PIMv2 Register Message Format
Register messages, the format of which is illustrated in Figure 5-64, used only by PIM-SM, are unicast from the source's DR to the RP, and they carry the initial multicast packets from the source. That is, Register messages are used to tunnel multicast traffic from the source to the RP when an SPT has not yet been established from the source's DR to the RP.
Figure 5-64 The PIMv2 Register Message Format \
32 bits
Version Type = 1
Reserved
Checksum
Reserved
Multicast Data Packet
The fields for the PIMv2 Register message are defined as follows:
• Checksum, in Register messages, is calculated only on the message header. The data packet portion is excluded.
• B is the Border bit. The bit is set to 0 if the originator is a DR with a directly connected source. The bit is set to 1 if the source is a PIM Multicast Border Router (PMBR). PMBRs, and other interdomain multicast issues, are discussed in Chapter 7.
• N is the Null-Register bit. A DR that is probing the RP before expiring its local Register-Suppression timer sets this bit to 1.
• Multicast Data Packet is a single packet from the source that is being tunneled to the RP in the Register message.
Continue reading here: PIMv2 Bootstrap Message Format
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