◦
Enable PIM sparse mode. For information about this procedure, see
page 124
.
◦
Configure SSM. For information about this procedure, see
•
Before you configure static SSM mapping, you must configure access control lists (ACLs) that define
the group ranges to be mapped to source addresses.
•
Before you can configure and use SSM mapping with DNS look ups, you must be able to add records
to a running DNS server. If you do not already have a DNS server running, you need to install one.
You can use a product such as
Cisco Network Registrar
to add records to a running
DNS server.
Note
Restrictions for Configuring SSM
The following are the restrictions for configuring SSM:
•
To run SSM with IGMPv3, SSM must be supported in the Cisco IOS router, the host where the application
is running, and the application itself.
•
The SSM mapping feature does not have all the benefits of full SSM. Because SSM mapping takes a
group join from a host and identifies this group with an application associated with one or more sources,
it can only support one such application per group. Full SSM applications can still share the same group
as in SSM mapping.
•
Enable IGMPv3 carefully on the last hop router when you rely solely on SSM mapping as a transition
solution for full SSM. When you enable both SSM mapping and IGMPv3 and the hosts already support
IGMPv3 (but not SSM), the hosts send IGMPv3 group reports. SSM mapping does not support these
IGMPv3 group reports, and the router does not correctly associate sources with these reports.
•
Existing applications in a network predating SSM do not work within the SSM range unless they are
modified to support (S, G) channel subscriptions. Therefore, enabling SSM in a network can cause
problems for existing applications if they use addresses within the designated SSM range.
•
IGMPv3 uses new membership report messages that might not be correctly recognized by older IGMP
snooping devices.
•
Address management is still necessary to some degree when SSM is used with Layer 2 switching
mechanisms. Cisco Group Management Protocol (CGMP), IGMP snooping, or Router-Port Group
Management Protocol (RGMP) support only group-specific filtering, not (S, G) channel-specific filtering.
If different receivers in a switched network request different (S, G) channels sharing the same group,
they do not benefit from these existing mechanisms. Instead, both receivers receive all (S, G) channel
traffic and filter out the unwanted traffic on input.
Because SSM can re-use the group addresses in the SSM range for many independent applications, this
situation can lead to decreased traffic filtering in a switched network. For this reason, it is important to
use random IP addresses from the SSM range for an application to minimize the chance for re-use of a
single address within the SSM range between different applications. For example, an application service
providing a set of television channels should, even with SSM, use a different group for each television
(S, G) channel. This setup guarantees that multiple receivers to different channels within the same
application service never experience traffic aliasing in networks that include Layer 2 devices.
IP Multicast Routing Configuration Guide, Cisco IOS XE Release 3SE (Catalyst 3650 Switches)
232
OL-29890-01
Configuring SSM
Restrictions for Configuring SSM
