Juniper Multicast

IP Services - Multicast

The E-series system supports IP multicasting. IP multicasting improves network efficiency by allowing a host to transmit a datagram to a targeted group of receivers. For example, a host may want to send a large video clip to a group of selected recipients. It would be time-consuming for the host to unicast the datagram to each recipient individually. If the host broadcasts the video clip throughout the network, network resources are not available for other tasks. The host uses only the resources it needs by multicasting the datagram. A multicast datagram is effectively a broadcast to a limited group of network devices. Routers use multicast routing algorithms to determine the best route and transmit multicast datagrams throughout the network. The E-series system supports up to 16,384 multicast forwarding entries (multicast routes) at any time.

IGMP: IP hosts use Internet Group Management Protocol (IGMP) to report their multicast group memberships to neighboring routers. Similarly, multicast routers, such as the E-series system, use IGMP to discover which of their hosts belong to multicast groups.

The IPv4 address scheme assigns Class D addresses for IP multicasting. IGMP is the protocol that uses these addresses, which can be in the range 224.0.0.0 to 239.255.255.255. This implementation of IGMP complies with RFC 2236 (IGMPv2). IGMPv2 routers support both IGMPv1 and IGMPv2 hosts.

PIM: Protocol Independent Multicast (PIM) is the protocol that allows multicast routers to identify other multicast routers that should receive packets. This implementation of PIM supports PIM dense mode (DM), PIM sparse mode (SM), and PIM sparse-dense mode (S-DM).

DVMRP: The E-series system supports Distance Vector Multicast Routing Protocol (DVRMP) on virtual routers to forward multicast datagrams through a network. DVMRP is an interior gateway protocol that supports operations within an autonomous system, but not between autonomous systems. The multicast backbone of the Internet, MBONE, uses DVMRP to forward multicast datagrams. DVMRP is a dense mode multicasting protocol and therefore uses a broadcast and prune mechanism. The protocol builds an SRT in a similar way to PIM-DM. DVMRP routers flood datagrams to all interfaces except the one that provides the shortest unicast route to the source. To prevent unnecessary sending of multicast messages through the SRT, DVMRP uses pruning. A DVMRP router sends prune messages to its neighbors if it discovers that:

• The network to which a host is attached has no active members of the multicast group
• All neighbors, except the next-hop neighbor connected to the source, have pruned the source and the group

When a neighbor receives a prune message from a DVMRP router, it removes that neighbor from its source group table, which provides information to the multicast forwarding table If a host on a previously pruned branch wants to join a multicast group, it sends an IGMP message to its first-hop router. The first-hop router then sends a graft message upstream.

BGP Multicasting: BGP multicasting is an extension of the BGP unicast routing protocol. Many of the functions available for BGP unicasting are also available for BGP multicasting.

The BGP multiprotocol extensions specify that BGP can exchange information within different types of address families. The address families available are unicast, multicast, and unicast vpn. When you enable BGP, the E-series system employs unicast IPv4 addresses by default. To enable BGP multicasting, you must configure commands for the multicast address family.

Datasheets:

• Juniper networks E-series broadband services routers
• Juniper networks E320 and E120 broadband services routers
• Juniper networks JUNOSe

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