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Wireless Networks Thread, Using AP as backup DHCP server in Technical; When my last Win98 "server" failed - the main problem I had in the school was the lack of DHCP ...
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    SimpleSi's Avatar
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    Using AP as backup DHCP server

    When my last Win98 "server" failed - the main problem I had in the school was the lack of DHCP server to let them print and go onto internet.

    So I changed the an AP into a router so that I could use it as DHCP server as an emergency device.

    Now I've got a proper w2k3 server up and running I was about to swap to using it for DHCP only but I'm thinking that I should maybe keep the two of them running at the same time to provide auto-backup but I'm wondering if there is something I've not though about that would prevent this being a good idea.

    I only use the w2k3 server as file/print/dns/dhcp server - I don't use it as a domain controller/AD.

    Any one do this?

    Any thoughts welcome

    regards

    Simon

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    SYNACK's Avatar
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    The windows server DHCP allows the clients to easily register in the servers DNS. It would depend on how good the options are in the AP with regard to setting DHCP options and default gateways as to how well this would work. I would probably stick to having the server as the sole DHCP source but have the configuration all thought out and saved to a config file to push the AP into service as a DHCP server in very little time.

    If you were going ahead I would divide the internal subnet into two and have half of the range served up by each device as long as you have enough space for all of the clients in each half of the subnet.

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    SimpleSi (11th February 2009)

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    SimpleSi's Avatar
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    Yes -I can see that DNS would be a problem (As I don't have a backup for that) - I think I can leave the AP set as a router (but with the gateway set to the schools main router) with the DHCP function just disabled so a simple click will enable it.

    What would be nice would be to have the AP be a bit slower to respond to DHCP requests so that the real one beat it to the draw

    I wonder if I put a longer cable in ...

    regards

    Simon

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    SYNACK's Avatar
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    Quote Originally Posted by SimpleSi View Post
    I think I can leave the AP set as a router (but with the gateway set to the schools main router) with the DHCP function just disabled so a simple click will enable it.

    What would be nice would be to have the AP be a bit slower to respond to DHCP requests so that the real one beat it to the draw

    I wonder if I put a longer cable in ...
    That setup should be fine so long as the APs link to the LAN is not its WAN port. If it is something like a linksys WRT54g with a WAN port and four LAN ports then you would need to have it connected via one of the LAN ports so that it is not acting as a router for the wireless traffic. If it is setup on the WAN port then the WAP will attempt to route and NAT the traffic heading to your main network so that it all uses the one external IP. It will also block off services like your main DHCP from wireless hosts which will case substantial issues with connectivity for some services.

    Depending on the WAP you may be able to reflash it with some opensource firmware which will give you enumerable additional features along will a full DHCP server and possibly the delay option.

    The Open Source WRT54G Story

    Or i guess a couple of hubs and 300meters of cable would probably do the trick

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    If one of your servers goes down, why not start DHCP on another server? Far faster acknowledgement times etc and DHCP can be setup again in 5 minutes. The only problem will be reservations as they will need inputiing again, but from my experience, you can't restore DHCp anyway, only move it which pre-empting a crash.

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    SimpleSi's Avatar
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    I work in primaries - we don't have another server

    regards

    Simon

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    Allow the AP to hand out a different scope to the main server?

    I.e: AP gives out 192.168.0.10 -> 192.168.0.100
    DHCP Server gives out 192.168.0.101 -> 192.168.0.190

    or something similar (assuming that you have twice the capaciaty in your subnet). Then if one goes down.. the other will continue to hand out addresses.

    Kyle

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    SimpleSi's Avatar
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    Yes - Synack was saying the same thing but I started thinking that if the main dhcp went down, the physical server is probably down and therefore DNS is gone as well and that it wasn't worth trying to get it work automatically.

    During my server failure, I had the ap doing dhcp and set it to hand out my RBC dns servers as dns servers for the clients so they could at least print to the network printers (they use direct ip to printer - not via a server queue so that works OK)

    Now I'm thinking, I could set the AP to hand out a range but to hand the main w2k3 server ip as primary DNS with a RBC one as secondary - then I could have best of both worlds - maybe ?

    Or I could take the attitude that my new server will last 5 years before failing and not worry about it

    regards

    Simon

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    If you have just the one server in your environment, if it went down I see little need to have a redundant DHCP. Users could print to printers, but chances are they probably wouldn't as the server would be unavailable (the data they'd like to print).

    If you want to offer redundancy (realistically) you should have two domain controllers with DNS AD integrated, two DHCPs and two Global Catalogs.

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    If you have just the one server in your environment, if it went down I see little need to have a redundant DHCP. Users could print to printers, but chances are they probably wouldn't as the server would be unavailable (the data they'd like to print).
    With no DHCP they could still open programs and save work on individual machines.

    With DHCP, they could do the above and go onto internet - use the moodle and print so a good gain was made


    If you want to offer redundancy (realistically) you should have two domain controllers with DNS AD integrated, two DHCPs and two Global Catalogs.

    I wouldn't even know what a global catalog was

    regards

    Simon

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