31.5.1 IPv6 multicast forwarding

(a) Forwarding interruption due to restarting the routing program

For the Switch, when the restart ipv6-multicast command is used to restart the IPv6 multicast routing program, IPv6 multicast communication is stopped until multicast path information is relearned.

(b) Point-to-point line

To perform IPv6 multicast communication using a point-to-point line for which a unicast static route has been set, explicitly specify the destination address (gateway specification).

(c) Packet overtaking by timing

When the Switch receives multicast data from a sender and a PIM-Join message from the receiver at the same time, some packets might overtake others due to timing, causing the order of the packets to be switched.

(a) Packet loss during software forwarding

When the Switch receives the first IPv6 multicast packet, it sets an IPv6 multicast forwarding entry in hardware so that the forwarding of IPv6 multicast packets is performed by hardware. Note, however, that because software performs the forwarding until the entry has been created in hardware, some packets might be temporarily lost.

(b) Packet overtake during hardware forwarding switching

The Switch stops forwarding IPv6 multicast packets by software, and starts forwarding IPv6 multicast packets by hardware, when an IPv6 multicast forwarding entry has been set in hardware. Some packets might be overtaken at this point, causing the order of packets to change.

(c) Duplex forwarding or packet loss during path switching

In the Switch, duplicate forwarding or packet loss might occur temporarily during forwarding of IPv6 multicast packets via the rendezvous point or during a switchover from forwarding via the rendezvous point to forwarding over the shortest path.

For details about forwarding IPv6 multicast packets through the rendezvous point and switching from the rendezvous point to the shortest path, see 31.4.2 IPv6 PIM-SM.

(d) Address setting to loopback interface required

When the Switch is used as a first-hop-router, IPv6 addressset for the loopback interface is used for communication to the rendezvous point. For this reason, IPv6 PIM-SM requires addressing to the loopback interface, unlike IPv4 PIM-SM, even if it is not a rendezvous point or BSR.

(e) Reachability to the address configured on the loopback interface

When the Switch is used as a rendezvous point and BSR, IPv6 address set for the loopback interface becomes the address of the rendezvous point and BSR. This address must be able to recognize and communicate unicast routes on all devices that IPv6 communicate with multicast.

(f) Static rendezvous point

Static rendezvous point functionality allows the rendezvous point to be specified without using a BSR. The static rendezvous point is set in configuration mode.

The static rendezvous point can also exist with rendezvous point candidates advertised by Bootstrap messages from a BSR. In that case, the static rendezvous point is given priority over the rendezvous point candidates advertised by Bootstrap messages from a BSR.

If a rendezvous point candidate router recognizes that its local address is the rendezvous point router address, the router functions as the rendezvous point. Therefore, if a network using the static rendezvous point is designed without using a BSR, the static rendezvous point settings must also be specified on all rendezvous point candidate routers.

Also, if the static rendezvous point is used, the same settings need to be specified for all routers on the same network.