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This document describes the Gatekeeper to Gatekeeper Redundancy and Load-Sharing Mechanism feature that was introduced in Cisco IOS Release 12.1(2)T. This document contains the following sections:
The Gatekeeper to Gatekeeper Redundancy and Load-Sharing Mechanism feature expands the capability that is provided by the Redundant H.323 Zone Support feature. The Redundant H.323 Zone Support feature, which was introduced in Cisco IOS Software release 12.1(1)T, allows users to configure multiple gatekeepers to service the same zone or technology prefix by sending location requests (LRQs) to two or more gatekeepers.
With the Redundant H.323 Zone Support feature, the LRQs are sent simultaneously (in a "blast" fashion) to all of the gatekeepers in the list. The gateway registers with the gatekeeper that responds first. Then, if that gatekeeper becomes unavailable, the gateway registers with another gatekeeper from the list.
The Gatekeeper to Gatekeeper Redundancy and Load-Sharing Mechanism feature enhances this capability by allowing the user to choose whether the LRQs are sent simultaneously or sequentially (one-at-a-time) to the remote gatekeepers in the list. If the LRQs are sent sequentially, a delay is inserted after the first LRQ and before the next LRQ is sent. This delay allows the first gatekeeper to respond before the LRQ is sent to the next gatekeeper. The order in which LRQs are sent to the gatekeepers is based on the order in which the gatekeepers are listed (using either the zone prefix or the gw-type-prefix command).
Once the the local gatekeeper has sent LRQs to all the remote gatekeepers in the list (either simultaneously or sequentially), if it has not yet received a location confirmation (LCFs) then it opens a "window". During this window, the local gatekeeper waits to see if a location confirmation (LCF) is subsequently received from any of the remote gatekeepers. If no LFC is received from any of the remote gatekeepers while the window is open, then the call is rejected.
This feature allows users to configure redundant gatekeeper support and give preference to specific gatekeepers.
The Gatekeeper to Gatekeeper Redundancy and Load-Sharing Mechanism feature has the following restrictions and limitations:
The Gatekeeper to Gatekeeper Redundancy and Load-Sharing Mechanism feature is related to the H.323 VoIP Gatekeeper for Cisco Access Platforms feature, the Gateway Support for Alternate Gatekeepers feature, and the Redundant H.323 Zone Support.
The Gatekeeper to Gatekeeper Redundancy and Load-Sharing Mechanism feature is supported on any existing IOS gatekeeper platforms, including the following:
Standards
No new or modified standards are supported by this feature.
MIBs
No new or modified MIBs are supported by this feature.
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Note Although the Gatekeeper to Gatekeeper Redundancy and Load-Sharing Mechanism feature allows multiple gatekeepers to service a specific prefix or technology zone, the MIB can query only the first gatekeeper that is configured to handle a particular E.164 address. Likewise, the MIB is allowed to configure only one gatekeeper for a specific E.164 address. |
For descriptions of supported MIBs and how to use MIBs, see the Cisco MIB web site on CCO.
RFCs
No new or modified RFCs are supported by this feature.
The Gatekeeper to Gatekeeper Redundancy and Load-Sharing Mechanism feature requires the Cisco H.323 VoIP Gatekeeper for Cisco Access Platforms feature.
See the following sections for configuration tasks for the Gatekeeper to Gatekeeper Redundancy and Load-Sharing Mechanism feature. Each task in the list indicates if the task is optional or required.
Regardless of whether you specify sequential or blast, there is an order to how the LRQs are sent. With sequential, the LRQs are sent one-at-a-time with a delay between each. With blast, the LRQs are sent back-to-back in a rapid sequence without any delay between them. The order in which zone and technology prefixes are configured determines the order in which the LRQs are sent to the remote gatekeepers. Using zone prefixes as an example, the local gatekeeper routes the call to the first zone that responds with an LCF. If the local gatekeeper is configured for a zone prefix that already has remote gatekeepers configured, the local gatekeeper will automatically put that zone prefix at the top of the list.
For example:
gatekeeper zone local gnet-2503-2-gk cisco.com zone remote gnet-2600-1-gk cisco.com 172.18.194.131 1719 zone remote gnet-2503-3-gk cisco.com 172.18.194.134 1719 zone prefix gnet-2600-1-gk 919....... zone prefix gnet-2503-6-gk 919.......
With this configuration, LRQs are first sent to gnet-2600-1-gk (which is the first zone prefix because it has a remote gatekeeper configured for it) and then to gnet-2503-6-gk (which is the second zone prefix). If you add the local gatekeeper to that zone prefix, it automatically goes to the top of the list, as shown below:
gatekeeper zone local gnet-2503-2-gk cisco.com zone remote gnet-2600-1-gk cisco.com 172.18.194.131 1719 zone remote gnet-2503-3-gk cisco.com 172.18.194.134 1719 zone prefix gnet-2503-2-gk 919....... zone prefix gnet-2600-1-gk 919....... zone prefix gnet-2503-6-gk 919.......
As you can see, the zone prefix for the local gatekeeper (gnet-2600-2-gk) has been inserted at the top of the zone prefix list. If the local gatekeeper can resolve the address it will not send LRQs to the remote zones.
This also applies to the configuration of technology prefixes.
| Command | Purpose | |
|---|---|---|
Step 1 | Router# config term | Enter configuration mode. |
Step 2 | Router(config)# gatekeeper | Enter gatekeeper configuration mode. |
Step 3 | Router(config-gk)# zone local gatekeeper-name domain-name [rasIPaddress] | Configure the local gatekeeper. |
Step 4 | Router(config-gk)# zone remote other-gatekeeper-name other-domain-name other-gatekeeper-ip-address [port-number] | Configure the remote gatekeeper. |
| Command | Purpose | |
|---|---|---|
Step 1 | Router# config term | Enter configuration mode. |
Step 2 | Router(config)# gatekeeper | Enter gatekeeper configuration mode. |
Step 3 | Router(config-gk)# zone prefix gatekeeper-name e164-prefix [blast|seq] [gw-priority priority gw-alias [gw-alias...]] | Configure the first gatekeeper to service the prefix zone and specify whether LRQs should be sent in blast or sequential fashion. The default is sequential. |
Step 4 | Router(config-gk)# zone prefix gatekeeper-name e164-prefix [blast|seq] [gw-priority priority gw-alias [gw-alias...]] | Configure the first gatekeeper to service the prefix zone and specify whether LRQs should be sent in blast or sequential fashion. The default is sequential. |
You can configure multiple remote gatekeepers for the same zone, but only one of the gatekeepers defined for any given zone prefix can be local. We recommend that you limit the number of remote gatekeepers that service the same zone prefix to two.
By default, LRQs are sent sequentially to the remote gatekeepers. If you would like the LRQs to be sent simultaneously (blast), you need only specify the blast keyword on one zone prefix command per E.164 prefix.
| Command | Purpose | |
|---|---|---|
Step 1 | Router# config term | Enter configuration mode. |
Step 2 | Router(config)# gatekeeper | Enter gatekeeper configuration mode. |
Step 3 | Router(config-gk)# gw-type-prefix type-prefix hopoff gkid1 hopoff gkid2 ... hopoff gkidn [seq|blast] | Configure the gatekeepers to service a technology zone and specify whether LRQs should be sent in blast or sequential fashion. The default is sequential. |
You can enter the hopoff keyword and gkid argument multiple times in the same command to define a group of gatekeepers that will service a given technology prefix. After you have listed all of the gatekeepers that will service that technology zone, you can specify whether the LRQs should be sent in blast or sequential fashion.
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Note Only one of the gatekeepers in the hopoff list can be local. We recommend that you limit the number of remote gatekeepers that service the same technology prefix to two. |
To verify the order in which LRQs will be sent to the gatekeepers defined for a zone prefix, enter the show gatekeeper zone prefix command. The output lists all the gatekeepers, in order, and the zone prefixes serviced by each.
router# show gatekeeper zone prefix
ZONE PREFIX TABLE
=================
GK-NAME E164-PREFIX
------- -----------
c3620-1-gk 917300....
c2514-2-gk 917300....
c2600-1-gk 919.......
c2514-1-gk 919.......
To verify the whether the LRQs will be sent sequentially or simultaneously to the gatekeepers, enter the show run command. If the LRQs will be sent simultaneously, blast will appear beside the first entry for a particular zone (as shown for zone 919).
router# show run Building configuration... Current configuration: ! . . . gatekeeper zone remote c3620-1-gk cisco.com 172.18.194.79 1719 zone remote c2514-2-gk cisco.com 172.18.194.89 1719 zone remote gk-cisco-paul cisco.com 172.18.193.155 1719 zone prefix c3620-1-gk 917300.... zone prefix c2514-2-gk 917300.... zone prefix c2514-2-gk 919....... blast zone prefix c3620-1-gk 919....... . . .
To verify that multiple gatekeepers are defined for a zone prefix, enter the show gatekeeper gw-type-prefix command. The output lists all the gatekeepers and the zone prefixes serviced by each.
router# show gatekeeper gw-type-prefix (GATEWAYS-TYPE PREFIX TABLE ================================ Prefix:3#* (Hopoff zone c2600-1-gk c2514-1-gk)
To verify the whether the LRQs will be sent sequentially or simultaneously to the gatekeepers, enter the show run command. If the LRQs will be sent simultaneously, blast will appear at the end of the gw-type-prefix line.
router# show run Building configuration... Current configuration: ! . . . gatekeeper zone remote c2600-1-gk cisco.com 172.18.194.70 1719 zone remote c2514-1-gk cisco.com 172.18.194.71 1719 gw-type-prefix 3#* hopoff c2600-1-gk hopoff c2514-1-gk blast . . .
This section provides the following configuration examples:
In the following example, two remote gatekeepers are configured to service the same zone prefix. By default, the LRQs will be sent sequentially to each of the remote gatekeepers.
gatekeeper zone remote c2600-1-gk cisco.com 172.18.194.70 1719 zone remote c2514-1-gk cisco.com 172.18.194.71 1719 zone prefix c2600-1-gk 919....... zone prefix c2514-1-gk 919.......
In the following example, two remote gatekeepers are configured to service the same technology prefix. In this case, the LRQs will be sent simultaneously (blast) to all of the remote gatekeepers.
gatekeeper zone remote c2600-1-gk cisco.com 172.18.194.70 1719 zone remote c2514-1-gk cisco.com 172.18.194.71 1719 gw-type-prefix 3#* hopoff c2600-1-gk hopoff c2514-1-gk blast
This section documents new or modified commands. All other commands used with this feature are documented in the Cisco IOS Release 12.1 command reference publications.
To configure a technology prefix in the gatekeeper, use the gw-type-prefix command. To remove the technology prefix, use the no form of the command.
gw-type-prefix type-prefix [ [hopoff gkid1] [hopoff gkid2] [hopoff gkidn] [seq | blast] ] [default-technology] [[gw ipaddr ipaddr [port ]] ...]
Syntax Description
type-prefix A technology prefix is recognized and is stripped before checking for the zone prefix. It is strongly recommended that you select technology prefixes that do not lead to ambiguity with zone prefixes. Do this by using the # character to terminate technology prefixes, for example, 3#. hopoff gkid (Optional) Use this option to specify the gatekeeper where the call is to hop off, regardless of the zone prefix in the destination address. The gkid argument refers to a gatekeeper previously configured using the zone local or zone remote comment. You can enter this keyword and argument multiple times to configure redundant gatekeepers for a given technology prefix. seq | blast (Optional) If you list multiple hopoffs, this indicates that the LRQs should be sent sequentially or simultaneously (blast) to the gatekeepers based on the order in which they were listed. The default is to send them sequentially. default-technology (Optional) Gateways registering with this prefix option are used as the default for routing any addresses that are otherwise unresolved. gw ipaddr ipaddr [port] (Optional) Use this option to indicate that the gateway is incapable of registering technology prefixes. When it registers, it adds the gateway to the group for this type-prefix, just as if it had sent the technology prefix in its registration. This parameter can be repeated to associate more than one gateway with a technology prefix.
Defaults
By default, LRQs are sent sequentially to all the gatekeepers listed.
Command Modes
Gatekeeper configuration
Command History
11.3(6) NA2 This command was introduced. 12.1(1)T This command was modified to allow the user to specify multiple hop offs. 12.1(2)T This command was modified to allow the user to specify whether LRQs should be sent simultaneously or sequentially to the gatekeepers.
Release
Modification
Usage Guidelines
You do not have to define a technology prefix to a gatekeeper if there are gateways configured to register with that prefix, and if there are no special flags (such as hopoff gkid or default-technology) that you want to associate with that prefix.
Examples
The following example defines two gatekeepers for technology zone 3:
gw-type-prefix 3#* hopoff c2600-1-gk hopoff c2514-1-gk
Related Commands
show gatekeeper gw-type-prefix Displays the list of currently defined technology zones and the gatekeepers responsible for each.
Command
Description
To configure the timeout window for use when sending multiple LRQs (either sequentially or simultaneously), use the lrq timeout blast window command. To return to the default value, use the no form of the command.
lrq timeout blast window value
Syntax Description
value The duration of the window in seconds. Possible values are 1 through 10. The default is 6.
Defaults
By default, the duration of the window is 6 seconds.
Command Modes
Gatekeeper configuration
Command History
12.1(2)T This command was introduced.
Release
Modification
Usage Guidelines
None
Examples
The following example sets the window to three seconds:
lrq timeout blast window 3
Related Commands
gatekeeper gw-type-prefix Sets the gatekeepers responsible for each technology prefix. If more than one gatekeeper is used to service technology prefix, this command can be used to determine whether the LRQs are sent sequentially or simultaneously. zone prefix Adds a prefix to a gatekeeper's zone list. If more than one gatekeeper is used to service a zone, this command can be used to determine whether the LRQs are sent sequentially or simultaneously.
Command
Description
To configure the delay for use when sending LRQs sequentially, use the lrq timeout seq delay command. To return to the default value, use the no form of the command.
lrq timeout seq delay value
Syntax Description
value The duration of the delay in 100 millisecond units. Possible values are 1 through 10. The default is 5 (500 ms or .5 seconds).
Defaults
By default, the duration of the window is 5 ms.
Command Modes
Gatekeeper configuration
Command History
12.1(2)T This command was introduced.
Release
Modification
Usage Guidelines
None
Examples
The following example sets the window to three seconds:
lrq timeout seq delay 5
Related Commands
gatekeeper gw-type-prefix Sets the gatekeepers responsible for each technology prefix. If more than one gatekeeper is used to service technology prefix, this command can be used to determine whether the LRQs are sent sequentially or simultaneously. zone prefix Adds a prefix to a gatekeeper's zone list. If more than one gatekeeper is used to service a zone, this command can be used to determine whether the LRQs are sent sequentially or simultaneously.
Command
Description
To add a prefix to the gatekeeper zone list, use the zone prefix command in gatekeeper configuration mode. To remove knowledge of a zone prefix, use the no form of this command with the gatekeeper name and prefix. To remove the priority assignment for a specific gateway, use the no form of this command with the gw-priority option.
zone prefix gatekeeper-name e164-prefix [blast | seq ] [gw-priority priority gw-alias [gw-alias, ...]]
Syntax Description
gatekeeper-name The name of a local or remote gatekeeper, which must have been defined by using the zone local or zone remote command. e164-prefix An E.164 prefix in standard form followed by dots (.). Each dot represents a number in the E.164 address. For example, 212....... is matched by 212 and any seven numbers. Although a dot representing each digit in an E.164 address is the preferred configuration method, you can also enter an asterisk (*) to match any number of digits. seq | blast (Optional) If you list multiple hopoffs, this indicates that the LRQs should be sent sequentially or simultaneously (blast) to the gatekeepers based on the order in which they were listed. The default is to send them sequentially. gw-priority priority gw-alias (Optional) Use the gw-priority option to define how the gatekeeper selects gateways in its local zone for calls to numbers beginning with prefix e164-prefix. Do not use this option to set priority levels for a prefix assigned to a remote gatekeeper. For priority, use values from 0 to 10. A 0 value prevents the gatekeeper from using the gateway gw-alias for that prefix. Value 10 places the highest priority on gateway gw-alias. If you do not specify a priority value for a gateway, the value 5 is assigned. To assign the same priority value for one prefix to multiple gateways, list the additional gateway names (gw-alias) in a comma-separated string after the initial gw-alias. The gw-alias name is the H.323 ID of a gateway that is registered or will register with the gatekeeper. This name is set on the gateway with the h323-gateway voip h.323-id command.
Defaults
By default, multiple LRQs are sent sequentially and the priority for a gw-alias is 5.
Command Modes
Gatekeeper configuration
Command History
11.3(6) Q This command was introduced. 11.3(7)T This command was modified for H.323 Version 1. 12.0(5)T This display format was modified for H.323 Version 2. 12.1(2)T This command was modified to allow the user to specify whether LRQs should be sent simultaneously or sequentially to the gatekeepers.
Release
Modification
Usage Guidelines
A single gatekeeper can handle more than one zone prefix. In addition, you can configure multiple remote gatekeepers for the same zone, but only one of the gatekeepers defined for any given zone prefix can be local. We recommend that you limit the number of remote gatekeepers that service the same zone prefix to two.
When choosing a gateway, the gatekeeper first looks for the longest zone prefix match; then it uses the priority and the gateway status to select from the gateways. If all gateways are available, the gatekeeper chooses the highest priority gateway. If all the highest priority gateways are busy (see the gateway resource threshold command), a lower priority gateway is selected.
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Note The zone prefix command matches a prefix to a gateway. It does not register the gateway. The gateway must register with the gatekeeper before calls can be completed through that gateway. |
Examples
The following example defines two gatekeepers for technology zone 3:
gw-type-prefix 3#* hopoff c2600-1-gk hopoff c2514-1-gk
Related Commands
resource threshold Configures a gateway to report H.323 resource availability to the gatekeeper of the gateway. register Configures a gateway to register or deregister a fully qualified dial-peer E.164 address with a gatekeeper. show call resource voice threshold Displays the threshold configuration settings and status for an H.323 gateway. show gateway Displays the current gateway status.
Command
Description
gatekeeper---A gatekeeper maintains a registry of devices in the multimedia network. The devices register with the gatekeeper at startup, and request admission to a call from the gatekeeper.
The gatekeeper is an H.323 entity on the LAN that provides address translation and control access to the LAN for H.323 terminals and gateways. The gatekeeper may provide other services to the H.323 terminals and gateways, such as bandwidth management and locating gateways.
gateway---A gateway allows H.323 terminals to communicate with non-H.323 terminals by converting protocols. A gateway is the point at which a circuit-switched call is encoded and repackaged into IP packets.
A H.323 gateway is an endpoint on the LAN that provides real-time, two-way communications between H.323 terminals on the LAN and other ITU-T terminals in the WAN, or to another H.323 gateway.
E.164---ITU-T recommendation for international telecommunication numbering, especially in ISDN, BISDN, and SMDS. An evolution of standard telephone numbers.
H.323---An International Telecommunication Union (ITU-T) standard that describes packet-based video, audio, and data conferencing. H.323 is an umbrella standard that describes the architecture of the conferencing system, and refers to a set of other standards (H.245, H.225.0, and Q.931) to describe its actual protocol.
hop off---The point at which a call transitions from H.323 to non-H.323, typically at a gateway.
LRQ---A RAS message sent as a location request.
POTS---Plain old telephone service. Basic telephone service supplying standard single line telephones, telephone lines, and access to the PSTN.
PSTN---Public switched telephone network. PSTN refers to the local telephone company.
RAS---Registration, admission, and status protocol. This is the protocol that is used between endpoints and the gatekeeper to perform management functions. The RAS signaling function performs registration, admissions, bandwidth changes, status, and disengage procedures between the VoIP gateway and the gatekeeper.
technology prefix---Discriminators used to distinguish between gateways having specific capabilities within a given zone. In the exchange between the gateway and the gatekeeper, the technology prefix is used to select a gateway after the zone has been selected. Technology prefixes can be used to tell the gatekeeper that a certain technology is associated with a particular call (for example, 15# could mean a fax transmission), or it can be used like an area code for more generic routing. No standard defines what the numbers in a technology prefix mean; by convention, technology prefixes are designated by a pound (#) symbol as the last character.
VoIP---Voice over IP. The ability to carry normal telephone-style voice over an IP-based Internet with POTS-like functionality, reliability, and voice quality. VoIP is a blanket term which generally refers to Cisco's standards-based (H.323, etc.) approach to IP voice traffic.
zone prefix---A prefix that identifies the addresses to be serviced by a given gatekeeper. Zone prefixes are typically area codes and serve the same purpose as the domain names in the H.323-ID address space.
Posted: Fri May 19 12:21:06 PDT 2000
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