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Packet loss, not my modem (Comcast network engineer please read!)

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Packet loss, not my modem (Comcast network engineer please read!)

Summary for Comcast network engineer: Your router at  66.31.244.1 is dropping ipv4 packets! Please consider checking it out.

 

Details:

 

I've been experiencing ipv4 packet loss between 5 and 20% for about a month. No loss on ipv6. Comcast sent a tech to my house. He tested the coax signal, all good power levels and SNR. He suggested that my modem was old and faulty (Netgear CM400, DOCSIS 3.0), and I should get a new one.

 

Before buying a new modem, I did a little more digging. Since I was getting zero packet loss on ipv6, I didn't think the modem was at fault. I checked for a duplicate ipv4 assignment (saw in another thread)- but no, I had a unique ipv4 address.

 

Then I connected my laptop directly to the modem, bypassing my home router (pfsense). There was no packet loss on ipv4 anymore! But, I noticed that Comcast's DHCP server assigned my laptop a different gateway. Hmmm. So I spoofed my router's MAC over to my laptop. Comcast then assigned my laptop the old gateway... and the ipv4 packet loss returned. Then I spoofed my router's MAC to a new value, and Comcast assigned it yet another gateway, and no more packet loss!

 

I believe this proves that Comcast's router is the source of the ipv4 packet loss, not my modem.

 

I'm sure that router is affecting dozens if not hundreds of other customers, too. I hope this helps! 

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Expert

Re: Packet loss, not my modem (Comcast network engineer please read!)

FWIW, this is mainly a peer to peer type of help forum here. It's not likely that a Comcast network engineer will be here.

 

That said, hmmm... I'm not getting any packet loss when I ping that router from my end;

 

Pinging 66.31.244.1 with 32 bytes of data:
Reply from 66.31.244.1: bytes=32 time=22ms TTL=246
Reply from 66.31.244.1: bytes=32 time=19ms TTL=246
Reply from 66.31.244.1: bytes=32 time=19ms TTL=246
Reply from 66.31.244.1: bytes=32 time=20ms TTL=246
Reply from 66.31.244.1: bytes=32 time=21ms TTL=246
Reply from 66.31.244.1: bytes=32 time=20ms TTL=246
Reply from 66.31.244.1: bytes=32 time=20ms TTL=246
Reply from 66.31.244.1: bytes=32 time=21ms TTL=246
Reply from 66.31.244.1: bytes=32 time=20ms TTL=246
Reply from 66.31.244.1: bytes=32 time=22ms TTL=246
Reply from 66.31.244.1: bytes=32 time=31ms TTL=246
Reply from 66.31.244.1: bytes=32 time=20ms TTL=246
Reply from 66.31.244.1: bytes=32 time=19ms TTL=246
Reply from 66.31.244.1: bytes=32 time=23ms TTL=246
Reply from 66.31.244.1: bytes=32 time=19ms TTL=246
Reply from 66.31.244.1: bytes=32 time=20ms TTL=246
Reply from 66.31.244.1: bytes=32 time=22ms TTL=246
Reply from 66.31.244.1: bytes=32 time=20ms TTL=246
Reply from 66.31.244.1: bytes=32 time=23ms TTL=246
Reply from 66.31.244.1: bytes=32 time=20ms TTL=246
Reply from 66.31.244.1: bytes=32 time=20ms TTL=246
Reply from 66.31.244.1: bytes=32 time=26ms TTL=246
Reply from 66.31.244.1: bytes=32 time=22ms TTL=246
Reply from 66.31.244.1: bytes=32 time=20ms TTL=246
Reply from 66.31.244.1: bytes=32 time=19ms TTL=246
Reply from 66.31.244.1: bytes=32 time=21ms TTL=246
Reply from 66.31.244.1: bytes=32 time=19ms TTL=246
Reply from 66.31.244.1: bytes=32 time=20ms TTL=246
Reply from 66.31.244.1: bytes=32 time=23ms TTL=246
Reply from 66.31.244.1: bytes=32 time=29ms TTL=246
Reply from 66.31.244.1: bytes=32 time=26ms TTL=246
Reply from 66.31.244.1: bytes=32 time=24ms TTL=246
Reply from 66.31.244.1: bytes=32 time=21ms TTL=246
Reply from 66.31.244.1: bytes=32 time=19ms TTL=246
Reply from 66.31.244.1: bytes=32 time=20ms TTL=246
Reply from 66.31.244.1: bytes=32 time=21ms TTL=246
Reply from 66.31.244.1: bytes=32 time=33ms TTL=246
Reply from 66.31.244.1: bytes=32 time=20ms TTL=246
Reply from 66.31.244.1: bytes=32 time=22ms TTL=246
Reply from 66.31.244.1: bytes=32 time=21ms TTL=246
Reply from 66.31.244.1: bytes=32 time=23ms TTL=246
Reply from 66.31.244.1: bytes=32 time=20ms TTL=246
Reply from 66.31.244.1: bytes=32 time=22ms TTL=246
Reply from 66.31.244.1: bytes=32 time=24ms TTL=246
Reply from 66.31.244.1: bytes=32 time=24ms TTL=246
Reply from 66.31.244.1: bytes=32 time=20ms TTL=246
Reply from 66.31.244.1: bytes=32 time=20ms TTL=246
Reply from 66.31.244.1: bytes=32 time=20ms TTL=246
Reply from 66.31.244.1: bytes=32 time=20ms TTL=246
Reply from 66.31.244.1: bytes=32 time=20ms TTL=246
Reply from 66.31.244.1: bytes=32 time=20ms TTL=246
Reply from 66.31.244.1: bytes=32 time=22ms TTL=246
Reply from 66.31.244.1: bytes=32 time=20ms TTL=246
Reply from 66.31.244.1: bytes=32 time=21ms TTL=246
Reply from 66.31.244.1: bytes=32 time=19ms TTL=246
Reply from 66.31.244.1: bytes=32 time=22ms TTL=246
Reply from 66.31.244.1: bytes=32 time=20ms TTL=246
Reply from 66.31.244.1: bytes=32 time=20ms TTL=246
Reply from 66.31.244.1: bytes=32 time=19ms TTL=246
Reply from 66.31.244.1: bytes=32 time=19ms TTL=246
Reply from 66.31.244.1: bytes=32 time=20ms TTL=246
Reply from 66.31.244.1: bytes=32 time=21ms TTL=246
Reply from 66.31.244.1: bytes=32 time=23ms TTL=246
Reply from 66.31.244.1: bytes=32 time=22ms TTL=246
Reply from 66.31.244.1: bytes=32 time=18ms TTL=246
Reply from 66.31.244.1: bytes=32 time=21ms TTL=246
Reply from 66.31.244.1: bytes=32 time=28ms TTL=246
Reply from 66.31.244.1: bytes=32 time=19ms TTL=246
Reply from 66.31.244.1: bytes=32 time=22ms TTL=246
Reply from 66.31.244.1: bytes=32 time=20ms TTL=246
Reply from 66.31.244.1: bytes=32 time=21ms TTL=246
Reply from 66.31.244.1: bytes=32 time=21ms TTL=246
Reply from 66.31.244.1: bytes=32 time=19ms TTL=246
Reply from 66.31.244.1: bytes=32 time=20ms TTL=246

Ping statistics for 66.31.244.1:
Packets: Sent = 74, Received = 74, Lost = 0 (0% loss),
Approximate round trip times in milli-seconds:
Minimum = 18ms, Maximum = 33ms, Average = 21ms

 

Control-C
^C

 

Tracing route to c-66-31-244-1.hsd1.ma.comcast.net [66.31.244.1]
over a maximum of 30 hops:

1 2 ms 1 ms 3 ms 192.168.1.1
2 10 ms 18 ms 11 ms 96.120.73.93
3 16 ms 12 ms 13 ms 68.85.119.97
4 12 ms 14 ms 10 ms 96.110.60.101
5 14 ms 18 ms 14 ms 96.108.142.253
6 15 ms 15 ms 17 ms be-98-ar03.plainfield.nj.panjde.comcast.net [68.85.35.37]
7 14 ms 20 ms 14 ms be-33659-cr01.newark.nj.ibone.comcast.net [68.86.90.21]
8 16 ms 37 ms 16 ms be-10203-cr02.newyork.ny.ibone.comcast.net [68.86.85.186]
9 19 ms 23 ms 22 ms be-7922-ar01.needham.ma.boston.comcast.net [68.86.90.218]
10 25 ms 21 ms 23 ms 96.108.44.218
11 22 ms 22 ms 19 ms c-66-31-244-1.hsd1.ma.comcast.net [66.31.244.1]

 

Trace complete.

 

What do you get when you ping your Comcast WAN / default gateway IP ?



I am not a Comcast Employee.
I am a Customer Expert volunteering my time to help other customers here in the Forums.
We ask that you post publicly so people with similar questions may benefit from the conversation.
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New Poster

Re: Packet loss, not my modem (Comcast network engineer please read!)

Thanks for your response!

 

I only see dropped packets when that router is my default gateway. It doesn't drop packets for me when pinged from another source (either inside or outside of Comcast).

 

When that router is set to my default gateway, I get ipv4 packet loss between 5 and 20%. I tried two other upstream Comcast routers as my default gateway, and there is no packet loss.

 

I'm not a certified network engineer, but I do build and program embedded Ethernet devices for a living. From my point of view, it seems like the packet buffer handling one of the residential-facing ports on that router is overflowing. This should be throwing an alert in their logs. I can't imagine they don't have an automated system in place to detect this.

 

Honestly, I'm posting here for two reasons: 1) in case it helps anyone else, and 2) to document the fact that my equipment is not at fault, and therefore they really shouldn't charge me $100 for the tech's visit.

 

I could not find another way to inform Comcast with this level of detail. Is there a more direct way to get in touch with a network engineer? Their phone staff seems completely scripted- which is certainly fine for many problems. Is there a secret phrase I can utter to be transferred someone who has the router management logins?

 

At this point, my service is working fine. So I don't really care if they fix their router. But maybe my solution will help other folks.

 

Cheers!

Highlighted
Expert

Re: Packet loss, not my modem (Comcast network engineer please read!)

Did you ping the WAN default gateway for the haibut (the hop after your home router's hop) ?



I am not a Comcast Employee.
I am a Customer Expert volunteering my time to help other customers here in the Forums.
We ask that you post publicly so people with similar questions may benefit from the conversation.
Was your question answered? Mark the post as Best Answer!