The following figure displays DNS-based SSM mapping.
Figure 11: DNS-Based SSM Mapping
The SSM mapping mechanism that enables the last hop router to join multiple sources for a group can provide
source redundancy for a TV broadcast. In this context, the last hop router provides redundancy using SSM
mapping to simultaneously join two video sources for the same TV channel. However, to prevent the last hop
router from duplicating the video traffic, the video sources must use a server-side switchover mechanism.
One video source is active, and the other backup video source is passive. The passive source waits until an
active source failure is detected before sending the video traffic for the TV channel. Thus, the server-side
switchover mechanism ensures that only one of the servers is actively sending video traffic for the TV channel.
To look up one or more source addresses for a group that includes G1, G2, G3, and G4, you must configure
these DNS records on the DNS server:
G4.G3.G2.G1 [multicast-domain] [timeout] IN A source-address-1
IN A source-address-2
IN A source-address-n
See your DNS server documentation for more information about configuring DNS resource records.
How to Configure SSM
For a complete description of the source-specific multicast (SSM) commands in this section, see the IP
Multicast Command Reference, Cisco IOS XE Release 3SE (Catalyst 3850 Switches). To locate documentation
for other commands that appear in this chapter, use the command reference master index, or search online.
Configuring Source Specific Multicast
This section describes how to configure Source Specific Multicast (SSM).
IP Multicast Routing Configuration Guide, Cisco IOS XE Release 3SE (Catalyst 3650 Switches)
OL-29890-01 237
Configuring SSM
How to Configure SSM
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