Skip to main content

NTT FLET'S IPv6 setup

This page covers connecting routerd to NTT's FLET'S IPv6 service in Japan, where the Home Gateway (HGW) is in the path and delegates IPv6 prefixes by DHCPv6-PD.

Topology this page assumes​

  • An NTT HGW (e.g. PR-400NE) on the upstream side, with IPv6 enabled.
  • Hikari Denwa (NTT IP telephony) subscription. The HGW only runs a DHCPv6-PD server when this is provisioned.
  • routerd's host on the LAN side of the HGW. Its WAN interface is in the HGW's LAN.

Minimum config​

- apiVersion: net.routerd.net/v1alpha1
  kind: Interface
  metadata:
    name: wan
  spec:
    ifname: ens18
    adminUp: true
    managed: true

- apiVersion: net.routerd.net/v1alpha1
  kind: IPv6DHCPAddress
  metadata:
    name: wan-ra
  spec:
    interface: wan

- apiVersion: net.routerd.net/v1alpha1
  kind: IPv6PrefixDelegation
  metadata:
    name: wan-pd
  spec:
    interface: wan
    profile: ntt-hgw-lan-pd

The ntt-hgw-lan-pd profile pulls in the right defaults:

  • DUID type: link-layer (MAC-derived). NTT's documented terminal models use DUID-LL or DUID-LLT.
  • Prefix length: /60 (the HGW divides the upstream prefix into 16 sub-prefixes and hands out /60s).
  • Rapid Commit: disabled. NTT's option tables mark it as unused for this profile.
  • IA_NA: not requested. NTT's profile is PD-only.

Lab notes​

If you are running routerd on a virtual machine on Linux (e.g. Proxmox) and the HGW does not seem to reply to your Solicit, check the following before suspecting the HGW:

  • The Linux bridge between the host NIC and the VM has multicast_snooping=0. With the default =1, RA and DHCPv6 multicast is silently dropped on some kernels.
  • Any L2 switch in the path has IGMP/MLD snooping disabled, or has an MLD querier so that snooping tables stay populated.
  • tcpdump filter is udp port 546 or udp port 547. NTT HGWs reply from an ephemeral source port, not 547.

These facts are documented in the design notes under "Lab-specific issues".

Verifying​

routerctl describe ipv6pd/wan-pd

Look for currentPrefix and a recent lastObservedAt. The HGW UI page "DHCPv6 Server payout status" should also list a row for your router's MAC.

Common pitfalls​

  • Setting an explicit iaid and then changing it later. The HGW keeps a binding keyed on the client identity; if the client identity changes between leases, the old binding ages out instead of being reused. Pick an IAID once and keep it.
  • Sending DHCPv6 Release on every routerd restart. NTT HGWs handle Release immediately, which can disturb the lease table during routine apply cycles. routerd's NTT profile does not restart dhcp6c for unrelated config changes.
  • Assuming the prefix you got last time will be the same. NTT HGWs may reassign a different /60 after a fresh acquisition. The lastPrefix field in routerd state is for diagnostics; do not hard code the value into LAN-side YAML.

See also​