Cisco Cisco TelePresence Video Communication Server Expressway
Appendix 6 – Configuring endpoints to work with a Cisco VCS cluster
Appendix 6 – Configuring endpoints to work
with a Cisco VCS cluster
with a Cisco VCS cluster
For additional details about DNS SRV and round-robin DNS see the URI dialling section in the Cisco
VCS Administrator Guide.
VCS Administrator Guide.
H.323 endpoints
The options below are listed in preference order for providing resilience of connectivity of endpoints to
a cluster of Cisco VCSs where 1 or more Cisco VCS cluster peers become inaccessible. The choice
of option will depend on what functionality the endpoint you are using supports.
a cluster of Cisco VCSs where 1 or more Cisco VCS cluster peers become inaccessible. The choice
of option will depend on what functionality the endpoint you are using supports.
Option 1 – DNS SRV (preferred)
To use this option, there must be a DNS SRV record available for the DNS name of the Cisco VCS
cluster that defines an equal weighting and priority for each cluster peer.
cluster that defines an equal weighting and priority for each cluster peer.
On each H.323 endpoint, configure the Gatekeeper Settings as:
Discovery = Manual
IP Address = DNS name of the Cisco VCS cluster
If the endpoint supports DNS SRV, on startup the endpoint issues a DNS SRV request and receives a
DNS SRV record back defining an equal weighting and priority for each cluster peer. It may also
receive a list of lower priority entries pointing at a fallback cluster.
DNS SRV record back defining an equal weighting and priority for each cluster peer. It may also
receive a list of lower priority entries pointing at a fallback cluster.
The endpoint then tries to register with a relevant cluster peer (having taken into account the priority /
weightings). If that peer is not available, the endpoint will try and register to another listed peer at the
same priority, or if all peers at that priority have been tried, a peer at the next lower (higher numbered)
priority.
weightings). If that peer is not available, the endpoint will try and register to another listed peer at the
same priority, or if all peers at that priority have been tried, a peer at the next lower (higher numbered)
priority.
This will be repeated until the endpoint can register with a Cisco VCS. On registering with the Cisco
VCS, the Cisco VCS will respond with the H.323 “Alternate Gatekeepers” list containing the list of
Cisco VCS Cluster peer members.
VCS, the Cisco VCS will respond with the H.323 “Alternate Gatekeepers” list containing the list of
Cisco VCS Cluster peer members.
The endpoint will continue to use the first Cisco VCS that it registered to for re-registrations and for
calls. If it ever loses connection to its Cisco VCS then it will select an “Alternate Gatekeeper” from the
list it was supplied with.
calls. If it ever loses connection to its Cisco VCS then it will select an “Alternate Gatekeeper” from the
list it was supplied with.
DNS SRV cache timeout should be set to a fairly long time (e.g. 24 hours) to minimize DNS traffic.
Option 2 – DNS Round-Robin (2nd choice)
To use this option, there must be a DNS A-record available for the DNS name of the Cisco VCS
cluster that supplies a round-robin list of IP addresses.
cluster that supplies a round-robin list of IP addresses.
On each H.323 endpoint configure the Gatekeeper Settings as:
Discovery = Manual
IP Address = DNS name of the Cisco VCS cluster
If the endpoint does not support DNS SRV, on startup the endpoint will perform a DNS A-record
lookup. The DNS server will have been configured to support round-robin DNS, with each of the
cluster peer members defined in the round-robin list.
lookup. The DNS server will have been configured to support round-robin DNS, with each of the
cluster peer members defined in the round-robin list.
The endpoint will take the address given by the DNS lookup and will then try and register with the
relevant cluster peer. If that peer is not available, then the endpoint will perform another DNS lookup
relevant cluster peer. If that peer is not available, then the endpoint will perform another DNS lookup
Cisco VCS Deployment Guide: Cluster creation and maintenance (Cisco VCS X5)
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