I have an Airport Extreme set up to do PPPoE (modem is in bridged mode), DHCP, NAT, etc.

Whenever the ADSL connection goes down and the AE has to renegotiate the PPPoE connection, the WLAN slows down. Ping times between wireless devices goes from insignificant to four seconds or more. Once the PPPoE connection is reestablished, the WLAN returns to normal throughput.

This is a relatively recent phenomenon. I ran this set up for a long time without having that kind of trouble.

I posted this on the Apple support site, but got zero replies.

Any ideas?

I was thinking of having the modem Huawei HG521c do the PPPoE on it's own. Think that would help?

make sure the wan port does NOT negotiate port speeds automaticall.

if the modem does some sort of reset the airport will renegotiate automatically, and this will lead to performance issues because the network is beeing reset a few times.

you could do the pppoe via the modem .. but only if you can do a dmz setting and forward everything to the airport ... so you wont have double-nat .. which is a tricky thing you not really want to have.

also you need to make sure the modem and the rest of your network do use different network's ... this is VERY important ..

not doing so also can lead to performance issues as the airport have to take care this then software sisded ..

Have you tried reloading mDNS?

1 - How do I stop the WAN port from renegotiating?

2 - You mean reload mDNS AE? I don't know how to do that, either.

PM me your email address and I'll send you a packaged script that will do it for you. mDNSreloader.