Tips for WDS Success
But before we forge ahead into the examples, there's some prep work you'll need to do to give yourself the best chance of having your WDS setup work the first time. Here are three mandatory and two optional steps to take before putting your APs in bridging mode:
- Check that your wireless client can associate and pass data through each AP.
You'll want to do this with each AP connected to your LAN via its Ethernet port. The last thing you want is to be debugging basic wireless functionality if your bridge doesn't work.
- Assign a static IP address to each AP
This is good general practice when dealing with the gear that runs your network. But it's especially important for APs in WDS networks, since you'll know where to look for each AP and have one less variable to consider when trying to debug a broken connection.
Make sure that you assign the static IPs outside the range of your LAN's DHCP server or you'll risk getting a duplicate IP leased at some point... usually when it's least convenient!
- Set all APs to the same (clear) channel
Since all APs in a WDS network need to communicate with each other wirelessly, they need to be on the same channel. For 2.4 GHz WLANs, I recommend you use Channel 1, 6, or 11. Whichever channel you choose, make sure it's not in use by neighboring WLANs, or at least not one right close by. See our When Wireless LANs Collide! if you have trouble getting a clear channel.
- [Optional] Set each AP to a different SSID
WDS APs know each other by MAC address and could care less what their SSID is set to. On the other hand, wireless clients associate by SSID. Technically, each AP in a WDS network is part of the same Extended Service Set (ESS) and should therefore have the same SSID.
But the roaming algorithms incorporated into most wireless clients don't "aggressively" roam and tend to stay associated with an AP long after they should, resulting in poor performance. This can be especially frustrating when you've gone to the trouble and expense of adding repeaters to your WLAN, and your notebook refuses to use them!
By assigning different SSIDs to your WDS APs, you'll first have the advantage of being able to see each one, even if you're using WinXP's built-in "Zero Config" utility, which doesn't show multiple APs with the same SSID. You'll also be able to easily force your client to connect to the closest AP without having to remember its MAC address.
- [Optional] Assign a static IP to your wireless clients
I've found that it sometimes takes awhile to lease a new IP after associating with an AP. Assigning static IP information to your wireless clients (don't forget to include gateway and DNS info) gives you one less thing to go wrong when switching association among APs. It also works around the problem that some products have (or at least had!) with properly passing DHCP messages to bridged clients.
In addition to the above, you also need to carefully consider placement of your WDS APs. As with any other wireless LAN equipment, the speed of a WDS link depends primarily on signal strength. Since each WDS "hop" already cuts available throughput approximately in half, you don't want to further reduce your link speed by spacing your WDS APs too far apart.
You'll need to experiment to get an combination of range and performance that's acceptable to you, but don't expect good link speed if you try to place your repeater near the limit of your current wireless range! A good compromise is to place your repeater in an area where the link speed (as indicated by your client utility) is about half the maximum transmit rate. That would be around 24 Mbps for 802.11g gear and 65 Mbps for dual-stream 11N products in 20 MHz bandwidth mode.
With the preliminaries out of the way, we next need to gather the MAC address information we need and we'll be on our way!
Gather the MAC addresses
As described earlier, WDS links are MAC address based. Some products have a mode that doesn't require you to enter the MAC addresses of each network member. But I recommend that you disable that mode (if offered) and enter the MAC addresses. This will keep your bridge (and LAN) secure by not allowing "anonymous" APs to join your bridge. It will also, in my experience, give you the best chance of getting things working, especially if you're trying to mix equipment from different vendors.
Your first stop for gathering AP MAC address information is the APs that you'll be bridging. If all manufacturers followed NETGEAR's lead, I could write a shorter article! Figure 2 shows the WNDR3700's [reviewed] Wireless Repeating Function admin page, where each radio's MAC address couldn't be clearer! (I've outlined them with yellow, just in case.) Note that for simultaneous (two radio) dual-band routers, each radio has a different MAC address. So be sure you use the correct one!
Figure 2: NETGEAR WNDR3700 clear MAC address indication
In contrast, you need to read between the lines to find the MAC address in EnGenius products. Figure 3 shows the ESR7750 dual band N router [reviewed], where the MAC address information masquerades as the BSSID.
Figure 3: EnGenius ESR7750 unclear MAC address indication
This is perfectly valid, since the BSSID in an infrastructure wireless LAN (using an AP, not client-to-client ad Hoc) , is the MAC address of the AP. But it's not very helpful to those who aren't versed in the details of 802.11 nomenclature. The same terminology is used in EnGenius' ESR9850 [reviewed], which I've shown in Figure 4 because I'll be using it in an example, shortly.
Figure 4: EnGenius ESR9850 unclear MAC address indication
IMPORTANT! If you have to go hunting around in your router's admin pages for the MAC address, be sure to get the wireless MAC address. The WAN port also has a MAC address. And if you try to use that one to make a WDS connection, it won't work.
Another way to find an AP's MAC address is from a client utility. Unfortunately, Windows' built-in wireless utilities are no help for finding AP MAC addresses. But MetaGeek's inSSIDer comes to the rescue. Figure 5 shows a scan I took with the EnGenius and NETGEAR routers active (there's also a TRENDnet thrown in for good measure). By the way, as good wireless security practice, you shouldn't use the obvious SSID's that I did!
Figure 5: inSSIDer scan showing AP MAC addresses
Now that you have the MAC addresses of the AP's, you can make a table similar to Table 1, so that you have all the info you'll need in one handy place. You really need only the MAC address info when setting up the bridge. But the other info will come in handy when you go to check that the bridge is working.
|Device||SSID||MAC address||IP address|
|NETGEAR WNDR3700 - 2 GHz||shutmeoff||00:24:B2:51:C0:AF||10.168.3.254|
|NETGEAR WNDR3700 - 5 GHz||meoff||00:24:B2:51:C0:B1||10.168.3.254|
|EnGenius ESR7750 - 2 GHz||EnGenius7750-2ghz||00:02:6F:74:FD:48||10.168.3.77|
|EnGenius ESR7750 - 5 GHz||EnGenius7750-5ghz||00:02:6F:74:FD:4C||10.168.3.77|
Table 1: AP info for WDS setup
With your table in hand, and everything else ready to go, it's finally time to set up WDS.
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