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How to get DHCPv6 RA Prefix Delegation working on systemd-networkd in Debian? (feddit.de)

submitted 10 months ago by Helix@feddit.de to c/linux@lemmy.ml

3 comments fedilink hide all child comments

I operate a Debian router. IPv4 works perfectly. However, I am facing issues with IPv6.

In my sysctl.conf, I have the following configuration:

# accept router advertisements on WAN interface
net.ipv6.conf.1und1.accept_ra = 2

In /etc/systemd/network/1und1.network, the configuration is as follows:

[Match]
Name=1und1

[Network]
Description=Fritz!Box 7510 providing 1und1 VDSL
IPv6AcceptRA=yes
DHCP=yes

[DHCPv4]
Hostname=claptrap
UseHostname=no
UseDNS=no
UseNTP=no
UseSIP=no
UseRoutes=no
UseGateway=yes

[IPv6AcceptRA]
UseDNS=no
# Force starting the DHCPv6 client even if the Router Advertisement
# indicates it's not required.
DHCPv6Client=yes

[DHCPv6]
UseHostname=no
UseDNS=no
UseNTP=no

In my dnsmasq.conf, the configuration is as follows:

dhcp-range=interface:br0,::,constructor:br0,ra-stateless,ra-names,12h

Additionally, the /etc/nftables.conf contains:

icmpv6 type {
    echo-request,
    nd-neighbor-solicit,
    nd-router-solicit,
    mld-listener-query,
    nd-neighbor-advert,
    nd-router-advert
} accept

On the WAN interface.

I receive a /64 IP on the 1und1 interface; however, I do not receive a prefix on br0. What am I doing wrong? Do I need to instruct systemd-networkd to request a larger prefix somehow?

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[–] progandy@feddit.de 0 points 10 months ago (1 children)

You'll have to enable prefix delegation. dnsmasq should not be necessary though, I think. This appears to explain all steps:

https://major.io/p/dhcpv6-prefix-delegation-with-systemd-networkd/

[–] Helix@feddit.de 0 points 10 months ago* (last edited 10 months ago) (1 children)

I don't want systemd-networkd to delegate the prefixes and instead use dnsmasq for that.

However, systemd-networkd should at least be able get the prefix on the 1und1 interface, where I configured IPv6AcceptRA, but for whatever reason it only gets a single address with a /64 prefix.

The following configuration pulled from your article didn't help either:

[DHCPv6]
PrefixDelegationHint=::/56

Apparently, the article has a few minor errors as well, e.g. they configure lanbridge.network twice with different settings and once call a setting ConfigureWithoutCarrier=yes and once ConfigureWithoutCarrier=true. I don't really trust inconsistent tutorials 😅

Checking systemd-networkd logs, I also get the following error:

Could not set NDisc address: Invalid argument

Currently upgrading to Debian 12, maybe this is a bug…>

[–] progandy@feddit.de 0 points 10 months ago* (last edited 10 months ago)

The tutorials give a good overview for further research, though. If you do not want to use systemd to manage the delegation you probably need a separate dhcpv6 client that does this and disable dhcp for systemd-networkd (slaac is probably ok to keep)