Cisco Cisco TelePresence Video Communication Server Expressway Maintenance Manual
URI dialing via DNS
By using DNS as part of URI dialing, it is possible to find an endpoint even though it may be registered to an
unknown system. The VCS uses a DNS lookup to locate the domain in the URI address and then queries
that domain for the alias. See the
unknown system. The VCS uses a DNS lookup to locate the domain in the URI address and then queries
that domain for the alias. See the
section for more information.
URI dialing via DNS is enabled separately for outgoing and incoming calls.
Outgoing calls
To enable your VCS to locate endpoints using URI dialing via DNS, you must:
n
configure at least one DNS zone and an associated search rule
n
configure at least one DNS server
section.
Incoming calls
To enable endpoints registered to your VCS to receive calls from non-locally registered endpoints using URI
dialing via DNS, you must:
dialing via DNS, you must:
n
ensure all endpoints are registered with an AOR (SIP) or H.323 ID in the form of a URI
n
configure appropriate DNS records, depending on the protocols and transport types you want to use
Firewall traversal calls
To configure your system so that you can place and receive calls using URI dialing through a firewall, see the
section.
URI resolution process using DNS
When the VCS attempts to locate a destination URI address using the DNS system, the general process is
as follows:
as follows:
H.323
1. The VCS sends a query to its DNS server for an SRV record for the domain in the URI. (If more than one
DNS server has been configured on the VCS, the query will be sent to all servers at the same time, and all
responses will be prioritized by the VCS with only the most relevant SRV record being used.) If available,
this SRV record returns information (such as the FQDN and listening port) about either the device itself or
the authoritative H.323 gatekeeper for that domain.
responses will be prioritized by the VCS with only the most relevant SRV record being used.) If available,
this SRV record returns information (such as the FQDN and listening port) about either the device itself or
the authoritative H.323 gatekeeper for that domain.
l
If the domain part of the URI address was resolved successfully using an H.323 Location SRV record
(that is, for _ h323ls) then the VCS will send an A/AAAA record query for each name record returned.
These will resolve to one or more IP addresses, and the VCS then sends, in priority order, an LRQ for
the full URI to those IP addresses.
(that is, for _ h323ls) then the VCS will send an A/AAAA record query for each name record returned.
These will resolve to one or more IP addresses, and the VCS then sends, in priority order, an LRQ for
the full URI to those IP addresses.
l
If the domain part of the URI address was resolved using an H.323 Call Signaling SRV record (that is,
for _ h323cs) then the VCS will send an A/AAAA record query for each name record returned. These will
resolve to one or more IP addresses, and the VCS then routes the call, in priority order to the IP
addresses returned in those records. (An exception to this is where the original dial string has a port
specified - for example, user@example.com:1719 - in which case the address returned is queried
via an LRQ for the full URI address.)
for _ h323cs) then the VCS will send an A/AAAA record query for each name record returned. These will
resolve to one or more IP addresses, and the VCS then routes the call, in priority order to the IP
addresses returned in those records. (An exception to this is where the original dial string has a port
specified - for example, user@example.com:1719 - in which case the address returned is queried
via an LRQ for the full URI address.)
Cisco VCS Administrator Guide (X8.1.1)
Page 204 of 507
Dial plan and call processing
About URI dialing