Important Question and Answer – DHCP
Today we are discuss some important question and answer dynamic host configuration protocol purpose fifth part.
Q:-01:-Do you have more users than addresses?
If so,you want to keep the lease time short so people don’t end up sitting on leases.Naturally,there are degrees.In this situation,I’ve heard examples cited of 15 minutes,2 hours,and 2 days.Naturally if you know you will have 20 users using 10 addresses in within a day,a 2 day lease is not practical.
Are you supporting mobile users?
If so,you may be in the situation of having more users than addresses on some particular IP number range.See above.
do you have a typical or minimum amount of time that you are trying to support?
If your typical user is on for an hour at minimum,that suggest a hour lease at minimum.
How many clients do you have and how fast are the communications lines over which the DHCP packets will be run?
The shorter the lease,the higher the server and network load.In general,a lease of at least 2 hours is long enough that the load of even thousands of clients is negligible.For shorter leases,there may be a point beyond which you will want to watch the load.Note that if you have a communication line down for a long enough time for the leases to expire,you might see an unusually high load it returns.If the lease-time is at least double the communication line outage,this is avoided.
How long would it atke to bring back up the DHCP server,and to what extent can your users live without it?
If the lease time is at least double the server outage,then running clients who already have leases will not lose them.If you have a good idea of your longest likely server outage,you can avoid such problems.For example,if your server-coverage is likely to recover the server within three hours at any time that clients are using their adderesses,then a six hour lease will handle such an outage.If you might have a servergo down on Friday right after work and may need all Monday’s work-day to fix it,then your maximum outage time is 3 days and a 6-day lease will handle it.
Do you have users who want to tell other user about their IP number?
If your users are setting up their own web servers and telling people how to get to them either by telling people the IP number or through a permanent DNS entry,then they are looking for an IP number that won’t be changing.While some sites would manually allocate any address that people expected to remain stable,other sites want to use DHCP’s ability to automate distribution of relatively permanent addresses. The relevant time is the maximum amount of time that you wish to allow the user to keep their machine turned off yet keep their address.For example,in a university,if students might have their computers turned off for as long as three weeks between semesters,and you wish them to keep their IP address,then a lease of six weeks or longer would suffice.
Some examples of lease-times that sites have used & their rationals:
To keep the maximum number of addresses free for distribution in cases where there will be more users than addresses.
Long enough to allow the DHCP server to be fixed,e.g.3 hours.
If you need to take back an address, then you know that it will only take one night for the users’ lease to expire.
This is apparently Microsoft’s default,thus many sites use it.
Long enough that a weekend server outage that gets fixed on Monday will not result in leases terminating.
Long enough that students can keep their IP address over the summer hiatus. I believe this is rational is workable if the summer hiatus is no more than 2 months.
If a user has not used their address in six months,then they are likely to be gone.Allows administrator to recover those addresses after someone has moved on.