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WDS route priority?

Discussion in 'Tomato Firmware' started by Misato, Jun 2, 2008.

  1. Misato

    Misato LI Guru Member

    I have three routers in my home; one on each floor.
    They are currently setup in a loop (triangle) configuration with STP enabled for redundancy.

    My setup:
    / \

    I would like to know if there is a way to configure STP or tomato to specify a priority for each route.

    For example, I want communication between #2 and #3 to use the short route by default but in my network, it seems to use the long route.
    How would I accomplish this?

  2. Kiwi8

    Kiwi8 LI Guru Member

    How did u know they use the long route? Did u actually do a bandwidth test over the connection?
  3. Misato

    Misato LI Guru Member

    - Bandwidth was halved when it went through the long route
    - I confirmed it with the real-time bw monitoring tool inside tomato to see which router was actually receiving/transmitting
  4. Kiwi8

    Kiwi8 LI Guru Member

    Have u seen the other thread that I started on the test results of WDS vs WEB? I had exactly the setup as yours during WDS mode.
  5. Misato

    Misato LI Guru Member

    Your results don't answer my question.
  6. Kiwi8

    Kiwi8 LI Guru Member

    Indeed. I apologise.

    I believe your router 1 was made the root bridge by the STP. Try to configure either router 2 or router 3 as the root bridge (set prio to be a smaller number than the other 2 routers) by the following command:

    brctl setbridgeprio br0 <prio>
  7. Misato

    Misato LI Guru Member

    However, since STP always blocks your alternate path until a link failure, I've come to realize that I don't really want to use STP anymore. I want to utilize both links and always use the shortest path on a per packet base.

    For example, from router #2 to router#3, I want to ensure I don't go through router #1. And from router #2 to router #1, I want to make sure I don't go through router #3.

    How would I set that up?
  8. jsmiddleton4

    jsmiddleton4 Network Guru Member

    You may not be able to do that automatically with just plain old wds setup. You might be able to do it with some mac filters that prevent a set of clients from accessing the router that would make it "long" route. You prevent certain clients from even getting into the long path in the first place.

    Might be able to use the ARP thing in Victek's mod too and limit access based on IP/ARP assignment in the router that would be the long path. Same concept though. Limit access so some clients never get on the long path in the first place.

    We'll call that the Yellow Brick Road network topology.... :)

    I have simple wds setup and found STP OFF is better as well.

    I still am confused about WEB mode. WET mode? WDS mode? What is WEB mode?

    Got it, wireless ethernet bridge.
  9. fyellin

    fyellin LI Guru Member

    Wet == Web

    Yeah, WET and WEB meaning the same thing is a bit confusing. I haven't figured out what WET stands for, other than Linksys's first wireless bridge was called the WET11.
  10. Kiwi8

    Kiwi8 LI Guru Member

    U just have to choose which of the three paths is the least used by your network. Based on your example, u want traffic moving to and fro router #2 and router #3, and to and fro router #1 and router #2. Thus I assume u do not need to move much data to and fro router #1 and router #3.

    Hence I suggest setting the bridge priority such that router #2 is the root bridge, so that data to and fro router #1 and router #3 will go through router #2.

    As for not STP, u can't really not be using it, as your linking of the three routers together constitutes a loop, which causes broadcast storms that cripple the network.
  11. Kiwi8

    Kiwi8 LI Guru Member

    Neither mac filters nor ARP thingy will be able to do anything if the WDS network has loops. If STP is turned off in a network that has loops, there will be connectivity problems once a broadcast packet is introduced, as every WDS node will simply retransmit the same packet until the number of packets increase exponentially and cripple the network.

    WET = Wireless Ethernet Bridge mode (I think Linksys uses WET since they have such an actual device)
    WEB = Wireless Ethernet Bridge mode (I first seen it in Tomato, so I shall use this term)
    WDS = Wireless Distribution System mode
  12. HennieM

    HennieM Network Guru Member

    The brctl utility has all sorts of options. I know too little about brdiging to make meaningful suggestions, but I would explore these two options to get to "shortest path":
    setpathcost     <bridge> <port> <cost>  set path cost
    setportprio     <bridge> <port> <prio>  set port priority
    Another way to do the "shortest path" might be to put the 3 WDS links on different subnets, so that routing metric can take care of the shortest path.

    I haven't really thought about how to it, but in short I think you would basically need 2 seperate WDS links from each AP, with the AP itself (and thus it's clients) bridged to one of the WDS interfaces. The other WDS interface would be like a WAN link; i.e. not bridged. DD-WRT has a feature where you can do "WDS on different subnet" from within the web interface (and this web means http, not WET), but this would still treat ALL WDS links from that node as being on one subnet (I think). To do 2 WDS links on different subnet would therefore require some scripting.... ;)

    If you get 2 seperate subnet WDS links going, the downside would be that as you walk with your laptop from the one AP's area to another AP's area, you'll get a different IP, so all existing connections would be broken. If you use fairly stationary devices, that might not be a problem.
  13. jsmiddleton4

    jsmiddleton4 Network Guru Member

    Certainly true kiwi but that doesn't mean you couldn't use some sort of filtering/persmission process to control what the entry point is into the "system". It means IF you used something like that you would HAVE to use STP.

    And with STP is it the case that it has to be turned on for all router/gateway/ap devices or if its on one, does that then control how data flows so that just having one on works?
  14. Kiwi8

    Kiwi8 LI Guru Member

    Whether be it "set path cost" or "setportprio", it will still result in one of the ports be blocked due to the STP. I suggest changing the bridge priority instead.

    As for the "WDS on different subnets" and scripting thingy, it's way beyond my ability. :)
    Anyway, I think even if it were possible, file sharing would be more complicated since routing has to take place.
  15. Kiwi8

    Kiwi8 LI Guru Member

    I dun quite understand your paragraph one... can explain again? :confused:

    Anyway, it is better to enable STP for all the bridges so that the redundancy can kick in.

    For example, suppose I link Router A, Router B and Router C together (with Router B being the root bridge), if I happen to turn off Router B, the remaining two routers (Router A and Router C) will reopen their previously blocked ports to directly communicate with one another.
  16. jsmiddleton4

    jsmiddleton4 Network Guru Member


    You were pointing out that using some type of filtering to limit access to a particular router will only be fully effective with STP on. Which is true but that does not mean you can't use some kind of filtering to keep certain clients off a router, etc. You just have to remember to use STP.

    Personally I think it would have to be a really LONG path between getting into a system via one particular router as compared to another that was really SHORT to notice any huge difference. When you consider how far the information flows before it gets to your home/office it seems like the distance that is spaced out between routers in any reasonable setup would not show up all that much difference in performance. Given how fast the signal is traveling the distance would have to be greatly different to notice getting into the system at this router as compared to that.

    So and I'm not saying the gentleman isn't experience a difference with data flow depending on which router is the "access" router. I'm saying if there is a noticeable and measurable difference, I'd be looking at some other cause than some minor difference in distances the signal has to travel.

    That's just my two cents.

  17. Kiwi8

    Kiwi8 LI Guru Member

    I dun think I said the part in red even after I browsed through my posts in this thread. Please point it out to me. And I'm not even talking about the clients (I assume u are talking about wireless clients). Even when no wireless clients are involved, communication amongst the three routers cannot be at full speed. For example, if I have Router 2 as the root bridge, I can have throughput of 25Mbps to and fro Router 1 and Router 2, or Router 2 and Router 3. But to and fro Router 1 and 3, throughput will be halved to 12Mbps due to Router 2 having to retransmit the data.

    As for the rest of the paragraphs, I dun think they are relevant, and I'm confused.
  18. HennieM

    HennieM Network Guru Member


    Sorry JS, as Kiwi has pointed out, you're way off the pace here...
    The whole WDS speed thing is the determining factor here: Every single radio that has to retransmit what it received, takes your speed down by a factor:

    Speed through retransmitting nodes = 1/(1+x) of full speed
    where x = number retransmitting nodes

    Thus, in

    / \

    WDS2 --- WDS1 --- WDS3

    whould be half [1/(1+1), as WDS1 has to retransmit] the speed of

    WDS2 --- WDS3

    If it were

    WiredSwitch2 --- WiredSwitch1 --- WiredSwitch3

    there would be little difference to

    WiredSwitch2 --- WiredSwitch3

    because in wired switches data comes in on port A of WiredSwitch1 and out through port B of WiredSwitch1 - no retransmitting.
  19. jsmiddleton4

    jsmiddleton4 Network Guru Member

    Yes I understand the number of routers and having one wireless radio will have no other impact but to slow the traffic down. The issue I addressed is distance not how many routers in a system.

    In otherwords if an unnecessary router is in the system presumed to be needed because data will flow faster, given the nature and context of the kinds of distances we are talking about in the homes/soho environment, the slow down is probably not distance but the extra router.

    I pointed out the issue with distance being a bit suspect. Not multiple routers.
  20. jsmiddleton4

    jsmiddleton4 Network Guru Member

    "Neither mac filters nor ARP thingy will be able to do anything if the WDS network has loops. If STP is turned off in a network that has loops, there will be connectivity problems once a broadcast packet is introduced, as every WDS node will simply retransmit the same packet until the number of packets increase exponentially and cripple the network."

    I guess I misunderstood what you were saying here kiwi.
  21. Kiwi8

    Kiwi8 LI Guru Member

    It is ok. I myself is also a noob who took a long time to accept the limitations of bridges (that of the WDS bridge too), and that it is susceptible to broadcast packet storms if the bridge network ends up in a loop. I was also thinking of ways that I can avoid using STP, and spent a lot of time searching the web and reading some articles. I had also hoped that somehow each router could be able to talk to the other router without having to go through the third router. It seems that this could only be done through some routing scheme, which is way beyond my league at this point. :redface:
  22. HennieM

    HennieM Network Guru Member

    My turn to apologize to JS. I misread the "distance" emphasis.
  23. jsmiddleton4

    jsmiddleton4 Network Guru Member

    No apology necessary. I think people forget that this is a dialog. If we were chatting face to face we'd just say, "Did you mean...", etc. and the misconception/misunderstanding would be addressed in seconds. Something about forums that create a time lag in the dialog that makes misunderstandings and the need to clarify "feel" more important than they are. Its all good.

    I'd say IF someone was tweaking a network for performance at the level of being concerned about through-put differences between even normal differences in distances, which is probably not a bad thing to be concerned about mind you and I'm not saying it isn't important, the first thing I'd do is make sure that the bare minimum of routers is in the "system". I remember "back in the day" some folks were absolutely certain that a really short pigtail of a phone cable from the wall to the modem made their dial-up faster. I just didn't have the heart to try and explain to them how long the phone cable was from the back of their jack, out their house, to the street, etc....... Wireless signals, wired LAN signals are traveling so fast that, again we're talking realistic distances and not someone with a Pringle antenna-can trying to connect 18 miles away, that the speed differences IF its just distances one is looking at, you probably can't even measure the impact of normal distances practically anyway.

    I'd like to see WEB/WET ironed out for the little "issues" still hanging around with it like duplicated mac/ip's, etc. and at least be able to use a mode that in and of itself doesn't add a delay. WDS is very cool and it works quite well in Tomato. Don't want to go back to dd-wrt as its gotten so complicated and frankly confusing with its releases.

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