[Dnsmasq-discuss] Issue with circuit-id matching on dhcp requests

[Max Boon]

I post a message on the discussion list and... now it's working as it should. I think possibly the issue was cached mac/IP bindings in dnsmasq.leases. Some of the switches earlier managed to get IPs in the dynamic range (due to misconfiguration on my part), so they've been requesting the wrong IP vs the one they've been assigned in the dhcp-host declaration. Now I see those leases are eventually expiring and going through the full discover/offer/request/acknowledge process and getting the correct static IP.

Yay!

________________________________
Från: Dnsmasq-discuss <dnsmasq-discuss-bounces at lists.thekelleys.org.uk> för Max Boon <Max.Boon at bjurholm.se>
Skickat: Söndag, 10 maj 2026 11:25
Till: dnsmasq-discuss at lists.thekelleys.org.uk <dnsmasq-discuss at lists.thekelleys.org.uk>
Ämne: [Dnsmasq-discuss] Issue with circuit-id matching on dhcp requests

Hello,

I have a bunch of switches that have previously been supplied with IP addresses using isc-dhcpd that I am now replacing with dnsmasq. There is an address range for automatically assigned IP's and the rest with static host assignments, all in the same /24 subnet.

The static assignments are assigned using option 82 circuit-id to set a tag which is then matched in the dhcp-host declaration. For the most part I have managed to get it working, but I have noticed something in my logs which I am not sure is a bug or just my general lack of understanding...

Basically, if a DHCP inform packet comes in, the circuit-id gets matched, and a corresponding ack gets sent by the server. However, if a DHCP request comes in, the server doesn't seem to be able to match the circuit ID at all and responds with "dnsmasq-dhcp[5631]: no address range available for DHCP request via eth0"

I have confirmed using tshark that the incoming DHCP request packet contains a circuit-id that matches an assigned dhcp-host entry.

My dnsmasq.conf has only the following range:

dhcp-range=172.16.127.16,172.16.127.49,255.255.255.0,12h

I have a seperate .conf containing the static entries, repeated like so:

dhcp-circuitid=set:lag_103_1309_91,lag-103:1309.91
dhcp-host=net:lag_103_1309_91,172.16.127.141,Switch1
dhcp-option=net:lag_103_1309_91,12,Switch1

dhcp-circuitid=set:lag_104_1408_93,lag-104:1408.93
dhcp-host=net:lag_104_1408_93,172.16.127.139,Switch2
dhcp-option=net:lag_104_1408_93,12,Switch1

Best Regards,

Max


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