Cisco H.323 VC-289 - Manual (Page 3)

Configuring H.323 Gatekeepers and Proxies
H.323 Gatekeeper Features
VC-291
Cisco IOS Voice, Video, and Fax Configuration Guide
• Interzone Routing Using E.164 Addresses, page 294
• HSRP Support, page 296
Zone and Subnet Configuration
A zone is defined as the set of H.323 nodes controlled by a single gatekeeper. Gatekeepers that coexist
on a network may be configured so that they register endpoints from different subnets.
Endpoints attempt to discover a gatekeeper and consequently the zone of which they are members by
using the Registration, Admission, and Status (RAS) message protocol. The protocol supports a
discovery message that may be sent multicast or unicast.
If the message is sent multicast, the endpoint registers nondeterministically with the first gatekeeper that
responds to the message. To enforce predictable behavior, where endpoints on certain subnets are
assigned to specific gatekeepers, the zone subnet command can be used to define the subnets that
constitute a given gatekeeper zone. Any endpoint on a subnet that is not enabled for the gatekeeper will
not be accepted as a member of that gatekeeper zone. If the gatekeeper receives a discovery message
from such an endpoint, it will send an explicit reject message.
Redundant H.323 Zone Support
Redundant H.323 zone support allows for the following:
• Gatekeeper Multiple Zone Support, page 291
• Gateway Support for Alternate Gatekeepers, page 291
• Zone Prefixes, page 291
• Technology Prefixes, page 292
Gatekeeper Multiple Zone Support
Redundant H.323 zone support allows users to configure multiple remote zones to service the same zone
or technology prefix. A user is able to configure more than one remote gatekeeper to which the local
gatekeeper can send location requests (LRQs). This allows for more reliable call completion.
Redundant H.323 zone support is supported on all gatekeeper-enabled IOS images.
Gateway Support for Alternate Gatekeepers
Redundant H.323 zone support in the gateway allows a user to configure two gatekeepers in the gateway
(one as the primary and the other as the alternate). All gatekeepers are active. The gateway can choose
to register with any one (but not both) at a given time. If that gatekeeper becomes unavailable, the
gateway registers with the other.
Redundant H.323 zone support is supported on all gateway-enabled images.
Zone Prefixes
The zone prefixes (typically area codes) serve the same purpose as the domain names in the H.323-ID
address space.