I figured this was worth forking a new thread rather than dragging out an old one.

I've now got two 802.11n (2.4GHz) APs: one upstairs in the wiring closet and one downstairs in the home theater rack. I've got them current set to automatically select their frequencies, and they seem to be consistently selecting the same frequency as each other. At different times that I check, that frequency will move around, but nonetheless it doesn't seem like the optimal answer.

The immediate neighborhood isn't what you'd call a congested WiFi environment. I can pick up maybe three or four other APs, but they're all -80dB or lower.

I suppose I could just tell my APs to occupy two specific (and different) frequencies and not worry about my neighbors. Or, is the "auto" frequency support genuinely doing the right thing and I should leave well-enough alone?

I'd specify the channels.

Are you seeing performance issues when the routers both pick the same channel?

Agreed. Choose channel 1 for the first AP and 6 (or 11) for the second. Your problem will most likely be solved.

Do not use a 40Mhz channel, because that uses channel overlapping and isn't "neighbour friendly" at all. 40Mhz is also less stable and even if it provides you extra speed (which is not guaranteed) in 99% of the cases you won't need it. (if all you're using your wifi for is internet surfing, like most people. )

Everything I've read says that you should have the separate APs on different channels.

A recent article I read expanded a bit on this common channel layout. The specific part is on the second part of page 3 here:
http://arstechnica.com/gadgets/news/2011...ilt-wi-fi.ars/3
(I'd recommend the whole article if you are interested in the origins of WiFi and how each revision is different)

I'm not seeing any interference issues, but that's because we tend to be either upstairs or downstairs, not both at once. This whole "take you turn" thing, if it really works, is probably is why it's working for us.

My router offers "up to 270Mbits/sec" or "up to 130Mbits/sec". Can I assume those map to 40 and 20MHz, respectively? I certainly don't want to be gratuitously unfriendly to my neighbors, but it's not like any of them are complaining.

Yes, with 20 Mhz, 130Mbits/s is the max speed you'll be able to achieve, higher is 40 Mhz.

Yep. 130 is 2x2 MIMO with 20MHz channels. Unlike past WiFi specs, it looks like the formal spec this time was a bit more forward thinking, avoiding the mess of "Super G" and other vendor proprietary speed extensions. N should be able to grow up to about 600MBit officially. The current generation Macs and Airport Extremes sit in the 450MBit range.

This thread inspired me to take another whack at setting up a second router as an AP at the far end of the house.

Cabler modem > wire > DIR-655 > wire > DIR-825.

The 825 was nutered by disabling its dhcp, upnp, and setting a static ip. That last is what stumped me before. In this mode of operation the 825 cannot pull an ip via dhcp from the 655.

I noticed while digging around in the 655's configuration, there was a setting "Local Domain Name" setting.

The help says:

Local Domain Name
This entry is optional. Enter a domain name for the local network. The router's DHCP server will give this domain name to the computers on the wireless LAN. So, for example, if you enter mynetwork.net here, and you have a wireless laptop with a name of chris, that laptop will be known as chris.mynetwork.net. Note, however, if the AP's settings specify "DHCP (Dynamic)" Address, and the router's DHCP server assigns a domain name to the AP, that domain name will override any name you enter here.

Is there a benefit I'm forgoing by omitting this?

Really depends on how you use your network. If all your machines already see each other, and you connect by name, this setting won't add much beyond complexity. However, if you ever find yourself trying to get to another machine by IP address, this can help move you to using names.

My personal preference is to connect to anything by name, and my network does this via Bonjour. This setting in the router is another way, where everything on the network can have a name like "laptop.gbeer.net". Then, the router can also hand out DNS search domains, allowing you to connect to the system just by typing the name "laptop" instead of "laptop.gbeer.net".

All you've done is correct, it should work like that. Also make sure you give your 825 a different IP address than the 655. The 655 is standard 192.168.0.1 (I have the same router. ). So I would suggest 192.168.0.2 for your 825.
Also, make sure you connect your ethernet cable to a LAN port of your 825 and not the WAN port!

Just so.

Going to have to try that. The connect by number is what I've been doing, and it's getting old.

Will it help the windows machines to discover each other? That's been a problem too.

I can't say for certain how it will help Windows, but it can't hurt. The key way to test this would be to turn this on, enter a fake domain, and try it out. I checked the defaults on Windows 7, and it should work assuming the router hands it out as "Connection-specific DNS Suffix" as reported by "ipconfig /all" run in a command window.

If you want to adhere to the specs for the fake domain, use something that ends in .local instead of .com/.net. For example, gbeer.local.

The only concern I have now reading back is this part:

That may mean the router will not hand out your fake domain if your ISP hands out a real one. Mine for example sets the Connection-specific DNS Suffix to "oc.cox.net".

Yay! I think I've got it correct now.

Both routers are squaking the same SSID, operating on separated channels, and the Tx power was lowered on both.

My iPad now seems able to move from one end of the house to the other, enjoying full bars, without needing to force it to switch between the routers.