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Thread: intermittent packet loss, tried many things, have data, expert opinion needed.

  1. #1
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    intermittent packet loss, tried many things, have data, expert opinion needed.

    OK, I'm sorry that this is so long, but I want to give you as much detail and information about what I've done so far.

    I've had this Comcast cable problem for about a month, maybe a month and a half. I don't recall exactly when it started, but I do know the first time I noticed it we had a lot of thunderstorms in the area for a week. I figured that was the cause and let it go for a while, figuring that Comcast was probably working on the issue already (indeed, when I called Comcast support, for three days in a row a message played that said they were aware of a problem in our area and were actively working to resolve the issue and no call was necessary).

    Basically, the problem manifests itself as extremely slow speed when browsing the web, worse than dial-up, and often just unusable (we're talking 5+ minutes to load a simple page, in extreme circumstances).

    The problem is intermittent, sometimes things are great and fast. Up until this problem began, my connection has been rock solid (for 3+ years). I've always been with Comcast during this time.

    After the problem didn't go away for a week, I started troubleshooting on my own. I restarted everything, cold booted, defaulted my cable modem. I have a main computer and two laptops, all on a wireless network and the wireless router connects to the cable modem. I hooked up a laptop directly to the cable modem via ethernet cable to eliminate as much as I could from the scenario, the problem persisted. I swapped out the ethernet cable twice, using a brand new, tested, short cable finally. Always I can ping my cable modem and get, as expected, excellent response times, and 0% packet loss. So I assume the problem must be beyond it.

    Pings show varied, but often high, packet loss (anywhere from 17% to 56%). I never really noticed a pattern to the problem it wasn't like it was just evident during peak times, though for the last week I have noticed that it seems to be occurring late at night/early morning, though this isn't a hard and fast rule. Sometimes it will be really slow in the middle of the afternoon (I work from home a lot, and often need my internet connection to check my work email, etc. So I get to monitor its performance frequently).

    I eventually replaced my cable modem (I was on an older model Motorola Surfboard, now I'm on a 5120), but that didn't help. I have my cable modem and wireless router (and computer) on two separate power conditioners (to make sure the power coming in is never spiking or dripping, etc.). I worked UNIX/legacy hardware tech support for 4 years and know that cables do go bad, and often bad power is a culprit.

    When I called Comcast, after doing all the tests I've already mentioned, they said they could see my modem was going offline occasionally throughout the past week. Maybe this was because I kept rebooting it during testing, I'm not sure. Once when I called, they said they couldn't see my modem at all, that it appeared as if I was offline, but I was able to pull a web page up (I set my web cache to 0, and wiped it for this testing) albeit very, very slowly. They sent out a tech, who despite being a nice fellow, didn't understand was a ping was, or packet loss, and the most he did was change a splitter out and measure the signal (or, that's what he said, he wouldn't elaborate) with a little device. I demonstrated for him, while he was there, the packet loss. I showed him a running input/output traffic graph from my firewall showing how the traffic spiked in an abnormal way, I explained to him that when the packets were getting through, they were typically moving fast, so the "speed" really wasn't an issue, but since half of the packets were never returning, they were "leaking" out of the pipes so to speak, the problem ended up looking like a slow connection. He shrugged and said that since I was online and the signal looked good to him that was the best he could do, and then suggested I upgrade to the highest speed package. I'm at normal, middle ground offering right now, but I felt confident upgrading to a higher package would probably not affect the situation.

    Recently after reading about other people with similar problems I tried to do more things on my own. Yesterday I thought I had the problem solved after I switched the cable running from the box outside of my house all the way into the basement where the first splitter appears. I also changed the splitter to be a newer two-way 3.5db/3.5db out, with the line that runs to my cable modem going into one and the line going to our TVs going to the other. The line going to the TVs is further split by a three way, with the 3.5 out going to our main, HDTV. I used my best cable for everything I replaced, newer stuff with nice clean ends. In the process of replacing cable I was able to eliminate one splitter entirely from the mix. So now, this is what my cabling looks like:

    Cable 1: runs from the street post to a box outside of my house where it joins cable 2 with a coupler.

    Cable 2: (new cable) runs from the box outside of my house, into a hole in the brick of my basement, to a newer two-way splitter. This splits input from cable 2 into output for cable 3 and cable 4.

    Cable 3: runs from the two-splitter into my cable modem.

    Cable 4: runs to the input of a three-way splitter. Each cable on the output runs to a separate TV in the house.

    I thought this fixed the problem, because after doing this my ping was excellent and I had 0% packet loss for about 6 hours straight. And what convinced me more so is that moments before I swapped the cabling out, I was getting some of the worse packet loss ever. In fact, at each step of the change I ran a ping test to measure the difference (once after swapping out each cable, coupler, splitter) and it appeared to be getting gradually better, and only after I swapped everything out did it all get perfect. You can see then how I was convinced that what I did fixed the problem.

    Then around 1:30am at night (this is last night) I was playing halo 3 with my buddies and I started to lag. Sure enough, the packet loss was back. I measured it just about every 10-15 minutes until 2:30 or so, and it gradually got worse and worse. Rebooting the modem didn't help.

    So then I started searching more, and I found ping plotter and started running it. Here's what I've got now from it running all night and all of today so far. I see a number of things here that don't make sense to me. Why is the 2nd hop always 100% packet loss and why no address? Why is the packet loss in strict vertical blocks on 100% on and off, while my average latency otherwise is stagnant? Can anyone see a pattern here, is there a culprit router out there in the mix? This is where my own knowledge begins to fail me.

    Ping Plotter graph link here

    Here's my current Modem Signal levels:


    Here's my current Modem log

    And here's the output from running the TCP Analyzer:

    SpeedGuide.net TCP Analyzer Results
    Tested on: 10.21.2007 14:19
    IP address: 67.191.xxx.xxx

    TCP options string: 020405b401010402
    MSS: 1460
    MTU: 1500
    TCP Window: 64512 (NOT multiple of MSS)
    RWIN Scaling: 0
    Unscaled RWIN : 64512
    Reccomended RWINs: 64240, 128480, 256960, 513920
    BDP limit (200ms): 2580kbps (323KBytes/s)
    BDP limit (500ms): 1032kbps (129KBytes/s)
    MTU Discovery: ON
    TTL: 112
    Timestamps: OFF
    SACKs: ON
    IP ToS: 00100000 (32)
    Precedence: 001 (priority)
    Delay: 0 (normal delay)
    Throughput: 0 (normal throughput)
    Reliability: 0 (normal reliability)
    Cost: 0 (normal cost)
    Check bit: 0 (correct)
    DiffServ: CS1 001000 (8) - class 1 (RFC 2474). Similar forwarding behavior to the ToS Precedence field.

    What should I do next? Is there something specific I can tell Comcast to look into?

    Any input or thoughts would be greatly appreciated.

    Thanks,
    Jeff
    Last edited by cubeblue; 10-21-07 at 05:38 PM.

  2. #2
    Ohh Hell yeah.. Sava700's Avatar
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    www.pingplotter.com

    download the regular version.. set to 1second trace intervals and see where the problem is.. save the data and call them and say "Hey I see a problem and here it is" Then keep on them to fix it!

  3. #3
    Elite Member trogers's Avatar
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    Quote Originally Posted by cubeblue View Post
    And here's the output from running the TCP Analyzer:

    SpeedGuide.net TCP Analyzer Results
    Tested on: 10.21.2007 14:19
    IP address: 67.191.xxx.xxx

    TCP options string: 020405b401010402
    MSS: 1460
    MTU: 1500
    TCP Window: 64512 (NOT multiple of MSS)
    RWIN Scaling: 0
    Unscaled RWIN : 64512
    Reccomended RWINs: 64240, 128480, 256960, 513920
    BDP limit (200ms): 2580kbps (323KBytes/s)
    BDP limit (500ms): 1032kbps (129KBytes/s)
    MTU Discovery: ON
    TTL: 112
    Timestamps: OFF
    SACKs: ON
    IP ToS: 00100000 (32)
    Precedence: 001 (priority)
    Delay: 0 (normal delay)
    Throughput: 0 (normal throughput)
    Reliability: 0 (normal reliability)
    Cost: 0 (normal cost)
    Check bit: 0 (correct)
    DiffServ: CS1 001000 (8) - class 1 (RFC 2474). Similar forwarding behavior to the ToS Precedence field.

    What should I do next? Is there something specific I can tell Comcast to look into?

    Any input or thoughts would be greatly appreciated.

    Thanks,
    Jeff
    What speed did you pay your ISP to give you?

  4. #4
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    troger:

    Currently I get the middle package called "Performance (6 Mbps)", but I've clocked up to 12Mbps before (a couple nights ago when there wasn't any packet loss, and I speed testing against a server in the same city).

    I should add that I ran the TCP Optimizer and now my TCP Analyzer results look like this:

    SpeedGuide.net TCP Analyzer Results
    Tested on: 10.22.2007 09:31
    IP address: 67.191.xxx.xxx

    TCP options string: 020405b40103030301010402
    MSS: 1460
    MTU: 1500
    TCP Window: 513920 (multiple of MSS)
    RWIN Scaling: 3
    Unscaled RWIN : 64240
    Reccomended RWINs: 64240, 128480, 256960, 513920
    BDP limit (200ms): 20557kbps (2570KBytes/s)
    BDP limit (500ms): 8223kbps (1028KBytes/s)
    MTU Discovery: ON
    TTL: 48
    Timestamps: OFF
    SACKs: ON
    IP ToS: 00100000 (32)
    Precedence: 001 (priority)
    Delay: 0 (normal delay)
    Throughput: 0 (normal throughput)
    Reliability: 0 (normal reliability)
    Cost: 0 (normal cost)
    Check bit: 0 (correct)
    DiffServ: CS1 001000 (8) - class 1 (RFC 2474). Similar forwarding behavior to the ToS Precedence field.


    Also, I've been running PingPlotter in 1 second intervals since late afternoon yesterday. You can see how there's very little packet loss in the earlier part of the day, but later on it just skyrockets, and stays that way pretty much until now.

    Here's the new pingplotter graph, with a nearly 24 hour spread

    I'm not entirely sure how to interpret the results. I don't see a specific hop that always causes the packet loss, except for the nameless hop 2 (what's going on there?) which always reports 100% packet loss. I guess the router there doesn't return ICMP requests or something? I'm not sure.

  5. #5
    Elite Member trogers's Avatar
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    Hop 2 is probably blocking ICMP pings and it is likely to be the firewall in your router.

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