[asterisk-users] OT: Problems with Linksys IP Phone SPA 942

[Tilghman Lesher]

On Wednesday 24 February 2010 19:23:01 Shanon Swafford wrote:
> One thing made be feel dumb the other day.  We boot these phones 10 at a
> time and a new guy had accidentally plugged in one of them using the LAN
> port.  This caused all sorts of problems in the network for some reason.
> After chasing my tail in the DHCP server and power cycling the switch and
> this and that for 2 hours, I found that one, changed it to the WAN, and am
> still too mad at myself to actually investigate why that broke the whole
> system.

DHCP is designed in such a way that you can legitimately have multiple DHCP
servers on the same network.  The first DHCP server which replies and meets
the DHCP client's requirements will be the server to which the client
registers.  If the Linksys DHCP server is faster (or if you have several
switches and it replies to some hosts faster), then those hosts will likely
use the Linksys as their DHCP server.

You could technically avoid this situation by provisioning some DHCP option
that the Linksys does not and making all of your DHCP clients require that
option, but that takes quite a bit away from the zeroconf usage of DHCP.
Or you could set up a rule on your managed switch such that broadcasts to
UDP port 67 only hit the switch port on which your intended DHCP server is
located.

-- 
Tilghman Lesher
Digium, Inc. | Senior Software Developer
twitter: Corydon76 | IRC: Corydon76-dig (Freenode)
Check us out at: www.digium.com & www.asterisk.org