Roaming Network Latency?

The IP’s for each Airport were actually different this time around, but I’m not sure if this was a mis-read on my part previously, or an error on the previous installation..

I suppose anything is possible, but I've never seen two devices using the same IP address on a network.

After setting up the first AirPort Extreme, as before, the 2nd AirPort Extreme was connected via ethernet (Airport 1 LAN > Airport 2 WAN) prior to setting up the extended network. Airport Utility confirmed the Airports had been extended via ethernet on completion - as below.

And yet, there is no setting in AirPort Utility that you can manually choose for an AirPort that is labeled "extend using Ethernet". Your choices for WiFi on an AirPort are 1) Create a wireless network, 2) Extend a wireless network, and 3) Off.

Extend a wireless network is used only if an AirPort connects using a WiFi connection back to the main AirPort, so the correct setting for your extending AirPort is "Create a wireless network", which you have confirmed. Don't know why Apple does things like this, but they do.

Performance is however fairly similar - when both Airports are in the chain, there is a small but noticeable drop in wifi response - especially when caches are cleared. Most people probably wouldn’t notice, but having lived with the single Airport for a while, (& compared with & without 2 units), the difference is perceivable to me. (As someone who works in Audio, latency is a concept I’m all too familiar with)!

There is always going to be some effect when you add a second access point to a network, but it should not be significant in terms of slow downs.

My conclusion is that the passthrough on Apple Airports is somehow not completely passive?

Nor is a simple Ethernet switch completely passive in my experience.

1. Is it OK to have both Airports connected directly to my BT Hub 6 router ports, (rather than direct from AP > AP as advised by Apple)? Am I likely to encounter any errors if they’re set to a roaming network, but feeding direct from my router?

Yes, of course. Another case of Apple being Apple. In fact, if you think about things, it is a better way to set things up. Why? Let's say that you have AirPort 1 connected to your BT Hub, and Airport 2 is connected to AirPort 1. If AirPort 1 has a problem, AirPort 2 will likely have a problem. Troubleshooting becomes more difficult because you won't know which device really is causing the problem.

If both AirPort 1 and AirPort 2 are connected to the Hub, and AirPort 1 has a problem, AirPort 2 will not be affected. So, best practice would have both AirPorts connecting to the Hub.

2. Also, is it possible to lock certain devices to a particular AP Extreme (for best coverage) within the Airport Utility?

I think you already know the answer to this one. There are no settings in AirPort Utility.....or any other Apple device for that matter......to lock a particular device to a particular access point or vice versa.

Also, it might be useful to remember that even the "latest" version of the AirPort Extreme was designed in 2012 and introduced in early 2013. Apple made no improvements at all in the hardware of the AirPorts up until the time that they were discontinued in early 2018. So, if the AirPorts are working well, that is pretty impressive.

I set this up using the Airport utility Wizard, & both Airports have identical settings, & both are set to Bridge Mode. No switches are involved & firmware on both units is 7.9.1. The Airport utility displays them vertically (with solid line connections), so my assumption is that they are correctly connected.

The AirPort Utility "wizard" assumes that you have already connected the second AirPort to the first using an Ethernet cable......before......you run the setup on the second AirPort. If you haven't, then the utility will set up the second AirPort to "extend a wireless network" and then when you connect the Ethernet connection, that will create a feedback loop that slows down the second AirPort network considerably, almost to a crash.

If both AirPorts really are set up identically..........."Create a wireless network" that uses the exact same wireless network name, security and password, and both AirPorts are running in Apple's setting of "Off (Bridge Mode), then I cannot explain why the AirPorts would perform differently, assuming that the Ethernet wiring is working correctly.

I have also tried connecting both Airport Extremes directly to the ports on my Router (BT Business Hub6, with 4 Gigabit ports). The Airports still have the same identical roaming configurations, but are displayed in an upside down "Y" pattern). Latency is much improved, but I suspect this could potentially cause issues as they share the same IP address?

Both AirPorts do not share the same iP address because every device on a network must have a different IP address.

Open AirPort Utility and click on an AirPort Extreme and a smaller window will appear with information about the device. Note the IP Address for the AirPort. It is the first listing in the information window. It might look something like 192.168.x.x for example.

Then, do the same with the other AirPort.

What are the IP Addresses of each AirPort? They should be different.

I'd read that there should be no performance drop when using Airports connected via Ethernet, so can someone please confirm that this is either expected behaviour, or that I might have overlooked something?

Assuming the AirPorts are configured correctly......it appears that they are.....there should be no difference between them. I use two AirPort Extremes on the network here connected together using Ethernet and they perform virtually identically. They should also perform the same no matter whether you have one AirPort connected to the main router and the second AirPort connected to the first.....or.....whether you have both AirPorts connected directly to the main router.

So, I'm scratching my head here on your issue.

Post screenshots of the actual setup of both Airports.. We should be able to spot any major problems.

Same comment as Bob.. if it works fine with both plugged into the BT router there is no way you are getting duplicate IP. Bridged both will pickup different IP from the router.

It is odd as I have never seen the issue and cannot replicate it.

Do make sure IPv6 is set to link-local only on both Airports.. although I don't see why it would cause problems without.

Post a trace route as well to show how you are affected by going through both airports..

Also run a ping to the 1st airport, the BT router as well as the first edge router in the BT network.