[Dnsmasq-discuss] dhcp-host option

[Simon Kelley]

On 30/10/11 16:21, Tom Metro wrote:
> The dhcp-host option has a complex syntax, and the man page doesn't
> cover all the rules.
>
> One aspect not mentioned is that the order of the arguments don't have
> to match what it is specified. The man page indicates:
> --dhcp-host=[<hwaddr>][,id:<client_id>|*][,set:<tag>][,<ipaddr>][,<hostname>][,<lease_time>][,ignore]
>
> and yet it show the example:
> --dhcp-host=lap,192.168.0.199
>
> where hostname appears *before* IP address. Can any argument appear in
> any oder? If not, what are the rules?
>
> Generally, some of these arguments are used by Dnsmasq to identify the
> client making the request to see if it matches this static rule, while
> other arguments are used to define the static entry. The behavior of
> dhcp-host may be clearer if you identified which arguments fall into
> which of those groups.
>
> Some rather useful behaviors, such as being able to assign a host name
> to a MAC address, without assigning a static IP, are not covered by the
> man page. There should be an expanded collection of examples that cover
> things like this.
>
> There should be a sentence or two describing each of these options (for
> example, the format of lease_time is never defined, other than
> mentioning the special cases of 'infinite 'and 'ignore.' This would also
> be the place specify default values if the argument is omitted.
>
I don't disagree with any of the above, but my available dnsmasq time if 
going into the IPv6 DHCP project at the moment. Patches towards this, 
from anybody, gratefully accepted.

>
>> The special option id:* means "ignore any client-id and use MAC
>> addresses only." This is useful when a client presents a client-id
>> sometimes but not others.
>
> How is that different from specifying a mac address and no client-id?

Without this option, if a client presents different client-ids at 
different times, it will be treated as two different clients, even if 
the MAC address is the same. With this option the client-id is ignored 
so that same MAC address -> same client. (It used to be that two 
requests, one with and one without a client-id would also be treated as 
different. This is the most common case, for instance when a DHCP client 
in netboot ROM behaves differently to the OS that finally gets booted. 
Eventually, more subtle behaviour was added for this case, which renders 
the id;* option redundant most of the time.)

Simon.

>
>   -Tom
>