Visitor
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3 Messages
Brand new Comcast Modem broken in bridge mode (dropping packets)
3 days ago I switched from my motorola modem to the latest comcast modem (to get unlimited data). It has been nothing but a disaster.
All Tech support does is look at the speed test look and claims everything is working. Meanwhile, just opening this web page took 15 seconds. I am dropping packets like crazy - See below (masked one IP address). Trying to discuss packet loss with tech support goes nowhere (they say the speed test is good so it must be good - and then tell me they have no idea what packet loss means). Turning off bridge mode will eliminate most of the dropped packets but then I am double-NATed and other things don't work correctly. My personal modem ran great for years. Comcast won't let me temporarily switch back to prove the issue is with the modem as it will change my account causing me to lose the modem special.
Any suggestions on how I may get this resolved?
My traceroute [v0.95]
Mac.local (10.0.1.117) -> 8.8.8.8 (8.8.8.8) 2022-12-23T14:34:34-0800
Keys: Help Display mode Restart statistics Order of fields quit
Packets Pings
Host Loss% Snt Last Avg Best Wrst StDev
1. home 0.0% 244 0.5 0.4 0.2 2.3 0.2
2. 10.60.1xx.xxx 71.2% 244 32.7 33.6 10.5 90.7 14.5
3. 24.153.81.145 82.7% 244 23.6 15.0 9.4 33.6 5.3
4. po-2-rur902.seattle.wa.seattle.c 85.2% 244 38.6 16.7 9.6 38.6 6.5
5. be-20-ar01.seattle.wa.seattle.co 86.8% 244 10.6 13.3 9.1 24.1 3.4
6. be-220-ar01.seattle.wa.seattle.c 84.4% 244 12.3 20.6 9.5 64.4 9.8
7. be-501-arsc1.seattle.wa.seattle. 87.7% 244 29.3 32.4 9.9 236.5 51.3
8. 50.218.57.26 84.0% 244 12.1 15.7 10.4 47.9 7.6
9. 142.251.50.47 86.4% 244 17.3 16.1 10.2 38.8 6.3
10. 142.251.48.213 83.1% 244 15.5 15.1 9.2 27.5 4.4
11. dns.google 79.8% 244 11.6 14.9 11.0 38.1 4.8
The_Nephilim
Contributor
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11 Messages
1 year ago
umm are you using Googles DNS IP's? if so why? also packet loss is a bit tricky and it would take someone who knows what they are talking about. I think that is above most techs we can talk to to help. I am unsure who you can talk to but if the tech you are talking to does not know what packet loss is I would ask for another tech or bump me up to an advanced tech.
Also I remeber some time back they had a post showing what the modems info on the line static and such should read and you should be able to see it and check yourself maybe it is just line interferance from the modem to the pole..
(edited)
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SiteX
Visitor
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3 Messages
1 year ago
Ugh. Looks like my reply got eaten because the page timed out 😕
Using the google dns address just for a stable end point to ping against - not actually using their dns server. Same issue happens with 1.1.1.1 (cloud flare).
everything worked great with my owned modem. Internet is randomly unusable (aka - timed out just replying) even though the speed tests looks great with the Comcast modem. Only reason I switched is to get unlimited bandwidth and faster uploads from using the Comcast modem. Comcast won’t temporary swap me back to my modem so I can prove it’s an issue with bridge mode on their modem so I am stuck.
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flatlander3
Problem Solver
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1.5K Messages
1 year ago
FYI: If you use Xfinity equipment, you can't change DNS servers anyway even if you wanted to, and changing them on an internal client won't work. They hijack that with their equipment. I think it's a problem and have never had good luck with their DNS, but I guess they want the marketing info.
If you log into your xfinity gateway locally, take a look at the power, snr, and channels for correctable/uncorrectable errors on both upstream and downstream plus the log files (if visible then -- I don't know how much info you can get in bridge mode with their stuff). Maybe you got something else going on.
If your old modem terminated the coax just fine, and the new one does not, or is less forgiving in bridge mode, you may have your answer. Look at it in 'gateway mode' as a double natd and run some traffic. Look at it when you shift to bridge mode and run some more traffic. Let it run for a while in each mode. You are looking at a moment in time when you pull up the line stats. Cable distribution is a bit touchy. Signal power too high/too low, erratic, doesn't help and causes all kinds of problems.
This link points out potential issues you may have, and if your wiring is marginal, or you got splitters or an amp that isn't working right, perhaps you can make it better or more workable: https://forums.xfinity.com/conversations/your-home-network/internet-troubleshooting-tips/602dae4ac5375f08cde52ea0 Ideal, is a clean short, straight run from where it enters your house with decent connectors with good cabling.
(edited)
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user_bc0494
Visitor
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1 Message
1 year ago
I had the same issue. Drove me mad for a while and Xfinity didn’t help at all. At the end it turned out that the modem that Xfinity has requires ARP request for the GWs IP at least once every 5 min or starts dropping packets. I’m using OPNSense (FreeBSD) and it turned out that FreeBSD caches ARP entries for 20min by default.This is much longer than Windows/Linux (which cache for a minute or two). I ended up setting net.link.ether.inet.max_age tunable to 120 and that solved the problem. It would be nice if Xfinity had real support where you can report that so they can fix the modem.
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jeffsponaugle
Visitor
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1 Message
1 year ago
I had the same type of problem - Documented here:
https://sponaugle.com/wp/2023/01/22/comcast-2gig-200m-service-upgrade-issues/
I ended up adding a cronjob that reset the ARP which fixed it, and all is good now.
I'm still on the 1.x release, so I'll be curious when I upgrade if it is fixed.
Also - I did a slightly more precise arp delete:
sudo arp -d `arp -i eth9 | awk 'BEGIN { FS="[ ]" } ; NR==1 {print $1 }'`
(note eth9 is the comcast interface in this case)
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