Chapter 4: Web configuration
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NS3552-8P-2S-V2 User Manual
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:
IGMP message format
Octets:
0
8
16
31
Type
Response Time
Checksum
Group Address (all zeros if this is a query)
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)
IGMP packets allow multicast routers to keep track of the membership of multicast
groups on their respective sub networks. The following outlines what is communicated
between a multicast router and a multicast group member using IGMP.
• A host sends an IGMP “report” 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 routers send IGMP queries (to the all-hosts group address: 224.0.0.1)
periodically to see whether any group members exist on their sub networks. If there is
no response from a particular group, the router assumes that there are no group
members on the network.
The Time-to-Live (TTL) field of query messages is set to 1 so that the queries will not
be forwarded to other sub networks.
IGMP version 2 introduces some enhancements such as a method to elect a multicast
queried for each LAN, an explicit leave message, and query messages that are specific
to a given group.
The states a computer will go through to join or to leave a multicast group are as
follows:
Summary of Contents for NS3552-8P-2S-V2
Page 1: ...NS3552 8P 2S V2 User Manual P N 1073552 EN REV B ISS 25JAN19 ...
Page 41: ...Chapter 3 Switch management NS3552 8P 2S V2 User Manual 39 ...
Page 73: ...Chapter 4 Web configuration NS3552 8P 2S V2 User Manual 71 ...
Page 147: ...Chapter 4 Web configuration NS3552 8P 2S V2 User Manual 145 ...
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