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Configuration Guide - IP Multicast

S7700 and S9700 V200R013C00

This document describes the configurations of IP multicast, including IP multicast basics, IGMP, MLD, IPv4 PIM, IPv6 PIM, MSDP, multicast VPN, layer 3 multicast CAC, IPv4 multicast route management, IPv6 multicast route management, IGMP snooping, MLD snooping, static multicast MAC address, multicast VLAN replication, layer 2 multicast CAC, multicast network management.
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MSDP Packets

MSDP Packets

MSDP packets are encapsulated in TCP datagrams, in the format of Type Length Value (TLV), as shown in Figure 6-2.

Figure 6-2  MSDP packet format

  • Type: indicates the packet type. Table 6-1 lists types of MSDP packet.
  • Length: indicates the packet length.
  • Value: indicates the packet content, which varies depending on the packet type.
Table 6-1  Types of MSDP packet

Value

MSDP Packet Type

Function

Major Information Contained

1

Source-Active

(SA)

Carries multiple (S, G) entries and is transmitted among several RPs.

  • IP address of the source RP
  • Number of (S, G) entries contained in an SA message
  • List of active (S, G) entries in the domain

Encapsulates PIM-SM multicast data.

  • IP address of the source RP

  • PIM-SM multicast data

2

Source-Active Request

(SA-Req)

Requests (S, G) list of a specified group G to reduce the delay in joining the group.

Address of the group G

3

Source-Active Response

(SA-Resp)

Responds to SA request messages.

  • IP address of the source RP
  • Number of (S, G) entries contained in an SA-Resp message
  • List of active (S, G) entries in the domain

4

Keepalive

Maintains MSDP peer connections. Keepalive packets are sent only when no other protocol packets are exchanged between MSDP peers.

-

5

Reserved

This packet type is reserved and used as Notification messages at present.

-

6

Traceroute in Progress

Traces and detects the RPF path along which SA messages are transmitted.

  • IP address of the source RP
  • List of active (S, G) entries in the domain
  • Search ID
  • Returned search information
  • Number of hops

7

Traceroute Reply

As described in Table 6-1, SA messages carry (S, G) information and encapsulate multicast packets. MSDP peers share (S, G) information by exchanging SA messages. If an SA message contains only (S, G) information, remote users may not receive multicast data because the (S, G) entry has already timed out when reaching the remote domain. If multicast data packets are encapsulated in an SA message, remote users can still receive multicast data when the (S, G) entry times out.

When a user joins a group, the user must wait for the SA message sent from the MSDP peer in the next period because SA messages are sent periodically. To reduce the delay for the user to join the source SPT, MSDP supports SA request and response messages of Type 2 and Type 3, which enables active source information to be updated more quickly.

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Updated: 2019-04-08

Document ID: EDOC1100065742

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