Replacing dhcpcd with dhcp6leased in OpenBSD

I have been using OpenBSD as a router at home for a long time. There are many reasons to choose OpenBSD for this task, being one of them that the base install includes everything you need.

If your Internet provider has IPv6 support there is a chance it uses DHCPv6-PD to delegate your network a prefix. In the past, if you wanted to get an IPv6 prefix in OpenBSD you had to use a third party package like dhcpcd. Not to be confused with dhcpd(8), note the additional c in the former.

It works fine, but it is not part of the base installation. It is not a very big issue, but it is considered good practice sticking with the base system for simplicity and security reasons.

Fortunately OpenBSD 7.6 ships with a new daemon in the base system called dhcp6leased(8), which can be easily used to replace dhcpcd. Let me show you how I did it.

dhcpcd configuration

My dhcpcd configuration looked like this:

allowinterfaces pppoe0
ipv6only
nooption domain_name_servers
nooption domain_name
duid
persistent
option rapid_commit
option interface_mtu
require dhcp_server_identifier
slaac private
waitip 6

nohook resolv.conf, yp, hostname, ntp

interface pppoe0
        ipv6rs
        ia_na 1
        # request /56 prefix from the provider to use for downstream networks
        ia_pd 2/::/56 igc3/0

It is the result of reading multiple guides and articles about dhcpcd and testing it once and again. My provider uses PPPoE, so testing DHCPv6-PD required re-restablishing the connection on every change.

The most important part of the configuration is the interface section. My Internet provider (DIGI) assigns every customer a /56 IPv6 prefix which I propagate to the igc3 interface. This interface is connected the rest of my local network, and rad(8) automatically advertises it to the rest of the clients connected to the network.

Upgrading to OpenBSD 7.6

The upgrade process in OpenBSD was very quick and painless, as usual. It only took around 5 minutes, and required no configuration changes at all.

Configuring dhcp6leased

After taking a look at the dhcp6leased.conf(5) man page, I was able to quickly write the following configuration file:

request prefix delegation on pppoe0 for { igc3/64 }

Updated 2024-12-04: I noticed SLAAC was not working as expected in my machines. They were configuring themselves using a prefix that did not match the one the firewall was getting from the PPPoE connection. In the end, I found that SLAAC does not work with prefixes that are not /64, and also that Amazon Echo devices send Router Advertisements. I have updated the configuration file to use a /64 prefix, even if my ISP assigns a /56.

I commented out all lines related to dhcpcd in the /etc/rc.conf.local file, and then enabled dhcp6leased:

# rcctl enable dhcp6leased

One reboot later, the IPv6 prefix was being correctly assigned and everything was working as expected:

Oct 11 19:54:16 firewall dhcp6leased[15122]: Soliciting lease on pppoe0
Oct 11 19:54:16 firewall dhcp6leased[15122]: Requesting lease on pppoe0
Oct 11 19:54:16 firewall dhcp6leased[64076]: prefix delegation #0 2a0c:5a81:[...]:4c00::/56 received on pppoe0 from server 0 0020000863800000080b7aee13e7b1eb1bc751302be1f8b8a

I was able to remove dhcpcd from the system and call it a day:

# pkg_delete dhcpcd
# /usr/sbin/userdel _dhcpcd
# /usr/sbin/groupdel _dhcpcd

Configuring rad

Added on 2024-12-04

rad(8) is tasked with sending Router Advertisements in OpenBSD. I found that an Amazon Echo device was sending RAs, messing with the prefix my ISP assigned.

I solved it by setting the router preference to High in the /etc/rad.conf file:

interface igc3 {
        default router yes
        router preference high

        dns {
                nameserver fe80::1
                search myhomedomain.home
        }
}