Application Of Gre Tunnel In Multicast Forwarding; Multicast Traceroute - HP A6600 Configuration Manual

static route on Router C and Router D, specifying Router B as the RPF neighbor of Router C and specifying
Router C as the RPF neighbor of Router D, the receivers can receive multicast data that the multicast
source sent.
A multicast static route only affects RPF check; it cannot guide multicast forwarding. Therefore, a multicast
static route is also called an "RPF static route".
A multicast static route is effective only on the multicast router on which it is configured, and will not be
advertised throughout the network or redistributed to other routers.

Application of GRE tunnel in multicast forwarding

Some networking devices might not support multicast protocols in a network. Multicast devices forward
multicast traffic from a multicast source hop by hop along the forwarding tree. When the multicast traffic
is forwarded to a next-hop device that does not support IP multicast, the forwarding path is blocked. In
this case, you can enable multicast traffic forwarding across the unicast subnet where the
non-multicast-capable device resides by establishing a GRE tunnel between the devices at both ends of
the unicast subnet.
For more information about GRE tunneling, see Layer 3—IP Services Configuration Guide.
Figure 21 Multicast data transmission through a GRE tunnel
Multicast router
Source Router A
As shown in
encapsulates multicast data in unicast IP packets, which unicast routers then forward to Router B across
the GRE tunnel. Then, Router B strips off the unicast IP header and continues to forward the multicast data
down toward the receivers.
If unicast static routes are configured across the tunnel, any unicast packet can be transmitted through the
tunnel. If you want to dedicate this tunnel to multicast traffic delivery, you can configure only a multicast
static route across the tunnel, so that only multicast packets are transmitted through this tunnel.

Multicast traceroute

The multicast traceroute utility traces the path that a multicast stream flows down from the first-hop router
to the last-hop router.
Concepts in multicast traceroute
Last-hop router—If one of the interfaces of a router connects to the subnet that contains the given
•
destination address, and if the router can forward multicast streams from the given multicast source
onto that subnet, that router is called the "last-hop router".
Unicast router
GRE tunnel
Unicast router
Figure 21, with a GRE tunnel established between Router A and Router B, Router A
Unicast router
Multicast router
Router B
Unicast router
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Receiver