DHCP "static" assignments

Glenn Satchell glenn.satchell at uniq.com.au
Mon Aug 12 11:33:12 UTC 2013


On Fri, August 9, 2013 6:07 am, Sten Carlsen wrote:
>
> On 08/08/13 21:26, Chris Buxton wrote:
>> On Aug 8, 2013, at 9:21 AM, Sten Carlsen <stenc at s-carlsen.dk
>> <mailto:stenc at s-carlsen.dk>> wrote:
>>
>>> It seems to me that the man-page is not quite in agreement with this:
>>> ~~~~
>>> The *host* declarations will only match a client if one of their
>>> /fixed-address/ statements is viable on the subnet (or shared
>>> network) where the client is attached. _Conversely, for a
>>> __*host*__declaration to match a client being allocated a dynamic
>>> address, it must *not* have any __/fixed-address/__statements. _
>>> ~~~~
>>> This text says "not have any fixed-address statements", it does not
>>> say any fixed addresses in this subnet.
>>>
>>> I also find the following a bit confusing:
>>> ~~~~
>>> The /fixed-address/ declaration is used to assign one or more fixed
>>> IP addresses to a client. It should only appear in a /host/
>>> declaration. If more than one address is supplied, then when the
>>> client boots, it will be assigned the address that corresponds to the
>>> network on which it is booting._If none of the addresses in the
>>> __/fixed-address/__statement are valid for the network to which the
>>> client is connected, that client will not match the
>>> __/host/__declaration containing that __/fixed-address/__declaration.
>>> _Each /address/ in the /fixed-address/ declaration should be either
>>> an IP address or a domain name that resolves to one or more IP
>>> addresses.
>>> ~~~~
>>> What does it mean "will not match"? Does that mean that the client is
>>> then an "unknown client"?
>>
>> These are both good questions.
>>
>> In my experience, one should never assume that the DHCP man pages are
>> 100% accurate. They are not.
> Maybe we could try to improve that situation? First step is to realize
> what is not perfect.
>>
>> Regards,
>> Chris Buxton
>
> --
> Best regards
>
> Sten Carlsen
>
> No improvements come from shouting:
>        "MALE BOVINE MANURE!!!"

There is no "they" in the solution to this, it's down to "us".

The various dhcpd man pages are quite long with related information in
many places. Often it may be updated in one but not all, leading to
inconsistencies. Perhaps we can work out a better description to go in the
man page. Then a bug can be logged to update the appropriate text.

S, in the spirit of offering solutions, my suggestion to "What does it
mean "will not match"?" In my mind it means that it ignores that host
statement. If there is no other host statement for that mac address, then
it becomes an unknown client. Now how to word that is a clear and concise
manner?

"If none of the addresses in the /fixed-address/ statement are valid for
the network to which the client is connected, that client will not match
the /host/ declaration containing that /fixed-address/ declaration."

"If none of the addresses in the /fixed-address/ statement are valid for
the network to which the client is connected, that client will not match
the /host/ declaration containing that /fixed-address/ declaration. The
contents of that /host/ declaration will not be evaluated, and if there
are no other matching /host/ statements then the device will be an
"unknown client"."

Alternatively under the section where "unknown clients" is defined there
could be a statement clarifying how a client becomes known or unknown.
Currently the definition is

"An unknown client is simply a client that has no host declaration."

I'm not quite sure hot to reword this. Over to you.

regards,
-glenn




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