Multicast for ipv6

IPv6 Multicast

©Fred Bovy EIRL 2012 1

Topics

 Multicast IPv6 Addresses
 PIM
 PIM SM
 PIM-SSM
 PIM Bidir
 Rendez-Vous point
 Static
 Anycast RP
 BSR
 MLD
 MLDv1
 MLDv2

© Fred Bovy EIRL 2012 2

Multicast. RFC 4291
128 bits
FF Flag Scope 0 Interface ID
 Scope – 4 bits
 1=node
 2=link
 R
 4=admin
 Embedded Rendez-Vous
 5=site
 RFC 3956
 8=Organization
 P  E=Global
 Multicast based unicast  6, 7, 9-D not assigned. F est reserved.
 RFC 3956 et RFC 3306
 T  Only the link-local is filtered by the routers, others must be
 0 Permanent address fitered by routers (Access-List)
 1 for temporary


Multicast IPv4 and IPv6

IP Service IPv4 Solution IPv6 Solution
Étendue d’adresse 32-bits, Class D 128 bits. 112 bits Groups
Routing PIM, MBGP, DVMRP, PIM and MBGP
MOSPF
Forwarding PIM-DM, PIM-SM, PIM- PIM-SM, PIM-SSM, PIM-
SSM, PIM-Bidir Bidir
Groups Management IGMPv1, v2, v3 MLDv1, v2
Domain Control Boundary, Border Scope
Interdomains Solutions MSDP Unic RP


PIMv6 Basics

 PIM uses the unicast routing protocol to implement the Reverse Path
Forwarding
 MP-BGP can be used to build divergent routing tables
 PIMv6 between Routers, MLD between Hosts and Routers


PIMv6 Sparse Mode Basics. RFC 4601
 The Rendez-Vous point allows Source and Receivers (listeners) to meet..
 The result is a tree shared by all sources (shared tree) toward a group of
listeners.
 Once the traffic start to flow on the Shared Tree, it is possible to switch on the
Shortest Path Tree (SPT)


The PIM Designated Router
 The 1st Hop Router, near the source is the PIMv6 Designated Router
 Elected with PIMv6 Hello Protocol
 Highest Priority
 Highest IPv6 address
 Forward traffic from the source to the RP (Register)


The MLD Querier
 The Last Hop Router is the MLD Querier
 Lowest IPv6 Address
 Discover the local Listeners and start to build a path to the RP
 A shared tree is then built from the RP to the listener


Multicast Routing Initialization

 Routers must be IPv6 Multicast Routing enabled
 PIM and MLD are started on their interfaces
 Rendez-Vous Point address MUST be configured
 Static, Embedded or
 Dynamic with BSR


PIMv6-SM: Shared Tree Initialisation

 When a listener starts to listen to a given group, it sends Unsolicited Reports
 A (*.G) entry is created in the Last Hop Router Multicast Routing Table
(MRIB)

(*,G)

(*,G)
MLD Multicast Listener Report (*,G)
Hop-by-Hop Router Alert.
Hop Limit=1


PIMv6-SM: PIM Join travel toward the RP

 Because it has a (*,G) entry in its MRIB, the Last Hop Router starts to send
PIM Join (*,G) to its Rendez-Vous Point Upstream Neighbor.
 The reception of a PIM Join (*,G) creates a (*,G) entry in the MRIB which
triggers the sending of a PIM Join (*,G) to its Rendez-Vous Point Upstream
Neighbor PIM Join (*,G)
 PIM Join reaches the RP Dest: ff02::d
Router Alert

(*,G) (*,G) (*,G)

(*,G)
MLD Multicast Listener Report (*,G)
Hop-by-Hop Router Alert.
Hop Limit=1

PIMv6-SM: Source starts to send traffic
 The source can start to send traffic at any time
 No Signaling requires


PIMv6-SM: Source Registers with the RP
 First Hop Multicast Router intercepts the Multicast flow
 Multicast traffic is encapsulated in PIM Register unicast paquets to the RP

Register


PIMv6-SM: Register at the RP
 The RP removes the unicast encapsulation of the PIM Register
 The RP duplicates (if multiple outgoing interfaces) and forwards the multicast
toward all the Listeners


PIMv6-SM: Join toward the Source
 When the RP receives multicast in Register paquets, it initializes a native
multicast path by sending a PIM Join (S,G) toward the source
 It travels hop by hop to until it reaches the first hop router

PIM Join (S,G)


PIMv6-SM: Building the Multicast Shared Tree
 When the First Hop DR receives the PIM join, it is able to forward the
multicast natively to the RP
 When the RP receives two copies of the same multicast paquet, it discards
the encapsulated copy


PIMv6-SM: Register-Stop
 … and sends a PIMv6 Register-Stop to the First Hop DR.
 The DR knows that it does not have to encapsulate the multicast traffic in
unicast anymore

Register-Stop


PIMv6-SM: Flowing down the Shared Tree
 Traffic can now travel from the Source to all the listeners using
the Shared Tree


PIMv6-SM: PIM Last-Hop Switchover to the
SPT
 Last Hop Router notices that it receives the traffic from an
interface which does not point to the best path back to the
Source (RPF).

!!!


PIMv6-SM: Last-Hop Switchover to the SPT
 Last Hop Router sends a PIMv6 Join (S,G) toward the Source

 (S,G) states are created in the MRIB by the PIMv6 Join (S,G)
travelling hop by hop to the Source

PIM JOIN (S,G)


PIMv6-SM: Building the Shortest Path Tree (SPT)
 When the DR receives the PIM JOIN (S,G), it starts to forward
paquets down the Shortest Path Tree but also down the
Shared Tree.


PIMv6-SM: Pruning the Shared Tree
 When the Last Hop router receives two copies of the same flow, it decides
to prune the Shared Tree
 It sends a (S,G,rpt-bit) Prune toward the RP

(S,G,rpt-bit) Prune


PIMv6-SM: Shortest Path Tree Only (SPT)
 When the Shortest Path Tree has been Pruned, traffic only flows on the
Shortest Path Tree
 If traffic on the Shortest Path goes down below a configurable threshold, it is
possible to switch back to the Shared Tree.


PIM-SM Summary

 Sources and Listeners meet at the Rendez-Vous point
 It is possible to stay forever on the Shared Tree to minimize the
states on the routers.
 The Rendez-Vous point must be carefully choosen on the network
 It is possible to use an Anycast Address for the RP with longest
match prefix to choose a primary.
 BSR is the only dynamic RP configuration method
 Using MLDv2 and SSM, there is no more need for a RP


Introduction to MLD

 ICMPv6 with IPv6 Hop-by-Hop Router Alert Option
 Hop Limit is 1
 On each link a Querier is elected.
 Lower IPv6 address is elected.
 The Querier sends a Query on a regular basis to ask if there any receiver
present.
I won ! 3 I am the
I am the
Querier
Querier 2
1 FE80::1 FE80::100

Query FE80::1 FF02::1

Query Interval

Host A Host B

FE80::
Query FF02::1
1

 The interval between General Query sent by the Querier.

Default: 125 seconds


Robustness

Host A Host B

State Change FE80::
FF02::1
R 1

 This is the basis for the computation of many parameters
 MLD is robust to [Variable Robustness] – 1 paquet loss
 Default: 2. MLD has no problem loosing one MLD paquet


Introduction to MLDv1

 All MLD paquets are sent with Link-Local address as source.
 Hop Limit is 1
 MLDv1 (RFC 2710) is IPv6 version of IGMP Version 2 (RFC 2236)
o Multicast Listener Query
 General Query. Sent to the all-nodes Link-Local multicast address to figure out which
group has members.
 Address-Specific Query is used to identify the members of a given group. It is sent to
the address of the group which is being queried.
o Multicast Listener Report
 Response to a Query
o Multicast Listener Done
 Sent by a Listener which does not listen to this group any more.

MLDv1 General Query

Host A Host B

FE80::
General Query FF02::1
1

 The Querier sends a general Query
 A and B starts a random timer


MLDv1 Listener Report

Host A Host B

Listener Report FE80::A FF02::1

 Host timer A expires
 Host A responds to the Query
 B listens that A replied to the router Query, stops its timer and suppress its
response not to send a duplicate response.


MLDv1 Leave Process

Host A Host B

FE80::
Done FF1E::1 FF02::2
1

 A is no longer interested by FF1E::1 and sends a Done message


MLDv1 Leave Process

Host A Host B

Address-Specific Query FE80::5 FF1E::1

 Router sends a Last Listener Query to the Multicast address left by A


MLDv1 Leave Process

Host A Host B

Report FE80::5 FF1E::1

 If B is still interested it sends a Listener Report and the router ignores the
Done message
 If B is not interested it does not send anything and the group is removed


MLDv2 (RFC 3810)

 MLDv2 is the IPv6 translation of IGMP Version 3 (RFC 3376)
 MLDv2 is backward compatible with MLDv1
 No duplicate response suppression
 No Done message
 IANA allocated FF02::16 called all MLDv2-capable routers
 MLDv2 introduced source filtering
 INCLUDE Mode : if the message includes all the source we want to ear
 EXCLUDE Mode : if the message includes all the source we don’t want to ear


Queries

 General Queries
 Sent periodically
 Responses are sent in Current State Report

 Multicast Address Specific Queries
 Multicast Address and Source Specific Queries.
 Sent after a state change.
 Sent in response to a State Change Report


Multicast Listener Reports

MLDv2 needs two types of Reports :
 Current State Change Report.
o Sent in response to a Query
o MODE_IS_INCLUDE
o MODE_IS_EXCLUDE
 State Change Report
o Sent after a state change
o Sent many times (Robustness)
o Filter Mode Change Records
• CHANGE_TO_INCLUDE
• CHANGE _TO_EXCLUDE
o Source List Change Records
• ALLOW_NEW_SOURCE
• BLOCK_OLD_SOURCES

MLDv2 Query Messages

Type = 130 Code Checksum

Maximum Response Code Reserved

Multicast Address

Resv S QRV QQIC Number of Sources (N)

Source Address [ 1 ]


Source Address [ N ]


MLDv2 Multicast Listener Report Messages

Type = 143 Code Checksum

Reserved Nr of Mcast Address Records (M)

Multicast Address Record [1]

Multicast Address Record [2]

…

Multicast Address Record [M]


MLDv2 Multicast Address Record

Record Type Aux data Len Number of Sources (N)

Multicast Address



Source Address [ N ]

Auxiliary Data


MLDv2 General Query

Host A Host B

FE80::
General Query FF02::1
1

 Sent periodically to discover which group has listener on a link
 Includes:
 Multicast Address=0,
 Number of Source=0


MLDv2 Multicast Address Specific Query

Host A Host B

FE80::
Multicast @ specific Query FF34::16 S:0 FF34::16
1

 The Querier sends this Query to ask if a particular group has Listener on a
particular interface.
 Includes:
 The address, by example: FF34::16
 Number of Source:0


MLDv2 Multicast Listener Query


MLDv2 Address and Source Specific Query

Host A Host B

FE80::
Multicast Listener Query FF34::16 S:1 FF34::16
1

 The Querier sends this message to discover if a multicast address with one
or many source addresses has a Listener on a particular interface.
 Elle contient
 The address, by example: FF34::16
 Number of Source, by example: 1


Reception of a Query

Source is valid Link-Local ? NO
Hop Limit = 1 ? DROP
Router Alert set in the Hop-
by-Hop Option ?

YES

Process the Query.
Wait before the Response. Delay max= Maximum Response Delay

MLDv2 State Change Report

Host A Host B

State Change FE80::
FF02::1
Report 1

 The State Change Report contains a change:
 Filter Change Report
 Source List Change Report
 Both Change Report
 Reports are sent robustness times on the link
 Default Robustness: 2


MLDv2 State Change Report Exemple
Internet Protocol Version 6
0110 .... = Version: 6
.... 1110 0000 .... .... .... .... .... = Traffic class: 0x000000e0
.... .... .... 0000 0000 0000 0000 0000 = Flowlabel: 0x00000000
Payload length: 52
Next header: IPv6 hop-by-hop option (0x00)
Hop limit: 1
Source: fe80::38b1:e73c:c0f0:4442 (fe80::38b1:e73c:c0f0:4442)
Destination: ff02::16 (ff02::16)
Hop-by-Hop Option
Next header: ICMPv6 (0x3a)
Length: 0 (8 bytes)
Router alert: MLD (4 bytes)
PadN: 2 bytes
Internet Control Message Protocol v6
Type: 143 (Multicast Listener Report Message v2)
Code: 0 (Should always be zero)
Checksum: 0x50d2 [correct]
Allow new sources: ff34::16 (ff34::16)
Mode: Allow new sources
Aux data len: 0
Multicast Address: ff34::16
Source Address: 2001:db8:cafe::7 (2001:db8:cafe::7)

PIM-SSM

 With PIM-SSM the Listener must provide the Source address.
 Rendez-Vous point are no more needed.
 The source can be configured statically
 The source can be learned from DNS with the Record G
 PIM-SSM is supported with MLDv2

 RFC 3306. Unicast-Prefix-based IPv6 Multicast
Flags: 00PT. P=1, T=1
plen = 0
network prefix = 0
FF3x::/96
x=n’importe quel scope valide

Rendez-Vous Point

 Static
 Must be manually configured on each multicast router
 Anycast RP
 Static but the same address is configured many time with different mask length
 Longest match select the preferred RP
 Embedded RP
 RP address is embedded in the Multicast Group
 Dynamic with PIM BSR
 BSR is a dynamic protocol which allow the Rendez-vous point automatic configuration.


Anycast RP + Longest Match

 RP1 is preferred because routing prefers the longest match

RP1: RP2:
2001:db8:1::1/64 2001:db8:1::1/63


Embedded RP – RFC 3956

 The RP address can be embedded in the Multicast
Group


Embedded RP – Flags

FF76:0130:2001:db8:9abc::4321

Flags: 7
R: Rendez-Vous Point = 1 then
P: Prefix =1 and
T: Temporary Prefix = 1


Embedded RP – Prefix

FF76:0130:2001:db8:9abc::4321

Plen = 30 Hex = 48 dec
2001:db8:9abc::


Embedded RP – Adresse du RP

FF76:0130:2001:db8:9abc::4321

Rendez-Vous Point Address
2001:db8:9abc::1

o RFC3956


PIM Boot Strap Router

 Many routers are Candidates BSR (C-BSR).
 The C-BSR elect a BSR by sending C-BSR message with priorities
 The message travels hop by hop.
 The C-BSR with the best priority becomes the BSR
 During the election it announces its presence on the network.
 This is similar to the election of the root of the spanning-tree.
 Some routers are configured as Candidates RP (C-RP).
 C-RP unicast their presence of C-RP to the C-BSR.
 The C-BSR sends its list of C-RP to all the PIM routers
 All the PIM routers receive the list of C-RP and execute the same hashing
function to choose a RP for each group.


Books on the Web: Safari Books Online


REFERENCES


Multicast for ipv6

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