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I'm a Telstra ADSL customer and recently bought a Archer D9 modem router, mostly to improve network coverage in my home. For the first couple of days I experienced very poor reliability, with connections to all wireless devices repeatedly freezing for many minutes then dropping out, typically whenever a new device made a connection. After spending some time on the problem I found the cause and all is now working well. I'm not sure how unusual my circumstances are but I thought I'd describe them here in case anyone else is having the same frustrating experience.

The key was making a change to this part of the default configuration;

Advanced -> Network -> Internet -> WAN Interface




The User Guide at the TP-Link support site here;

http://static.tp-link.com/res/down/doc/Archer_D9(EU)_V1_UG.pdf

(Section 4.3, "Set up an IPv6 Connection") shows this "WAN Interface" table with just a single entry - "pppoe_8_35_0_d", whereas the unit I bought has an additional "bridging" interface "br_8_35_0" in its default configuration, as shown above. The short story is that I solved my problem by deleting this bridging interface (clicking the garbage can icon and confirming), so that the updated display looked like the one in the User Guide.

This second bridging interface may be harmless for many users but caused havoc for me because my ISP (Telstra) is apparently running two parallel services on my single copper connection - the usual PPPoE (over ATM) authenticated service, plus a second unauthenticated service presumably over IPoA or similar. I'm not sure how common this is - maybe it is quite unusual.

Having both interfaces active meant that a client device connecting to the router could get a WAN connection through either interface. A connection through the bridging interface could be made as soon as the phone line was connected, even before I'd configured the PPPoE username and password. Once I'd configured the PPPoE (with Telstra username and password) a new device connecting to my router could get a WAN connection through one interface or the other, more or less at random. Connections on the bridging interface typically took much longer than normal (many tens of seconds) to get an IP address and were "invisible", meaning they did not show up in the list of clients on the router's "Network Map" display. They could be confirmed by checking the client device for the assigned IP address, which would be in the Telstra 101.190.n.n domain for the bridging interface, instead of the expected 192.168.1.n assigned by the router's DHCP server for the PPPoE interface. Another possibly related symptom was the random appearance and disappearance of "wired clients" in the "Network Map" display, when there were in fact no wired connections.

The result of having devices on both WAN interfaces was chaotic - all might work well for a short while until a new device joined the network. If it got a connection on the bridging interface all existing connections would come to screeching halt. E.g. a continuous "ping" on the router gateway address 192.168.1.1 from any established connection would time-out for a minute or more, usually requiring the device connection to be re-established.

For reference the firmware on my router identifies itself as;

Archer_D9v1_0.9.1_0 / 0.9.1 0.1 v0041.0 Build 160303 Rel.58582n

which appears to be newer by several months than the most recent TP-Link download.