option 242 tricks question

[biggizod]

I found here

https://downloads.avaya.com/elmodocs2/one-X_Deskphone_Edition/R1.5/output/16_300698_4/admn054.html

that I can set up more than 1 CM for DHCP option 242 . I have no more licenses on one of my IPO500 so I wanted second one as CM for the rest of the ip phones. both IPO500 are in SCN . I moved some of my unregistered phones to that second IPO500 but didn't change DHCP server (Windows based) option yet .
Has anybody know will it work if I setup second CM/IPO500 on option 242 on the SAME dhcp server for the same ip pool ?

 

[kyle555]

I don't think you'll be able to do it that way.

You can administer multiple MCIPADD IPs in 242. Consider local DHCP, central CM, WAN drops, then you have a power failure. You'd like your phones to come back up, register to a local CM server for failover, and be able to have DHCP tell the phones to get there. That's typically why you'd administer multiple IPs in 242.

Now, the phones will hunt down the list for a valid gatekeeper only if they do not get a response from the first entry in 242. So, a phone that does a gatekeeper request (GRQ) and gets a gatekeeper confirm (GCF) will stay on that entry even if it cannot do a registration request/confirm (RRQ/RCF) thereafter. To say, the GRQ/GCF process will get you to a login screen and you'd be stuck at that. The RRQ/RCF is you keying in your extension and password and getting on the system.

I think your easiest options are to either statically configure those phones or build out a VLAN for the ones that'll be on the other IPO - just depends how many you have to do.

 

[biggizod]

thank you for response, I programmed second CM and it works . Also regarding that issue u described I am not sure about the details but I could register the rest of my phones to the second IPO500 . I guess it also depends on where those extensions are configured.

 

[derfloh]

With IPO extensions can only register to the system they are configured at. You are free to register local phones with a remote IPO. For fallback purposes you have to set that up as an option in your SCN trunk. When the phones register IPO tells them - based on the SCN config - that the remote system will be the secondary call server.

 

[Albus2]

@derfloh

Are you sure about this? If IPO is the dhcp server, all happens just fine.
But is it the MCIPADD option or another method which is used to tell the phone about the 2nd IPO?
The H.323 phone guide explains about the option to give multiple callserver adresses, and there is a delay of 3 minutes before the next adress is probed. Sounds like our fallback mechanism. However, its also thinkable, there is another protocol used for this.
There is not much documenation available for the combination of 'alternative' DHCP server and SCN.