Cisco Systems 78-11741-02 manual Configuring an IP Multicast Boundary, IPC-438

Configuring IP Multicast Routing

Configuring an IP Multicast Boundary

Configuring an IP Multicast Boundary

You can set up an administratively scoped boundary on an interface for multicast group addresses. 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-autorpkeyword 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.

To set up an administratively scoped boundary, use the following commands beginning in global configuration mode:

	Command	Purpose
Step 1
	Router(config)# access-listaccess-list-number	Creates a standard access list, repeating the command as
	{deny permit} source [source-wildcard]	many times as necessary.
		Note An access-list entry that uses the deny keyword
		creates a multicast boundary for packets that match
		that entry.
Step 2
	Router(config)# interface type number	Configures an interface.
Step 3
	Router(config-if)#ip multicast boundary	Configures the boundary, specifying the access list you
	access-list[filter-autorp]	created in Step 1. Optionally configures Auto-RP message
		filtering.

See the section “Administratively Scoped Boundary Example” later in this chapter for an example of configuring a boundary.

Configuring an Intermediate IP Multicast Helper

When a multicast-capable internetwork is between two subnets with broadcast-only-capable hosts, you can convert broadcast traffic to multicast at the first hop router, and convert it back to broadcast at the last hop router to deliver the packets to the broadcast clients. Thus, you can take advantage of the multicast capability of the intermediate multicast internetwork. Configuring an intermediate IP multicast helper prevents unnecessary replication at the intermediate routers and can take advantage of multicast fast switching in the multicast internetwork.

See Figure 73 and the example of this feature in the section “IP Multicast Helper Example” later in this chapter.

An extended IP access list controls which broadcast packets are translated, based on the UDP port number.

Cisco IOS IP Configuration Guide

IPC-438