[ale] Slightly OT: Reasonable Latency with Comcast Business

jc.lightner at comcast.net jc.lightner at comcast.net
Thu Nov 14 15:42:09 EST 2024 

Rebooting the modem is probably a good idea.

I used to have regular issues with Comcast “slowness” but they always told me they saw no such issue from their end.   Rebooting the modem is something I do these days at home and I haven’t seen those issues in a long time.  (Of course, they do still go down on rare occasion but that is a problem with most ISPs.)   At my former job we’d lose AT&T less often than Comcast Business.   Rebooting the cable modem there (which looked suspiciously like the one in my home) sometimes resolved issues.   We did NOT do that daily.   




From: Ale <ale-bounces at ale.org> On Behalf Of Jason Jessico via Ale
Sent: Thursday, November 14, 2024 11:53 AM
To: Atlanta Linux Enthusiasts <ale at ale.org>
Cc: Jason Jessico <jjessico at gmail.com>; Derek Atkins <derek at ihtfp.com>
Subject: Re: [ale] Slightly OT: Reasonable Latency with Comcast Business

 

You may also find it helpful to have something specific to check for DNS resolution.  In some systems/cases the failure to resolve an FQDN used as part of the check will show up as a generic "no/lost connection".  Provided the system has the capability a set of hosts to test to could be something like localhost, the LAN default gateway, the modem's default gateway, the FQDN the system uses by default for testing, and a well known IPv4 endpoint like Google's 8.8.8.8.

 

On Thu, Nov 14, 2024 at 11:25 AM Derek Atkins via Ale <ale at ale.org <mailto:ale at ale.org> > wrote:

What concerns me is the "empty" part of your graph..  At the 45ms peak,
there appears to be a section of "no response".  Note that depending on
the service being used, it's possible that the service is down.

FWIW, I run mrtg to monitor my network -- I run pings to several different
places to test latency across my uplink.  Specifically, one place I ping
is my 1st-hop upstream router.  If that router goes down or doesn't
respond, it is 100% correlated to my connection being down for everything.

Of course, YMMV.

-derek

On Thu, November 14, 2024 11:08 am, Neal Rhodes via Ale wrote:
> Thanks for the reply.
>
> I just got off the phone with Comcast.   To my delight it only took 12
> minutes total.
>
> Their criteria is, they don't get concerned until:
>
>       * Packets get lost;
>       * Latency exceeds 100ms.
>
> To which I can only say, wow.
>
> Comcast tech also says I should reboot their router.  (uptime over 140
> days.)
>
> My bet is the Ubiquiti router has much tighter assumptions.    Next I
> need to ask them precisely what their criteria is for concluding
> disconnection.
>
> regards,
>
> Neal
>
> On 2024-11-14 10:56, Derek Atkins wrote:
>
>> Hi Neal,
>>
>> I ditto what James says (and was going to say the same thing).  Take a
>> laptop that you KNOW can handle 1Gb, to be sure it's not a laptop
>> limitation, and then plug into the router to be sure you can show the
>> issue from their CPE.  Showing it from the Ubiquiti equipment is not
>> sufficient.
>>
>> Also, it helps if you can have a tech on the phone while the problem is
>> occurring.  I used to have Comcast Biz and would lose network every
>> time
>> there was a neighborhood power outage.  It took a 3hr outage during the
>> day and me calling just as the outage stopped for them to find the node
>> with the bad battery.
>>
>> So back to your issue.  It looks like it could be a network drop, a
>> DHCP
>> renew that takes too long, or possibly even an upstream issue with
>> Comcast.
>>
>> Expect to spend time trying to reproduce it, especially if it's
>> something
>> that isn't reliably reproducible.  You might also want to look at
>> potential buffer bloat, and also explore the possibility of NAT Table
>> overload.
>>
>> Having said that, the RTT you see (17ms) is reasonable for a cablemodem
>> plant.
>>
>> -derek
>>
>> On Thu, November 14, 2024 10:41 am, James Taylor via Ale wrote: My
>> experience with Comcast Business says that the you need to spend time
>> in the furnace room.
>> They are going to test from their router and if you don't show the
>> problem
>> there, they are unlikely (i.e. - never) to look further.
>> -jt
>>
>> James Taylor
>> 678-697-9420
>> james.taylor at eastcobbgroup.com <mailto:james.taylor at eastcobbgroup.com> 
>>
>> Neal Rhodes via Ale <ale at ale.org <mailto:ale at ale.org> > 11/14/2024, 10:36 AM >>>
>   This feels like a classic three party finger pointing exercise, and I'm
> doing a bit of research before we jump in.
>
> A couple of years ago, our church put in a sophisticated (at least by MY
> Measure) Ubiquity Unifi Mesh network, mostly to support security camera
> for the community pre-school.
>
> The core is a UDM Pro router, feeding all Ubiquiti stuff.
>
> And it has run totally steady.
>
> Here's the rub: Now that the "Last Guy That Touched it" moved to
> Florida, I'm getting multiple alerts per day to the effect of:
>
> * Your primary internet Comcast Business was disconnected and has been
> restored multiple times in last 24h. If this persists, please try
> restarting your ISP Modem.
> * Primary internet is experiencing high latency. Please restart the
> modem or contact the ISP if this persists.
>
> Aaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaand, nobody complains. Occasionally,
> I will see Zoom meetings from home where the church participants go
> really fuzzy and blocky, like Zoom has downshifted their resolution.
>
> Apparently it measures ping time to Ping.UI.Com <http://Ping.UI.Com>  to decide this.
>
> The Unifi Console reports the Comcast Business router as providing
> typical 14ms latency. With the occasional spike to 45ms.
>
> When I ping that address from my Uverse internet from home, I'm seeing
> consistently results from 7ms to 10ms.
>
> I don't know whether to ask Ubiquiti about raising their thresholds, or
> Nag Comcast about their performance. I guess I could ask Ubiquiti
> precisely what does "Internet Disconnected" mean?
>
> My personal experience with Business Comcast in the past has been.......
> not impressive. Usually, a service call just makes it worse. Is
> Comcast going to take my report from Ubiquiti seriously? Or tell me to
> pound sand? What additional evidence need I present?
>
> Yes, I could spend a quality hour in the furnace room, with a notebook
> connected to the LAN side of the Comcast router, (the only way I can
> talk to it) and see what I can see.
>
> I suppose I could just call Comcast, and give up another hour of my life
> to try and talk to someone with a clue.
>
> regards,
>
> Neal
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-- 
       Derek Atkins                 617-623-3745
       derek at ihtfp.com <mailto:derek at ihtfp.com>              www.ihtfp.com <http://www.ihtfp.com> 
       Computer and Internet Security Consultant

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