lease limit 1 and Apple Mac Computers creates duplicate IP address

Matt Jenkins matt at smarterbroadband.net
Thu Sep 12 23:11:19 UTC 2013


Config:

default-lease-time 600;

class "Canopy" {
   match if ( (binary-to-ascii(16,8,":",substring(option 
agent.circuit-id,0,3))="a:0:3e")  );
   spawn with option agent.remote-id;
   lease limit 1;
}

shared-network "15-Wolf" {
         #Wolf MGT IP Block for DHCP Matching.
         subnet 10.128.128.0 netmask 255.255.255.0 {
         }
         # Public Range
         subnet 173.195.180.128 netmask 255.255.255.240 {
                 option broadcast-address 173.195.180.143;
                 option routers 173.195.180.129;
                 option subnet-mask 255.255.255.240;
                 pool {
                         allow members of "Canopy";
                         range 173.195.180.131 173.195.180.142;
                 }
         }
}


This is for deployment on a Canopy wireless network. The Access Point 
does DHCP relay. The remote-id is each bridged CPE (Customer Premises 
Unit). This prevents multiple devices behind the CPE from getting IP 
addresses. So far this works well, however I found a major problem with 
Apple Mac Computers.

I can reproduce both of the following situations. All result in a 
duplicate IP address issues. All appear to be the fault of Apple Mac OS. 
Has anyone else ever seen this or found a fix for it?

CPE connected to a switch.
1. Apple computer gets IP address then disconnects cable.
2. Lease expires.
3. Other non-Apple computer connects and gets same IP address.
4. Apple computer connects and is unable to get a lease. It then assigns 
itself the original IP address it had. Now there is an IP conflict.

CPE connected to a switch.
1. Apple computer gets IP address then disconnects cable.
2. Lease expires.
3. Other non-Apple computer connects and gets a new IP address.
4. All other unused IP addresses are given out.
5. New CPE connects and customers computer gets IP address Apple 
computer had. (This will be a different household)
6. Original Apple computer connects and is unable to get a lease. It 
then assigns itself the original IP address it had. Now there is an IP 
conflict.

Thanks,

- Matt



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