Cisco 2911 DHCP and 3COM NBX Phone system

Posted on 2013-01-21
Medium Priority
Last Modified: 2013-01-24
I have  a client that is using a 3COM NBX phone system.  We are moving DHCP off of their servers on to their Cisco 2911 and eventually to their ASA.  Right now I don't see a DHCP scope for their phones on the windows DHCP server, even though the server's IP address is set as a helper address. This being said, I DO see and DHCP optoin for OPtoin 184, which 3COM phones need.  My quesitona are:

1.  How do I know if these phones are even using DHCP?  When I go into the phone setting on the system's admin console, I see for IP address and Mask, and for manually set IP, mask and GW settings. The NCP IP address is the same as the phone management system.  Could this client be using broadcast for VoIP?  (Horrible idea if they are).

2.  How can I set the option for DHCP option 184 in my Cisco 2911.  I have the scope coniferous I just can't figure our that custom option.

Thanks in advance.
Question by:SuperTaco
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Author Comment

ID: 38801673
Just saw that they are using something called "IP on the Fly"  Here's the definition:
IP on-the Fly is a term used by 3Com to signify the ability of assigning IP addresses to a group of devices, without precommitting them in the dial plan. Standard IP or IP Serve, requires that every device has in IP address, whether they are Lan devices, that are within the local power of the NCP, or not. In other words,all NBX devices become permanently labeled, with an IP address, in this configuration.. This includes the phones, cards ports; literally all connectivity to the system. IP on-the-fly uses a different set of algorithms to more efficiently manage the components. It does not require that each point have an IP address, There is a preconfigured pool of addresses available, in the NCP, and all the phones or line ports are able to dynamically allocate the use of a pool IP address. After the completion of the task, the number reverts to the pool. The primary use of IP on-the-fly, is in multiple location installations, with Virtual Tie Lines,or VTL,s. In this configuration, the multiple boxes need the ability to assign the addresses to fully distribute the call groups and devices. This is primarily due to the fact that there are two, or more NCP's, not one.

Now here's the screwy part, unless someone knows something about 3COM  I don't.  (and I know nothing about their phone systems)  The ranges assigned to "IP on the fly" are not set in the phone VLAN.  Actually there are no ip addresses reporting in the phone VLAN.  is htis standard?  There is no support contract that I've found for this device so any help is great.
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Accepted Solution

agonza07 earned 2000 total points
ID: 38801761
Here's how to configure option 184 on a Cisco router.


I dont know much about the NBX, but if you put a sniffer in between do you get an IP address? I doubt its all layer 2 communication, or broadcast.

Put a laptop in that VLAN and see what your DHCP server is, and if you get an IP address.
LVL 10

Author Closing Comment

ID: 38815614
Thanks, turn out we don't have to configure an option is they're usingIP On the fly, but thanks for the article.

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