I have a Juniper switch that has a dhcp-client configured like this:

show interfaces irb unit 0 family inet dhcp                      
client-identifier {
    prefix {

I want dnsmasq to assign the juniper switch a ip-address and use the client-identifier.

tcpdump shows that the juniper switch sends

Client-ID Option 61, length 10: "MSWI:MSWI"

if I configure this string in dnsmasq like so:


the ip address gets not assigned. user-id ascii MSWI works, but I have to use prefix host-name in production

I suspect that my dnsmasq configuration is wrong, but I don't know what to change

Any ideas?


1 Answer 1


I found the solution. dnsmasq must be started with --dhcp-authorative.

Otherwise dnsmasq ignores requests from unknown leases. In my case I changed the configuration of dnsmasq and the switch until it worked. However, these changes did not solve the problem. Instead, when I rebooted the switch the address was not assigned again.

The solution has nothing to do with the client-identifier. The switch got an ip-address without a client-identifier and none with a client-identifier. This lead me on the wrong track.

Instead it is a timing-problem.

The timeout mentioned in the manpage explains this behaviour.

the manpage says:

-K, --dhcp-authoritative Should be set when dnsmasq is definitely the only DHCP server on a network. For DHCPv4, it changes the behaviour from strict RFC compliance so that DHCP requests on unknown leases from unknown hosts are not ignored. This allows new hosts to get a lease without a tedious timeout under all circumstances.


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