15.5.1 IPv4 multicast forwarding

(a) Operating Interface

Operation is performed on interfaces whose IP address mask length is between 8 bits and 30 bits.

(b) 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.

(c) Forwarding interruption due to restarting the routing program

Keep in mind that when the restart ipv4-multicast command is used to restart the IP multicast routing program, multicast communication is stopped until multicast routing information is relearned.

(d) Connecting to neighboring routers when using multihoming

When IPv4 multicast is used on interfaces that use multihoming, neighboring routers recognize the primary IP address. Therefore, the neighboring routers must connect to the primary IP addressnetwork.

(e) Sender Connections When Using Multihoming

When using IPv4 multicast on an interface that uses multihoming, the sender must connect to the primary IP addressnetwork.

(a) Packet loss during software forwarding

The Switch sets a multicast forwarding entry in hardware when the first multicast packet is received to perform multicast communication. Because multicast packets are forwarded in software until the multicast forwarding entry is created, some packets might be temporarily lost depending on the amount of multicast communication traffic.

(b) Duplex forwarding or packet loss during path switching

When the Switch switches from sending packets by forwarding multicast packets via a rendezvous point to sending packets via the shortest path, duplicate forwarding or packet loss might occur temporarily.

For details about how multicast packets are forwarded through the rendezvous point and how they are switched from the rendezvous point to the shortest path, see "15.4.2 IPv4 PIM-SM".

(c) Packet overtake during hardware forwarding switching

When a multicast forwarding entry is finished being set in hardware, the Switch switches from software-based multicast packet forwarding to hardware forwarding. Some packets might be overtaken at this point, causing changes in packet order.

(d) Reachability to IP addressconfigured as a rendezvous point candidate /BSR candidate

When the Switch is used as a rendezvous point or BSR, IP address of the interface that is set as a rendezvous point candidate or BSR candidate is selected as the rendezvous point and BSR address. This IP must be able to recognize and communicate unicast routes on all multicast devices.

(e) Checksum of PIM-Register message

In a system configuration that contains both the Switch and other switches, multicast communication might not be possible depending on differences in calculated checksum ranges for PIM-Register messages (encapsulation packets). If multicast forwarding is not performed due to checksum errors for Register messages on rendezvous points, use the ip pim register-checksum configuration command for the Switch to change the range for calculating PIM checksums.

(f) Static rendezvous point

Static rendezvous point functionality allows the rendezvous point to be specified without using a BSR. Static rendezvous points are set by configuration.

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.