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BT Full Fibre IPv6 Provisioning

sizzleplop
Member

January

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

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15 REPLIES 15

sizzleplop
Member

January

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.

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sizzleplop
Member

January

 

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.

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sizzleplop
Member

January - last edited January

 

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)

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sizzleplop
Member

January - last edited January

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

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sizzleplop
Member

January

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

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sizzleplop
Member

January

Summary of Key Lessons Learned

  1. Always enable “Allow IPv6” globally before expecting DHCPv6 to work

  2. Neighbor Discovery must be enabled for RA / SLAAC and DHCPv6 to function

  3. Soft toggles may not be enough if previous IPv6 state was disabled — a full WAN / PPPoE reset clears stale state

  4. BT Business IPv6 may not assign a global IPv6 to WAN — look at LAN / delegated prefix instead

  5. Prevent Release should be enabled to keep static BT prefix stable

  6. 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.

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