The Role Of Auto-Rp In A Pim Network; Multicast Boundaries - Cisco Catalyst 3850 series Configuration Manual

Configuring PIM
advantage of Auto-RP is that it offers the ability to scope the RP address within a domain. Scoping can be
achieved by defining the time-to-live (TTL) value allowed for the Auto-RP advertisements.
Each method for configuring an RP has its own strengths, weaknesses, and level of complexity. In conventional
IP multicast network scenarios, we recommend using Auto-RP to configure RPs because it is easy to configure,
well-tested, and stable. The alternative ways to configure an RP are static RP, Auto-RP, and bootstrap router.
Related Topics
Setting Up Auto-RP in a New Internetwork (CLI), on page 146
Example: Configuring Auto-RP, on page 182
Example: Sparse Mode with Auto-RP , on page 183
Restrictions for Configuring Auto-RP and BSR, on page 123
Restrictions for Auto-RP Enhancement, on page 125

The Role of Auto-RP in a PIM Network

Auto-RP automates the distribution of group-to-rendezvous point (RP) mappings in a PIM network. To make
Auto-RP work, a device must be designated as an RP mapping agent, which receives the RP announcement
messages from the RPs and arbitrates conflicts. The RP mapping agent then sends the consistent group-to-RP
mappings to all other devices by way of dense mode flooding.
Thus, all routers automatically discover which RP to use for the groups they support. The Internet Assigned
Numbers Authority (IANA) has assigned two group addresses, 224.0.1.39 and 224.0.1.40, for Auto-RP.
The mapping agent receives announcements of intention to become the RP from Candidate-RPs. The mapping
agent then announces the winner of the RP election. This announcement is made independently of the decisions
by the other mapping agents.

Multicast Boundaries

Administratively-scoped boundaries can be used to limit the forwarding of multicast traffic outside of a domain
or subdomain. This approach uses a special range of multicast addresses, called administratively-scoped
addresses, as the boundary mechanism. If you configure an administratively-scoped boundary on a routed
interface, multicast traffic whose multicast group addresses fall in this range cannot enter or exit this interface,
which provides a firewall for multicast traffic in this address range.
Multicast boundaries and TTL thresholds control the scoping of multicast domains; however, TTL thresholds
Note
are not supported by the device. You should use multicast boundaries instead of TTL thresholds to limit
the forwarding of multicast traffic outside of a domain or a subdomain.
The following figure shows that Company XYZ has an administratively-scoped boundary set for the multicast
address range 239.0.0.0/8 on all routed interfaces at the perimeter of its network. This boundary prevents any
multicast traffic in the range 239.0.0.0 through 239.255.255.255 from entering or leaving the network. Similarly,
the engineering and marketing departments have an administratively-scoped boundary of 239.128.0.0/16
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IP Multicast Routing Configuration Guide, Cisco IOS XE Release 3.6E (Catalyst 3850 Switches)
Rendezvous Points
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