Configure DHCP to exclude static addresses or don't include in address pool? Reservations?

italo5696
italo5696 used Ask the Experts™
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I have to switch my LAN to a new ip range. I am using DHCP service for most workstations. If I plan on using say for example .2-.50 as static addresses is it best practice to configure the pool as .51-.100 or configure the pool as .1-.100 and exclude .1-.50?

Also, what are the advantages and disadvantages to reservations as opposed to static ip's?
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Jeff GloverSr. Systems Administrator
Commented:
Advantages to reservations. You can specify Options to pass to the reserved client along with the scope and server options. You don't have to really do anything on the client. Leaving it set to Automatically get an address works with Reservations. Disadvantages, you have to know the MAC address to set the reservation. And reservations are one at a time.
  Static IPs mean you have to set the IP but other than that, not a real issue. I would make sure the Register this connections IP in DNS is checked but since it is the default, that is normally not an issue.
  Exclusions are not the same as Reservations. An exclusion zone is a range of addresses inside your scope that DHCP will not give out. In your case, I would not bother to do an exclusion since your static range is not inside your DHCP range.
  I am sure others will give you some examples of where one is superior to another but for me, I tend to stay away from reservations unless I have a one off. (a client that needs a specific address). I have used Exclusions in the past but now, I just plan my DHCP scopes so they don't need them
JohnBusiness Consultant (Owner)
Most Valuable Expert 2012
Expert of the Year 2018

Commented:
I use Reservations and the overhead of knowing MAC addresses is not high for me. We make sparing use of Reservations.

We use Static IP addresses for servers, routers and like gear as these addresses do not change.

Otherwise we do not use static IP addresses. DHCP works so much better

We have a static pool from 1 to 50, DHCP from 51 to 200 and do not mix them up.
JohnBusiness Consultant (Owner)
Most Valuable Expert 2012
Expert of the Year 2018

Commented:
Another possible reason for a Reservation (applies to me (business consultant) at a client).  I have a reserved IP at the client for specific and proper activities I do. But my machine is set for DHCP. When I move to another client or my home office, DHCP still works. A static IP would be a real problem here.
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Jeff GloverSr. Systems Administrator

Commented:
As you can see, there is no right or wrong answer, We all configure DHCP according to our needs.
No argument with what has already been posted; those are good comments.

I generally use static IP addresses for servers and routers and not much else.  I do reservations for printers and other devices where I don't want their IP addresses to change.  I like doing it as a reservation as that gives me control in a single place (the DHCP server).  Others may find it easier to control it at the device itself.

I set the static IP addresses outside of the DHCP range.  I can't be sure that the DHCP server won't assign one of those addresses.

I've used excluded ranges before when changing DHCP servers.  For example, if the DHCP range is .100-199 and I'm changing what is doing DHCP, I'll look at what is in use.  If the only leases are in the .100 - .149 range, for example, I'll exclude that in the new server.  Once everyone has gotten new leases in the .150-199 range, I'll drop the exclusion.  With this method I can ensure that IP conflicts are not likely to occur.
atlas_shudderedSr. Network Engineer

Commented:
I'll concur that there is really no right or wrong however, I will say propose that there is a works/works better methodology.

I always limit my dynamic range to only include those addresses which will be truly dynamic.  Any static addresses I place outside this scope.  There are a couple of reasons why I do this:

1.  It forces me to aware and intentional of any hosts added to my network and where/how they are deployed
2.  When I have a need to identify a node by IP, it can often help to immediately limit the scope of what I am looking at based on whether it is a static or a dynamic and I don't have to go digging into my DHCP database to determine in which Cat it actually belongs.
3.  Riding on the back of 2, it often has measurable impact on troubleshooting and MTR.

In short, put in the little bit of extra effort up front.  Most every technologist I know complains about how difficult their life is.  Most every one of those guys don't do a lot to help their own situation.  Don't be one of them.

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Commented:
thank you everybody, I appreciate it.

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