8.3.17.0 - Force10 Networks

IGMP Version 3
Conceptually, IGMP version 3 behaves the same as version 2. However, there are differences:
• Version 3 adds the ability to filter by multicast source, which helps the multicast routing protocols
avoid forwarding traffic to subnets where there are no interested receivers.
• To enable filtering, routers must keep track of more state information, that is, the list of sources that
must be filtered. An additional query type, the group-and-source-specific query, keeps track of state
changes, while the group-specific and general queries still refresh existing state.
• Reporting is more efficient and robust. Hosts do not suppress query responses (non-suppression helps
track state and enables the immediate-leave and IGMP snooping features), state-change reports are
retransmitted to insure delivery, and a single membership report bundles multiple statements from a
single host, rather than sending an individual packet for each statement.
To accommodate these protocol enhancements, the IGMP version 3 packet structure is different from
version 2. Queries (Figure 9-2) are still sent to the all-systems address 224.0.0.1, but reports (Figure 9-3)
are sent to all the IGMP version 3-capable multicast routers address 244.0.0.22.
Figure 9-2. IGMP version 3 Membership Query Packet Format
Type
(0x11)
Code: 0x11: Membership Query
Max. Response
Code
Maximum Response Time
derived from this value
Checksum
Group Address
Reserved S Querier Robustness
Value
(2)
Bit flag that when set to
1 suppresses router query
response timer updates
Number of times that a
router or receiver transmits
a query or report to insure
that it is received
Figure 9-3. IGMP version 3 Membership Report Packet Format
Version
(4)
IHL TOS
(0xc0)
Total Length Flags Frag Offset TTL
Protocol
Header
(1)
(2)
Checksum
Querier's Query
Interval Code
Query Interval derived
from this value
Type Reserved Checksum Reserved Number of Group
Records
0x12: IGMP version 1 Membership Report
0x16: IGMP version 2 Membership Report
0x17: IGMP Leave Group
0x22: IGMP version 3 Membership Report
Src IP Addr
Dest IP Addr
(224.0.0.22)
Record Type
Options
(Router Alert)
Auxiliary Data
Length
(0)
Length of Auxiliary
Data field
Number of
Sources
Number of source addresses
to be filtered
Group Record 1
Value used by IGMP to calculate
multicast reception state
Number of
Sources
Range: 1-6
Number of source addresses
Code: 1: Current state is Include to be filtered
2: Current state is Exclude
3: State change to Include
4: State change to Exclude
5: Allow new sources and no state change
6: Block old sources and no state change
Source Addresses
Source addresses to be
filtered
Padding IGMP Packet
Group Record 2 Group Record N
Multicast Address
Group address to which
the group record pertains
Source
Addresses
Source addresses
to be filtered
Auxiliary Data
None defined in RFC 3376
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Internet Group Management Protocol (IGMP) | 109