31.4.10 IPv6 PIM-SSM

PIM-SSM is extended PIM-SM functionality. PIM-SM and PIM-SSM can run at the same time. The multicast addresses used by PIM-SSM are assigned by the IANA. The Switches allow the address range of multicast addresses (group addresses) for which PIM-SSM runs to be specified by configuration. PIM-SM runs on addresses other than those specified.

Whereas PIM-SM requires multicast forwarding packets when creating multicast entries, PIM-SSM creates IPv6 multicast forwarding entries by exchanging multicast routing information (PIM-Join), and forwards multicast packets based on the corresponding entries. Note that PIM-SSM does not require a rendezvous point or bootstrap router. This means that packet encapsulation and decapsulation are not needed when multicast packets are forwarded, enabling more efficient multicast forwarding. The Switch provides measures that enable PIM-SSM to run by using MLD.

<Structure of this section>

(1) IPv6 PIM-SSM messaging support spec

The supported specifications for IPv6 PIM-SM messages are the same as those for PIM-SM messages.

(2) Prerequisites for Running IPv6 PIM-SSM

The following settings must be specified in configuration mode for the Switch:

Settings for each switch

Set the range of group addresses for which PIM-SSM runs.
Switches directly connected to hosts running MLD

Set the addresses of the groups and the sender for which PIM-SSM runs for MLD reception.

(3) IPv6 PIM-SSM operation (when hostis MLDv1 or MLDv2(EXCLUDE)

Sender information is needed to use PIM-SSM. The Switch allows PIM-SSM to be used by setting the sender in configuration mode if MLDv1 is used.

IPv6 PIM-SSM operation is as follows when the multicast distribution server (source address S1) sends multicast packets to multicast group G1:

Hosts send an MLD Report (G1) message as a request for joining the multicast group.
The switch receiving the MLD Report message compares the group address (G1) reported in the message and the group address set in configuration mode. If these group addresses match, a PIM-Join message is sent to the source address (S1) set in configuration over the shortest path (determined by the unicast routing information). In this case, the PIM-Join message contains information about the source address (S1) and group address (G1). Each switch receiving the PIM-Join message sends it hop-by-hop to the source address (S1) over the shortest path. Switches receiving the PIM-Join message learn IPv6 multicast routing information for the source address (S1) and group address (G1).
The multicast packet distribution server (S1) sends multicast packets bound for group 1 (G1). Switches receiving multicast packets forward the packets based on the multicast forwarding entries generated by learned IPv6 multicast routing information.

The following figure provides an overview of IPv6 PIM-SSM operation.

Figure 31-18: Outline of IPv6 PIM-SSM operation (when hosted in MLDv1 or MLDv2(EXCLUDE)

(4) IPv6 PIM-SSM operation (when the host is in MLDv2(INCLUDE)

Sender information is needed to use PIM-SSM. For MLDv2, PIM-SSM can be used by specifying the sender in a Report message.

IPv6 PIM-SSM operation is as follows when the multicast distribution server (source address S1) sends multicast packets to multicast group G1:

Hosts send an MLDv2 Report (G1, S1) message as a request for joining the multicast group.
The switches receiving the MLDv2 Report (G1, S1) message send a PIM-Join message that contains the group address G1 and source address S1 that were contained in the Report message.
The switches receiving the PIM-Join message forward the message to source address S1 hop-by-hop over the shortest path. These switches form an S1-to-G1 delivery tree so that multicast packets from source address S1 are forwarded only to the interfaces from which the PIM-Join message was received.
Switches receiving multicast packets sent by multicast distribution server S1 bound for group G1 forward the multicast packets based on multicast forwarding information.

The following figure provides an overview of IPv6 PIM-SSM operation.

Figure 31-19: Outline of IPv6 PIM-SSM Operation (When Hosted in MLDv2(INCLUDE Mode)

(5) IPv6 path control when MLDv1/MLDv2 hosts are mixed

The following explains IPv6 path control operation when PIM-SSM is set to be used on MLDv1, and both MLDv1 hosts and MLDv2 hosts are used.

If a request to join a group whose address is within the PIM-SSM target address range specified in configuration mode is received, PIM-SSM is used as shown in the table below. If an MLDv1 Report message is received as a group-join request, the source addresses set in configuration mode are used as the sender list. Note, however, that both an MLDv1 Report message and an MLDv2 Report (EXCLUDE mode) message might be received as join requests for the same group address.In that case, a combination of the source addresses set in configuration mode and the sender list contained in the MLDv2 Report (INCLUDE mode) message is used as the sender list.

Table 31-12: IPv6 path control operation when MLDv1/MLDv2 hosts are mixed
Subscription group addresses	MLDv1 Report MLDv2 Report (EXCLUDE mode)	MLDv2 Report (INCLUDE mode)
Within the SSM address range	PIM-SSM	PIM-SSM
Outside the SSM address range	PIM-SM	PIM-SM

(6) Neighbor Detection

Same as PIM-SM("31.4.3 Neighbor Detection).

(7) Determining Forwarder

Same as "Determining PIM-SM("31.4.4 Forwarder").

(8) Determining and Working with DR

Same as "Determining and working with PIM-SM("31.4.5 DR").

(9) Notes on Redundant Routes

Same as PIM-SM("31.4.7 redundant route precautions.