Extension Mobility Redundancy Issue

[alfonso.cornejo]

Hi to all,

I have an scenario of a publisher and a subscriber in my telephony infrastructure and i have configured EM for some extensions, the issue that i have is that the url for the EM service is pointing to my publisher server so when i turn it off for a HA test the EM service is no longer available.

I've searched for HA scenarios, there are suggestions about configuring a "redundant" EM service but this time the url should be pointing to the subscriber server, i did that and also the two services were showed in the ip phones and i was able to login using both EM services but when i turned off the publisher server to test it all the services were gone from my phones.

Is there something else besides the phone service for EM that i need to configure???? i also checked a dns solution using a name instead of an ip address in the url for the EM service but it doesn't work because of the behavior of dns that it doesn't know when a server is down so it could be resolving wrong ip addresses.

Thanks in advance for your help.

[Harmit Singh]

Hi Alfonso,

Did you get a chance to review the following doc:

http://www.cisco.com/en/US/products/sw/voicesw/ps556/products_tech_note09186a008097cd93.shtml

It talks about configuring IP Phone service redundancy which is what you would need in this scenario.

HTH.

Regards,

Harmit.

[Harmit Singh]

Just to add to my earlier response, please refer to the SRND which talks in alot of detail on EM and IP Phone service redundancy:

http://www.cisco.com/en/US/docs/voice_ip_comm/cucm/srnd/7x/cmapps.html#wp1043795

http://www.cisco.com/en/US/docs/voice_ip_comm/cucm/srnd/7x/cmapps.html#wp1043648

Regards,

Harmit.

[alfonso.cornejo]

Hi guys,

I've read this docummentation but unfourtunately my customer doesn't have a load balancer to perform the best redundancy mechanism but for me it sounds like a "manual" redundancy the fact that you can configure a second EM service but with it's url pointing to one of the subscribers ip address and use this to log in to the phones when the publisher is down.

Do you agree??

My problem with this is that once i turn off the publisher no services are being showed in the phones, do you know if there is something else that has to be configured in order to have services that are being handled by the subscribers available after turning off the publisher???

Thanks in advance for your help.

[Aaron Harrison]

Hi Alfonso

The problem is that the first thing the phone does is retrieves the 'services' URL, and then gets the list of services (e.g. EM and so on) from that URL.

So you need that first URL to be resilient; and you can only enter one in Enterprise Parameters.

Aaron

[Ayodeji Okanlawon]

Alfonso you can use cisco IOS SLB feature for load balancing, rather than a load balancer appliance.

The link below shows how to configure SLB in IOS.

http://www.cisco.com/en/US/docs/ios-xml/ios/slb/configuration/12-4/Configuration_Examples_for_IOS_SLB.html

I must point out that if your Load balancer goes down, then your EM service will also not be available. So to have a full resiliency your load balancer has to be resilient.

If that is still not an option then you are left with using DNS. This is not reliable because DNS servers do not have a way to know if a resolved host is down or not.

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"'Nature is too thin a screen, the glory of the omnipresent God bursts through it everywhere"-Ralph Waldo Emerson

[William Bell · Accepted solution]

All excellent replies! A round of 5's for everyone. I have actually done this using DNS solely. I had a customer that was planning to add SLB at a later time but wanted an interim solution. I leveraged DNS round-robin for non-enterprise services and associated URLs (like the actual Services button). I found that in 8.5(3)+ version of firmware on 79xx phones (yes, dated) that the phones will actually handle the scenario where DNS returned an IP address for a server that was actually off line. In my tests, the phones would simply bypass the "broken" host and use one of the other A records returned by DNS.

I have not tested this with conference stations, 69xx, 89xx, or 99xx stations. But I have tested several versions of firmware after 8.5(3) and the behavior was consistent.

I have more details here:

http://www.ucguerrilla.com/2012/05/redundancy-considerations-and-cisco-ip.html

As noted by others, the SRND, and the blog entry above - a SLB solution is recommended and ideal but I think DNS round robin is worth testing. Of course, if you don't trust your DNS infrastructure then maybe that won't work for you.

HTH

-Bill (@ucguerrilla)

[Ayodeji Okanlawon]

Thanks for sharing the DNS improvement with us. As always great post (+5).

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"'Nature is too thin a screen, the glory of the omnipresent God bursts through it everywhere"-Ralph Waldo Emerson

[Ayodeji Okanlawon]

In addition to the excellent guide provided by Harmit (+5 Buddie and Happy New year!), there are several threads that have covered this in detail..Pls see below

https://supportforums.cisco.com/message/3785431#3785431

https://supportforums.cisco.com/message/3732050#3732050

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"'Nature is too thin a screen, the glory of the omnipresent God bursts through it everywhere"-Ralph Waldo Emerson

[alfonso.cornejo]

Hi guys!

First of all thank's alot for all your suggestions and tips, i finally got this thing working with the elements that i had...at the end i did this:

1) Configure a dns record name with the ip addresses of my publisher and subscriber servers

2) Change all the enterprise parameters that had the url pointing to the ip address of the publisher with the dns record name

3) Change the EM service url that was pointing to the ip address of the publisher with the dns record name

4) In my phones I verified that the services url had the name instead of the ip address (you will have to manually reboot all your phones in order to update that)

5) In the HA test once I turned off the publisher and checked the services in the phones and it took like 1 minute to refresh the ip address that the phone was resolving but at the end it loaded and all the users were able to login

[Harmit Singh]

Hi Alfonso,

Thanks for sharing this on the thread, it will surely help anyone who refers to it, +5!!

Regards,

Harmit.

[Risat]

Hi,

I did the same but its not working. Once i change the ip address and give the hostname, it gives error Host not found. I tried giving FQDN as well on all the enterprise parameter phone urls and the extension mobility service URl. Am i missing something.

I am not sure whether DNS ips are set in the CUCM servers, i will check this next time when i visit the site, but just to confirm with u that this is also required ?..

[Aaron Harrison]

Hi

It the DNS conffiguration that is assigned to the phones that is important. You should have the servers configured for DNS as well, but that on it's own will not help the phones.

Ensure that:

- Phones have at two DNS servers assigned from DHCP

- That you use FQDN for all URLs

- Ideally, have the phones and CUCM servers in the same DNS domain. If this is not possible, then use of FQDNs rather than hostnames consistently will still work.

Regards

Aaron

[alfonso.cornejo]

Hi,

I just configured the DNS in the DHCP for the phones and verified that they had it in their ip config, it was not necesary to configure the DNS in the CUCM.

In the CUCM I changed in the Enterprise Parameters the ip add of the PUB with the name that I configured in the DNS server (not FQDN just a name such as customercucms but I tested in my customer network with a normal ping from DOS expl.: ping customercucms to verify that the DNS was ok) then you can just change the EM service config with the name instead of the ip of the PUB or you can configure a primary and a secondary EM service one pointing to the PUB and the other to the SUB (both worked for me).

Remember to reset your phones after doing all those changes in the CUCM and verify that they get the services url with the name instead of the ip add.

Hope this help.

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Regards

Sent from Cisco Technical Support iPhone App

[Risat]

It is working for me now.. I missed one step in the above and also customer firewall was blocking the traffic (UDP/53) between the phone and the DNS.. Thanks for the reply :-)