AMT Overview

Automatic Multicast Tunneling (AMT) facilitates dynamic multicast connectivity between multicast-enabled networks across islands of unicast-only networks. Such connectivity enables service providers, content providers, and their customers to participate in delivering multicast traffic even if they lack end-to-end multicast connectivity.

AMT is supported on MX Series Ethernet Services Routers except the MX80 router and all Modular Port Concentrators (MPCs) that use the Junos Trio chipset. AMT supports graceful restart (GR) but does not support Graceful Routing Engine switchover (GRES).

AMT dynamically establishes unicast-encapsulated tunnels between well-known multicast-enabled relay points (AMT relays) and network points reachable only through unicast (AMT gateways).

The AMT protocol provides discovery and handshaking between relays and gateways to establish tunnels dynamically without requiring explicit per-tunnel configuration.

AMT relays are typically routers with native IP multicast connectivity that aggregate a potentially large number of AMT tunnels.

The Junos OS implementation supports the following AMT relay functions:

• IPv4 multicast traffic and IPv4 encapsulation
• Well-known sources located on the multicast network
• Prevention of denial-of-service attacks by quickly discarding multicast packets that are sourced through a gateway.
• Per-route replication to the full fan-out of all AMT tunnels desired
• The ability to collect normal interface statistics on AMT tunnels

Multicast sources located behind AMT gateways are not supported.

AMT supports PIM sparse mode. AMT does not support dense mode operation.