[j-nsp] DHCP static bindings on J2320

[David Sinn]

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I've noticed the same problem on my J's too.  Looks to be a uniqueness  
in the implementation of the DHCP server in JunOS.  DHCPd under Linux  
and Cisco's built-in DHCP server do not exhibit the same behavior.

What I've been able to track it to is that it is a interaction when  
the client re-requesting the address it originally had since it does  
not believe that it has expired.  So when the client comes back up it  
promptly does a DHCP-request to re-validate the address is still OK to  
use.  The server happily give the address back to them (it's not in  
use since you cleared it), and ignores the static.  That   would imply  
that statics only come into play when a DHCP-Discover is generated by  
a client and not validated when a DHCP-request comes in.

The way I got around it was to clear the lease, plop the device onto a  
wholly different network allowing it get a different address there and  
then move it back.  Since the client no longer has a address that will  
work correctly with just a DHCP-request, it has to do a DHCP-discover  
and gets the new static in the DHCP-offer response.

David


On Jul 16, 2009, at 3:51 AM, Alexander Shikoff wrote:

> Hello,
>
> I'm using J2320 (JunOS 9.5R1.8) as a router in office network with  
> ~10 VLANs.
> DHCP works good on it but there is confusing issue with DHCP static  
> bindings.
> I've configured binding:
>
> minotaur at cr1-kur.ki> show configuration system services dhcp static- 
> binding 00:40:01:27:e2:87
> fixed-address {
>    10.3.1.143;
> }
> router {
>    10.3.1.129;
> }
>
> But when device reboots it still receives IP address from dynamic  
> pool:
>
> minotaur at cr1-kur.ki> show system services dhcp binding detail |  
> match 00:40:01:27:e2:87
> 10.3.1.143       00:40:01:27:e2:87  static    
> never                    active
> 10.3.1.184       00:40:01:27:e2:87  dynamic  2009-08-15 11:11:18  
> EEST active
>
> Well, I tried to clear dynamic lease, then rebooted device again,  
> but without
> any effect: device still receives IP address from dynamic pool in  
> spite of fact
> that static binding is configured.
>
> Any help is kindly appreciated! Thanks.
>
> -- 
> MINO-RIPE
> _______________________________________________
> juniper-nsp mailing list juniper-nsp at puck.nether.net
> https://puck.nether.net/mailman/listinfo/juniper-nsp

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