCell Technical Guide by Otto Pylot


I am not an AT&T employee. For additional help, please send a PM to ATTCustomerCare

*The views and opinions expressed on this forum are purely my own. Any product claim, statistic, quote, or other representation about a product or service should be verified with the manufacturer, provider, or party.
Message 17 of 30 (4,939 Views)
Mentor

Re: New problem - not Activating w/ Centurylink VDSL, Zyxel C1000Z, and Netgear R7000 Nighthawk

Hi Otto, yep, but what's different here is that the MTU of 1492, which is the MTU listed as a microcell requirement, does not work. 

Setting the MTU to 1480 is what worked.

Message 18 of 30 (4,932 Views)
ACE - Professor

Re: New problem - not Activating w/ Centurylink VDSL, Zyxel C1000Z, and Netgear R7000 Nighthawk

[ Edited ]

Interesting that lowering the maximum transmission unit from a default setting of 1492 down to 1480 would fix the problem for you.  A MTU setting of 1492 is the standard for PPPoE on a LAN, not so much a requirement of the Mcell.  The fact that lowering the MTU for your LAN made the Mcell functional would indicate to me that your LAN suffers from packet fragmentation at a MTU of 1492 for whatever reason and that packet fragmentation was causing a problem with your Mcell.

 

Lowering the MTU can improve "responsiveness" of a LAN at the expense of throughput.  It is always advisable to run at the highest MTU setting that your LAN will allow in order to maximize throughput but each LAN is different and sometimes changes to the MTU must be made in order to account for variations in the underlying network.  There is no single "best" solution for all applications.

 

I am also wondering if you have "Block Fragmented Packets" disabled in your router settings.  If it is enabled, it could be causing the problem and disabling this setting may allow you to increase the MTU back to 1492. 

___________________________________________________________

MicroCell Technical Guide by Otto Pylot


I am not an AT&T employee. For additional help, please send a PM to ATTCustomerCare

*The views and opinions expressed on this forum are purely my own. Any product claim, statistic, quote, or other representation about a product or service should be verified with the manufacturer, provider, or party.
Message 19 of 30 (4,918 Views)
Mentor

Re: New problem - not Activating w/ Centurylink VDSL, Zyxel C1000Z, and Netgear R7000 Nighthawk

Hi Avedis, yes, this is strange, I thought of the same.  However, this "advanced" router has no setting that I can see as a user to control packet fragmentation.

And this same exact router used to work fine on a different type of DSL circuit (ADSL) and a different modem (that was compatible w/ that circuit).

 

My only conclusion at this point is that this combination of circuit, modem, router, and microcell cause the issue.  Which exact device or configuration of the combination results in the potential packet fragmentation is beyond me, and I don't have the time or access to internal configuration to deal w/ it.   (See, if I just put the modem in router mode w/ its mtu default [which is 1492], then the microcell connects fine.  and I don't want to run the "advanced" router in ap mode).

 

Go figure, but at least if someone runs into this, reducing the MTU is another workaround to try.

Message 20 of 30 (4,895 Views)
ACE - Master

Re: New problem - not Activating w/ Centurylink VDSL, Zyxel C1000Z, and Netgear R7000 Nighthawk

[ Edited ]

Avedis53 - Good points. I read that as the MTU was set at 1480 and setting to the required 1492 worked. I know there are a lot of issues with CenturyLink as reported by Broadband Reports so maybe they are still working on fixing some issues.

___________________________________________________________

MicroCell Technical Guide by Otto Pylot


I am not an AT&T employee. For additional help, please send a PM to ATTCustomerCare

*The views and opinions expressed on this forum are purely my own. Any product claim, statistic, quote, or other representation about a product or service should be verified with the manufacturer, provider, or party.
Message 21 of 30 (4,893 Views)
ACE - Master

Re: New problem - not Activating w/ Centurylink VDSL, Zyxel C1000Z, and Netgear R7000 Nighthawk

@partymonkey- you may have future issues if you can't set the router to meet the minimum requirements needed. Checking with the mfr might be a good idea in case they have defaults that are going to cause issues later on, like SIP ALG as a default for example. VDSL can have as many issues if not more that ADSL2+ if it is not installed and/or maintained correctly.

___________________________________________________________

MicroCell Technical Guide by Otto Pylot


I am not an AT&T employee. For additional help, please send a PM to ATTCustomerCare

*The views and opinions expressed on this forum are purely my own. Any product claim, statistic, quote, or other representation about a product or service should be verified with the manufacturer, provider, or party.
Message 22 of 30 (4,887 Views)
Mentor

Re: New problem - not Activating w/ Centurylink VDSL, Zyxel C1000Z, and Netgear R7000 Nighthawk

Hi Otto, yes, good point.   Although the microcell is the only piece of equipment that had difficulty with the 1492 MTU, and everything else was and is operating correctly.  (I do use IPSEC VPN as well on something else and SIP ALG enabled without a problem).

 

On the other hand, changing the MTU setting is less concerning but it fixes issues that are not apparent or easy to understand for many folks.  Reducing the MTU to accommodate an ISP configuration and network equipment (your own and the ISPs) does not impact much other than throughput potentially, and actually the MTU can be optimized to your network's characeristics.   The Microcell is picky about breaking up packets, yet it has no problem at all working with 1480.  I think the listed "requirement" of 1492 is simply to point out that you can't set it to 1500 which is the default in LAN network cards under Windows, because you need to account for the 8 bytes of PPPoE, but that doesn't mean that you can't use any of the other common lower settings (1480, etc) to solve a simple but frustrating to troubleshoot problem. 

 

What I've observed is that many modern advanced consumer routers are starting to do away with complicated settings and automating configuration through detection and firmware, so you may not find settings like "disable packet fragmentation", etc.  Since Microcells are both used in home, soho, and other business settings, we will run into routers that are less user "tweakable" unless you apply 3rd party firmware.

 

So I think it's still a very valid troubleshooting step to try without a major impact.

BTW, there is a simple command in windows to identify the point at which packets start fragmenting:    ping att.com -f -l MTUsize

if you do that repeatedly (reducing by 10) until you stop seeing fragmentation messages, then you start adding 1 to the mtu size until you start seeing them again, the prior number that worked is the right size, add 28 to it for the IP overhead, and you hit the optimized size for your LAN/isp config.

 

And, maybe I won't need a Microcell after all one day.

 

Cheers, and thank you for all of your help.  The guide is a wonderful piece of work.

Message 23 of 30 (4,781 Views)
ACE - Master

Re: New problem - not Activating w/ Centurylink VDSL, Zyxel C1000Z, and Netgear R7000 Nighthawk

Thank  you. I for one would love to be able to do away with my MicoCell but with the "rules and regulations" imposed by the FCC for competing cellular carriers, dead zones and zones of minimal coverage are always going to exist. And with this competitive winner take all atmosphere, and method that a carrier can do to increase subscribers, or keep what they have, they will do. I have high hopes for the new MicroCell but only time will tell if my "suspicions" come to pass.

 

SIP ALG has been problematic for a lot of folks so if issues do occur, you might want to disable that if possible. In theory, it shouldn't cause any interference but proper implementation of that protocol is still an issue.

 

The MicroCell is still particular about it's secure VPN tunneling and anything tha can possibly interfer with that, or take resources away, is going to be a problem. Verizon has a femtocell as well and they have similar issues. However, for them, it's just easier to hobble another carrier from using their network than to try and work with that carrier on their issues.

___________________________________________________________

MicroCell Technical Guide by Otto Pylot


I am not an AT&T employee. For additional help, please send a PM to ATTCustomerCare

*The views and opinions expressed on this forum are purely my own. Any product claim, statistic, quote, or other representation about a product or service should be verified with the manufacturer, provider, or party.
Message 24 of 30 (4,777 Views)
ACE - Professor

Re: New problem - not Activating w/ Centurylink VDSL, Zyxel C1000Z, and Netgear R7000 Nighthawk

I've seen that procedure for optimizing LAN MTU before.  I've never used it because I've never had an issue that required reducing packet size.  Good to post though.

___________________________________________________________

MicroCell Technical Guide by Otto Pylot


I am not an AT&T employee. For additional help, please send a PM to ATTCustomerCare

*The views and opinions expressed on this forum are purely my own. Any product claim, statistic, quote, or other representation about a product or service should be verified with the manufacturer, provider, or party.
Message 25 of 30 (4,764 Views)
Contributor

Re: New problem - not Activating w/ Centurylink VDSL, Zyxel C1000Z, and Netgear R7000 Nighthawk

I know this is an old post, but I am another individual who had to change their MTU size to 1480 (from 1492) in order to get their Microcell to work, so I cannot thank the posters in this post enough for that solution.  

 

Quick question:  what are the chances of my throughput decreasing due to this change in MTU?

 

Thanks!

 

- John

Message 26 of 30 (2,585 Views)
ACE - Professor

Re: New problem - not Activating w/ Centurylink VDSL, Zyxel C1000Z, and Netgear R7000 Nighthawk

MTU (Maximum Transmission Unit) is the designated packet size in bytes for data transmission.  1500 bytes is the MTU for Ethernet.  1492 bytes is the MTU for PPPoE.  556 bytes is the typical MTU for dialup.

 

Changing the MTU from 1492 bytes to 1480 bytes is a slight change that I doubt you will notice as far as bandwidth. On one hand, the packet size is smaller so less data is transferred per one physical frame on the network.  However, running a smaller MTU will also decrease the time to transfer that packet.  The net difference is always slightly slower though because of increased packet header information that has to be transmitted per a given amount of packet data.

 

Ignoring the calculations which nobody is interested in, assuming a 1 Mbyte file size and let's say a 10 hop link over a T-1 line, the time it takes to transmit that file with a MTU of 1492 bytes would be 5.6526 seconds.  If you reduce the MTU to 1480 bytes, the time required would be 5.6529 seconds.

 

As you can see, a slight change in the MTU from 1492 bytes to 1480 bytes has no real world difference in bandwidth.

 

Generally, it's logical to assume larger packets (higher MTU) are better, because of all the following factors:

 

1.  network - reduce number of packet headers

2.  routers - less routing decisions

3.  clients - less protocol processing and device interrupts

 

However, if pure throughput is not the ultimate goal, smaller packets might be more "responsive" since they take less time to travel throughout the network.  That effect might be preferred in some applications and online gaming, at the expense of throughput.

 

Ultimately, packet size should be decided based on the type of the desired result, considering the underlying network as well, to avoid negative factors such as fragmentation of packets.  Still one has to realize the fact that larger packets will still transmit more useful data than smaller packets, and that there is no single "best" solution for all applications.

 

So to answer your question, your throughput will be theoretically decreased but I doubt you will notice any difference in your network changing the MTU from 1492 to 1480.

___________________________________________________________

MicroCell Technical Guide by Otto Pylot


I am not an AT&T employee. For additional help, please send a PM to ATTCustomerCare

*The views and opinions expressed on this forum are purely my own. Any product claim, statistic, quote, or other representation about a product or service should be verified with the manufacturer, provider, or party.
Message 27 of 30 (2,530 Views)
Contributor

Re: New problem - not Activating w/ Centurylink VDSL, Zyxel C1000Z, and Netgear R7000 Nighthawk

That completely answered my question and was extremely thorough.  Thank you so much!

 

- John

Message 28 of 30 (2,518 Views)
ACE - Professor

Re: New problem - not Activating w/ Centurylink VDSL, Zyxel C1000Z, and Netgear R7000 Nighthawk

We aim to please!

___________________________________________________________

MicroCell Technical Guide by Otto Pylot


I am not an AT&T employee. For additional help, please send a PM to ATTCustomerCare

*The views and opinions expressed on this forum are purely my own. Any product claim, statistic, quote, or other representation about a product or service should be verified with the manufacturer, provider, or party.
Message 29 of 30 (2,513 Views)
ACE - Master

Re: New problem - not Activating w/ Centurylink VDSL, Zyxel C1000Z, and Netgear R7000 Nighthawk

Thanks Wingman!

___________________________________________________________

MicroCell Technical Guide by Otto Pylot


I am not an AT&T employee. For additional help, please send a PM to ATTCustomerCare

*The views and opinions expressed on this forum are purely my own. Any product claim, statistic, quote, or other representation about a product or service should be verified with the manufacturer, provider, or party.
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