IP Multicast Boundary
As shown in the figure, address scoping defines domain boundaries so that domains with RPs that have the
same IP address do not leak into each other. Scoping is performed on the subnet boundaries within large
domains and on the boundaries between the domain and the Internet.
Figure 4: Address Scoping at Boundaries
You can set up an administratively scoped boundary on an interface for multicast group addresses using the
ip multicast boundary command with the access-list argument. A standard access list defines the range of
addresses affected. When a boundary is set up, no multicast data packets are allowed to flow across the
boundary from either direction. The boundary allows the same multicast group address to be reused in different
administrative domains.
The Internet Assigned Numbers Authority (IANA) has designated the multicast address range 239.0.0.0 to
239.255.255.255 as the administratively scoped addresses. This range of addresses can be reused in domains
administered by different organizations. They would be considered local, not globally unique.
You can configure the filter-autorp keyword to examine and filter Auto-RP discovery and announcement
messages at the administratively scoped boundary. Any Auto-RP group range announcements from the
Auto-RP packets that are denied by the boundary access control list (ACL) are removed. An Auto-RP group
range announcement is permitted and passed by the boundary only if all addresses in the Auto-RP group range
are permitted by the boundary ACL. If any address is not permitted, the entire group range is filtered and
removed from the Auto-RP message before the Auto-RP message is forwarded.
Auto-RP Benefits
Auto-RP uses IP multicast to automate the distribution of group-to-RP mappings to all Cisco routers and
multilayer devices in a PIM network. Auto-RP has these benefits:
•
Easy to use multiple RPs within a network to serve different group ranges.
•
Provides load splitting among different RPs and arrangement of RPs according to the location of group
participants.
•
Avoids inconsistent, manual RP configurations on every router and multilayer device in a PIM network,
which can cause connectivity problems.
IP Multicast Routing Configuration Guide, Cisco IOS XE Release 3SE (Catalyst 3650 Switches)
OL-29890-01 119
Configuring PIM
Auto-RP
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