CS计算机代考程序代写 Slide 1

Slide 1

CMPT 471
Networking II

IGMP (IPv4) and MLD (IPv6)
© Janice Regan, 2006-2013

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Group Management Protocols
Internet Group Management Protocol (IGMP)
RFC 2236 IGMPv2, RFC 3376 IGMPv3
Multicast Listener Discover Protocol (MLD)
Part of ICMPv6
RFC 2710 MLDv1, RFC 3810 MLDv2
Governs exchange of multicast group information between hosts and multicast routers, and between multicast routers
IGMPv3 and MLDv2 support SFM (source filtered multicast)

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IGMPv2 (MLDv1) and IGMPv3 (MLDv2)
Three types of Messages transmitted in IP datagrams
Membership Query: sent by router to monitor group membership
Membership Report: sent by hosts to
join a group, leave a group
Update source filtering information for the host (IGMPv3 and MLDv2 only)
Reply to a membership query and indicate desire to remain a member of the group
Leave group message (IGMPv2 only)

Encapsulation IGMP
IGMP messages are sent in the IP layer
ttl for IGMP messages is 1
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IP Header

IGMP message

Encapsulation MLD

Hop by hop options header contains Router Alert Option to allow routers to receive messages sent to multicast addresses to which the router is not yet listening
MLD messages are sent with a hop count of 1 using link local addresses
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IP Header
Next Header = 0

MLD message

Hop by Hop Header
Next header = 58

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IGMP and MLD Group membership
A host can send traffic to any multicast group, group membership is not required.
A host must be a member of a multicast group to receive multicast messages from that group
A host leaves a group by sending and IGMP or MLD message indicating it is leaving the group
A host joins group by sending an IGMP or MLD message indicating it is joining the group
Details of joining and leaving groups (including details of message types) are different for IGMPv2, IGMPv3, MLDv1 and MLDv2

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IGMP and MLD Operation
Routers periodically issue query message
Sent to all-hosts multicast address ( 224.0.0.1 or FF02::1), includes records for each multicast group that has been joined by at least one host in the net
Hosts that want to stay in groups must read all-hosts query messages and respond with one or more reports
To prevent overload caused by many reports from many members on a LAN each host will be assigned a random delay before it will transmit its response.
Details of how the reports are generated and sent are dependent on the version of IGMP or MLD being used

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IGMPv2 and MLDv1 Operation: (1)
Each host receiving the query chooses the multicast groups to which belongs. For each group it is a member of the host builds a response message and

Sets a timer, (random time between 0 and maximum response time, the maximum time before a response can be sent )
Watches for response messages to the same multicast group sent by other hosts on the network.

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IGMPv2 and MLDv1 Operation:(2)
Each host receiving the query chooses the multicast groups to which belongs.
For each group it is a member of the host builds a response message and

Drops its own response message and stops its timer, if it sees a response message for the same multicast group from another host
Transmits the response when the timer expires, and no other response messages have been seen

IGMPv2 and MLDv1 messages
Begin by considering report messages MLDv1 done messages and IGMPv2 leave group messages
Report messages are used to
Maintain membership in a group
Join a group
MLDv1 done messages and IGMPv2 leave messages are used to
Leave a multicast group
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IGMPv2 report messages
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Diagram from RFC 2236
Reply to query: type 0x16 Membership Report
sent to group address in response to a membership query,
join message: type 0x16 Membership Report, sent to group address,
unsolicited, sent when host wants to join a group
Leave message: type 0x17 sent to the all routers address (224.0.0.20 when host wishes to leave the group, not always sent, must be sent by the last host to respond to a membership solicitation for the group. Group address field hold the multicast address of the group

MLDv1 Multicast listener report
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Type (131 )
Message Checksum
Multicast address of group

Type 131: response to query send to the multicast address in response to query
Type 131: join message: send to the multicast address, unsolicited
Type 132: done (leave) send to all routers multicast address (FF02::2), may not be sent if node did not reply to the last periodic query
Diagram from RFC 2710

IGMPv2 and MLD1 queries
Sent by multicast router
General query (to 224.0.0.1, or :: )
Which groups have members on attached network
Group address field and number of sources are 0
Group-specific query (to group address)
Does group have members on an attached network
Group address field contains IP address of the multicast group being queried
Send to verify if there are any remaining hosts on the network after the router receives leave msg

IGMPv2 query messages
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Diagram from RFC 2236
Checksum for all IGMPv2 messages is the ones complement of the ones complement sum of all 16 bit words in the IGMPv2 message
Membership query: type 0x11.
General query, used to learn which groups have members on the network attached to the router. Group address is 0.0.0.0. message sent to all hosts (224.0.0.1)
Group specific query: used to learn if a particular group still has members on the network attached to the router. Group address is the group being queried Sent to group being queried.

MLDv1 query
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Type (130 )
Multicast address of group

Analogous to IGMPv3 query
IPv6 all hosts address is FF02::1
:
Diagram from RFC 2710

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Joining a group
To join group, host sends either
IGMP membership report message
or MLD multicast listener report
The multicast address of the multicast group being joined is in both
the multicast address field of the IGMPv2 or MLDv1 message
the Destination Address field in the encapsulating IP header.
Router will receive report message and add the group if there are no current members of the group, or add the host to the group if there are current members.

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Leaving a group
An IGMPv2 host leaves a multicast group by sending leave group message to all-routers static multicast address (224.0.0.2). The multicast address is the leave message is the multicast address of the group being left.
An MLDv1 host leaves a multicast group by sending a multicast listener done message to the all routers multicast address (FF02::2). The multicast address in the done message is the multicast address of the group being left

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Leaving a group
If the process that joined the multicast group is terminated a leave message is also sent
When the multicast router for the network receives a leave message it determines if there are any remaining group members using group-specific query message (more about query messages later)
If there are any other hosts who are member of the multicast group the host just left they will send reports to the router and the router will know to keep the multicast group alive.

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IGMPv2, MLDv1: Keeping Lists Valid
Router does not need to know every host in a group
Needs to know at least one group member still active
Each host in group sets timer with random delay
Host that hears another claim membership cancels own report
If timer expires, host sends report
Only one member of each group reports to router

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IGMP states: 1
Consider a router with at least one host on a connected network that is a member of a particular multicast group
Every 125 seconds the router will generate a query and send it to the multicast group..
When the host receives the query it moves from member state to delaying member state, it builds its report and sets its random delay timer (random in a specified interval which defaults to 10 sec)
If it hears another report before it is due to send its own it will drop the report without sending an moves back to idle member state.
When its timer expires it sends its report and moves back to idle member state.

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IGMP states: 2
Consider a router with a connected network. No host on that connected network is a member of the multicast group. Then consider that one host on the connected network wishes to join the multicast group
The host will be in the nonmember state.
The host builds a membership report packet.
The host starts a timer and sends the membership report packet
The host moves into the delaying member state.
When the timer expires the host resends the member report packet and moves into the member state.
Sending the membership report twice (each time in a best effort UDP packet) provides a measure of security that the membership report will reach the server

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IGMPv3 and MLDv2 Operation
Each host receiving the query chooses the multicast groups it belongs to
Each host builds a response message, containing information (one record per multicast group) for all multicast groups it belongs to
Each host sets a timer for a random time (0-maximum response delay), and transmits the report when that timer expires (sent to 224.0.0.22 or FF02::16)
Responses to multiple queries may in some cases be sent as a single response. A responses to a previous query will be dropped if a response to a newer query for the same group is being scheduled
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IGMPv3 and MLDv2 messages
Begin by considering report messages
Report messages are used to
Maintain membership in a group
Join a group
Leave a group
To filter group membership accepting or rejecting traffic from certain members in the group
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Stallings 2003:

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IGMPv3 Message types
Type Number Message Name
0x11 Membership Query
0x22 V 3 Membership Report 0x16 V2 Membership Report
0x17 V2 Leave Group

Unrecognized message types are silently ignored

MLDv2 Multicast listener report
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Type (143 )
Reserved
Reserved
Checksum
Number of multicast address records
Multicast address record of group
Can be many such records one for each group

.
.
.

Sent to all MLDv2 capable routers (multicast address FF01::16

The IGMPv3 checksum the ones complement of the ones complement sum of all 16 bit words in the IP payload (the membership message)
The MLDv2 checksum also includes a pseudo-header in the calculation.

Group records each contain information about one multicast group. This information included the list of hosts to include or exclude

Stallings 2003:

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Other group record fields
Auxiliary data length should be 0, there is no auxiliary data defined for IGMP3 or MLDv2, this field is available for future expansion of the protocols

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IGMPv3 and MLDv2 group records
The number of group records included in the membership report.
When joining a single group there will be one group record
When joining multiple groups there will be one group record for each group
When responding to a query one response will be built. It will include one group record for each multicast groups.
Each group record will include a multicast address, a record type (see next slide) and may include a list of hosts to include / exclude

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Record type
Value Name
1 MODE_IS_INCLUDE
2 MODE_IS_EXCLUDE
indicates the interface filter mode for the specified multicast addresses.
3 CHANGE_TO_INCLUDE_MODE.
4 CHANGE_TO_EXCLUDE_MODE
indicates that the interface has changed filter mode
5 ALLOW_NEW_SOURCES
6 BLOCK_OLD_SOURCES
this Group Record contains a list of the sources that the system wishes to add or no longer wishes to hear from,

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IGMPv3 and MLDv2 Operation
A member host will send a report packet containing updates to its filtering information for a group as soon as the filtering information changes. This report package may modify the list of included or excluded hosts, or change from include mode to/from exclude mode.
This report can be a MLDv2 multicast listener report or IGMPv3 report containing “state change” records
“filter mode change” records that allow changes from include mode to exclude mode
“source list change” records that add new hosts to or remove existing hosts from the list of excluded or included hosts

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Joining a group: IGMPv3, MLDv2
A member host will send a report packet containing updates to its filtering information for a group as soon as the filtering information changes.
To join a group, a host sends a report message
Message is sent to multicast group address
Message contains multicast group address of group to join
The host filtering information indicates EXCLUDE mode, and specifies no host list.

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Leaving a group: IGMPv3, MLDv2
A member host will send a report packet containing updates to its filtering information for a group as soon as the filtering information changes.
To leave a group, a host sends a report message
Message is sent to multicast group address
Message contains multicast group address of group to join
The host filtering information indicates INCLUDE mode, and specifies no host list.

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IGMPv3, MLDv2: Keeping Lists Valid
Routers periodically issue general query message in a datagram with all-systems multicast address (224.0.0.1 or FF02::1)
Hosts that wish to remain in groups must read datagrams with this all-hosts address
Every host on the network that belongs to a least one of the queried multicast groups responds by preparing a report message
The report message contains one group record for every multicast group the host is a member of
The host sends the prepared report (after waiting a randomized time)

Stallings 2003:

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Membership Query Fields (1)
Max Response Time
Max time before sending report in units of 1/10 second. (>=128 indicates floating point, see RFC)
The IGMPv3 checksum the ones complement of the ones complement sum of all 16 bit words in the IP payload (the membership message)
The MLDv2 checksum also includes a pseudo-header in the calculation.
S Flag
1 indicates that receiving routers should suppress normal timer updates done on hearing query

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Membership Query Fields (2)
QRV (querier’s robustness variable)
Routers adopt value from most recently received query
A default or statically configured value used if most recently received QRV is 0
RV dictates number of retransmissions to assure report not missed (maximum 7)
QQIC (querier’s querier interval code)
Timer for sending multiple queries
Routers not current querier adopt most recently received QI
Unless QI was zero, when default QI value used
If you want to know what these are for and understand the details of how these work see RFC’s

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IGMPv3, MLDv2 Membership Queries
Sent by multicast router
General query (to 224.0.0.1, or :: )
Which groups have members on attached network
Group address field and number of sources are 0
Group-specific query (to group address)
Does group have members on an attached network
Group address field contains IP address of the multicast group being queried, number of sources is 0
Group-and-source specific query (to group address)
Do attached devices want packets sent to specified multicast address (response to leave by BLOCKing all sources)
From any of specified list of sources

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