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CLI-based Configuration Guide - IP Multicast

AR100, AR120, AR160, AR1200, AR2200, AR3200, and AR3600 V300R003

This document provides the basic concepts, configuration procedures, and configuration examples of the interfaces supported by the device.
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MSDP Packets

MSDP Packets

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

Figure 6-2  Format of MSDP packets

  • Type: indicates the packet type. Table 6-1 lists types of MSDP packets.
  • Length: indicates the packet length.
  • Value: indicates the packet content that depends on the packet type.
Table 6-1  Types of MSDP packets

Value

MSDP Packet Type

Function

Major Information Contained

1

Source-Active

(SA)

Carries multiple groups of (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)

Actively requests (S, G) list of a specified group G to reduce the delay for 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. The Keepalive packet is sent only when no other protocol packet is 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 new user joins the group, the user must wait for the SA message sent by the MSDP peer in the next period because SA messages are sent periodically. To reduce the delay for the new user to join the source SPT, MSDP supports SA request and response messages of Type 2 and Type 3 to improve the update efficiency of active source information.

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Updated: 2019-03-06

Document ID: EDOC1100069332

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