Older Macs (again)

Simon Hobson dhcp1 at thehobsons.co.uk
Wed Dec 20 15:46:26 UTC 2006


James Keating wrote:

>The machines, mainly PCs, on the 10.10.0.0 network acquire leases and IPs
>without a problem. Most of the machines on the 10.1.0.0 network, mainly
>Macs running OS X and OS9.x, do the same.
>
>However, some Macs running OS9.x on the 10.1.0.0 network don't acquire
>a lease and don't receive an IP. Prior to switching to the MacMini with
>dhcpd,
>there was an NT server running DHCP server on that network, and there were
>always a lot of BAD_ADDRESS entries. The event viewer showed a lot of NAKs
>from Macs requesting IPs such as 0.0.2.234 and the like. This led me to
>believe
>that certain Macs running OS9.x and earlier were not properly requesting
>leases.

It's a Mac thing, they release their address when they shut down, and 
when they start up they request something like that from the dhcp 
server - I don't know if it's some sort of attempt at self 
configuration. Normally the DCHP server will just NAK it and the 
client will then start off on a discover cycle.

>On the MacMini, here's what /var/log/asl.log says. I don't know if
>they're the result
>of the specific machines that can't get an IP since there's no MAC addr.
>
>[Time 2006.11.29 17:38:45 UTC] [Facility daemon] [Sender dhcpd] [PID -1]
>[Message Abandoning IP address 10.1.18.206: pinged before offer] [Level
>3] [UID -2] [GID -2] [Host earths-computer]
>[Time 2006.11.29 20:02:19 UTC] [Facility daemon] [Sender dhcpd] [PID -1]
>[Message Abandoning IP address 10.1.17.207: declined.] [Level 3] [UID
>-2] [GID -2] [Host earths-computer]
>[Time 2006.11.29 20:11:59 UTC] [Facility daemon] [Sender dhcpd] [PID -1]
>[Message Abandoning IP address 10.1.18.205: pinged before offer] [Level
>3] [UID -2] [GID -2] [Host earths-computer]
>[Time 2006.11.30 13:42:09 UTC] [Facility daemon] [Sender dhcpd] [PID -1]
>[Message Abandoning IP address 10.1.18.208: declined.] [Level 3] [UID
>-2] [GID -2] [Host earths-computer]
>
>Has anyone else seen this?

How long ago did you switch servers ? How did you do it ?

If you just turned off one server and turned on another then you 
would expect that. The new server has no record of what addresses are 
already leased out, so when a client comes along asking for a new 
lease, the server will pick an address, and there's a good chance 
that there's a client using it - so it gets abandoned.

Some devices will have a firewall enabled that blocks pings (yuck), 
in which case the dhcp server will not see it (so can't abandon the 
address), but the client will do an arp request and find it before 
accepting the address - in which case the client will decline the 
address.

Eventually things will settle down, and once all old leases have 
expired the messages will stop. What you should do then is to stop 
the dhcp server, and delete the abandoned leases from the leases 
file. They are never deleted, and they are only recovered for use as 
a last resort - the result can be a significant increase in address 
churn on the network it the result is few free leases (or even no 
free leases).

Also, do you have any devices with fixed addresses in the dynamic 
ranges - this can also give this sort of message.

Finally, it suggested that you avoid the .0 and .255 addresses. 
Whilst it's perfectly legal, there are some client implementations 
out there which are "not quite 100%" and don't work properly with 
them. So some people prefer to put :

     range 10.1.17.1 10.1.17.254;
     range 10.1.18.1 10.1.18.254;


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