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

[Simon Kelley]

On 10.05.2026 13:31, Max Boon wrote:
> 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.
> 

Under those circumstances, they should have got a DHCPDECLINE reply from 
dnsmasq and been forced into the four-phase process. Not all DHCP 
clients get this right, however.


Glad it's fixed.

Simon.

> 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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