HP 5920 series Configuration Manual page 124

RPF check implementation in IPv6 multicast
Implementing an RPF check on each received IPv6 multicast packet would heavily burden the router. The
use of an IPv6 multicast forwarding table is the solution to this issue. When the router creates an IPv6
multicast routing entry and an IPv6 multicast forwarding entry for an IPv6 multicast packet, it sets the RPF
interface of the packet as the incoming interface of the forwarding entry. After the router receives an IPv6
multicast packet, it searches its IPv6 multicast forwarding table:
• If no forwarding entry matches the packet, the packet undergoes an RPF check. The router creates
an IPv6 multicast routing entry with the RPF interface as the incoming interface and installs the entry
into the IPv6 multicast forwarding table.
If the interface that received the packet is the RPF interface, the RPF check succeeds and the
router forwards the packet out of all outgoing interfaces.
If the interface that received the packet is not the RPF interface, the RPF check fails and the
router discards the packet.
If a forwarding entry matches the packet, and the interface that received the packet is the incoming
•
interface of the forwarding entry, the router forwards the packet out of all outgoing interfaces.
If a forwarding entry matches the packet, but the interface that received the packet is not the
•
incoming interface of the forwarding entry, the IPv6 multicast packet undergoes an RPF check.
If the RPF interface is the incoming interface, it indicates that the forwarding entry is correct but
the packet traveled along a wrong path. The router discards the packet.
If the RPF interface is not the incoming interface, it indicates that the forwarding entry has
expired, and the router replaces the incoming interface with the RPF interface. If the interface
that received the packet is the RPF interface, the router forwards the packet out of all outgoing
interfaces. Otherwise, it discards the packet.
Figure 39 RPF check process
IPv6 Routing Table on Switch C
Destination/Prefix
2000::/16
Source
2000::101/16
As shown in
packets travel along the SPT from the multicast source to the receivers. The IPv6 multicast forwarding table
on Switch C contains the (S, G) entry, with Vlan-interface 20 as the RPF interface.
When Vlan-interface 20 of Switch C receives an IPv6 multicast packet, because the interface is the
•
incoming interface of the (S, G) entry, the router forwards the packet out of all outgoing interfaces.
When Vlan-interface 10 of Switch C receives an IPv6 multicast packet, because the interface is not
•
the incoming interface of the (S, G) entry, the router performs an RPF check on the packet. The router
Interface
Vlan-int20
Switch A
IPv6 Multicast packets
Figure 39, assume that IPv6 unicast routes are available in the network, and IPv6 multicast
Switch B
Vlan-int10
Vlan-int10
Vlan-int20
Switch C
117
Receiver
Receiver