topic Re: BT Full Fibre IPv6 Provisioning in Broadband

BT Full Fibre IPv6 Provisioning

sizzleplop — Sun, 25 Jan 2026 23:53:56 GMT

I have recently switched to using a third party router - BT supplied the PPPoE details and I'm connected using IPv4 only. The original router (Smart Hub 3) was automatically setup for IPv6. I require IPv6 (for several BT business lines at different locations).

I have looked online and used the settings that have been seemingly been successful for many users. However, they do not work for this installation. It is my understanding that this service needs to be provisioned by BT for my line when using a third party router.

When I spoke with BT support on the telephone, I was told that I first needed a static IPv4 address - which I'm very sceptical about - but this has now been done.

I am using the following settings:

DHCPv6

Prefix delegation size: /56

Request prefix only: Disabled

Send prefix hint: Enabled

Re: BT Full Fibre IPv6 Provisioning

sizzleplop — Sun, 25 Jan 2026 23:55:53 GMT

I have tried various combinations, but only receive a fe80:: IPv6 address, rather than a 2a00: on the WAN interface. I'm happy to provide full details on the account, if that helps? Any assistance would be much appreciated.

Re: BT Full Fibre IPv6 Provisioning

sizzleplop — Sun, 25 Jan 2026 23:58:40 GMT

Having read a couple of posts on here, it appears that @BethM may be able to assist - if not if someone else can that would be fantastic!

Re: BT Full Fibre IPv6 Provisioning

BethM — Mon, 26 Jan 2026 12:37:28 GMT

Hi sizzlepop

I will need to query this with our technical team - can you please send over a private message with your account details?

Re: BT Full Fibre IPv6 Provisioning

sizzleplop — Mon, 26 Jan 2026 20:15:08 GMT

Hi Beth,

thank you for your reply. I have messaged you with the details of the account.

Re: BT Full Fibre IPv6 Provisioning

sizzleplop — Sat, 31 Jan 2026 00:37:11 GMT

We have a ball game! A big thank you to BethM for your assistance. Since BT don't provide any details, I would like to outline what's required for OPNsense configuration - to follow...

Re: BT Full Fibre IPv6 Provisioning

sizzleplop — Sat, 31 Jan 2026 00:55:13 GMT

Step 0 — Initial OPNsense state

WAN: PPPoE connected for IPv4 only
IPv6 previously disabled globally on OPNsense interfaces
Neighbor Discovery (NDP) was disabled
WAN interface showed only fe80::…
DHCPv6 logs were empty
LAN IPv6 not yet configured

Symptoms:

No global IPv6 address on WAN
No IA_PD prefix delegated
DHCPv6 client never started

Re: BT Full Fibre IPv6 Provisioning

sizzleplop — Sat, 31 Jan 2026 00:40:40 GMT

Step 1 — Enable IPv6 globally

Interfaces → Settings → Allow IPv6 → Enabled
DHCP Unique Identifier → use existing LLT DUID
Log level → Standard Info

✅ This allows OPNsense IPv6 stack to start on all interfaces.

Re: BT Full Fibre IPv6 Provisioning

sizzleplop — Sat, 31 Jan 2026 00:41:48 GMT

Step 2 — Enable Neighbor Discovery

Interfaces → Neighbors → Automatic Discovery → Enabled
Reason: required for IPv6 RA / NDP / SLAAC to work correctly on LAN

Re: BT Full Fibre IPv6 Provisioning

sizzleplop — Sat, 31 Jan 2026 00:42:51 GMT

Step 3 — Configure WAN IPv6 client

Interfaces → WAN → IPv6 Configuration Type → DHCPv6
Request prefix only → ✅
Send prefix hint → ✅
Prefix delegation size → /56
PPPoE username/password → correct

Re: BT Full Fibre IPv6 Provisioning

sizzleplop — Sat, 31 Jan 2026 00:43:47 GMT

Step 4 — Configure LAN IPv6 tracking

Interfaces → LAN → IPv6 Configuration Type → Track Interface
Track IPv6 Interface → WAN
Assign Prefix ID → 0x0
Router Advertisements → Assisted
LAN firewall rule → IPv6 any → any

✅ Ensures delegated /56 is split into /64 for LAN and clients receive IPv6 automatically.

Re: BT Full Fibre IPv6 Provisioning

sizzleplop — Sat, 31 Jan 2026 00:45:46 GMT

Step 5 — Soft restart of WAN IPv6 client

Toggle WAN IPv6 config:
1. IPv6 = None → Save & Apply (Wait 10 Seconds)
2. IPv6 = DHCPv6 → Save & Apply

Purpose: restart dhcp6c without dropping PPPoE / IPv4.

Logs began to appear:

dhcp6c: Errordhcp6ctransmit failed: Can't assign requested address

✅ This showed that DHCPv6 was attempting to start but failed due to stale PPPoE interface state.

Re: BT Full Fibre IPv6 Provisioning

sizzleplop — Sat, 31 Jan 2026 02:59:49 GMT

Step 6 — Verify DHCPv6 / IA_PD

System → Log Files → General → filter dhcp6c
Expected log lines:

dhcp6c: Sending Solicit dhcp6c: received Advertise dhcp6c: IA_PD prefix: 2a00:xxxx::/56

WAN interface: may show link-local (fe80::xxx...)/ temporary IPv6 (BT only guarantees PD) - this is normal.
LAN interface: receives /64 from delegated /56 (2a00:xxx...)
Clients: get IPv6 via RA/SLAAC automatically

✅Confirmed working when LAN shows:

2a00:xxxx:xxx:xxxx:xxxx:xxxx:xxxx:xxxx/64

Clients can ping external IPv6 addresses (ping -6 google.com)

Re: BT Full Fibre IPv6 Provisioning

sizzleplop — Sat, 31 Jan 2026 00:51:42 GMT

Step 7 — Adjust DHCPv6 / Logging settings

Logging level → StandardInfo (after troubleshooting)
Prevent Release → ✅ Enabled
- Keeps delegated prefix tied to DUID
- Prevents temporary loss of IPv6 if OPNsense restarts
DHCP Unique Identifier (DUID) → existing LLT DUID kept stable

Re: BT Full Fibre IPv6 Provisioning

sizzleplop — Sat, 31 Jan 2026 00:52:48 GMT

Step 8 — Final validation

LAN clients receiving IPv6 addresses in /64
Default IPv6 route set via WAN
External IPv6 connectivity working (ping -6 google.com)
test-ipv6.com confirms full functionality
No errors in dhcp6c logs once interface was reset

Re: BT Full Fibre IPv6 Provisioning

sizzleplop — Sat, 31 Jan 2026 00:53:41 GMT

Summary of Key Lessons Learned

Always enable “Allow IPv6” globally before expecting DHCPv6 to work
Neighbor Discovery must be enabled for RA / SLAAC and DHCPv6 to function
Soft toggles may not be enough if previous IPv6 state was disabled — a full WAN / PPPoE reset clears stale state
BT Business IPv6 may not assign a global IPv6 to WAN — look at LAN / delegated prefix instead
Prevent Release should be enabled to keep static BT prefix stable
DUID must remain stable to retain delegated prefix across restarts

✅ At this point your OPNsense setup is fully functional with BT Business IPv6, LAN clients are receiving IPv6, and logging is clean.