AW: DHCP configuration on RHEL6
Glenn Satchell
glenn.satchell at uniq.com.au
Thu Jul 21 06:30:57 UTC 2011
A host statement with fixed-address creates a special lease that does not
go through the normal lease discover/renew/release cycle.
This can be a problem, for example, when dhcpd decides that it wants to
assign that particular address. dhcpd will attempt to ping the ip address.
If the device is down (or has a firewall that ignores icmp) then dhcpd
will think it is ok and go ahead and assign that ip address. Now you have
two devices with the same ip ...
If you are using omapi, then you could set the lease as "reserved". This
will give it an infinite lease time, so it will survive any downtime
period. A reserved lease is different to a fixed-address lease in that it
goes through the normal cycle of processing and is recorded in the leases
file.
The other option is to keep a bunch of ip addresses outside the dynamic
range for use with fixed-address devices.
regards,
-glenn
> The "static" in my previous mail means we put a IP into the lease file
> with
> a host declaration and a fixed-address, not mean the client with a static
> ip. This IP is in the middle of a dynamic range which is setting in
> dhcpd.conf.
>
> Giving the lease a long expired time is another choice for us, but there
> is
> still an error window if the client indeed down for a long time.
>
> So we would still want to know what exactly will happen if we put the
> dynamic ip which is in a dynamic ip range to be delared in the lease file
> by omapi?
>
>
>
> Best Regards,
>
> --------------------------------------------------------------
> Wang Huazhong(Íõ»ªÖÒ)
>
> IBM CSTL HPC System Management Development
> Tel: 86-10-82452279
> Email: wanghuaz at cn.ibm.com
> Address: Ring Building 28,ZhongGuanCun Software Park,No.8 Dong Bei Wang
> West Road, Haidian District Beijing P.R.China 100193
>
>
>
>
> Glenn Satchell
> <glenn.satchell at u
> niq.com.au> To
> Sent by: Users of ISC DHCP
> dhcp-users-bounce <dhcp-users at lists.isc.org>
> s cc
> +wanghuaz=cn.ibm.
> com at lists.isc.org Subject
> Re: AW: DHCP configuration on RHEL6
>
> 2011-04-14 19:17
>
>
> Please respond to
> Users of ISC DHCP
> <dhcp-users at lists
> .isc.org>
>
>
>
>
>
>
> 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.
>
> --
> regards,
> -glenn
> --
> Glenn Satchell | Miss 9: What do you
> Uniq Advances Pty Ltd, Sydney Australia | do at work Dad?
> mailto:glenn.satchell at uniq.com.au | Miss 6: He just
> http://www.uniq.com.au 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 cn.ibm.com>/ schrieb am *Mi, 13.4.2011:
>>
>>
>> Von: Hua Zhong Wang <wanghuaz at cn.ibm.com>
>> Betreff: DHCP configuration on RHEL6
>> An: dhcp-users at lists.isc.org
>> 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(Íõ»ªÖÒ)
>>
>> IBM CSTL HPC System Management Development
>> Tel: 86-10-82452279
>> Email: wanghuaz at cn.ibm.com
>> 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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