Where do DHCP ASSIGNED addresses fall re: the DHCP range?
I did some research on this and didn't come up with a good answer. So, with the broader experience of EE folks, I'll ask it here:
Assume that there is a single DHCP server of some kind, really any kind, being used.
Assume that there will be some devices that have STATIC IP address settings configured in the host - so these are naturally outside the DHCP range, right?
Assume that there will be some devices that will operate on the network and will have ASSIGNED IP addresses according to their MAC addresses.
The questions are:
Relative to the DHCP server itself (and not your idea of what "should be"):
1) Can the ASSIGNED IP addresses fall outside the scope of dynamic DHCP addresses?
2) Must the ASSIGNED IP addresses fall outside the range of dynamic DHCP addresses?
3) Must the ASSIGNED IP addresses fall inside the range of DHCP addresses (where I dropped "dynamic" because it no longer really applies here).
I figure that the answers may well vary according to the DHCP server (manufacturer or firmware) and I think I've run into that but my memory is fuzzy on the details.
So, answers may vary.
1) Yes, No, sometimes
2) Yes, No, sometimes
3) Yes, No, sometimes
Some things I have learned in the past:
With some Netgear routers, DHCP address allocations become, or may become, ASSIGNED automatically. This rather assures IP address stability.
But that's a variation that isn't so important to me right now.
Is there a definition or RFC or...?
Is there a rule that you use consistently and it just always works?
Assume that there is a single DHCP server of some kind, really any kind, being used.
Assume that there will be some devices that have STATIC IP address settings configured in the host - so these are naturally outside the DHCP range, right?
Assume that there will be some devices that will operate on the network and will have ASSIGNED IP addresses according to their MAC addresses.
The questions are:
Relative to the DHCP server itself (and not your idea of what "should be"):
1) Can the ASSIGNED IP addresses fall outside the scope of dynamic DHCP addresses?
2) Must the ASSIGNED IP addresses fall outside the range of dynamic DHCP addresses?
3) Must the ASSIGNED IP addresses fall inside the range of DHCP addresses (where I dropped "dynamic" because it no longer really applies here).
I figure that the answers may well vary according to the DHCP server (manufacturer or firmware) and I think I've run into that but my memory is fuzzy on the details.
So, answers may vary.
1) Yes, No, sometimes
2) Yes, No, sometimes
3) Yes, No, sometimes
Some things I have learned in the past:
With some Netgear routers, DHCP address allocations become, or may become, ASSIGNED automatically. This rather assures IP address stability.
But that's a variation that isn't so important to me right now.
Is there a definition or RFC or...?
Is there a rule that you use consistently and it just always works?
1. Yes, as long as they are still in the correct subnet.
2. No, however it is advisable. If a DHCP server attempts to allocate an IP that is already manually assigned somewhere on the network, generally the client will detect this and end up with a different IP, however this does not always happen. If, for instance a printer has been assigned 10.0.0.200, and it is being power cycled when a client gets assigned 10.0.0.200, you will end up with 2 devices with the same IP and a major headache.
3. No, provided it is one the correct subnet.
So basically, use a separate range for statically assigned IPs. Maybe 10.0.0.10 - 10.0.0.50 for static IPS, and 10.0.0.100 10.0.0.250 for the DHCP range.
2. No, however it is advisable. If a DHCP server attempts to allocate an IP that is already manually assigned somewhere on the network, generally the client will detect this and end up with a different IP, however this does not always happen. If, for instance a printer has been assigned 10.0.0.200, and it is being power cycled when a client gets assigned 10.0.0.200, you will end up with 2 devices with the same IP and a major headache.
3. No, provided it is one the correct subnet.
So basically, use a separate range for statically assigned IPs. Maybe 10.0.0.10 - 10.0.0.50 for static IPS, and 10.0.0.100 10.0.0.250 for the DHCP range.
ASKER CERTIFIED SOLUTION
membership
This solution is only available to members.
To access this solution, you must be a member of Experts Exchange.
CompProbSolv> I think you are talking about DHCP reservations, while the OP was asking about IPs set statically on devices, and not using DHCP at all.
Using DHCP reservations rather than static IPs is actually not a bad idea, I usually set printers up this way. It means everything is controlled centrally, and one less spreadsheet to keep updated.
Using DHCP reservations rather than static IPs is actually not a bad idea, I usually set printers up this way. It means everything is controlled centrally, and one less spreadsheet to keep updated.
SOLUTION
membership
This solution is only available to members.
To access this solution, you must be a member of Experts Exchange.
ASKER
Thank you!
Rather than address all the responses, in the interest of time, let me clarify:
I refer to STATIC addresses in the preamble.
I intended to ASK about [DHCP] ASSIGNED/RESERVED addresses in the questions.
Some read my question as including STATIC addresses which wasn't my intent.
I hope this clarifies.
I will restate the questions:
1) May/can the ASSIGNED/RESERVED IP addresses fall outside the scope of dynamic DHCP addresses?
1A) May/can the ASSIGNED/RESERVED IP addresses fall inside the scope of dynamic DHCP addresses?
2) Must the ASSIGNED/RESERVED IP addresses fall outside the range of dynamic DHCP addresses?
3) Must the ASSIGNED/RESERVED IP addresses fall inside the range of DHCP addresses (where I dropped "dynamic" because it no longer really applies here).
Rather than address all the responses, in the interest of time, let me clarify:
I refer to STATIC addresses in the preamble.
I intended to ASK about [DHCP] ASSIGNED/RESERVED addresses in the questions.
Some read my question as including STATIC addresses which wasn't my intent.
I hope this clarifies.
I will restate the questions:
1) May/can the ASSIGNED/RESERVED IP addresses fall outside the scope of dynamic DHCP addresses?
1A) May/can the ASSIGNED/RESERVED IP addresses fall inside the scope of dynamic DHCP addresses?
2) Must the ASSIGNED/RESERVED IP addresses fall outside the range of dynamic DHCP addresses?
3) Must the ASSIGNED/RESERVED IP addresses fall inside the range of DHCP addresses (where I dropped "dynamic" because it no longer really applies here).
Not a problem! I caught on to the fact that you were asking about reserved addresses, and answered based on such.
@Mal: yes, you are correct. My answer wasn't specific enough. I was referring to how I read the third assumption about how some IP addresses would be assigned by MAC address. I took that to mean a reservation in the DHCP server.
Mansrock makes a good technical point about scope range vs. non-excluded ranges. One can have a static IP address that technically is in the scope range, but it is excluded. That should certainly work.
My general approach (with Windows Server as DHCP server) has been as follows (assume /24 mask):
Set the scope to .1-.254
Exclude ranges within the scope in groups with comments on what they are used for. For example: .1-.9 for routers and switches, .10-.99 for future use, leave .100-.149 alone for general DHCP, .150-.179 for MAC-based reservations, .180-.229 for static IPs, .230-.244 for printers (static or assigned IPs), and .245-.254 for (static IP) servers.
This gives me an easy way to document where devices should be found in the IP ranges.
I am a big fan of address reservations by MAC for the reasons that Mal mentioned: centralization and less updating.
Mansrock makes a good technical point about scope range vs. non-excluded ranges. One can have a static IP address that technically is in the scope range, but it is excluded. That should certainly work.
My general approach (with Windows Server as DHCP server) has been as follows (assume /24 mask):
Set the scope to .1-.254
Exclude ranges within the scope in groups with comments on what they are used for. For example: .1-.9 for routers and switches, .10-.99 for future use, leave .100-.149 alone for general DHCP, .150-.179 for MAC-based reservations, .180-.229 for static IPs, .230-.244 for printers (static or assigned IPs), and .245-.254 for (static IP) servers.
This gives me an easy way to document where devices should be found in the IP ranges.
I am a big fan of address reservations by MAC for the reasons that Mal mentioned: centralization and less updating.
There is no automatic way for static addresses to be assigned avoiding a DHCP range.
You need to know the DHCP range and assign Static outside the range and Reserve inside the Range.
We do this at ALL clients.
You need to know the DHCP range and assign Static outside the range and Reserve inside the Range.
We do this at ALL clients.
ASKER
Well, the one thing I'd missed because I've not run into it is the exclusion. So that makes for a nicer set of tools.
So, yes, I can well see with that ability that one could put ALL addresses in the DHCP scope and then "back out" with exclusions.
My main concern, without using exclusions, was knowing / planning to have ASSIGNED/RESERVED addresses and where they were going to need to reside: inside the DHCP scope or outside the DHCP scope. Kind of a fundamental question, eh? Now, if I have the choice, and without exclusions, then it's likely going to be OUTSIDE.
I don't think I said anything suggesting automatic/static. I don't even know what that *is*. To me, static is manually-entered and nothing automatic about that.
My perspective is that RESERVED/ASSIGNED addresses are close enough to STATIC in terms of "how do I want things to be?" that I'd choose OUTSIDE for them unless the server demands they be inside. Less accounting to do. Then, INSIDE is for dynamics only and it's nice to know how many there are without having to subtract assignments first. Just my opinion.
So, yes, I can well see with that ability that one could put ALL addresses in the DHCP scope and then "back out" with exclusions.
My main concern, without using exclusions, was knowing / planning to have ASSIGNED/RESERVED addresses and where they were going to need to reside: inside the DHCP scope or outside the DHCP scope. Kind of a fundamental question, eh? Now, if I have the choice, and without exclusions, then it's likely going to be OUTSIDE.
I don't think I said anything suggesting automatic/static. I don't even know what that *is*. To me, static is manually-entered and nothing automatic about that.
My perspective is that RESERVED/ASSIGNED addresses are close enough to STATIC in terms of "how do I want things to be?" that I'd choose OUTSIDE for them unless the server demands they be inside. Less accounting to do. Then, INSIDE is for dynamics only and it's nice to know how many there are without having to subtract assignments first. Just my opinion.
My main concern, without using exclusions, was knowing / planning to have ASSIGNED/RESERVED addresses and where they were going to need to reside: inside the DHCP scope or outside the DHCP scope. Kind of a fundamental question, eh? Now, if I have the choice, and without exclusions, then it's likely going to be OUTSIDE.This literally depends on the DHCP server. For example, if I recall properly, Sonicwall's DHCP server forces reserved IPs to be outside of the DHCP range. Windows Server's DHCP server I believe is far more flexible in this sense (can be in or out of the DHCP range).
My perspective is that RESERVED/ASSIGNED addresses are close enough to STATIC in terms of "how do I want things to be?" that I'd choose OUTSIDE for them unless the server demands they be inside. Less accounting to do. Then, INSIDE is for dynamics only and it's nice to know how many there are without having to subtract assignments first. Just my opinion.I agree with you here. Maintain a block of addresses that can be used either for reserved or static scenarios.
We use a block for Static IP addresses, but Server Reserved are just the same DHCP address all the time (must be carefully managed) and sit in the DHCP range.
ASKER
Thanks all!
1. Must do
2. Yes Always
3. Yes
You can get around this on a server by using IP Reservations and not using Static IP addresses in many cases.
We use Static IP addresses for Printers and ensure these addresses are outside the DHCP range.