Slashdot Mirror

← Back to Stories (view on slashdot.org)

Beating Comcast's Sandvine On Linux With Iptables

Posted by timothy on from the and-then-I'd-be-all-like-pow-and-reconfigure-iptables dept.

HiroDeckard writes "Multiple sites reported a while ago that Comcast was using Sandvine to do TCP packet resets to throttle BitTorrent connections of their users. This practice may be a thing of the past as it's been found a simple rule in the Linux firewall, iptables, can simply just block their reset packets, returning your BitTorrent back to normal speeds and allowing you to once again connect to all your seeds and peer. If blocking the TCP packet resets becomes a common practice, on and off of Linux, it'll be interesting to see the next move in the cat-and-mouse game between customers and service providers, and who controls that bandwidth."

26 of 361 comments (clear)

  1. It's a trace buster buster buster by Anonymous Coward · · Score: 5, Funny

    It'll bust their trace buster buster.

    1. Re:It's a trace buster buster buster by Tubal-Cain · · Score: 5, Insightful

      Straight-up blocking it is probably more clearly illegal than throttling.

    2. Re:It's a trace buster buster buster by Kadin2048 · · Score: 5, Interesting

      Last time this came up for discussion, some people suggested that RST-injection was computationally easier than packet blocking, because it works on the connection level rather than the packet level.

      It still seems to me like you'd have to do quite a bit of DPI to determine which connections are being used for Bittorrent, but maybe you can identify a connection, send a forged RST packet, and then ignore the packets in that connection for a while (saving you load on the DPI box) for a while, maybe just until it closes.

      I'm not entirely clear how these Sandvine boxes work, but it seems like it would be easier to identify "okay, this connection is being used for x," "this connection is being used for Y," and then not have to pay more attention to them, than it would be to examine every single packet. That's where you get your cost reduction, I suspect.

      Sandvine has a few patents out there that probably describe in greater detail how their QoS tool works (and which I haven't read yet); apparently the QoS RST-forging are part of their "Stateful Policy Management" product.

      --
      "Ladies and gentlemen, my killbot features Lotus Notes and a machine gun. It is the finest available."
  2. Tag: !news by Mr2001 · · Score: 5, Insightful

    This trick has been around for a while, hasn't it?

    The problem is, you can only filter out the RST packets on your end of the connection. But Sandvine also sends RSTs to the other end of the connection. That means it isn't enough for you to be running this iptables rule - all the peers you connect to have to be running it too.

    --
    Visual IRC: Fast. Powerful. Free.
    1. Re:Tag: !news by cryptoluddite · · Score: 5, Insightful

      The problem is, you can only filter out the RST packets on your end of the connection.

      That's only a temporary problem. The real problem -- for the ISPs -- is that the same software is running on each end of a p2p, so all of their efforts are guaranteed to fail eventually.

      For instance, p2p programs can start using UDP spread spectrum... pass packets on random ports. The receiver then basically implements a quick and dirty tcp-like connection over this (ie much worse for an ISP than actual TCP). Add encryption and random length so it's harder to filter out. Or there can be a shared random number seed for the shared ports. Just for example...

      There's probably some computer science or information theory law stating this, but they can't ultimately reduce the targeted traffic by more than the loss from encoding it as 'normal' traffic. For instance, if they limit torrents to 100k/s and the loss is 33% from 'base64' encoding the data as some kind of an html-ish doc then if normal web pages get more than 133k/s then torrents would be faster encoding them as 'normal' traffic.

      ... then they have to try to figure out what are real web pages/servers and what are really some other protocol pretending.

  3. Good, but shouldn't be necessary by corsec67 · · Score: 5, Interesting

    While it is good that it is easy to ignore reset packets that were created by the ISP, the question still remains:

    Why should we have to block forged packets made by the ISP? If the MAFIAA suits are banking on IP == identity, and the ISP is forging packets with an IP that doesn't belong to any computer they own, isn't that a fairly serious form of forgery?

    And, wow that site went down fast.

    --
    If I have nothing to hide, don't search me
  4. Re:Already slashdotted... by MadTinfoilHatter · · Score: 5, Informative

    Here's a link to Google's cache of the article.

  5. encryption by socsoc · · Score: 5, Interesting

    As a Comcast customer, I've never had my torrents completely stop, they just go around 300k... I did notice a speed increase when I chose to encrypt the traffic (uTorrent has it under Speed Guide).

    Comcast is evil and I want them to DIAF, but my torrents, which are legal, haven't been that impacted.

    When I want fast, I use the Comcast sponsored newsgroups through Giganews.

  6. Exactly. by plasmacutter · · Score: 5, Informative

    I noticed my WoW connection suddenly became unstable at the beginning of the month.

    I implemented similar firewall rules on my mac and the instability was cut in half.

    Guess the other half is being forged to the blizzard servers.

    --
    VLC FOR MAC IS DYING! IF YOU DEVELOP, PLEASE SAVE IT!!
  7. This is why you select a specific port.... by Fallen+Kell · · Score: 5, Informative

    As my subject says. This is why you only put the filter on the specific port you are using for P2P traffic. For instance, my rule is as follows:

    iptables -I FORWARD 3 -p tcp --dport 36745 --tcp-flags RST RST -j DROP;

    The above does what it says, drop TCP RST packets on port 36745. That is all you need to do to keep it from affecting your other network applications which may be getting legit reset packets.

    --
    We were all warned a long time ago that MS products sucked, remember the Magic 8 Ball said, "Outlook not so good"
    1. Re:This is why you select a specific port.... by darkonc · · Score: 5, Interesting
      Well, if you're getting bitten by ComCast (or other e.g. Canadian) ISPs that are resetting connections, then it's probably better to leave connections open that shouldn't be than to close connections that should stay open.

      It's a response to a violation of the TCP protocol to begin with, so it's not surprising that it has some negative side effects.

      Probably the best thing to do would be to build a filter that registers the presence of the RST packet and waits to see if you get more data from the site that supposedly sent it.
      * If the site that the RST packet supposedly came from continues to act like it's got an open session, then you can ignore the RST as a forgery.
      * If you have no more non-closure packets after the RST, then you can apply an aggressive timeout and then deliver the RST after 2-3 seconds of silence.

      --
      Sometimes boldness is in fashion. Sometimes only the brave will be bold.
    2. Re:This is why you select a specific port.... by emc · · Score: 5, Interesting

      Although, I've never had this issue and am not a Comcast customer...

      I'd assume that the RST coming from Comcast would probably have a different TTL than a legitimate RST.. As a matter of fact, all the RST coming from Comcast would probably have the same TTL.

      Anyone looked into this?

  8. You know what I hate? by deek · · Score: 5, Insightful

    It's when I see a comment on Slashdot, that seems to have no relation to the comment above it. Then I discover that the real parent post has been hidden by Slashdot's new comment system, and the child post linked to the grandparent.

    It's damn annoying! Slashdot, please, at least link the child to the "hidden comments" link. That way, I won't get head spins when someone appears to viscously lash out at an interesting post.

  9. Comcast has moved on; now they're delaying packets by SuperBanana · · Score: 5, Interesting

    They recently bumped up service to a full megabit upload speed, mostly because of Verizon FiOS service (which still isn't available anywhere in MA except the rich white suburbs- Boston's completely "dark", yet surrounded by towns and cities which have it.) However, if you use it past the old limit (384kbit), after a few minutes, latency skyrockets.

    It takes anywhere from a minute to several minutes to kick in, but when it does, ping times to google jumped from 20-30ms to over 300ms. Sometimes I found ping times would be *seconds* long, and ssh became almost completely unresponsive. Curiously, none of the packets would actually be dropped- they'd just very, very badly delayed.

    Seems very clearly designed to a)look the same as Verizon "on paper", 2)Satisfy people who want to email photos of the kids to grandma and grandpa (I will admit, it's insanely nice to be able to upload at four times the speed, when it works).

    --
    Please help metamoderate.
  10. Re:Sandvine? by Anonymous Coward · · Score: 5, Funny
    I'll bet you're wondering how I knew,
    Why my packets never made it through,
    With some other peer I was sharin' files,
    Between the two of us Comcast was runnin' wild,
    Reset me by surprise (reset by surprise), I'm afraid,
    From the R-I-Double-A,
    Don'tcha know,

    I heard it through the sandvine.



    Not much bandwidth's gonna be mine.
    Oh, I heard it through the sandvine...
    Oh, I'm just about to lose my mind,
    Honey, honey, yeah...

    I know a geek ain't supposed to cry,
    But these fears I can't hold inside,
    Losin' the 'net and it's neutrality,
    Yeah, it means that much to me,
    You coulda told me (you coulda told) yourself,
    That you're forgin' packets for someone else,

    Instead I heard it through the sandvine...
    Not much bandwidth's gonna be mine.
    Oh, I heard it through the sandvine...
    Oh, I'm just about to lose my mind,
    Honey, honey, yeah...

    People say "Believe half of what you see,
    Son, and none of what you hear",
    But my router's mighty confused,
    So if it's true, please tell me dear,
    Do you want (do you want) to make me go,
    Back to the ISP (and USENET feed) I used before,

    Or should I drop packets from your sandvine...
    Plenty bandwidth's gonna be mine.
    Oh, I don't listen to your sandvine...
    MPAA's 'bout to lose its mind,
    Honey, honey, yeah...

    - Original work, composed under the influence of Slashdot and beer. Lyrics in public domain. Someone with vocal talent, feel free to improve, record, and youtube it as a parody under the fair use exemptions.

  11. They are doing it because they are crooks...... by ciscoguy01 · · Score: 5, Interesting

    Technical merit? I think not.
    They can't block the packets, they sold their users "unlimited" internet. If certain packets are just blocked that's not really unlimited, is it?
    They sure didn't tell anyone they were secretly installing Sandvine boxes that nobody had heard of specifically to screw up certain kinds of traffic. They did it in secret. It was subterfuge. A dirty trick. Mischief.
    Now that they are found out their story is they are just "managing bandwidth".
    But what they are really doing is trying to stop 2% of their customers from using 98% of the bandwidth, bandwidth they have to pay for. Remember, though they are selling "unlimited" internet access at some level *all* bandwidth is measured. Theirs is certainly measured by their upstream provider. There is really no "unlimited" bandwidth.

    --
    .
    1. Re:They are doing it because they are crooks...... by Stormwatch · · Score: 5, Insightful

      But what they are really doing is trying to stop 2% of their customers from using 98% of the bandwidth, bandwidth they have to pay for. Remember, though they are selling "unlimited" internet access at some level *all* bandwidth is measured. Theirs is certainly measured by their upstream provider. There is really no "unlimited" bandwidth.

      Their own damn fault for selling something they don't have!

      --
      Circumcision is child abuse.
    2. Re:They are doing it because they are crooks...... by Crayon+Kid · · Score: 5, Insightful

      Their own damn fault for selling something they don't have!

      They always have. ISP's, especially those on the last mile, have historically sold 10 to 20 times the actual bandwidth to their customers. Except a while back the last mile was not a hot zone. There weren't so many things you can use huge amounts of bandwidth on.

      Today there are lots. Desktop apps move to the web, there's streaming, online gaming, all kinds of legal, semi-legal and illegal things to download, malware and the list goes on and on.

      The ISP's are caught in the middle of all this. They've entered this time period with pricing policies that belong in gentler times, and their infrastructure is also outdated and getting more so every day.

      On top of everything, everybody seems to think it's their job to carry the Internet on its back and figure it out somehow. The end customer likes to have huge amounts of bandwidth for pennies. The websites and online apps have bulk deals for bandwidth with providers that have efficient distribution infrastructures all over the world. And the last mile ISP is left to fight a dog eat dog fight with other similar local ISP or with a bigger area ISP, both of which will drive it out of business eventually.

      Not to mention the crazy politics involved, where they are required to act as copyright cops and other idiocies.

      So they're desperate. They're trying anything to "fix things". There are a couple of sane solutions but not without problems. The obvious move would be to rethink their pricing and start selling capped amounts of bandwidth. Filtering will always be passed somehow but a hard cap upstream is a hard cap. And nobody will be able to protest they're not getting what they're paying for.

      But this isn't easy either, because of the fierce competition. You do hard caps, you piss of customers. If they have a choice, they'll run to that new ISP that popped up in the neighborhood a week ago. Sure, that ISP will experience the same problems a while from now, but in the meantime you're short some income.

      Another solution is a world-wide effort to update infrastructure (better throughput, either hardware or software). But who's gonna pay for that? The last mile ISP's can't and won't and granted, it's not fair they should pay all of it. But the other interested parties like the status quo and won't pay either, but will bitch just as readily about filtering and caps and whatnot. In the end, the ISP's will probably turn to insightful investors like Google's dark fiber and become their prisoners and people won't like that either, but will conveniently forget they're the ones that pushed the ISP's into that corner.

      It's not just the ISP's fault, it's everybody's. The Internet has become an ecosystem, you gotta work together on all parts of it to see proper overall change.

      --
      i ate crayons when i was a kid and now i have two braincells and the blue ones taste nicer
    3. Re:They are doing it because they are crooks...... by grimwell · · Score: 5, Insightful

      But what they are really doing is trying to stop 2% of their customers from using 98% of the bandwidth, bandwidth they have to pay for. Remember, though they are selling "unlimited" internet access at some level *all* bandwidth is measured. Theirs is certainly measured by their upstream provider. There is really no "unlimited" bandwidth.

      Pisshaw. Large regional and national ISPs don't have "upstream" providers. They have a presence in a NAP(s) and peering agreements with other networks. The only costs they have is for the infrastructure; physical cables, equipment, power and people. They don't pay for bandwidth on a "meter". Their bandwidth is limited by equipment; available technology and costs.

      They are "managing bandwidth" to control last mile congestion. It is cheaper to mangle traffic than to upgrade the last mile. Plain and simple.

      --
      If the govt becomes a lawbreaker, it breeds contempt for law, it invites man to become his own law, it invites anarchy
    4. Re:They are doing it because they are crooks...... by CyberDog3K · · Score: 5, Insightful

      I might be less critical of them if they actually spent some of their abusively high rates on upgrading said failing infrastructure instead of god knows what.

    5. Re:They are doing it because they are crooks...... by PieceofLavalamp · · Score: 5, Insightful

      You've used "fierce competition" to describe the ISP market place. So i must assume you are being sarcastic. You really shouldn't bury sarcasm like that in between rather insightful points, you'll confuse people who aren't familiar with the issue... New ISPs haha funny.

  12. Re:Usenet by BiggerIsBetter · · Score: 5, Funny

    The first rule of Usenet is, you do not talk about usenet.
    The second rule of Usenet it, YOU DO NOT TALK ABOUT USENET.

    Fscking n00bs.

    --
    Forget thrust, drag, lift and weight. Airplanes fly because of money.
  13. A Fitness center analogy.. by AftanGustur · · Score: 5, Insightful
    Fitness centers operate similarly, they have numbers on how many times each member comes per week, and based on that (and other parameters) they price access to the center.

    Now, imagine you buy a year membership card.

    Then you start showing up each morning, and again in the evening.

    Then the fitness center comes to you and says: "You can come here, but we are going to lock all the doors when you show up, because you are using up to much resources and thus denying them to our other members.

    Do you think there would be any outrage ?

    --
    echo '[q]sa[ln0=aln80~Psnlbx]16isb572CCB9AE9DB03273snlbxq' |dc
    1. Re:A Fitness center analogy.. by Maxo-Texas · · Score: 5, Insightful

      Say that you found out a way to earn or safe a lot of money by staying on the fitness machines 16 hours a day.

      Suddenly, the 28 fitness machines they expected to service 5,000 people are being used from opening until closing by the same 28 people.

      Do you think the fitness companies and their customers would say "ah well... they've got us because of our advertising unlimited service."

      No- the next time your contract came up, it would have a clause that allowed them to force people to share the machines or something to protect them.

      You are being unreasonable. The cable companies are trying a weaselly scummy way to get out of the situation instead of just doing what they should do up front.

      1) Determine the real usage of their desired customer (say 20gb a month).
      2) Advertise 24gb a month for one "low rate" with a "reasonable $1 per gb"

      And eventually they will. Even if you have you current company in an iron clad contract, if it is losing money the situation *will* fix it self.

      ---

      The current isp situation in america is a complete joke and anti-capitalistic. We basically have duopolies in 99% of cities between AT&T and a cable company. That needs to stop and be broken up. The internet wires, like the roads, should put be put by the government.

      --
      She was like chocolate when she drank... semi-sweet at first and then increasingly bitter.
  14. Re:When comments become articles by Misanthrope · · Score: 5, Informative

    I posted the kludge last time this got mentioned, I'm rather amused that this actually got posted again
    http://tech.slashdot.org/comments.pl?sid=591167&cid=23888479

  15. Re:Port 25 by EdIII · · Score: 5, Informative

    Not sure what you mean by sending work email from home.

    If you mean your ability to establish a connection with a corporate mail server not located on your ISP's network, then port 25 is unnecessary. You should use port 465 with SSL instead. Problem solved since no ISP ever blocks port 465 in any direction. At least not that I am aware of.

    If you mean your ability to run a mail server at your house, then your shit out of luck period. There are a large number of mail servers now that use policy block lists. Every ISP publishes their policy block lists which includes your IP address range. The moment your mail server tries to establish a connection to another mail server using this block list your packets could be dropped right at the router, or your connection terminated by the mail server itself.

    Now as upsetting as that might be, it really is for the greater good. The vast majority of all the SPAM being sent every day comes from compromised windows machines on dynamic IP address ranges. Using the policy block list is very effective at immediately stopping those communications from ever reaching the mail server.

    If you are absolutely determined to run your own mail server from home I would suggest getting a static IP address. Not only will port 25 not be blocked, but you will have a MUCH BETTER chance of your packets not being dropped by routers servicing the mail servers you will be sending email to.

    Another option, depending on the amount of money you want to spend, is to retain the services of an email services provider. There are more than a few out there. You can use your own domain and they will host it for you. They can also provide a fair amount of security and usually are more reliable in getting the email to the destination.

    Additionally, you could always get a virtual server someplace and run your own mail server software on it. They have linux and microsoft systems available pretty cheaply. Then you would be operating on IP address ranges used by big ISPs and data centers.