Stateless Multicast with - clnv.s3.amazonaws.com · Stateless Multicast with Bit Indexed Explicit Replication IJsbrand Wijnands, Distinguished Engineer LTRIPM-3001

Stateless Multicast withBit Indexed Explicit Replication

IJsbrand Wijnands, Distinguished Engineer

LTRIPM-3001

© 2018 Cisco and/or its affiliates. All rights reserved. Cisco Public

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How

cs.co/ciscolivebot#LTRIPM-3001

• Introduction

• Solution Overview

• Encapsulation

• Sets and Areas

• Forwarding

• ECMP

• BIER Overlay

• Deployment Scenarios

• Conclusion

Agenda

Introduction


BIER history

• A team was formed to investigate solutions for multicast in the context of Segment Routing.

• Encoding a Sourced routed Multicast tree path using MPLS labels is difficult.

• The packet header would get very large, and its very hard to parse such header.

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© 2016 Cisco and/or its affiliates. All rights reserved. Cisco PublicLTRIPM-3001 7


The BIER Epiphany

• Only encode the end-receivers (as a Bit Position) in the packet header.

• Not the intermediate nodes.

• Encode the Bit String in the packet header.

• Using some sort of encapsulation.

• Create a Bit Forwarding Table on all BIER nodes to allow multicast packet forwarding using the Bit String in the packet.

• Derived from the RIB, SPF based.

• We call it, Bit Indexed Explicit Replication (BIER).

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IETF

• The BIER idea was presented in a BOF at the IETF in Hawaii.

• November 2014.

• A new BIER Working Group has been formed ([email protected])

• Vendors collaborating (co-authoring) with us;

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IETF drafts

• draft-ietf-bier-problem-statement

• draft-ietf-bier-architecture (now rfc8279)

• draft-ietf-bier-encapsulation-mpls (now rfc8296)

• draft-ietf-bier-use-cases

• draft-ietf-l3vpn-mvpn-bier

• draft-ietf-ospf-bier-extensions

• draft-ietf-bier-isis-extensions

• draft-xu-idr-bier-extensions

10LTRIPM-3001

Solution Overview


What is the problem with Multicast

• Each Tree has its own unique receiver population.

• To efficiently forward/replicate there is a Tree per flow!

• This means State is created in the network.

12LTRIPM-3001

S1

S2

S3

S4

S5


Multicast Routing State

• State is created in the network using a Multicast routing protocol like PIM, mLDP, RSVP-TE.

• State means resources consumed, memory/CPU.

• Convergence is impacted by the amount of State.

• In order to manage the network, the protocol needs to be understood by the network operator.

• Different levels of complexity based on protocol choice.

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What is BIER

• BIER is a new forwarding paradigm to forward and replication multicast packets through the network.

• Packets are forwarded using a special Header that is embedded into the packet.

• Routers build a special forwarding table to forward/replicate using the BIER header.

• BIER forwarding is State Less!

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How does BIER work

• We give the Egress routers an identifier.

• The Ingress router includes the “identifiers in the packet.

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1, 2, 3, 4

1

2

3

4

Egress

Ingress

IP Mcast


How does BIER work

• Packet is forwarded hop-by-hop using the “identifier”

• Each “identifier” is forwarded along the unicast (SPF) path.

16LTRIPM-3001

1, 2, 3, 4

1

2

3

4

Egress

Ingress

IP Mcast

IP Mcast

IP Mcast

IP Mcast

IP Mcast


How does BIER work

• The smaller the identifier, the more we can fit into a single packet, how small can an identifier be?

• A single Bit!!!

• With BIER the Egress Identifier is a Bit Position.

• We include a BitString of 256 bits into the packet.

• Manipulations of a BitString is much easier compared to including a list of numbers.

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How does BIER work

• Each Egress BIER router has a unique Bit Position.

• Routers maintain a forwarding table of Bitmask's

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1111

0001

Egress

Ingress

IP Mcast

IP Mcast

IP Mcast

IP Mcast

IP Mcast

0010

0100

1000

BIER Fwd TBL

Nbr BM

E 0011

F 1100

E

F


Bit Index Forwarding Table

• Based on shortest path route to RID, the Bit Mask Forwarding Table is created

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CA B

D

FE

BM Nbr

0111 B

BM Nbr

0011 C

0100 E

BM Nbr

0001 D

0010 F

BFR-ID 1

BS:0001

BM Nbr

0011 C

B

BM-ER

BM-ERBM-ER

BFR-ID 2

BS:0010BFR-ID 3

BS:0100


Forwarding Packets

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CA B

D

FE

BM Nbr

0111 B

BM Nbr

0011 C

0100 E

BM Nbr

0001 D

0010 F

00010001

AND ANDAND

0001

&0011&0111 &0001

BFR-ID 1

BS:0001

BFR-ID 2

BS:0010BFR-ID 3

BS:0100

Nbr

0011 C

B

Suppose A leans about D’s interest,

in the blue multicast flow.

(via BGP, SDN, STATIC, etc…)


Forwarding Packets

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A CA B

D

FE

Nbr

0111 B

Nbr

0011 C

0100 E

Nbr

0001 D

0010 F

00010101

AND ANDAND

0101

&0011&0111 &0001

&0100

AND

BFR-ID 1

BS:0001

BFR-ID 2

BS:0010BFR-ID 3

BS:0100

Nbr

0011 C

B

Suppose A leans about D and E’s interest,




Forwarding Packets

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A CA B

D

FE

Nbr

0111 B

Nbr

0011 C

0100 E

Nbr

0001 D

0010 F

00110111

AND ANDAND

0111

Nbr

0011 C

B

&0011&0111 &0001

&0100 &0010

AND

BFR-ID 1

BS:0001

BFR-ID 2

BS:0010BFR-ID 3

BS:0100

Suppose A leans about D, E and F’s interest,




Forwarding Packets

• As you can see from the previous slides, the result from the bitwise AND (&) between the Bit Mask in the packet and the Forwarding table is copied in the packet for each neighbor.

• This is the key mechanism to prevent duplication.

• Look at the next slide to see what happens if the bits are not reset

• If the previous bits would not have been reset, E would forward the packet to C and vice versa.

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Forwarding Packets

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A CA B

D

FE

Nbr

0111 B

Nbr

0011 C

0100 E

Nbr

0001 D

0010 F

01110111

AND ANDAND

0111

Nbr

0011 C

B

&0011&0111

&0100

AND

0111

BFR-ID 1

BS:0001

BFR-ID 2

BS:0010BFR-ID 3

BS:0100

Encapsulation


How many Bits and Where?

• The number of multicast egress routers that can be addressed is depending on the number of Bits that can be included in the BitString

• The BitString length is dependent on the encapsulation type and router platform.

• We’ve analyzed the MPLS option, CRS, ASR1K and ASR9K platform.

• Both these platforms can do 256 bits.

• Other vendors confirmed they can do 256.

• We identified 5 different encoding options, most attractive below;

1. MPLS, below the bottom label and before IP header.

2. IPv6, extensions header.

26LTRIPM-3001


MPLS encapsulation

• The Top Label is allocated by BIER from the downstream platform label space.

• The BIER Header follows directly below the BIER label.

• There is a single BIER label on top, unless the packet is re-encapsulated into a unicast MPLS tunnel.

• The VPN label is allocated from the upstream context label space (optional).

27LTRIPM-3001

BIER Label BIER Header VPN Label Payload

MPLS Label IPv4/IPv6/L2Upstream Label

(optional)

BIER header

EO

S

EO

S


BIER Header

• http://www.ietf.org/id/draft-ietf-bier-mpls-encapsulation-01.txt

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0 1 2 3

0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1

+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+

|0 1 0 1| Ver | Len | Entropy |

+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+

| BitString (first 32 bits) ~

+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+

~ ~

+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+

~ BitString (last 32 bits) |

+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+

|OAM| Reserved | Proto | BFIR-id |

+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+

256bits = 32bytes

Sets and Areas


BIER Sets

• To increase the scale we group the egress routers in Sets.

30LTRIPM-3001

I

A

G B

1:0001

C

D

E

F

H

1:0010

1:0100

2:0001

2:0010

2:0100

Set 1

Set 2

1:0111

2:0111

Set BM Nbr

1 0111 I

2 0111 I

Note, Bit Positions 1,2,3

appear in both Sets, and

do not overlap due to Sets.

Note, we create different

forwarding entries for each Set

J


BIER Sets

• There is no topological restriction which set an egress belongs to

31LTRIPM-3001

I

A

G B

1:0001

C

D

E

F

H

1:0010

2:0001

1:0100

2:0010

2:0100

Set 1

Set 2

1:0111

2:0111

Note, we create different

forwarding entries for each Set

J

Set 2

Set 1Set BM Nbr

1 0111 I

2 0111 I


BIER Sets

• If a multicast flow has multiple receivers in different Sets, the packet needs to be replicated multiple times by the ingress router, for each set once.

• Is that a problem? We don’t think so…

• The Set identifier is part of the packet.

• Can be implemented as MPLS label.

32LTRIPM-3001


BIER Areas

• BIER area’s are like IGP area’s, you only need reachability to the ABR

33LTRIPM-3001

I

A

G B

1:001

C

D

E

F

H

1:010

1:100

2:001

2:010

2:100

Area 1

Area 2J

BIER Forwarding

0:011

0:001

0:010

Area BM Nbr

0 0011 I

1:010

2:010

ABR

ABR

Area 0


BIER Areas

• The ABR removes the BIER header from Area 0, and imposes a new BIER header for Area 1 and 2.

• The new BIER header can be determined by a Group/Label lookup.• Look for the inner IPv4/6 packet group address, do a lookup in the MFIB

• Requires flow state on the ABR.

• Similar to Segmented Inter-AS MVPN

34LTRIPM-3001

Sub-domains


BIER Sub-domains

• Nodes are configured to be in a BIER sub-domain.

• BIER MPLS labels are not installed between sub-domains

36LTRIPM-3001

A B C D

E F G H

PIM/

IGMP

PIM/

IGMP

Domain 1

Domain 2


BIER Sub-domains

• When IGP changes SPF for B to F, traffic is dropped.

• BIER traffic is never leaked between sub-domains.

• Routers can be part of multiple sub-domains.

• This is a very easy mechanism to force dual plane.

37LTRIPM-3001

A B C D

E F G H

PIM/

IGMP

PIM/

IGMP

Domain 1

Domain 2

X

The BFR-id


The BFR-id

• A BFER is uniquely identified by a two tuple {Set ID, Bit Position}

• The number of Bit Positions is depending on the length of the support BitString in the network.

• To make the BFER identifier independent of the BitString length we defined the BFR-id as a number between [1,65535]

• We auto-generate the BFR-id into a {Set ID, Bit Position}, based on the BitString Length.

39LTRIPM-3001


The BFR-id

• Formula:SI = (BFR-id -1) / BitStringLength

BP = ((BFR-id -1) modulo BitStringLength) + 1

• Example BFR-id = 129.BitString Length 128 -> {SI = 1, BP = 1}

BitString Length 256 -> {SI = 0, BP = 129}

40LTRIPM-3001


The BFR-id

• By decoupling the BFR-id from the SetID and Bit Position tuple, the BFR identifier is agnostic to the supported BitString length in the network.

• This is very useful during migration.

• If a network supports multiple BitString lengths, an egress router only needs oneBFR-id, and is reachable via each BitString length.

41LTRIPM-3001

BIER Forwarding


BIER Forwarding

We define two different forwarding methods for BIER.

1. Neighbor based forwarding.

2. Bit Indexed forwarding

43LTRIPM-3001


BIER Forwarding, neighbor based.

• A packet BitString is matched against each Neighbor in the BFT.

• This model works well for systems that have multi-cores.

• Its works less well for serialized processing as it requires a neighbor walk for each packet

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BIER Forwarding Table

5 4 3 2 1 Nbr

1 A

1 B

1 C

1 1 D

Packet IN Packet OUT 00100=10101 10101&

1

2

3

4

Packet OUT 10001=10101&

&


BIER Forwarding, Bit Indexed

• We translate the BFT neighbor table in to a table sorting on Bit Position

(so not by neighbor)

• We walk the Bit Mask in the packet and Index into the FIB table.

45LTRIPM-3001

BFT Neighbors

5 4 3 2 1 Nbr

1 A

1 B

1 C

1 1 D

BFT Indexed

54321 Nbr

1 10001 D

2 00010 A

3 00100 B

4 01000 C

5 10001 D



• We walk the Bits in the packet, as soon as we hit a ‘1’, we copy the packet, index into the FIB table with the position of the Bit.

• The Bit Mask entry is reverse ‘&’ with the Bit Mask in the packet.

• This resets the Bits that where processed.

46LTRIPM-3001

BIER FIB Label

Forwarding Table

54321 Nbr

1 10001 D

2 00010 A

3 00100 B

4 01000 C

5 10001 D

10101Packet IN

1

Walk Bit Mask

Packet OUT 10001=

01110

&

10101

Copy

&



47LTRIPM-3001

BIER FIB Label

Forwarding Table

54321 Nbr

1 10001 D

2 00010 A

3 00100 B

4 01000 C

5 10001 D

00100Packet IN Packet OUT

Walk Bit Mask

1000110101 =

Copy

&






48LTRIPM-3001

BIER FIB Label

Forwarding Table

54321 Nbr

1 10001 D

2 00010 A

3 00100 B

4 01000 C

5 10001 D


2

Walk Bit Mask

1000110101 =

Copy

&






49LTRIPM-3001

BIER FIB Label

Forwarding Table

54321 Nbr

1 10001 D

2 00010 A

3 00100 B

4 01000 C

5 10001 D


3

Walk Bit Mask

1000110101 =

Copy

&






50LTRIPM-3001

BIER FIB Label

Forwarding Table

54321 Nbr

1 10001 D

2 00010 A

3 00100 B

4 01000 C

5 10001 D


Walk Bit Mask

1000110101 =

Copy

&

00100 &

Copy






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BIER FIB Label

Forwarding Table

54321 Nbr

1 10001 D

2 00010 A

3 00100 B

4 01000 C

5 10001 D


Walk Bit Mask

1000110101 =

Copy

&

00100= Packet OUT 00100 &

Copy






52LTRIPM-3001

BIER FIB Label

Forwarding Table

54321 Nbr

1 10001 D

2 00010 A

3 00100 B

4 01000 C

5 10001 D


Walk Bit Mask

1000110101 =

Copy

&

00100= Packet OUT 00100 &

Copy&

11011






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BIER FIB Label

Forwarding Table

54321 Nbr

1 10001 D

2 00010 A

3 00100 B

4 01000 C

5 10001 D


Walk Bit Mask

1000110101 =

Copy

&

00100= Packet OUT 00100 &

Copy

00000

&

11011






54LTRIPM-3001

BIER FIB Label

Forwarding Table

54321 Nbr

1 10001 D

2 00010 A

3 00100 B

4 01000 C

5 10001 D


4

Walk Bit Mask

1000110101 =

Copy

&

00100= Packet OUT 00100 &

Copy

00000

&

11011






55LTRIPM-3001

BIER FIB Label

Forwarding Table

54321 Nbr

1 10001 D

2 00010 A

3 00100 B

4 01000 C

5 10001 D


5

Walk Bit Mask

1000110101 =

Copy

&

00100= Packet OUT 00100 &

Copy

00000

&

11011






56LTRIPM-3001

BIER FIB Label

Forwarding Table

54321 Nbr

1 10001 D

2 00010 A

3 00100 B

4 01000 C

5 10001 D


Walk Bit Mask

1000110101 =

Copy

&

00100= Packet OUT 00100 &

Copy

00000

&

11011






• Walking the bits in a Bit String takes less clock cycles compared to walking a list of neighbors.

• For that reason its faster to walk the Bit String and index into the neighbor table.

• The table is a NxN bit matrix, where N is the Bit String length.

• Bits that where already processed are reset so we don’t processes them if they appears later in a Bit String. This way we avoid multiple copies being forwarded.

57LTRIPM-3001



• Walking the Bit String in the packet is basically a repeating of ‘Find First Set’ (FFS) Bit operation.

• Could be optimized to record the last position.

• http://en.wikipedia.org/wiki/Find_first_set

• http://graphics.stanford.edu/~seander/bithacks.html

• Checkout Bruijn sequence (Count the consecutive zero bits)

• Is supported in compilers FFS and can be done in HW fairly easily.

58LTRIPM-3001

ECMP


ECMP

• It is possible the same Bit Position is reachable over different interfaces if there are ECMP paths.

• We distinguish two different ECMP behaviors

• ECMP via parallel interfaces to a single neighbor.

• ECMP via different neighbors.

• The handling is different for both cases.

• If the ECMP path is going to a single neighbor, the Bit Mask is the same for each candidate path, no special processing needed.

• If the ECMP path is to different neighbors, the Bit Mask will be different for each neighbor because the Bit String in the packet is the end result of the lookup in BIER, which is different for each nbr.

60LTRIPM-3001


ECMP

61LTRIPM-3001

CA B

D

FE

Nbr

0111 B

Nbr

0011 C

0110 E

Nbr

0001 D

0010 F

00110111

AND ANDAND

0111

0001

0010

0100Nbr

0011 C

B

0010 F

&0011&0111 &0001

&0110 &0010

AND

Duplicate bit positions need to be resolved,

ECMP logic needs to select based on Hash.

In the example we selected C


ECMP

• We distribute the Bit Positions over multiple tables.

• Each Bit Position only appears once in each table.

• Table selection is based on entropy, done before Bit Index lookup

62LTRIPM-3001

ECMP Table 1

5 4 3 2 1

1 1 1

1

1

ECMP Table 2

5 4 3 2 1

1 1 1

1 1

ECMP Table 3

5 4 3 2 1

1 1

1

1 1

ECMP Table 4

5 4 3 2 1

A

1 1 B

C

1 1 1 D

BFT Neighbor

5 4 3 2 1 Nbr

1 1 1 A

1 1 1 B

1 1 C

1 1 1 D


ECMP

• The number of tables is depending on the number of ECMP paths to different neighbors.

• If the max number of ECMP paths is 4, but there is a Bit Position reachable via 3 paths, this will cause unequal distribution.

63LTRIPM-3001

Deployment Scenarios

Native BIER


Native BIER

• With Native BIER there is NO PIM involved, just IGMP and BIER.

• The Source and Receiver(s) are connected to BIER router.

• There are no RP’s.

• There is no equivalent of PIM modes, like sparse, ssm, bidir etc..

• We speak of ‘single’ sender and ‘multi’ sender, which is basically the same solution.

• The overlay can be BGP or SDN based.

66LTRIPM-3001


Native BIER

• E and F announce their Group membership via overlay to all other routers.

• A BIER router connected to the Source can immediately start sending.

67LTRIPM-3001

DC

E

F

A

B

0 Nbr

0001 E

0010 F

1100 C

0 Nbr

0011 D

0100 A

1000 B

0 Nbr

1011 C

0 Nbr

0111 C

0 Nbr

1110 D

0 Nbr

1101 D

0100

1000

0001

0010


Native BIER



68LTRIPM-3001

DC

E

F

A

B

IGMP

(*,G)

0 Nbr

0001 E

0010 F

1100 C

0 Nbr

0011 D

0100 A

1000 B

0 Nbr

1011 C

0 Nbr

0111 C

0 Nbr

1110 D

0 Nbr

1101 D

0100

1000

0001

0010


Native BIER



69LTRIPM-3001

DC

E

F

A

B(*,G):0:000

1

IGMP

(*,G)

0 Nbr

0001 E

0010 F

1100 C

0 Nbr

0011 D

0100 A

1000 B

0 Nbr

1011 C

0 Nbr

0111 C

0 Nbr

1110 D

0 Nbr

1101 D

(*,G):0:0001

(*,G):0:0001

0100

1000

0001

0010


Native BIER



70LTRIPM-3001

DC

E

F

A

B

(S1,G)

(*,G):0:000

1

IGMP

(*,G)

0 Nbr

0001 E

0010 F

1100 C

0 Nbr

0011 D

0100 A

1000 B

0 Nbr

1011 C

0 Nbr

0111 C

0 Nbr

1110 D

0 Nbr

1101 D

(*,G):0:0001

(*,G):0:0001

0100

1000

0001

0010


Native BIER



71LTRIPM-3001

DC

E

F

A

B

(S1,G)

(*,G):0:000

1

IGMP

(*,G)

0 Nbr

0001 E

0010 F

1100 C

0 Nbr

0011 D

0100 A

1000 B

0 Nbr

1011 C

0 Nbr

0111 C

0 Nbr

1110 D

0 Nbr

1101 D

(*,G):0:0001

(*,G):0:0001

0100

1000

0001

0010


Native BIER



72LTRIPM-3001

DC

E

F

A

B

(S1,G)

(*,G):0:000

1

IGMP

(*,G)

IGMP

(*,G)

0 Nbr

0001 E

0010 F

1100 C

0 Nbr

0011 D

0100 A

1000 B

0 Nbr

1011 C

0 Nbr

0111 C

0 Nbr

1110 D

0 Nbr

1101 D

(*,G):0:0001

(*,G):0:0001

0100

1000

0001

0010


Native BIER



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DC

E

F

A

B

(S1,G)

(*,G):0:000

1

IGMP

(*,G)

IGMP

(*,G)

0 Nbr

0001 E

0010 F

1100 C

0 Nbr

0011 D

0100 A

1000 B

0 Nbr

1011 C

0 Nbr

0111 C

0 Nbr

1110 D

0 Nbr

1101 D

(*,G):0:0001

(*,G):0:0001

0100

1000

0001

0010

(*,G):0:001

0

(*,G):0:001

0

(*,G):0:001

0


Native BIER



74LTRIPM-3001

DC

E

F

A

B

(S1,G)

(*,G):0:000

1

IGMP

(*,G)

IGMP

(*,G)

0 Nbr

0001 E

0010 F

1100 C

0 Nbr

0011 D

0100 A

1000 B

0 Nbr

1011 C

0 Nbr

0111 C

0 Nbr

1110 D

0 Nbr

1101 D

(*,G):0:0001

(*,G):0:0001

0100

1000

0001

0010

(*,G):0:001

0

(*,G):0:001

0

(*,G):0:001

0


Native BIER

• When B leans about a new source, it can immediately start sending.

75LTRIPM-3001

DC

E

F

A

B

(S1,G)

(*,G):0:000

1

IGMP

(*,G)

IGMP

(*,G)

0 Nbr

0001 E

0010 F

1100 C

0 Nbr

0011 D

0100 A

1000 B

0 Nbr

1011 C

0 Nbr

0111 C

0 Nbr

1110 D

0 Nbr

1101 D

(*,G):0:000

1

(*,G):0:000

1

0100

1000

0001

0010

(*,G):0:001

0

(*,G):0:001

0

(*,G):0:001

0

(S2,G)

MVPN over BIER


MVPN over BIER

• BIER replaces PIM, mLDP, RSVP-TE or IR in the core.

• BIER represents a full mesh (P2MP) connectivity between all the PE’s in the network.

• There is no need to explicitly signal any MDT’s (or PMSI’s).

• With MVPN there are many profiles,

• This is partly due to the tradeoff between ‘State’ and ‘Flooding’.

• Different C-multicast signaling options.

• MVPN over BIER, there is one profile.

• BGP for C-multicast signaling.

• No need for Data-MDTs.

77LTRIPM-3001


MVPN over BIER

• The BGP control plane defined for MVPN can be re-used.

• Big difference, there is no Tree per VPN…!!!

• The BIER packets needs to carry Source ID and upstream VPN context label

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C

D

A

B

0100

1000

0001

0010

BIER

PIM

PIM

PIM

PIM

PIM

PIM

RR(*,G):0:0001

(*,G)

(*,G)

(*,G)

(S,G)

(S1,G)

(S2,G)

(*,G):0:0010

(*,G):0:0001

(*,G):0:0001

Conclusion


Stateless

• There is no Multicast receiver or flow state in the core network (only edge).

• Imposition of the BIER Header may be done by application, removes state from ingress.

• There is no tree state in the network.

• There is no tree building protocol or logic in the network.

• There is only topology state for the BFER’s, derived from unicast routing.

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Scale

• Since there is no flow and tree state, converges as fast as unicast.

• Compared to Ingress Replication, saves 256x (minimum)

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Simplicity

• No Reverse Path Forwarding (RPF)

• No Rendezvous Points

• No shared tree / source tree switchover

• No receiver driven tree building

• BIER is like unicast

• State is in the packet (like Segment Routing)

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Thank you

Documents

Stateless Multicast with - clnv.s3.amazonaws.com · Stateless Multicast with Bit Indexed Explicit Replication IJsbrand Wijnands, Distinguished Engineer LTRIPM-3001