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AP541N's - confusion on WDS and other subjects

Hi All,

Anyone really good with WDS Bridging?  I'm trying to successfully understand how WDS Bridging works with all the SB Pro hardware I have, and to get it working optimally.  I have the following SB Pro hardware:

1 x SA520W

1 x ESW540 8P switch

2 x AP541N

2 x laptops for testing wireless client functionality (one is Vista with Wireless-G and the other is Win7 w/ a Wireless N adapter)

My sequence of connections (topology) from Internet to the laptops are:

Internet <-- SA520W <--ESW 540 <-- AP541N #1 (ESW Port 4)

                                                   <-- AP541N #2 (ESW Port 5, eventually will be wireless-only via WDS)<-- the laptops

The SA520W is my only DHCP server on the network, only IPv4.  It's working fine, I have several systems wired into it both directly and via the ESW 540.  The ESW is also working fine.  On both the SA and ESW I have very little configured beyond default - no port security etc.

During the course of my troubleshooting this WDS Bridge stuff I've often reset both the AP541N's to factory defaults. Also both are at 1.9(1) firmware.   Upon configuring them from scratch again, I configure each's LAN IP to be Static and they are in the same subnet as everything else here.  I set the time Settings, the admin password, and then I enable the radio.  I set radio to Canada, 802.11/b/g/n and Channel = Auto . I then go to the VAP's and delete the cisco-scan and cisco-voice ones, leaving just the default cisco-data.

On the first AP541N, I rename the SSID from cisco-data to "SSID1".  On the 2nd 541N, the one that will eventually be wireless-only, I set it to "SSID2" just so they're different.  I enabled WPA PSK on both, keeping all encryption options checked by default, set my key and save.

So far so good.  My laptops see both SSID's broadcasting.

At this point, both of my AP541N's are still wired to the network.

I then go into the WDS Bridge menu on both units, enable a WDS bridge on both, inputting each others MAC address as needed.  I then set the WDS Bridge's SSID to something unique to this WDS link, in this case WDSBRIDGETESTING so now both AP541N's WDS Bridge SSID is this value, and setting WPA for both with a pre-shared key that is the same between the two units.  I click Apply etc. and thigns are saved. lastly I change the radio channel to be the same between both 541N's, as the Help file tells me is required for WDS.

So in theory at this point I have a WDS Bridge created, yet my AP's are still wired to the network.  Next step is I go to AP541n #2, the one 30 feet away that I intend to use as wireless-only, and disconnect the CAT5e cable.

I then go to the laptops, have them join the WLAN with the SSID that matches the AP541N I just disconnected the CAT5e cable from ("SSID2"), and this connects them to the AP.  Signal strength = Very Good and I can see these clients in the Associated Clients menu on the 541N. The other AP541N is still wired into the network, so basically if everything is workign with the WDS Bridge, clients wirelessly connect to the wireless-only AP will be able to follow a logical datastream through the WDS Bridge to the wired AP541N, then to the ESW, then to the SA520W and out to the Internet.

So here are my issues:

1.  DHCP is not working to these laptops - it works fine to any wired-in system connected directly to the SA520W or indirectly through the ESW switch.  It appears anything over the WDS Bridge does not get an IP.  If I set static IP's on the laptops I get onto the internet.

2.  Speed of the WDS Brigde itself  is really, really poor and there's only 30 feet distance between the AP's.  My normal Internet speed ifrom is about 5.05 Mb/s downstream when I check it from a PC wired into the network.  Internal LAN speeds are of course, much faster being at Gb speeds.  From the wireless-G laptop I am only seeing 1.20 Mb/s from  yet when checking just the speeds between this laptop and it's AP I see a full 54Mbps rating.  I haven't tried the wireless N laptop but why bother if the bottleneck has me thottled down to 1.2Mbps.

So I can only assume that the WDS Bridge is extremely slow

So here are all my questions:

1.  How can one get DHCP across the WDS Bridge?

2.  Is there anything I can do about this WDS Bridge speed?

3.  Would installing and using CCA be useful in my situation?  Does it provide anything I can't get from 4 tabbed browser seesions in IE going to my 4 devices' web UI's?

5.  Does setting the radio channel to a fixed # on both AP's (as required by WDS) mean that all virtual AP's will also be fixed to this channel?  Is that not a peformance bottleneck?  Is there a way to set a channel just for the WDS link and leave the other chanenls for the other virtual AP's?

<Edited Oct 11 2010 to remove question # 4 )


Re: AP541N's - confusion on WDS and other subjects

I wish I had answers to all of your questions, but I'm afraid that I can mostly offer moral support.  I too have a pair of AP541N's doing WDS bridging.  In my case they are bridging two LAN's in separate buildings.  The AP's have line-of-sight to each other about 90-100 feet away from each other (same signal strength /speed as when they were in the same room for testing).  Firmware is 1.9.2 on both (came with 1.8.0).  I have tried WPA, WEP, and no encryption on the bridge.  5 GHz radio with 40 MHz channel bandwidth.  No other 5 GHz wireless devices in area.  Channels set to match.  Pretty much everything you have done.  My AP management cluster view shows 26 Mb/s wireless link.  Transfer speeds across bridge match this topping out at <3 MB/s.  It seems that consumer-level wireless G hardware can do better than this. 

My AP541Ns' sole purpose is for bridging wirelessly.  I currently have no need for wireless client access and plan to purchase separate AP's when and if that need arises.  One further issue is that my AP's reset their hostname to default when they are powered off and back on, not normally a problem, except after power outages.  This happens even when the config has been saved -- in fact, it's the only setting that changes after a power cycle.

So if I can be of any help:

1) DHCP works across my WDS bridge.  Win2003 Server is the DHCP server.  DNS and LDAP work fine also, as they should i suppose, since no ports or protocols are being blocked.  I believe I've heard of a registry mod for certain Windows situations to make DHCP jump further or not as far.

2) WDS bridge speed....I wish we could both make our AP's go faster, but I'm searching for answers on this like you.  Again, I've tried just about all encryption options from none to RADIUS, and it's always really slow.

3) CCA is not nearly as useful as the web config.  One advantage is that certain basic parameters (hostname, IP) can be easily set for your various access points from one interface.  However, there are no radio controls, bridging, or useful security options in CCA.  It redirects you to the AP web-config for important settings.

5) I do believe that setting the radio channel explicitly (which I had to do to complete my bridge) is a 'hard setting' for the device as a whole.  So yes, all VAP's are limited to that setting.  I initially set mine up for auto channel on 5 GHz band but when the two devices auto-selected different channels, I picked the higher of the two and set them to be the same.  I don't believe that this will result in a bottleneck, as the device is only using a certain channel width (20 or 40 MHz) in its spectrum (5 GHz in this case), whether it is auto-selected or not.