Unstable WDS Links

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Big_T
DD-WRT Novice


Joined: 22 Nov 2010
Posts: 7
Location: Ohio

PostPosted: Sun Apr 15, 2012 21:36    Post subject: Unstable WDS Links Reply with quote
Background:
I'm running DD-WRT on 4 routers that I have set up in a WDS mesh
(And yes, I'm running STP and have configured path costs and root bridge priority using brctl).


The Problem:
The issue I'm having is that after a random period of time some of my WDS links go down. Sometimes it's 24+ hours, other times its 10 minutes. The WDS watchdog doesn't help because the WDS links don't always come back up after a reboot. The only thing that does seem to work *most* of the time is clicking "Apply Settings" on the WDS page of each router.

Another odd thing I'm noticing is that sometimes one router reports that a link is up, but the router at the other end of the link shows that it's down.

One other thing worth mentioning is that it seems that one or two of the WDS links are flapping, specifcally AP2<->AP1 and sometimes AP3<->AP4.

Does anyone have any thoughts?


My Setup:
2 x Cisco Linksys E4200's running DD-WRT build 17990M NEWD-2 K2.6 Eko -- v24-sp2 mega
1 x Cisco Linksys E100 running DD-WRT build 16785 --v24-sp2 std-nokaid-small
1 x Cisco Linksys WRT160N running DD-WRT build 14471M NEWD Eko -- v24-sp2 std-nokaid


Topology:


I mean, as you can see I've built enough redundancies into my setup that the failing WDS links don't bring my network down. It's more of an annoyance/inconvience because it seems that it's usually my "preffered" WDS links that go down, i.e. the links with the lowest SNR, highest signal quality, and configured with the lowest path cost that go down, causing the routers to choose sub-optimal path's to my network core and internet, adding moderate amounts latency.
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phuzi0n
DD-WRT Guru


Joined: 10 Oct 2006
Posts: 10141

PostPosted: Mon Apr 16, 2012 2:37    Post subject: Reply with quote
Well I'm not very experienced with WDS but afaik this is pretty common, especially when mixing hardware and builds. GeeTek is probably the most experienced with WDS around here so he might have some good tips...

It seems to me that the mesh redundancy is more of a burden than a blessing because it's doing what it's supposed to but you don't want it to (you want the best links to be kept up afaict). It's impossible to tell from the info provided but if the links are even remotely close to how they're drawn then the only 2 links that STP would use when they're all up would be AP2<->AP4 and AP1<->AP3, so you could try just setting up those links with watchdog for the IP on the other ends.

If you want to keep that redundancy but check at certain times to make sure that the links are all up then you should be able to write a script to handle it. For a very simple solution you could try setting the routers to all reboot at a certain time of low/no usage like early morning. For a more complex solution you'd need to find some indication that the link is down (maybe the wds link interfaces will be down in ifconfig?) and then either use wl to bring the radio down and back up or reboot entirely with a cron job running your script.

_________________
Read the forum announcements thoroughly! Be cautious if you're inexperienced.
Available for paid consulting. (Don't PM about complicated setups otherwise)
Looking for bricks and spare routers to expand my collection. (not interested in G spec models)
Big_T
DD-WRT Novice


Joined: 22 Nov 2010
Posts: 7
Location: Ohio

PostPosted: Wed Apr 18, 2012 20:44    Post subject: Reply with quote
I don't think the problem is that STP is taking the links down, because when STP calculates the best path to a root bridge it keeps the ports up but puts them in a blocking state, so I believe that on the Info page the WDS links should still show as up. I think the only place the links should show as down (or blocking) is in the output of the brctl showstp br0 command. As far as best paths are concerned, here's my brctl config from each AP:
AP1:
# wds0.1=AP2 2.4Ghz
# wds0.2=AP3
# wds0.3=AP4
# wds1.1=AP2 5Ghz
brctl sethello br0 1
brctl setmaxage br0 4
brctl setfd br0 4
brctl setbridgeprio br0 50
brctl setpathcost br0 wds0.1 125
brctl setpathcost br0 wds1.1 125
brctl setpathcost br0 wds0.3 150
brctl setpathcost br0 wds0.2 300
brctl setportprio br0 wds0.1 25
brctl setportprio br0 wds1.1 50

AP2:
# wds0.1=AP1 2.4Ghz
# wds0.2=AP3
# wds0.3=AP4
# wds1.1=AP1 5Ghz
brctl sethello br0 1
brctl setmaxage br0 4
brctl setfd br0 4
brctl setbridgeprio br0 75
brctl setpathcost br0 wds0.1 125
brctl setpathcost br0 wds1.1 125
brctl setpathcost br0 wds0.3 125
brctl setpathcost br0 wds0.2 250
brctl setportprio br0 wds0.1 25
brctl setportprio br0 wds1.1 50

AP3:
#
# wds0.1=AP2
# wds0.2=AP1
# wds0.3=AP4
brctl sethello br0 1
brctl setmaxage br0 4
brctl setfd br0 4
brctl setbridgeprio br0 300
brctl setpathcost br0 wds0.1 250
brctl setpathcost br0 wds0.3 200
brctl setpathcost br0 wds0.2 300

AP4:
#
# wds0.1=AP1
# wds0.2=AP2
# wds0.3=AP3
brctl sethello br0 1
brctl setmaxage br0 4
brctl setfd br0 4
brctl setbridgeprio br0 150
brctl setpathcost br0 wds0.1 150
brctl setpathcost br0 wds0.3 200
brctl setpathcost br0 wds0.2 125

In the image below I've written path costs in purple and bridge priorities in blue to give you a better idea of what this configuration does. The AP with the lowest bridge priority value is elected the root bridge, and then STP uses the path with the lowest designated cost to reach the root bridge. The designated cost is the sum of all path costs for links traversed to reach the root bridge. E.x. The designated cost for AP4>AP3>AP1 would be 500. The 100 pointing to the gigabit switch indicates a total path cost of 100 for connecting through that switch.(It does not participate in the STP domain.)

Big_T
DD-WRT Novice


Joined: 22 Nov 2010
Posts: 7
Location: Ohio

PostPosted: Wed Apr 18, 2012 21:29    Post subject: Reply with quote
I just realized I didn't really clarify what I'm asking. I guess what I want to know is exactly what clicking "Apply Settings" on the WDS configuration page does, as that seems to be the only reliable way to bring ALL of the wds links back up. Rebooting the AP's seems to be a crap-shoot, some WDS links do come up, but which ones seems pretty random. So, I'd like to run a cron job that periodically checks the status of my WDS links, and if they're down do whatever clicking Apply Settings on the WDS page does.
phuzi0n
DD-WRT Guru


Joined: 10 Oct 2006
Posts: 10141

PostPosted: Wed Apr 25, 2012 23:16    Post subject: Reply with quote
phuzi0n wrote:
For a more complex solution you'd need to find some indication that the link is down (maybe the wds link interfaces will be down in ifconfig?) and then either use wl to bring the radio down and back up or reboot entirely with a cron job running your script.

Bringing the radio down and back up is the most likely reason that apply settings on the WDS page is reconnecting the links.

http://www.dd-wrt.com/wiki/index.php/Wl_command#Usage

Try playing with some of these:
wl -i eth1 radio off
wl -i eth1 radio on
wl -i eth1 down
wl -i eth1 restart
wl -i eth1 up


I can't tell you for sure everything that happens when you apply settings on that page but if you want to know then you can dig through the source code.


ps. I wasn't saying that STP has anything to do with the WDS links going down. I was only saying that STP will be blocking all the other links anyways and that the resiliency of the mesh prevents watchdog from being able to function since the nodes will still be able to reach each other through alternate paths when one link goes down.

_________________
Read the forum announcements thoroughly! Be cautious if you're inexperienced.
Available for paid consulting. (Don't PM about complicated setups otherwise)
Looking for bricks and spare routers to expand my collection. (not interested in G spec models)
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