Configuring IPv4 Multicast Attributes

You can configure IPv4 multicast attributes with the following tasks:

• Before You Begin Configuring IPv4 Multicast
• Enabling IP Multicast
• Defining Static Routes for Reverse-Path Forwarding
• Enabling and Disabling RPF Checks
• Specifying Unicast Routes for RPF
• Defining Permanent IP Multicast Forwarding Entries
• Defining a Multicast Bandwidth Map

Before You Begin Configuring IPv4 Multicast

You can configure multicasting on IPv4 and IPv6 interfaces.

For information about configuring IP and IPv6 interfaces, see JunosE IP, IPv6, and IGP Configuration Guide.

Enabling IP Multicast

In this implementation, IP multicast works on virtual routers (VRs). By default, IP multicast is disabled on a VR. To enable IP multicast on a VR, access the context for a VR, and then issue the ip multicast-routing command.

You can use the no version to disable IP multicast routing on the VR (the default).

Defining Static Routes for Reverse-Path Forwarding

Use the ip rpf-route command to define reverse-path forwarding (RPF) to verify that a router receives a multicast packet on the correct incoming interface.

You can use the no version to disable IP multicast routing on the VR (the default). In the disabled state, all multicast protocols are disabled, and the VR forwards no multicast packets.

Enabling and Disabling RPF Checks

By default, the router accepts multicast packets for each Source, Group (S,G) pair on an incoming interface (IIF), which satisfies the RPF check (RPF-IIF). When the router performs RPF checks, only the interface that first accepts traffic for an (S,G) pair accepts subsequent traffic for that pair. If traffic stops arriving on that interface and starts arriving on another interface, the router does not accept or forward the traffic.

Some network configurations require the router to accept traffic on any interface. To do so, you can disable the RPF check on a specified set of (S,G) pairs by issuing the ip multicast-routing disable-rpf-check command.

You can use the no version to restore the default, in which the router performs RPF checks for all (S,G) pairs.

When you disable RPF checks, the router accepts multicast packets for (S,G) pairs on any incoming interface. When the router has added the new route to its multicast routing table, it then accepts multicast packets for these pairs on any interface in the virtual router and forwards them accordingly. Multicast routes established before you issue this command are not affected.

Specifying Unicast Routes for RPF

You can specify that IS-IS, OSPF, or RIP routes be available for RPF. Routes available for RPF appear in the multicast view of the routing table.

Defining Permanent IP Multicast Forwarding Entries

An mroute is a multicast traffic flow (a (Source, Group) entry used for forwarding multicast traffic). By default, forwarding mroutes (with a valid RPF incoming interface) are timed out if data for them is not received for 210 seconds. However, you can specify an mroute as permanent by using the ip multicast-routing permanent-mroute command.

You can use the no version to prevent any new mroutes from becoming permanent. To remove existing permanent mroutes, use the clear ip mroute command.

Defining a Multicast Bandwidth Map

Multicast interface-level admission control, port-level admission control, and QoS adjustment all use a single multicast bandwidth map. The multicast bandwidth map is a route map that uses the set admission-bandwidth, set qos-bandwidth, set admission-bandwidth adaptive, or set qos-bandwidth adaptive commands. The adaptive commands configure an autosense mechanism for measuring the multicast bandwidth.

Note: Even though you can include any of the preceding commands several times in a route map entry, only the last admission-bandwidth command or qos-bandwidth command in the bandwidth map is used. In other words, if you included the set qos-bandwidth command first and then the set qos-bandwidth adaptive command, the bandwidth map uses the set qos-bandwidth adaptive command.

Interface-level and port-level admission control is performed when an OIF on the interface or port is added to the mroute for a given (S,G) multicast data stream and the multicast bandwidth map contains a set admission-bandwidth or set admission-bandwidth adaptive action for that (S,G).

QoS adjustment is performed on the joining interface when an OIF is added to the mroute for a given (S,G) data stream and the multicast bandwidth map contains a set qos-bandwidth or set qos-bandwidth adaptive action for that (S,G).

You can prioritize the traffic by configuring a priority value for the <S, G> data stream on a physical port by issuing the set priority command. Dynamic multicast admission control enables only prioritized groups to join the interface after the configured priority limit is reached on the physical port. The system records the priority when a new <S, G> entry is created.

Note: You can create a single route map with the set admission-bandwidth command, the set qos-bandwidth command, or both. However, creating an entry with only one of these set commands enables only that specific function for the matched address (that is, only multicast traffic admission control or only QoS adjustment). The same is true for the adaptive commands.