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Accepted
Marcus K
Asked: 2020-09-27 08:29:39 +0800 CST

DHCPCD does not delegate an assigned IPv6 prefix

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I've been trying to get IPv6 PD with dhcpcd working on my home server along with ppp and radvd to allow for SLAAC to work and eventually replace my ISP-provided router. Unfortunately, the prefix which dhcpcd receives on the ppp0 interface via RAs only gets configured as an address on that interface, instead of also being delegated to the lan interface on which radvd is operating.

What am I missing?

/etc/dhcpcd.conf:

# Ignore changes on docker interfaces
denyinterfaces veth*

duid

# Persist interface configuration when dhcpcd exits.
persistent

option domain_name_servers, domain_name, domain_search, host_name
option interface_mtu

require dhcp_server_identifier

slaac private

noipv6rs
waitip 6
ipv6only

#Prefix Delegation
interface ppp0
option rapid_commit
ipv6rs
iaid 1
ia_pd 1/::/64 lan/0/64

#don't use ISP DNS servers
nohook resolv.conf

/etc/radvd.conf:

interface lan
{
    AdvSendAdvert on;
    prefix ::/64
    {
    AdvOnLink on;
         AdvAutonomous on;
         AdvRouterAddr on;
    };
};

The lan and wan.7 (my ISP requires VLAN 7, so this is what ppp binds to) interfaces are managed by systemd-networkd (DHCP is not handled by it though), but ppp0 gets created dynamically by ppp.

networking ipv6 radvd dhcpcd

1 Answers

  1. Best Answer

    Old thread, but this is one of the few hits Google spits out in 2022 for configuring IPv6 PD with isc-dhcp-client, so for what it's worth:

    there is a known limitation in earlier versions of isc-dhcp-client that prevents this configuration from succeding on PPPoE interfaces like ppp0. Even when all parameters are entered exactly as in the official documentation, configuration ultimately fails due to ppp0 being an "unsupported interface type" (see syslog). The problem has been addressed upstream, but as of April 2022 the fix did not yet trickle down to the more "conservative" distros like Debian 11. Building the Package directly from upstream git will likely solve the problem, but even the official Debian Wiki recommends using alternative tools like wide-dhcp6-client instead to address the issue if you need to do prefix negotiation through PPPoE.

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