Course11:Advanced - Standby PBX

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This book discusses the installation of a standby PBX for enhanced availability.

Contents

Setup

As discussed in the basic training, a standby PBX can be set up and will take over the master PBX's role whenever it fails. 

The gateway platform used as a standby PBX needs to be able to handle as much registrations and object definition as the the master PBX does. However, it does not need to be the same type of device. E.g. an IP3010 may serve as a standby for an IP6000 in certain scenarios. 

To set up the standby correctly, you need to create an almost full replica. This involves
  • PBX Config 
  • PBX Objects
  • Licenses
Fortunately, most of this replication will actually happen automatically!

Config

The settings in the fish-help.png PBX/Config/General and fish-help.png PBX/Config/myPBX need to be copied manually from the Master PBX to the Standby PBX. 

Almost screenshot.png all properties from the master PBX general config must be screenshot.png set identically in the standby PBX, except the PBX Mode property which must be set to Standby instead of Master. The remaining settings in the other pages mentioned should be set identical in master and standby. Also, in the standby PBX general settings, there is an additional area Standby PBX. Set the Master property to the IP address of the master PBX. This will be used to screenshot.png register with the master PBX.

When maintaining a PBX installation with standby, make sure you update the standby whenever you change the master's settings!

All other settings underneath fish-help.png PBX/Config are replicated from the master PBX. 

Object Replication

In order to take over the master PBX's role, the standby PBX needs to know all of the PBX objects the master knows. This is done automatically using LDAP replication between master and standby PBX. It is activated by ticking the fish-help.png  Replicate from Master  check-mark in the PBX/Config/General tab. The current replication state is shown next to the Replicate from Master check-box.

For the replication to succeed, the standby PBX needs to know the master PBX's PBX password and the _KADMIN_ password. You thus need to set both in the PBX/Config/Security tab.

Licenses

To enable standby functionality, a standby license must be present on the standby PBX. This license (called Standby11) must have the same size as the port license installed on the device.

As the standby PBX takes over all duties, it in addition to that needs to have the same licenses (e.g. voicemail-lic, operator-lic) available as the master PBX has. 

There are two ways to achieve this.

Installing separate Licenses


It is possible to install separate licenses of the same type and with the same amounts on the standby PBX. While this is an option theoretically, there are only rare conditions where it makes sense as the licenses installed on a master cannot be used on the standby (licenses are bound to device MAC addresses). This implies that you would need to purchase a complete copy of the master's licenses. 

Replicating Licenses from the Master PBX


All relevant licenses can be replicated from the master PBX by virtue of a the PBXfish-help.png Central licensing concept. If no Port license is installed locally on a standby PBX it obtains automatically all PBX licenses from the master.

You will thus install no license on the standby, as it will replicate all licenses (including theStandby#XX license, which is not used by the master PBX) from the screenshot.png master PBX's license store

Verification

Once your setup is complete, you can easily verify it.

Master / Standby Registrations


On the master PBX, you should see screenshot.png an entry called_STANDBY_ in the registration list. Likewise, you will see screenshot.png an entry called _ACTIVE_ on the standby PBX.

If this is not the case, it is usually due to one of these problems:
  • Master property wrong in standby PBX
  • PBX password in master and standby differ
To debug, you should screenshot.png turn on the H.323 Registrations property in the fish-help.png Diagnostics / Logging settings of both the master and the standby PBX.

Licenses


There should be screenshot.png all expected licenses in the Licenses area of the standby PBX's PBX/Config/General tab.

PBX Objects


All objects known to the master PBX should be seen in the standby PBX's users list.
If this is not the case, replication doesn't work properly. Check the standby PBX's replicator state.

Please note that all settings in the PBX/Config/Filter tab are replicated as well!

Forcing Fail Over


Once everything looks good and your phones are registered to the master, you should simply turn off the master PBX. This is how the phone screen should look like (observe the symbol in the lower right):

screenshot.png good registration

After a minute or so, have look at the registration symbol: it should indicate loss of registration:

screenshot.png lost registration

After accessing the alternate gatekeeper (that is, the standby PBX), the symbol will look again as in the good registration screenshot above.

(Further Hints) Only interesting for students working with innovaphone for a longer time, i.e. before version 10(Service Release 3). There was also a specific symbol for the screenshot.png alternate registration, however the display of the alternate registration was removed in the current firmware.
The reason for it was that only in rather simple configurations the primary and the alternate gatekeeper can be clearly distinguished. In more complex PBX redundancy configurations it may be not possible to find out the role of the gatekeeper a phone is registered to. Thus it's better to leave off this information because it's not really important for the average phone user.

Setting up the Clients

For the standby scenario to work, it is essential that all affected clients (phones, gateways, etc.) are able to register with both the master PBX and the standby PBX. Apart from the fact that there must be appropriate IP routings, the clients either need to know both PBX's IP addresses or need to be able to find them dynamically. As already discussed in the basic training topic of PBX initial configuration, the fail over process relies on the clients ability to detect loss of the master PBX and subsequent registration with the standby PBX.

The following methods exist to make the PBX's IP addresses known to clients:

Discovery


Both for H.323 and SIP devices, a dynamic, IP multicast based discovery mechanism is available. This is known as gatekeeper discovery in H.323 and also available in SIP. For innovaphone devices, discovery is enabled when there is no gatekeeper or no SIP domain configured. 

This is the recommended method if a PBX is present in the LAN segment of the client as it is most robust and requires no configuration on the client side.

Hard Configuration


The IP addresses of both the master and the standby PBX can be hard configured into the clients. This is often the only method available for 3rd party devices. When doing so, it is critical to always configure (and test!) both IP address. These are often called primaryand secondary (or alternategatekeeper for H.323 devices. For SIP devices, the 2 IP addresses are usually retrieved from the domain name system (DNS) based on the domainprovided.

Mixed Hard Configuration and Discovery


It is possible to mix both. For example, if the Primary Gatekeeper Address is left empty in the fish-help.png Phone/User/General tab, gatekeeper discovery will be tried first. If this fails and Secondary Gatekeeper Address is non-empty, the IP address specified is tried. 

This configuration allows for the use of a PBX and it's standby in the local LAN segment (which both would be found using discovery) and a third PBX somewhere remote specified with an explicit IP address.

DHCP Vendor Option


This is a slight variation of the hard configuration setup. The PBX IP addresses are provided to the clients by fish-help.png DHCP vendor options. Works for both H.323 and SIP. This is the recommended method when using an fish-help.png innovaphone DHCP server or when there is no PBX local to the clients LAN segment.

Using the Standby as a Gateway

A standby PBX will do nothing as long as it's master PBX is available. However, the gateway the standby PBX runs on will be active even though the standby PBX itself is not. This allows to use the gateway's capabilities (most notably the fish-help.png interfaces) to be used in normal operation.

Assume a scenario where a customer has screenshot.png 2 physical trunk lines and asks for a redundant solution. In this case, the trunk lines can be connected to both gateways. In normal operation, both trunks are available. In the standby case, PRI#2 is still available.

When using gateways with support for looped-in configurations as PBX platforms, a screenshot.png solution can be implemented that makes both trunk lines available when the master PBX fails.
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