not getting same ip for same MAC

perl-list perl-list at
Wed Aug 8 19:20:29 UTC 2018

This could also be interesting tho I don't know how it affects lease assignment for sure (from man dhcpd.conf):

The ignore-client-uids statement 

ignore-client-uids flag ; 

If the ignore-client-uids statement is present and has a value of true or on , the UID for clients will not be recorded. 
If this statement is not present or has a value of false or off , then client UIDs will be recorded.

----- Original Message -----
> From: "Simon Hobson" <dhcp1 at>
> To: "Users of ISC DHCP" <dhcp-users at>
> Sent: Wednesday, August 8, 2018 1:40:49 PM
> Subject: Re: not getting same ip for same MAC

> Christopher Barry <christopher.r.barry at> wrote:

> > Problem:
> > I'm booting an embedded device via u-boot over tftp, and I am getting
> > one IP during boot, and another IP once Linux comes up.
> ...
> > In the leases file it can be seen that the uid value is different
> > between u-boot and linux, even though the MAC is the same.

> This is a known issue. The DHCP spec requires that the Client ID (uid in the
> leases file) is used as the primary key in the lease database, the MAC address
> is not used at all if there is a Client ID provided.
> There are 4 ways around this :
> 1) Just enlarge your pool
> 2) Use classes to make the u-boot and Linux use different pools. The booted
> Linux will then behave as you were used to. In a production environment, it can
> also be used to give the bootloader a short lease so that a smaller pool can be
> used.
> 3) Configure one or both clients so that they both use the same Client ID, or
> both use no Client ID
> 4) A long time ago someone wrote some patches - though I don't think they would
> be applicable to your case. IIRC the patches did something like "if there is no
> Client ID, add one using the MAC address" and were intended to deal with the
> known "Linux doesn't send a Client ID, Windows uses the MAC address" dual boot
> issue.

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