OPNsense Forum

English Forums => 26.1, 26,4 Series => Topic started by: Starjumper2821 on May 23, 2026, 10:55:14 AM

Title: [Solved] dnsmasq IPv6 leases without MAC address
Post by: Starjumper2821 on May 23, 2026, 10:55:14 AM
Recently migrated from ISC to dnsmasq for DHCP and it's working, but something is confusing me. A few of the IPv6 leases in the table don't have a MAC address. But somehow they have a hostname.

Here a partially redacted screenshot:
dnmasq_IPv6_leases.png

I do know that one of the clients without a MAC is a Linux Mint system, so Debian/Ubuntu base.

Is this supposed to happen? Evidence of a configuration error somewhere?

I thank any help you can give me in this regard.
Title: Re: dnsmasq IPv6 leases without MAC address
Post by: Monviech (Cedrik) on May 23, 2026, 12:14:21 PM
The MAC address is only an assumption based on the DUID of the client.

We try to extract it here:
https://github.com/opnsense/core/blob/e209de9719943a5224a06f8e155629d1052ddcba/src/opnsense/scripts/dnsmasq/get_dnsmasq_leases.py#L67

If you check the dnsmasq lease file /var/db/dnsmasq.leases you wont find any MAC addresses for DHCPv6 leases, only the DUID and IAID.
Title: Re: dnsmasq IPv6 leases without MAC address
Post by: Starjumper2821 on May 23, 2026, 12:59:19 PM
Ah, I see. That makes sense. And based on what I just looked up on how a DUID is created, the leases without a MAC address have type 4.

Well, that answers that. Thank you very much for your help.