Multicast for IPv6

IPv6 Multicast

©Fred Bovy EIRL 2012 1

Topics

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

© Fred Bovy EIRL 2012 2

Multicast. RFC 4291
128 bits

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

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


PIMv6 Sparse Mode Basics. RFC 4601
n  The Rendez-Vous point allows Source and Receivers (listeners) to meet..
n  The result is a tree shared by all sources (shared tree) toward a group of
listeners.
n  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
n  The 1st Hop Router, near the source is the PIMv6 Designated Router
n  Elected with PIMv6 Hello Protocol
n  Highest Priority
n  Highest IPv6 address
n  Forward traffic from the source to the RP (Register)


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


Multicast Routing Initialization

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


PIMv6-SM: Shared Tree Initialisation

n  When a listener starts to listen to a given group, it sends Unsolicited Reports
n  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

n  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.
n  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)
n  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

n  The source can start to send traffic at any time
n  No Signaling requires


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

Register


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


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

PIM Join (S,G)


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


PIMv6-SM: Register-Stop
n  … and sends a PIMv6 Register-Stop to the First Hop DR.
n  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
n  Traffic can now travel from the Source to all the listeners using
the Shared Tree


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

(S,G,rpt-bit) Prune


PIMv6-SM: Shortest Path Tree Only (SPT)
n  When the Shortest Path Tree has been Pruned, traffic only flows on the
Shortest Path Tree
n  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

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


Introduction to MLD

n  ICMPv6 with IPv6 Hop-by-Hop Router Alert Option
n  Hop Limit is 1
n  On each link a Querier is elected.
§  Lower IPv6 address is elected.
n  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

Query FE80::1 FF02::1

z  The interval between General Query sent by the Querier.

Default: 125 seconds


Robustness

Host A Host B

State Change R FE80::1 FF02::1

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


Introduction to MLDv1

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

MLDv1 General Query

Host A Host B

General Query FE80::1 FF02::1

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


MLDv1 Listener Report

Host A Host B

Listener Report FE80::A FF02::1

n  Host timer A expires
n  Host A responds to the Query
n  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

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

n  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

n  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

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


MLDv2 (RFC 3810)

n  MLDv2 is the IPv6 translation of IGMP Version 2 (RFC 3376)
n  MLDv2 is backward compatible with MLDv1
n  No duplicate response suppression
n  No Done message
n  IANA allocated FF02::16 called all MLDv2-capable routers
n  MLDv2 introduced source filtering
n  INCLUDE Mode : if the message includes all the source we want to ear
n  EXCLUDE Mode : if the message includes all the source we don’t want to ear


Queries

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

¥ Multicast Address Specific Queries
¥ Multicast Address and Source Specific Queries.
Ø  Sent after a state change.
Ø  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

General Query FE80::1 FF02::1

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


MLDv2 Multicast Address Specific Query

Host A Host B

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

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


MLDv2 Multicast Listener Query

Ethernet II, Src: ca:01:3a:67:00:08 (ca:01:3a:67:00:08), Dst: IPv6mcast_00:00:00:16 (33:33:00:00:00:16)
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::2038:148e:b9df:fd6d (fe80::2038:148e:b9df:fd6d)
Destination: ff34::16 (ff34::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: 130 (Multicast listener query)
Code: 0
Checksum: 0x9549 [correct]
Maximum response delay[ms]: 1000
Multicast Address: ff34::16
S Flag: OFF
Robustness: 2
QQI: 125
Source Address: 2001:db8:cafe::7 (2001:db8:cafe::7)


MLDv2 Address and Source Specific Query

Host A Host B

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

n  The Querier sends this message to discover if a multicast address with one
or many source addresses has a Listener on a particular interface.
n  Elle contient
n  The address, by example: FF34::16
n  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::1 FF02::1
Report

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

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

n  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

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


Anycast RP + Longest Match

n  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

n  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

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