AW: DHCP configuration on RHEL6

Glenn Satchell glenn.satchell at
Thu Apr 14 11:17:14 UTC 2011

Putting a static assignment in the middle of a dynamic range is not a 
good plan. There are a number of ways that the dynamic ip could be 
re-assigned to a different client, for example the static client has 
icmp blocked by local firewall, so the dhcp server can't tell if the ip 
is already in use. If you have several thousand clients, then managing 
them becomes cumbersome.

The way to ensure a dynamic IP is never reassigned is to ensure that 
there are always enough free IPs to cover the expected number of clients.

What if you just used a really long lease time, maybe a few months or a 
year? That way the client would need to be down for a really long time 
before the address was re-assigned.

Glenn Satchell                            |  Miss 9: What do you
Uniq Advances Pty Ltd, Sydney Australia   |  do at work Dad?
mailto:glenn.satchell at         |  Miss 6: He just tel:0409-458-580   |  types random stuff.

On 04/14/11 07:50, Rainer Stumbaum wrote:
> Hi,
> you could check if the infinite-is-reserved statement does what you require.
> Best regards
> Rainer
> --- Hua Zhong Wang /<wanghuaz at>/ schrieb am *Mi, 13.4.2011:
>     Von: Hua Zhong Wang <wanghuaz at>
>     Betreff: DHCP configuration on RHEL6
>     An: dhcp-users at
>     Datum: Mittwoch, 13. April, 2011 18:28 Uhr
>     Hi,
>     We are working on a solution to manage large clusters, there will be
>     thousands of clients requesting dynamic IP address from dhcp server,
>     and on each client, there are several services that are working and
>     heavily depending on the dynamic ips.
>     We know that the dynamic ip addesses on each client generally will
>     not be changed, except the client is down for a long time and dhcp
>     server re-use the expired leases.
>     But once this happens, it will take lots of effort to reconfigure
>     the client based on the dynamic ip on the client.
>     So we are trying to find a way to guarantee the ip address on clients
>     will never be changed. Static ip address with a host declaration in
>     lease file or dhcpd.conf could help it. But this way needs us to
>     firstly assign a dynamic ip to the clients, and commnunicate with the
>     clients to get their mac addresses, then write a host declaration
>     with a new ip/mac into lease file or dhcpd.conf. And with this
>     configuration, properly we need to prepare two ips to each client,
>     one ip range for dynamic ips and another ip for static. Also it
>     needs the clients to reset their adapters to switch from dynamic ips
>     to static ips.
>     This procedure is a little complicated especially for managing a
>     large cluster, we are trying to simplify it, one proposal would be
>     just to write the dynamic ip that is inside the dynamic range into
>     the lease file or dhcpd.conf with a host declaration, to make the
>     dynamic range to be static. Several benefits: it doesn't need two
>     ips per client, doesn't need to assign new static ip by admin
>     manually, and don't need to reset client's adapters. We got some
>     message that dhcp server doesn't like users to do so, so I would
>     know the answer to the following question:
>     What exactly will happen if we put the dynamic ip which is in a
>     dynamic ip range to be static with fixed-address? Is this way
>     acceptable by dhcp server and stable enough?
>     Best Regards,
>     --------------------------------------------------------------
>     Wang Huazhong(王华忠)
>     IBM CSTL HPC System Management Development
>     Tel: 86-10-82452279
>     Email: wanghuaz at
>     Address: Ring Building 28,ZhongGuanCun Software Park,No.8 Dong Bei
>     Wang West Road, Haidian District Beijing P.R.China 100193

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