1/13/2009 January Interim New Orleans 1

802.1aq Shortest Path Bridging Recap

Don Fedyk dwfedyk@nortel.com

János Farkas Janos.Farkas@ERICSSON.COM

1/13/2009 January Interim New Orleans 2

Shortest Path BridgingProject Authorization Request

• Scope :VLAN Bridges– Shortest Path within a region– Interwork with Spanning Tree Protocols, RSTP,

MSTP bridges• This standard specifies shortest path bridging of unicast and

multicast frames, including protocols to calculate multiple active topologies that can share learnt station location information, and support of a VLAN by multiple, per topology, VLAN identifiers (VIDs).

– Compatibility• This amendment will not change the conformance of IEEE

Std 802.1Q to Std 802. Overview and Architecture, or its relationship to that specification.

1/13/2009 January Interim New Orleans 3

802.1Q Data Planes

SA = Source MAC addressDA = Destination MAC addressVID = VLAN IDC-VID = Customer VIDS-VID = Service VIDI-SID = Service IDB-VID = Backbone VIDB-DA = Backbone DAB-SA = Backbone SA

Supports Data Plane OAM (CFM, MIP, MEPs)

We have a long standing Data Plane

2005 2008Standard Approved

1998

B-VIDI-TAG

B-TAG

B-DA

B-SA

DA

SA

Payload

EthertypeC-VID

Payload

Ethertype

Q-TAG

DA

SA

C-VID

S-VID

Payload

Ethertype

C-TAG

S-TAG

DA

SA

I-SID

Payload

Ethertype

S-TAG

DA

SA

S-VIDC-TAGC-VID

Ethernet

ProviderBackboneBridges802.1ah

ProviderBridges802.1ad

EthernetVLAN

1/13/2009 January Interim New Orleans 4

Applicability

Small VLANNetworks

2-100 bridges

Large PBBNetworks

2-1000 backbone bridges

Plug and playEfficientLow delayBackwards Compatible

Carrier GradeFast convergenceEfficient use of resourcesB-VLAN Partitioned Forwarding Compatible

IEEE 802.1aq

Shortest Path Bridging (SPB) Shortest Path Backbone Bridging (SPBB)

E-Line, E-Tree, E-LAN Services Provider E-Line, E-Tree, E-LAN Services

1/13/2009 January Interim New Orleans 5

Motivation

• RSTP/MSTP forwarding– Detours appear

– Manual configuration isneeded for disjoint trees

– Forwarding can be onlyoptimized by manual configuration

• Shortest path forwarding– Each bridge only sends

frames on its own Shortest Path Tree (SPT)

– Automatic SPT management

– Controlled by IS-IS

BA

DC

C

C

C

C

CC

Spanning tree forwarding

SPB forwarding

BA

DC

C

CC

C

CC

1/13/2009 January Interim New Orleans 6

SPT Region

MST Region

Interworking with RSTP and MSTP

• Common Spanning Tree (CST)• Internal Spanning Tree (IST)• Common and Internal Spanning Tree

RSTP bridges

SPT Region

IST

MST Region

IST CST

1/13/2009 January Interim New Orleans 7

IEEE 802.1aq variants

• Shortest Path Backbone Bridging (SPBB) is aimed to be deployed in PBB networks where all addresses are managed

• Shortest Path Bridging (SPB) is applicable in customer, enterprise or storage area networks

SPB SPBB

Metro Core Network• Reliability• Auto-discovery• Load sharing• Managed addresses

Access Network• Reliability• Bandwidth efficiency • Unknown or managed addresses

Enterprise Network• Plug & Play• Easy to operate• Unknown addresses

MAC learningin data plane

MAC learningin control plane

IEEE 802.1aq

1/13/2009 January Interim New Orleans 8

IS-IS controls IEEE 802.1aq

• Topology discovery– Each bridge is aware of the physical topology of the SPT Region

• Service discovery– I-SID registrations are included into a new TLV

• Shortest Path Tree computation• Maintenance of SPTs and CIST• SPTs can be set according to the discovered I-SID

membership information– MRP is not needed

• VID allocation to VLANs

1/13/2009 January Interim New Orleans 9

Source tree identification

VLAN ID• An SPT is identified by

the SPVID assigned to the source bridge

Applicable to both 802.1Q and 802.1ah bridges

Ingress check on VID Consumes VLAN space Unidirectional VIDs

MAC address• B-SA and its Nickname incorporated

into Group MAC DA identifies an SPT

Two VIDs only used for a whole set of Shortest Path Trees(Base VID and another VID) Each ECMT uses one more VID

Bidirectionality of VID is preserved Only applicable to 802.1ah bridges Ingress check on SA All multicast addresses take the local

bit mapping

1/13/2009 January Interim New Orleans 10

VID

VLAN assignmentVLAN Base VID

identified by

MSTISPT Set

SPVIDBase VIDB-SA

Group B-DA

IST CST

Base VID Base VID

LearningNon-learningSPBB

Base VID

ID

LearningNon-learningPBB-TE

LearningNon-learningSPBB

Non-learningSPBB

allocated to

supported bysupported by

Learning

IDID ID

MSTI CIST

Learning

SPT Set

VID*B-SA

Group B-DA

MSTI

Non-learningSPBB

IST

Base VID

LearningNon-learningSPBB

IEEE 802.1aq implements

SPVID

Non-Learning

SPBB

1/13/2009 January Interim New Orleans 11

Tree implementation

• By Port Roles

• SPT is formed from the Root Bridge

• By Filtering Entries

• Source rooted SPTs applied in 802.1aq

Root Bridge Source Bridge

Designated,Forwarding

Root,Forwarding

Alternate,Blocking

1/13/2009 January Interim New Orleans 12

MAC learning

• MAC learning in the data plane (Learning)

• MAC learning in the control plane (Non-learning)

Bridge

FD

B

Bridge

FD

B

Bridge

FD

B

Frames

IS-IS IS-ISIS-IS

Addresses

Add

ress

es

Frames

Addresses

Add

ress

es

Bridge

FD

B

IS-IS

Bridge

FD

B

IS-IS

Bridge

FD

B

IS-ISControl Messages Control Messages

Addresses Addresses Addresses

1/13/2009 January Interim New Orleans 13

SPB

• SPB (802.1Q compliant)– Uses VID for source identification, don’t own the C-

MAC– Solution Attributes

• VID Trees, one source per bridge, distributed in IS-IS• SVL learning of unicast forwarding supported

– Solution Requirements• Must Interwork at edges with RSTP, MSTP• The region may default to a single instance MSTP

(associated with the “Base VID”) if the VID allocation fails or detects errors

• Must support loop prevention, may support ingress check

1/13/2009 January Interim New Orleans 14

SPB ConceptsSPT Region

SPVID = 45

SPVID = 41

VID = 6

DASA

Payload

45

DASA

Payload

22

DASA

Payload

41

DASA

Payload

22

DASA

Payload

22

CSTIST

DASA

Payload

45

DASA

Payload

41

SPVID = 71

SPVID = 66SPVID = 44

SPVID = 22

DASA

Payload

22

Base VID 22

SPB Region Identifier!= Base VID

1/13/2009 January Interim New Orleans 15

SPBB

• SPBB (Shortest Path Backbone Bridging)– Solution Attributes

• Single VID for an SPT Region (may use VID Trees)

• Does not use learning of B-MACs – Provider addresses will all be known allows for more

efficient flooding (no B-MAC broadcast storms),

• Reduction in forwarding space Shared Forwarding,

– Solution Requirements• Must use Multicast loop Prevention, • Must use ingress check for unicast

1/13/2009 January Interim New Orleans 16

SPBB Operation

IS-IS IS-IS IS-IS

IS-ISIS-IS

IS-IS

BEB

BEBBEB

BCB BCBBEB “A”

BEB Backbone Edge Bridge BEB

PBBN

IS-IS

IS-IS IS-IS

Backbone Core Bridge BCB

Shortest Path Tree from “A”

Shortest path between any two points is both the same and symmetrical for unicast

and multicast

1/13/2009 January Interim New Orleans 17

SPBB Shortest Path Tree to/from “A”

IS-IS IS-IS IS-IS

IS-ISIS-IS

IS-IS

BEB

BEBBEB

BCB BCBBEB “A”

BEB Backbone Edge Bridge BEB

PBBN

IS-IS

IS-IS IS-IS

Backbone Core Bridge BCB

Uses the full mesh network

Shortest path between any two points is both the same and symmetrical for unicast

and multicast

All pairs shortest path computation

performed in parallel

1/13/2009 January Interim New Orleans 18

SPBB Multicast Groups

IS-IS IS-IS IS-IS

IS-ISIS-IS

IS-IS

BEB

BEBBEB

BCB BCBBEB “A”

BEB Backbone Edge Bridge BEB

PBBN

IS-IS

IS-IS IS-IS

Backbone Core Bridge BCB

I-SID 5

I-SID 5I-SID 5

MMAC for 5 from A

I-SIDs define efficient subsets

1/13/2009 January Interim New Orleans 19

Forward and Reverse path Congruency

• Necessary if MAC learning is in the data plane• Not necessary if MAC learning is in the control plane• Going to be assured by both SPB and SPBB

Bridge5

11

1

1

1

1

2

Bridge2

Bridge1

Bridge3

Bridge4

Bridge6

1/13/2009 January Interim New Orleans 20

Unicast and Multicast Congruency

• Necessary for MAC learning in data plane• Necessary for the proper operation of OAM• Going to be assured by both SPB and SPBB

Bridge5

11

1

1

1

1

2

Bridge2

Bridge1

Bridge3

Bridge4

Bridge6

unicast

multicast

1/13/2009 January Interim New Orleans 21

Implementation ofCongruency

• Tie-breaking extension to Dijkstra for the case of equal cost multiple paths– List of node IDs comprising a path are unique– {1,6,5} < {1,2,3,5} < {1,2,4,5}

• Same algorithm is used both for unicast and multicast

Bridge5

11

1

1

1

1

2

Bridge2

Bridge1

Bridge3

Bridge4

Bridge6

1/13/2009 January Interim New Orleans 22

Load sharing

• Two trees are calculated taking advantage of equal cost multiple paths: {1,6,5} < {1,2,3,5} < {1,2,4,5}

• SPT Primary Set Primary Base VID • SPT Alternate Set Secondary Base VID

Bridge5

11

1

1

1

1

2

Bridge2

Bridge1

Bridge3

Bridge4

Bridge6

1/13/2009 January Interim New Orleans 23

Loop Prevention and Mitigation

• Inconsistent view on network topology at different nodes may cause transient loops in case of a link-state control protocol

• Loop prevention– Tree Agreement Protocol (TAP)– Handshake mechanism between neighbors– Extension to MSTP’s handshake

• Loop mitigation– Ingress Checking (e.g. RPFC)– Frames not arriving on the shortest path from the Source Bridge are

discarded– Makes the tree directed– Good for loop prevention in most cases– Transient loops may appear

• Severe problem for multicast traffic• A chance of network melt-down remains if one does not care

– Ingress filtering has to be modified

1/13/2009 January Interim New Orleans 24

Neighbor handshake mechanism

• Let’s make it sure that bridges having different view on network topology do not exchange frames

• The link between adjacent neighbors has to be blocked after a topology change until they agree that both of them have the same topology database

• The agreement between neighbors is implemented by a handshake mechanism

• A digest of the topology database is exchanged– CRC– Cryptographic hash function (e.g. SHA-256)

• Agreements at different part of the network are independent of each other

1/13/2009 January Interim New Orleans 25

Handshake: MSTP extension

• Tree Agreement Protocol (TAP)

• Two-way Agreement = three-way handshake

• No per tree handshake• BPDUs contain

– Digest of LSP database– Info on the CIST

• Proposal-Agreement– Explicit on the CIST– Computed for SPTs

Pro

posa

l

Agr

eem

ent

Agreem

ent

1/13/2009 January Interim New Orleans 26

Handshake: Filtering entry manipulations

• SPBB networks• STPs are implemented by

Filtering Entries• Do not implement the TAP

extension to MSTP• Implement link-state database

synchronization (TAP logic)• Loops for unicast flows are

mitigated by Ingress Checking (RPFC)

• Remove ‘unsafe’ entries if neighbors are unsynchronized

Wait for LSP update

Unicast computation

Install Unicast andremove ‘unsafe’

Multicast FDB entries

Update Digest andsend it to neighbors

Multicast computation

Install ‘safe’ Multicast FDB entries

Wait for Digest synch

Install ‘unsafe’Multicast FDB entries

1/13/2009 January Interim New Orleans 27

Two Options

• BPDUs

• Link State

1/13/2009 January Interim New Orleans 28

SPB IS-IS TLVS 8

Per Adjacency

c) SPB Link Metric Sub TLVIS-IS Reachability TLV

SPB-Link Metric

Res

S Reserved16

16

M-T ID

24

Port Identifier 16

Source MAC

d) SPB Multicast Group TLV

Per Bridge

VID

Number of records

Res

S Reserved

M-T ID 16

12

48

Destination MMAC48

Number of VIDs

8

8

SPT Set 4

8

a)Hello PDU BASE-VID TLV

Per Bridge

8

16

12

4

12

8

M-T ID

Base VID

Number of-VIDs

Res

S Reserved

SPT SET

B

Algorithm

Reserved

4

VID

SPT Set

8

4

12

8

0

Algorithm

Reserved

Per Bridge

Nickname

b)SPB Instance TLV

Nickname Priority

Nickname Flags

SP-VID

Bridge Identifier

32

20

64

4

M-T IDResS Reserved

1616

12

SPT Set

Res 4

O

For the CIST

For the SPT

For the ST

1/13/2009 January Interim New Orleans 29

SPBB IS-IS TLVS8

Per Adjacency

c) SPB Link Metric Sub TLVIS-IS Reachability TLV

SPB-Link Metric

Res

S Reserved16

16

M-T ID

24

Port Identifier 16

e) SPBB I-SID & UnicastMAC TLV

Per Bridge

VID

Number of I-SIDs

Res

S Reserved

M-T ID 16

8

12

24I-SID

RT Res 8

8

Number of VIDs 8

MAC Address 48

TYP Res 8

SPT Set 4

a)Hello PDU BASE-VID TLV

Per Bridge

8

16

12

4

12

8

M-T ID

Base VID

Number of-VIDs

Res

S Reserved

SPT SET

B

Algorithm

Reserved

4

VID

SPT Set

8

4

12

8

0

Algorithm

Reserved

Per Bridge

Nickname

b)SPB Instance TLV

Nickname Priority

Nickname Flags

SP-VID

Bridge Identifier

32

20

64

4

M-T IDResS Reserved

1616

12

SPT Set

Res 4

O

For the CIST

1/13/2009 January Interim New Orleans 30

SPVID Allocation

• How to control the allocation? • Master Bridge

– Need a communication path before the allocation• SPVID neighbor is a proxy

– Need an allocation protocol– Need to deal with Master Bridge changing

• Deterministic Distributed algorithm– Neighbor performs the computation locally based on the Link

state database– Need a collision mechanism– Need an aging mechanism that is much slower than other aging

mechanism– SPVIDs are commited to some NVRAM

1/13/2009 January Interim New Orleans 31

SPVID Allocation

0 4096SPVID Set 1 SPVID Set 2

VID space

Configure Sets an let the allocation be from the set

1/13/2009 January Interim New Orleans 32

SPVID Allocation

0 4096

VID space

Configure an SPVID pool and sets come from the pool

SPVID Pool

VIDs VIDs

SPVID Region

1/13/2009 January Interim New Orleans 33

IEEE 802.1aq ProjectWhere are we now?

• Topology Distribution– IS-IS

• Loop Prevention– TAP or SPBB Multicast Loop Prevention

• Loop Mitigation – Optional Forwarding change Ingress Check

• SPVID allocation– Leverage link State

• SPBB – Multicast Source Tree identification

• SPVID or B-VID&Source DA• MRP and Link State

• Path Computation– Convergence time/algorithms

• MSTP/RSTP/STP backwards/forwards interoperability & coexistence• Provisioning

– Tree types (Shared Trees or Tree per source, etc) – MIBs– Mis-provisioning

• CFM – SPB CFM– SPBB CFM

Document Both

Only IS-IS need TLVs

Documenting compliance

Documenting options

Proposals in works

TBD

Proposal in works

TBD

Seems complete

Documented Clause 13

1/13/2009 January Interim New Orleans 34

What do we need from IS-IS?

• Some TLVs and Sub TLVS– Per SPT Region

– BASE VID (IST)– Shortest path tree algorithm– Define Single VIDs

• Per Bridge– Bridge Identifier– Per Base VID

» Define SPVID» Bridge Priority » Supported Multicast Groups/I-SIDs» Supported Unicast

• Per Port– Per Base VID

» Link Metric, Port Priority

1/13/2009 January Interim New Orleans 35

Other information and Pointers

• http://www.ieee802.org/1/

• http://www.ieee802.org/1/files/public/

• SPB-ISIS mailing list for SPB IS-IS related discussions– If you want to subscribe to the spb-isis list you

can subscribe by sending to:

spb-isis-request@ietf.org

With subscribe in the body.

1/13/2009 January Interim New Orleans 36

GlossaryB-MAC Backbone MACBEB Backbone Edge BridgeBCB Backbone Core BridgeC-VID Customer VIDCFM Connectivity Fault ManagementCST Common Spanning TreeELINE Ethernet Point to Point ServiceELAN Ethernet LAN ServiceETREE Ethernet Hub and Spoke ServiceFDB Filtering Data BaseI-SID (802.1ah) Service IdentifierIGP Interior Gateway Protocol (Typically link state) IS-IS Intermediate System to Intermediate System

(IGP)IST Internal Spanning TreeLAN Local Area NetworkMAC Media Access ControlMACinMAC see PBBMEP Maintenance End point

MIP Maintenance Intermediate pointMMAC Multicast MACMSTP Multiple Spanning tree protocol MMRP Multiple MAC Registration Protocol OAM Operations, Administration and

Maintenance PB Provider Bridges IEEE 802.1adPBB Provider Backbone Bridging IEEE 802.1ahPBB-TE PBB Traffic Engineering IEEE

802.1QayQinQ see PBS-VID Service VIDSPB Shortest Path Bridging IEEE 802.1aqSPBB Shortest Path Backbone Bridging SPT Shortest Path TreeSTP Spanning tree protocol RSTP Rapid Spanning tree protocol TTL Time To LiveVID VLAN IdentifierVLAN Virtual LAN