how to configure dnsmasq client-identifier for juniper prefix host-name

Question

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

show interfaces irb unit 0 family inet dhcp                      
client-identifier {
    prefix {
        host-name;
    }
}

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:

dhcp-host=id:"MSWI:MSWI",192.168.4.252,MSWI

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?

TIA

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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