Accepted Solutions
Hi
Firstly, a second for James post - that's what I do on most installs... a slow response from the round robin DNS is better than a failure. Hopefully at some point Cisco will improve the phone firmware so they fail over quicker; you'll notice if you browse to the round-robin hostname using IE that it always comes back near-instantly even when most of your servers are down.
Secondly - there's a couple of things to understand about EM.
There are two services - 'Extension Mobility' is the actual API that runs on each server. This is what you can start/stop from feature services in serviceablity. If you stop this on a server, the actual EM webpage/web service (which is found on the 'network' services page in CUCM serviceability) knows which servers are running the EM API, and can fail over automatically. So if you stop EM API on the publisher, the EM web service will just use the subcriber EM API. This is what has happened when you have 'stopped' EM.
This is all well and good, but in the case where your publisher is truly down, both the EM web service/web page and the EM API are gone. The key one here is that the EM webpage is gone, and this is the only service that the phones directly connect to - i.e. the target of the phone service URL, specified typically by hostname or IP.
To get around this limitation, you need to use James' solution of round robin DNS, or some other form of load balancer.
Regards
Please rate helpful posts...
Hi
Firstly, a second for James post - that's what I do on most installs... a slow response from the round robin DNS is better than a failure. Hopefully at some point Cisco will improve the phone firmware so they fail over quicker; you'll notice if you browse to the round-robin hostname using IE that it always comes back near-instantly even when most of your servers are down.
Secondly - there's a couple of things to understand about EM.
There are two services - 'Extension Mobility' is the actual API that runs on each server. This is what you can start/stop from feature services in serviceablity. If you stop this on a server, the actual EM webpage/web service (which is found on the 'network' services page in CUCM serviceability) knows which servers are running the EM API, and can fail over automatically. So if you stop EM API on the publisher, the EM web service will just use the subcriber EM API. This is what has happened when you have 'stopped' EM.
This is all well and good, but in the case where your publisher is truly down, both the EM web service/web page and the EM API are gone. The key one here is that the EM webpage is gone, and this is the only service that the phones directly connect to - i.e. the target of the phone service URL, specified typically by hostname or IP.
To get around this limitation, you need to use James' solution of round robin DNS, or some other form of load balancer.
Regards
Please rate helpful posts...
