I have a Vigour 2865. WAN1 is my DSL, which I use DDNS set to WAN1 only. Ive just added WAN2 which is setup via ethernet to an old 2860 router with a static IP assigned with 4G dongle(I know I can't use DDNS via this setup but its only for back-up so its not critical for me).
WAN2 is set to takeover on FAIL on WAN1 failing (90% packet loss). The fail over works fine and devices connected to the 2865 have internet connectivity as expected.
However the WAN2 connection keeps dropping within a 30second period (the 4G connection on 2860 is rock solid). There is no link detection set on WAN2. Running a constant ping to the 2860 every 15 or so pings is not being recieved.
In syslog Im seeing that DDNS constantly trying to update and is failing even when only WAN2 is up (4g connects alot quicker than DSL on reboot). Once DSL connects DDNS continues to fail to update. All I can deduce from this is that the "WAN" option and possibly also the update interval in DDNS is not working correctly, it seems like a bug in the firmware.
Im unsure why my WAN2 connection keeps dropping. any advice would be appreciated.

Laurence

Is this the same: https://forum.draytek.co.uk/viewtopic.php?t=24321

For the Vigor 2865 WAN2 > Vigor 2860 LAN connection, try setting the V2865's WAN2 to 1000M full duplex in the [WAN] > [General Setup] > WAN2 settings. What you're describing, especially with link detection disabled, suggests there's some Ethernet link / auto negotiation problem.

edinburgh wrote:
Is this the same: https://forum.draytek.co.uk/viewtopic.php?t=24321

Its not the same as this. my ddns is updating correctly, albeit it is updating more often than it should. which I assume is some kind of trigger associated with WAN2 dropping and coming back.

admin3 wrote:
For the Vigor 2865 WAN2 > Vigor 2860 LAN connection, try setting the V2865's WAN2 to 1000M full duplex in the [WAN] > [General Setup] > WAN2 settings. What you're describing, especially with link detection disabled, suggests there's some Ethernet link / auto negotiation problem.

I tried setting WAN2 to full duplex. This hasnt stopped WAN2 from constantly dropping its connection.

Im still at a loss as to whats going on. Both routers are running the latest firmware. Ive tried different ethernet cables.

Okay, that sounds like an ethernet interoperability problem - I believe I may have seen something similar connecting a 2865 to a 2860 or the other way around.
You can try changing the flow control in the web console (top-right slider icon). The command is "port wanfc 2 status" to see the state, then on or off to enable/disable it.

If that doesn't help, try out a basic switch inbetween the 2860's LAN ports and the 2865's WAN2 port to see if that helps. Either way, it might be a good idea to report this issue to the support team to look into WAN / LAN port compatibility problems.

Found my issue: I was setting fail over via the WAN configuration menu. I found a random redit post suggesting this didnt seem to work correctly.
I changed my configuration to use a route policy for failover and now WAN2 is solid all the time. The DDNS weird behaviour has gone away, as that appeared to just be a consequence of the constant WAN reconnections.
I used the guide below. which shows that either option should have worked correctly. N.B even when WAN1 was in failed state I would still get the same behaviour, so its not just a question of fail over not being active.

https://draytek.co.uk/support/guides/kb-wan-backup#failover-through-route-policy