DHCP Question

[tsheph]

How do you use DHCP and still use network regions to segment the phone system for E911?

In other words, how does DHCP hand out different IP ranges for different buildings on the same VoIP network?

[rvengco]

Hi tsheph,

The IP Phones get their network regions from the ip-network-map configuration of CM, you can add a specific IP or a range of IP address there and specify which network-region you would like for those IPs. If a phone whose IP address is not configured in the ip-network-map, it will obtain its network-region from the CLAN/PROCR where it is registered to.

Regarding your query on the DHCP, The DHCP client (Phone/PC) broadcasts on the network with a request. If there is a DHCP server which can receive the request, it replies with an offer of an IP in the same subnet as the NIC in the server which received the broadcast request.

If there is only a relay agent to receive the request, it will forward the request to a DHCP server. The DHCP server will make an offer in the same IP subnet as the NIC of the relay agent which recieved the original broadcast.

Hope this helps

[tsheph]

Thank you. Very helpful.

I can imagine then, using VLANs with a relay agent in the switch, I can segment IP phones into different IP-network-map areas. How then do I have each phone segment dial out it's own gateway for E911? The idea is to have the proper address appear for the PSAP.

The big picture is multiple building locations each in its own IP-network-map range and a local gateway with a POTS line attached to an analog card. When a phone in the building dials 911, it should route to the local gateway/pots line for dialing.

[rvengco]

You can setup a multi-location dialing. First check if Multiple locations license is enable from your display system-parameters customer-options
In a Multi-location, you can configure your IP phones to have their own location. They are getting it from the network-region where they are in.then you can configure your ARS or AAR analysis to route your calls per location
for example:
You need to add/configure location x from your change locations then "change ars analysis 9 location x", you can configure your routing on that setting and you can route there whichever trunk group you wanted, you might want to route your call to the trunk group connected to the mediagateway where you want the call to be routed to. If your IP phone is in location X it will use the ARS analysis based on the configuration or routing you did earlier.

[tsheph]

Thanks. This is giving me some great direction.

I was able to get the DHCP working today as well. Thanks again!