1 cmpt 471 networking ii igmp (ipv4) and mld (ipv6) © janice regan, 2006-2013
TRANSCRIPT
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CMPT 471Networking II
IGMP (IPv4) and MLD (IPv6)
© Janice Regan, 2006-2013
© Janice Regan, 2006-2013 2
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
(ICMPv3 and MLDv2 only) Reply to a membership query and indicate desire
to remain a member of the group Leave group message (ICMPv2 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 HeaderNext Header = 0
MLD messageHop by Hop HeaderNext 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
1. Sets a timer, (random time between 0 and maximum response time, the maximum time before a response can be sent )
2. 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
3. Drops its own response message and stops its timer, if it sees a response message for the same multicast group from another host
4. 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 ICMPv2 leave group messages
Report messages are used to Maintain membership in a group Join a group
MLDv1 done messages and ICMPv2 leave messages are used to Leave a multicast group
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IGMPv2 report messages
© Janice Regan, 2006-2013 11Diagram 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, unsolicitedType 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
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IGMPv2 query messages
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Checksum for all IGMPv2 messages is the ones complement of the ones complement sum of all 16 bit words in the IGMPv2 messageMembership 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 ICMPv3 queryIPv6 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 leave 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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State machine for an entry in host's multicast route table
Comer 2000: fig 17.4
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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
© Janice Regan, 2006-2013
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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IGMPv3 Membership Report
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 groupCan be many such records one for each group
...
...
Sent to all MLDv2 capable routers (multicast address FF01::16
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membership report fields Reserved fields are filled with zeros
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
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IGMP or MLD Group Record
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 mode5 ALLOW_NEW_SOURCES6 BLOCK_OLD_SOURCESthis 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
© Janice Regan, 2006-2013
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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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ICMPv3, 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)
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Membership Query: IGMPv3 + MLDv2
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