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Windows Thread, DHCP lease duration +increased traffic in Technical; I went to a secondary school today who have their own NM but he is off long term sick. I ...
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    Kyle's Avatar
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    DHCP lease duration +increased traffic

    I went to a secondary school today who have their own NM but he is off long term sick. I was just checking certain things on the DC which does DHCP and DNS when i noticed that the DHCP lease duration was set to one hour..????

    Now tell me i am wrong but i thought the default setting was 8 days. I have no idea why it was set to this or even if the NM knows. I changed it today to 3 days for the time being because this is the next time Will go into the school again. Was under the impression that having the lease set to 1 hour would cause increased DHCP traffic on the network, especially has this is a situation where everyone logs on on the our every hour.

    Am i correct in thinking this? If so what sort of increase in traffic would this cause in 600 client network?

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    Gatt's Avatar
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    Re: DHCP lease duration +increased traffic

    Ok my understanding of DHCP is..

    1)Client sends a DHCPDISCOVER packet across entire netowrk to locate a DHCP Server
    2)DHCP Server sends DHCPOFFER packet back to client
    3)Client send DHCPREQUEST packet back to DHCP server
    4)DHCP Server Sends DHCPACK or DHCPNAK
    5) If IP is in use then the Client sends back a DHCPDECLINE packet, then starts again.
    link...
    (repeat for each DHCP PC on the network..)

    IIRC, each packet can be anywhere from 312Bytes upto 512 (depending on what options u have in on the DHCP server) and think the max is 1400bytes

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    ChrisH's Avatar
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    Re: DHCP lease duration +increased traffic

    1 hour is far to short for that kind of environment where most PCs are always there and on every day. The only time you would set a lease so low would be when you were planning to migrate the DHCP over or something or if you were running some kind of hospot where you got many different devices connecting for a while and not returning.

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    Re: DHCP lease duration +increased traffic

    Yep, if you have lots of static devices then use long leases. Alternatively if you have lots of devices coming on and off your network then use shorter leases. If you have a mix, split them up into separate scopes. Desktop PC's vs Teacher Laptops for example.

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    ChrisH's Avatar
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    Re: DHCP lease duration +increased traffic

    In the situation of teachers laptops you can use ipconfig/setclassid so they can pull their IP from a defined range which will maybe have shorter leases.

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    Re: DHCP lease duration +increased traffic

    Yeah, sorry, that's what I meant.

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    Re: DHCP lease duration +increased traffic

    We assign very short leases to PDAs, longer leases to fixed workstations - all within the same scope, differentiated by classid.

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