31.5.4 Notes on Network Configuration

(a) Application configuration

If IPv6 PIM-SM or IPv6 PIM-SSM (abbreviated hereafter to PIM) is used, PIM must be set up on all routers existing on the paths from the sender to receivers. If there is a router on which PIM is not set up on a path, multicast packets can be forwarded no further. If PIM is not set up on neighboring routers, packet forwarding becomes possible by executing the ipv6 pim direct configuration command.

Figure 31-27: Example of application when a configuration command ipv6 pim direct is set is an example of application when a configuration command ipv6 pim direct is set. Router A and the Switch do not communicate via PIM because they belong to different multicast domains. In this example, sender S in domain X wants to send multicast data to the receivers in domain Y. However, Router A and the Switch do not communicate via PIM, so the multicast data sent by Sender S is discarded at the Switch. In such situations, if the ipv6 pim direct configuration command is used to set sender S for interface I of the Switch, multicast packets can be forwarded inside of domain Y.

Figure 31-27: Example of application when setting a configuration command ipv6 pim direct

The ipv6 pim direct configuration command is applicable to configurations such as the one shown in the above figure.If the command is used in other configurations, forwarding multicast packets might no longer be possible.

(b) Configuration that requires attention

Use caution if using IPv6 PIM-SM or IPv6 PIM-SSM in the following configurations:

• In a configuration such as the one in the figure below, multiple routers directly connect on the host on the same network. For such configurations, make sure that PIM-SM always runs at the interface.

  If only MLD runs and PIM-SM does not run at an interface on which multiple routers exist on the same network, multicast data might be forwarded twice.

  Figure 31-28: Configuration requiring attention (connection between multiple routers and hosts)

• In a configuration, such as the one in the figure below, in which the PIM protocol cannot detect the upstream router, multicast communication cannot be performed. This is because the environment has a static route for which the virtual interface set as the gateway has VRRP set by Switch C for Switch A and for Switch B. (This also applies when PIM-SSM is used.)

  To perform multicast communication in this configuration, a static route needs to be set for Switch C, with the real address of Switch A or Switch B used as the gateway address to the rendezvous point address, BSR address, and multicast data source address.

  Figure 31-29: Configuration that requires your attention (if you set up a VRRP)

• When multicast forwarding is performed without using PIM-SM/PIM-SSM protocol with a router on a different domain, the interface with that router is called PIM unconnected interface.

  As shown in the figure below, when multicast packets are forwarded by multicasting from Server S in a different domain over a non-PIM connection interface, the following settings must be specified:

  • On Router 2 connected downstream to the Switch, set a unicast route to Server S.

  • For the non-PIM connection interface of the Switch, set the ipv6 pim direct configuration command.

    Figure 31-30: Configuration requiring attention (forwarding through PIM unconnected interfaces)

• As shown in the following figure, the following settings are required when multicast packets sent from Server S on different domains in the upstream VPN1 (global network) are forwarded to VPN2(VRF20 through a PIM unconnected interface. [SL-L3A]

  • For the non-PIM connection interface of the Switch in the upstream VRF, set the ipv6 pim direct configuration command. In addition, configure an IPv6 multicast extranet, and then set a unicast route to Server S in the forwarding destination VRF of the Switch.

  • On the downstream router (Router 2) in the forwarding destination VPN, set a unicast route to Server S.

    Figure 31-31: Configuration requiring attention (forwarding through an PIM unconnected interface in an extranet)

(a) Recommended configuration

We recommend network configurations based on IPv6 PIM-SM for hierarchical network configurations and configurations with redundant routes. However, special care is needed for the placement of the rendezvous point. We recommend that the rendezvous point be as close as possible to the sender to reduce the processing load needed to change the IPv6 multicast sending path when the IPv6 PIM-SM mode is changed.

The following figure shows a recommended network configuration for IPv6 PIM-SM.

Figure 31-32: IPv6 PIM-SM recommended networking configuration

(b) Inappropriate configuration

Do not use IPv6 PIM-SM for configurations such as the following:

• Configuration in which a recipient exists between the sender and rendezvous point

  When IPv6 multicast communication with group 1 is performed from the server in the following configuration, forwarding via the rendezvous point cannot be done efficiently.

  Figure 31-33: Non-adaptive configuration (when there is a receiver between the sender and the rendezvous point)

(a) Configuration that requires attention

Use caution when using IPv6 PIM-SSM in the following configurations:

• Configuration in which multiple IPv6 PIM-SSM routers are running on the same line as the IPv6 multicast group (receiver)

  To operate PIM-SSM in the following configurations (MLDv1 or MLDv2(EXCLUDE), set the configuration command ipv6 pim ssm and ipv6 mld ssm-map static for all routers on the same line.

  Figure 31-34: Configuration requiring attention (connection between multiple routers and hosts)

(b) Notes on setting multiple addresses on the terminal side

Care is needed if multiple IPv6 addresses are assigned to a terminal that sends data by SSM communication. Accordingly, make sure that the sender address of the send data matches the sender address information set on the Switch by using the ipv6 mld ssm-map static configuration command. These addresses might not match when, for example, the RA automatic address setting function is used, in which case the terminal performs communication by using the automatically set address.

(a) Configuration that requires attention

The following configuration needs special attention:

• In an IPv6 multicast extranet that uses PIM-SM VRF gateways, if two or more VRF border routers are used to create a redundant configuration, make sure that one of the VRF border routers is set as the rendezvous point.

  If the rendezvous point is not a VRF border router, each VRF border router forwards the same IPv6 multicast packets until the shortest-path delivery tree is generated.

  The following figure shows an example configuration which uses PIM-SM VRF gateways and forwards the same encapsulated packets twice.

  Figure 31-35: Configuration requiring attention (when two or more VRF border routers are used to construct a redundant configuration)