Igmp Version 3 - Dell Force10 MXL Blade Configuration Manual

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
are sent to all the IGMP version 3-capable multicast routers address 244.0.0.22.
Figure 12-2. IGMP version 3 Membership Query Packet Format
Type Max. Response
Code
(0x11)
Maximum Response Time
derived from this value
Code: 0x11: Membership Query
Figure 12-3. IGMP version 3 Membership Report Packet Format
Version IHL TOS
Total Length
(4) (0xc0)
(Figure 12-2) are still sent to the all-systems address 224.0.0.1, but reports
Group Address
Checksum
Flags TTL Protocol
Frag Offset
(1) (2)
Type
0x12: IGMP version 1 Membership Report
0x16: IGMP version 2 Membership Report
0x17: IGMP Leave Group
0x22: IGMP version 3 Membership Report
Reserved S Querier Robustness Querier's Query
Value Interval Code
(2)
Query Interval derived
Bit flag that when set to
from this value
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
Src IP Addr Dest IP Addr
Header Options
Checksum (224.0.0.22) (Router Alert)
Reserved Checksum Reserved Number of Group
Auxiliary Data
Record Type
Length of Auxiliary
Data field
Range: 1-6
Code: 1: Current state is Include
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
Internet Group Management Protocol (IGMP) | 213
Source Addresses
Number of
Sources
Source addresses to be
filtered
Number of source addresses
to be filtered
IGMP Packet
Padding
Group Record 1 Group Record 2 Group Record N
Records
Value used by IGMP to calculate
multicast reception state
Number of Multicast Address Source
Length
Sources Addresses
(0)
Group address to which
the group record pertains
Number of source addresses Source addresses
to be filtered to be filtered
(Figure 12-3)
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Auxiliary Data
None defined in RFC 3376
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