Specifications

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3.2.6 IP Multicast Support
The Packet Forwarding Engine features a shared packet memory system that is
spread across all interface modules. The shared memory offers the advantage of
only having to buffer packets once through the entire system. This is especially
useful for multicast forwarding, as packets are written to memory once and can
be read from memory many times simultaneously, once for each outgoing next
hop. This makes the Juniper routers architecture inherently optimal for multicast
support.
The JUNOS software supports the following IP multicast routing protocols:
IGMP (Internet Group Management Protocol) version 1 and 2 (RFC 2236)
DVMRP (Distance Vector Multicast Routing Protocol) (Internet Draft draft-
ietf-idmr-dvmrp-v3-07)
PIM (Protocol-Independent Multicast), Sparse Mode and Dense Mode (RFC
2362)
PIM-Sparse Mode is an approach to multicast where a single multicast tree
is shared by multiple multicast sources. This single tree is centered at a
Rendezvous Point (RP). When a PIM-SM router receives a native multicast
packet sent to a particular group, that router encapsulates the multicast
packet in a unicast packet destined for the RP. Such encapsulation is
required when:
1) There are hosts directly connected to the router (e.g. over an Ethernet
LAN)
2) When the router is at the boundary between a PIM-SM cloud and either a
DVMRP or PIM-DM cloud.
When the RP receives that packet, it decapsulates the packet and then
forwards the native multicast packet down all branches of the shared tree. In
order for the M40 to be either the encapsulating or decapsulating router, a
Tunnel PIC is needed.
SAP (Session Announcement Protocol) (Internet draft draft-ietf-mmusic-sap-
00)
SDP (Session Description Protocol) (RFC 2327)
MSDP (Multicast Source discovery Protocol)
MBGP (Multiprotocol BGP) is an extension to BGP that enables BGP to
carry routing information for multiple different network layers and address
families. This allows MBGP to carry the unicast routes that are used for
multicast routing, separately from the routes that are used for unicast IP
forwarding.
Host sends a
multicast packet
destined for a
specified
multicast group.
First hop router
encapsulates
packet with a
unicast header
Packet is forwarded
through unicast “tunnel” to
Rendezvous Point (RP)
(Tunnel
PIC)
(Tunnel
PIC)
Hosts
RP decapsulates
packet and
transmits through
the multicast
tree.