Paul Hartman posted on Thu, 06 Jun 2013 15:11:59 -0500 as excerpted: > On Thu, Jun 6, 2013 at 2:09 PM, Mark Knecht <markkne...@gmail.com> > wrote: >> Hi, >> Just taking a shot at the dark on this list before I ask something >> in the forums. Is there a simple app (or even something at the command >> line) that I can use to measure network throughput between two Gentoo >> machines on my internal network? > > Check out net-analyzer/ttcp and net-misc/iperf
In addition to these which others mentioned, take a look at bing (NOT the MS search engine, "Bandwidth-PING"!). It's probably most useful outside the LAN once you've decided your LAN is fine, but it can be used inside as well, and bing can be /quite/ useful for looking at how latency is affected by packet size and/or content (compressible vs. not (pseudo- random), or you can specify the content). What's particularly nice on the WAN side is that you specify the near and the far end (neither of which you have to control), and bing tells you the difference in speed between them. So you can use a traceroute or the like to find the route taken, then focus in on segments of it. For instance, you can make the near end your ISP gateway and the far end the last ISP hop in your city, very useful for checking if there's a problem router in the local ISP's equipment. >> Background: We sold our house & moved. Comcast talked me into >> getting there new 'Blast' level Internet service with "speed up to >> 50Mb/S" but darned if it isn't slower than regular Comcast ISP service >> was a the previous house. In our house I typically got about 27Mb/S >> download using something like www.Speakeasy.net/speedtest at a >> measurement tool. Here I've never gotten higher than 22Mb/S. I do >> however get much better upload speeds - about 12Mb/S instead of the >> 5Mb/S I got at the house. > > I don't have Comcast but often ISPs will host a speed test server inside > their network, so you can ensure the speeds you're seeing are not being > limited by normal Internet slowdown issues outside of their system. FWIW as can probably be deduced from my mail address, I'm on cox, another cable ISP. Luckily for me (I happen to live in cox land, not comcast land), cox's internet service consistently comes out near the top in customer surveys, while comcast at least by reputation is rather nearer the bottom. So I've always felt fortunate that I'm in cox territory, not comcast's, tho I guess rather obviously not everyone's experience is so terrible with comcast or people would be finding other alternatives. > To take a page out of the generic ISP tech support, I would try plugging > your computer directly into the cable modem and seeing what kind of > speeds you get then, to eliminate any outside factors. Absolutely. This one was always pretty close to the first suggestion back when cox still had newsgroups and I hung out on them. > If you're using your own router, I would check to ensure it is fast > enough to handle that kind of speed. If it has Gigabit ethernet ports > that is usually a good sign. If it only has 10/100 then you might wind > up replacing it with something more modern. Strongly seconded once again. Because the router is normally doing NAPT (Network Address and Port Translation, aka PAT, Port Address Translation, the consumer level variant of the more generalized NAT, Network Address Translation) and often more active firewalling as well, and due to the cheap CPU and memory provisioning common consumer level routers have, very commonly the LAN/WAN thruput on a consumer level router is 50% or less the rated Ethernet port bandwidth. You'll often get near full port thruput on the LAN side as that's typically less router CPU processing, if any (sometimes the LAN side is simply an unmanaged switch, with the only real routing and processing actually done only between the LAN/WAN interfaces), but LAN/WAN thruput is all too commonly 25-33% port rating. Which means that a typical 100 Mb "fast ethernet" router will commonly top off at between 25-30 Mbit in real life. Thus, certainly Cox *VERY* strongly recommends a modern router with gigabit ports for all their higher tier internet services, as they're typically provisioned to do a couple hundred Mbit minimum (can't get /too/ far below the port rating) LAN/WAN thruput, while as I said it's VERY common to have 100 Mbit "fast ethernet" port routers top out at 25-30 Mbit. Meanwhile, I know a bit about cable modems from my cox newsgroup days as well. What brand and model modem do you have, and are you renting it or did you purchase? I'm personally quite partial to the Motorola Surf Board brand modems, as they tend to be reliably high quality, and to expose more troubleshooting information on the customer side if they know where to look. Other brand modems /can/ be as good, but the Motorola surf boards have seemed to have been consistently good quality (and as I said to expose more trouble shooting info to the customer) from the first dialup uplink cable modem models many years ago thru to the latest DOCSIS-3.x rated sb6xxx series. In your web browser, try going to http://192.168.100.1 (this assumes a stand-alone modem, a combined modem/router /may/ expose the same information differently, I'm not sure as I've never had one). On any DOCSIS certified modem, this should be the modem's internal web server troubleshooting interface (assuming comcast doesn't disable it entirely, cox doesn't). As I said above, however, some brand/model modems expose more information here than others, with the Motorola Surfboards being consistently really good. Depending on your modem's brand and model (and on what the ISP has configured as restricted), the interface will differ some. However, the most critical information is usually found on a signals page, or similar. There are three critical signal-strength numbers. In order of what tends to show problems first they are upstream power level, downstream power level, and downstream SNR (signal to noise ratio). Upstream power level is best in the 40s dBmV, tho I've seen people report connections at much lower values (into the lower 30s IIRC and even one at 27, tho I wonder how he could connect at all or maybe his firmware was weird and it was mis-reporting, he was having issues, tho), and depending on the modulation used, the numbers typically top out at 55-58. Above 50 means your modem is effectively having to shout to be heard properly by the cable head-end, to the point it's causing interference with the downstream signal as well, while below about 38-40 means your modem is whispering and even that is still coming thru painfully loud at the other end. But an upstream power in the 40s is good. =:^) Downstream power is ideally 0, and the two ends will adjust their transmission power levels within a range to try to keep (near) zero at the other end if possible, so this one doesn't go out of range as often as upstream power, but if it does, it definitely indicates problems. The equipment is rated to work at zero +/- 15 dBmV, but from all I've seen, you want it between about -8 and +2 if possible -- if it gets out of that range you can usually still connect, but there tend to be more issues as the connection gets more marginal. A positive value isn't very common and often indicates an additional line-amp in the line -- line-amps are often useful for (at least old style analog, I don't really know about the newer digital, tho I suspect it may be more like internet) video, but tend to be more problematic for internet, thus the unbalance favoring the negative side. If you're better than -6, solid connection. -8, still pretty good but you might have occasional temporary issues. -10 is getting marginal and often means intermittent issues. -12 or worse, better be worried. Downstream SNR. Ultimately, this is the number that really counts, the number that the power dynamically adjusts for to keep consistent, tho of course you can only see the modem's side of this one, not the number at the head-end. Higher is better. Typical good numbers are in the upper 30s, tho down to 32 or so should be usable. Honestly, I don't remember seeing this one go low too often, however, unless at least one of the other two were WAAYYY out, which isn't surprising, since by design the others adjust to try to keep this one in line, so the others will go out of line first. Finally, even if your numbers are reasonable, note whether they change dramatically over the course of hours. Some seasonal swing is normal -- colder typically better so summer is the critical time -- but if you're swinging 10 dBmV (or even 8, I'd actually be worried if it's more than 6) either upstream or downstream in a few hours and it's not due to some really serious weather changes, chances are good that there's a loose fitting or bad cable somewhere. The reason this matters even if the numbers stay reasonably good is that there's a limit to the dynamic adjustment the equipment can make while maintaining a connection. Thus, big swings often force the equipment to break the existing connection and renegotiate a new one with new parameters. That's fine if it's happening a time or two a season, but if it's happening several times a day, it's irritating, since you will obviously not be able to do anything on the net while it's renegotiating. So good numbers are 40s upstream power, 0 to -6 downstream power, and mid to upper 30s downstream SNR, without wild swings. With upstream power often being the first to show issues, if you're running over 50 or under 40 there, it's quite likely to be affecting your speeds. As I mentioned, even tho it's upstream, the two-way nature of the common TCP connection and the fact that there can be some interference between upstream and downstream does mean that an upstream power above 50, certainly above 52, can mean downstream issues as well. That has both my own experience and that I've seen on the cox newsgroups (and the general comp.dcom.xdsl and cable-modems newsgroups during the time I was reading them too) as well. Lastly, on Motorola Surfboards at least, and some but not all other brands, there's generally a log page available that can make interesting reading too. I won't cover it in nearly the detail I did the above but two hints for reading it: 1) At least Motorola Surfboard modems run Linux internally (modern versions even have an open source page with links to the appropriate sources, in compliance with the GPL... tho it doesn't do a lot of good unless you have a handy cable head-end lying around, since by DOCSIS standard, the firmware can only be flashed from the RFI side, not the Ethernet side), and thus have the same Linux/POSIX standard epoch time, January 1, 1970. Thus, any log events showing as 1970 indicate the modem wasn't able to contact a time server since its last reset at the time that event occurred, so it's effectively measuring the time since the modem booted, before it could get a connection. And AFAIK, times are in universal time, so offset from (basically) GMT, not local time. 2) Logged events can appear much more alarming than they actually are, and in fact, on some cable systems certain functions won't be used at all so will repeatedly timeout, unless/until the cableco decides to turn off the warnings entirely in the config, which it often does eventually, but not always right away. If you actually lose sync, either that or modem reset along with a few 1970 events until it can contact a time server again, show up. So if you're not seeing that very often (my log shows cox did something short early on June 6, but there weren't any 1970 times reported so it was short, and before that, the last outage was May 16, longer and more serious, as 1970 times reach back from then until the beginning of the log), nothing to worry about even if some of the logged events do look rather alarming. -- Duncan - List replies preferred. No HTML msgs. "Every nonfree program has a lord, a master -- and if you use the program, he is your master." Richard Stallman
