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I have setup a hotspot at my local harbor. I have encountered a problem with my setup. The accespoint that creates the hotspot connection is a out door long range antenna from UBNT. The distance from the nearest router, to the optimal position of the antenna is 1km. And it's not in straight open air :/

I have managed to get it to work with AirMax from UBNT. My setup looks like this:

  1. 192.168.1.1 - My Router
  2. 192.168.1.30 - My first AirMax antenna (in bridge mode). Creates a network called CARRIERONE
  3. 192.168.1.31 - A wireless station, that connects to CARRIERONE.
  4. 192.168.1.40 - My second AirMax Antenna (Bridge mode from point 3). Creates CARRIERTWO.
  5. 192.168.1.41 - A wireless station, that connects to CARRIERTWO.
  6. 192.168.1.50 - My access point that creates the hotspot (Bridge mode. Network from point 5)

This works like a charm, except that computers connected to the hotspot don't get dynamic IP's. The users have to assign static IP's.

I have tried the same setup, with only two links (Though with extremely poor link quality bc of buildings blocking the sight), and then the clients get assigned dynamical IP's.

I have managed to do a workaround by setting the access point up as a router. But we have plans to extend the network, and would really like to have everything in bridge mode.

Why does this work when we use 3 links, and not when we use 5 links? The setup is EXACTLY the same, except from the IP.

Is this a normal problem? Do I need special equipment, or is it maybe the router that is incapable of managing IP's when there are too many bridges?

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1 Answer 1

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If I remember correctly, the default number of routers a normal DHCP request/response (at least for Windows Server) can pass through is 4.

If your routers are behaving correctly, each time a DHCP request comes through, it is increasing the hop count by one. Once that hop count is larger than the maximum (4), it is thrown away, because it's expected that there will be a DHCP server somewhere within 4 hops from the server. It also stops the DHCP hops from flooding the network for longer than they need to.

This is why 3 works, and 5 does not.

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  • Cool :) Just the kind of answer I was looking for :) Do you know if there is a way to get the request to live more than 4 hops?
    – hogni89
    Oct 17, 2011 at 4:24
  • @hogni89 - I honestly don't know. It might be a part of the TCP/IP spec, in which case no, but it might also depend on your DHCP server. I've never run into that issue before, so I've never had to work around it.
    – Mark Henderson
    Oct 17, 2011 at 4:26
  • @Mark Henderson, since DHCP is broadcast it's not supposed to pass any router at all.
    – poige
    Oct 17, 2011 at 16:24
  • @poige - most routers have a dhcp forwarder in them. Additionally the unusual network setup of this installation using access points (which I am going to guess are also routers) probably are doing the same
    – Mark Henderson
    Oct 17, 2011 at 19:43
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    @MarkHenderson, it's called DCHP relaying.
    – poige
    Oct 18, 2011 at 6:07

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