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Catalyst 3550 Multilayer Switch Software Configuration Guide
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Chapter 34 Configuring IP Multicast Routing
Configuring Optional Multicast Routing Features
Configuring an IP Multicast Boundary
Like TTL thresholds, administratively-scoped boundaries can also 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 can not enter or exit this interface, thereby providing a firewall for multicast
traffic in this address range.
Figure 34-12 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 around the perimeter of their networks. This boundary prevents multicast
traffic in the range of 239.128.0.0 through 239.128.255.255 from entering or leaving their respective
networks.
Figure 34-12 Administratively-Scoped Boundaries
You can define an administratively-scoped boundary on a routed interface for multicast group addresses.
A standard access list defines the range of addresses affected. When a boundary is defined, 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 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 then be reused in domains administered
by different organizations. The addresses would be considered local, not globally unique.
45154
Company XYZ
Engineering
Marketing
239.128.0.0/16
239.0.0.0/8
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