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DSG 1.2 Clients and Agents
DSG 1.2 Clients and Agents
A-DSG 1.2 supports the DSG client and agent functions outlined by the CableLabs
(DSG) Interface Specification , CM-SP-DSG-I05-050812.
FQDN Support
You can specify either a fully-qualified domain name (FQDN) or IP address for A-DSG classifier multicast
group and source addresses using the cable dsg cfr command in global configuration mode. We recommend
that you use an FQDN to avoid modification of multicast group and source addresses when network changes
are implemented.
This feature allows you to use a hostname (FQDN) in place of the source IP address using the cable dsg cfr
command. For example, you have two A-DSG tunnel servers, in two locations, sending multicast traffic to
the same multicast address. In this scenario, you can specify a hostname for the source IP address and let the
DNS server determine which source is sending the multicast traffic.
If you configure an A-DSG classifier with a hostname, the Cisco CMTS router immediately verifies if the
hostname can be resolved against an IP address using the local host cache. If not, the router does not enable
the classifier until the hostname is resolved. If the hostname cannot be resolved locally, the router performs
a DNS query to verify the DSG classifiers.
The FQDN format does not support static Internet Group Management Protocol (IGMP) join requests initiated
on the Cisco CMTS router. The IGMP static group IP address created automatically under a bundle interface
at the time of A-DSG configuration is not displayed in the show running-config interface command output.
To display the A-DSG static groups configured under a bundle interface, use the show cable dsg static-group
bundle command in privileged EXEC mode.
DSG Name Process and DNS Query
Every DNS record contains a time to live (TTL) value set by the server administrator, and this may vary from
seconds to weeks. The DSG name process supersedes the TTL value criterion to update A-DSG classifiers
on the Cisco CMTS router.
The DSG name process enables the Cisco CMTS router to query the DNS server for faster classifier updates.
To enable the Cisco CMTS router to perform a DNS query for an A-DSG classifier verification, you must
configure one or more DNS servers using the ip name-server command in global configuration mode. You
can also specify the DNS query interval using the cable dsg name-update-interval command in global
configuration mode.
During a Cisco IOS software reload or a route processor switchover, the router may fail to query the DNS
server if the interfaces are down, and the router may not wait for the interval specified using the cable dsg
name-update-interval command to perform a DNS query. In this case, for an unresolved hostname, the router
automatically performs a DNS query based on a system-defined (15 seconds) interval to facilitate faster DSG
classifier updates. You cannot change the system-defined interval.
Cisco cBR Series Converged Broadband Routers Application—Voice and Video Configuration Guide
12
Advanced-Mode DOCSIS Set-Top Gateway 1.2 for the Cisco CMTS Routers
™
DOCSIS Set-top Gateway
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