I am a 3rd party contractor. I recently recommended a customer switch from a local provider to Comcast because they were paying about $3,000/mo for 25/25 internet and a PRI, where Comcast quoted 100/25 and the PRI at $400/mo.
We are switching in phases. Internet was installed 02/27/2014.
I immediately ran into problems with packet loss and latency.
After doing a bunch of testing, here's what I've found and *verified* using multiple machines (Linux, Windows, and BSD):
If I ping from any device on 'my side' of the Comcast modem (i.e. something plugged in to the ethernet jacks and assigned an IP from our Comcast-assigned block), to any device on my side of the Comcast modem, I have no packet loss.
I can also ping from a device on my side *to* the modem's public IP without packet loss.
If I ping anything past the modem, I get (over a period of ~6 hours) 30% packet loss and an increase of ~25 msec RTT.
I tested this with a few IPs like Google's DNS servers, my office (which is on Comcast), and the next upstream hop past my router (as determined by a traceroute).
From the opposite side of the modem (from my home and from my office), I also get zero packet loss to the Comcast modem itself.
But I get ~30% packet loss to any device I plug in to the modem and an increase of ~25 msec RTT.
...so I figured it was something bizarre with the modem and called support again.
They were zero help.
They can ping the modem IP just fine with no packet loss. (And so can I from either inside the building or remotely from my house)
The moment they ping something on 'my' side of the modem, they see packet loss which they attribute to my network being screwed up. (Actually, they said it's because I'm not using their DNS servers which us utter crap)
So I called the sales guy and asked if he could get someone to replace the modem.
He did. The tech came out, replaced the modem, re-provisioned it with our IP block, plugged himself in, and runs a few tests over 10 minutes. He sees no packet loss, no unreasonable delays, and leaves.
A few minutes later everything starts timing out with the occasional packet coming through, and then returns to intermittent periods of packet loss and 'normal' service.
Everyone says it's something on my end. I don't believe it.
I've tested with multiple pieces of hardware, multiple operating systems, different cables every time, various combinations of devices plugged into the modem--including one device at a time with no other hardware plugged into the modem.
I understand the position of the Comcast techs--they can ping their modem just fine, so my device must be bad. And my position is that my devices are working fine, but once traffic crosses the modem to the Comcast network there are problems. ..but the modem has been replaced, equipment has been swapped, signal levels have been checked.
Attached is a smokeping graph from a Linux box plugged directly into the modem pinging the 'next hop' past the modem with nothing else plugged into the modem.
Any pointers?
