D-Link DGS-3312SR [180/290] Ip multicast

DGS-3312SR Stackable Gigabit Layer 3 Switch

IP Multicast

ant to receive multicast transmissions need to inform nearby routers that they will

ps that have active members. The information received from

Controlling Multicast Routing on the Switch includes setting up IGMP for IP interfaces, PIM and DVMRP. This chapter

describes how to set these up. For an explanation of how these protocols function, read Appendix C.

IGMP

Computers and network devices that w

become members of a multicast group. The Internet Group Management Protocol (IGMP) is used to communicate this

information. IGMP is also used to periodically check the multicast group for members that are no longer active.

In the case where there is more than one multicast router on a subnetwork, one router is elected as the ‘querier’. This router

then keeps track of the membership of the multicast grou

IGMP is then used to determine if multicast packets should be forwarded to a given subnetwork or not. The router can

check, using IGMP, to see if there is at least one member of a multicast group on a given subnetwork. If there are no

members on a subnetwork, packets will not be forwarded to that subnetwork.

IGMP Versions 1 and 2

Multicast groups allow members to join or leave at any time. IGMP provides the method for members and multicast

routers to communicate when joining or leaving a multicast group.

IGMP version 1 is defined in RFC 1112. It has a fixed packet size and no optional data.

The format of an IGMP packet is shown below:

Figure 4- 80. IGMP Message Format

The IGMP Type codes are shown below:

Type Meaning

0x11 Membership Query (if Group Address is 0.0.0.0)

0x11 Specific Group Membership Query (if Group Address is Present)

0x16 Membership Report (version 2)

0x17 Leave a Group (version 2)

0x12 Membership Report (version 1)

Table 6- 1. IGMP Type Codes

IGMP packets enable multicast routers to keep track of the membership of multicast groups, on their respective

subnetworks. The following outlines what is communicated between a multicast router and a multicast group member

using IGMP.

A host sends an IGMP “re

uters send IGMP queries (to the all-hosts group address: 224.0.0.1) periodically to see whether any group

roup, the router assumes that there are no

port” to join a group

A host will never send a report when it wants to leave a group (for version 1).

A host will send a “leave” report when it wants to leave a group (for version 2).

Multicast ro

members exist on their subnetworks. If there is no response from a particular g

group members on the network.

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