I've recently been through the pleasure of installing a new Fibre connection for a client of mine. Now they've previously been using an aftermarket router(Asus RT-AC56U) via VDSL and now migrated to Fibre what I didn't think through and found out is it is complusary is that VOIP will be enabled and forcefully imposed on a business connection.
Now the RT-AC56U isn't VOIP (nor the more common Asus RT-AC68U) enabled, I was left really with the option of connecting the supplied fibre HG-659(via WAN, not LAN) to the RT-AC56U (Via LAN) and configure. Now Vodafone Support don't tend to have much experience with this, they just expect you to connect the very useless propriotry gear they supply but I've had multiple issues with the HG-659 dropping port forwarding rules when they reach their allocated max device count for DHCP leases, so I needed to avoid this being the DHCP Server at all costs.
After speaking with the Tech Support on 4 seperate occastions and being feed multiple reasons why this can't be done due to secuirty reasons or it just not being possible because the incoming VOIP connections will only work with the HG-659(which isn't true, it requires a basic internet connection), I was able to get enough collect the settings from them I needed to to resolve the issue.
This comes in 2 steps:
1. You'll need the Admin login for the HG-659, as the standard Vodafone/vodafone doesn't work for this) and access the router.
@########(please note this number is the last 8 digits of the serial number for your HG-659)
Connecting your HG-659 to your aftermarket router was extremely difficult, Support will tell you this need to be done via bridging which is incorrect(Bridging doesn't allow for voice from what I can see), I used the IP Ethernet uplink and removed all other preconfigured LAN interface types that the router comes with(I did this because they seem to conflict with each other, as 2 Ethernet interfacees are configured), once you configure the router with a WAN staticIP(192.168.1.2)/gateway(192.168.1.1) address from your 3rd Party it'll likely automatically change it's IP address range for it's on DHCP (The one I was on always used 192.168.3.2 as it's new gateway address).
Set up port forwarding for your aftermakrt router to the (now192.168.1.2)HG-659 5060, I set up both UDP and TCP as I note that the Vodafone may not be able to see the phones polling otherwise(just a guess)
These are loose instructions and I'm sure third party router may play a huge part but hopefully this helps. PM if you think I can help.