802.1aq Shortest Path Bridging
Recap
Don Fedyk dwfedyk@nortel.com
János Farkas Janos.Farkas@ERICSSON.COM
1/13/2009
January Interim New Orleans
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Shortest Path Bridging
Project 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.
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802.1Q Data Planes
Provider
Backbone
Bridges
802.1ah
We have a long standing Data Plane
Payload
Ethernet
VLAN
SA = Source MAC address
DA = Destination MAC address
VID = VLAN ID
C-VID = Customer VID
S-VID = Service VID
I-SID = Service ID
B-VID = Backbone VID
B-DA = Backbone DA
B-SA = Backbone SA
Ethernet
Provider
Bridges
802.1ad
Payload
Payload
Payload
Ethertype
SA
DA
Ethertype
C-VID
Q-TAG
SA
DA
1998
Ethertype
C-VID
C-TAG
S-VID
S-TAG
SA
DA
Ethertype
C-VID
C-TAG
S-VID
S-TAG
SA
DA
I-SID
I-TAG
B-VID
B-TAG
B-SA
B-DA
2005
2008
Standard Approved
Supports Data Plane OAM (CFM, MIP, MEPs)
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Applicability
IEEE 802.1aq
Shortest Path Bridging (SPB)
Small VLAN
Networks
2-100 bridges
Shortest Path Backbone Bridging (SPBB)
Large PBB
Networks
2-1000 backbone bridges
Plug and play
Efficient
Low delay
Backwards Compatible
Carrier Grade
Fast convergence
Efficient use of resources
B-VLAN Partitioned Forwarding Compatible
E-Line, E-Tree, E-LAN Services
Provider E-Line, E-Tree, E-LAN Services
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Motivation
• RSTP/MSTP forwarding
– Detours appear
– Manual configuration is
needed for disjoint trees
– Forwarding can be only
optimized by manual
configuration
A
B
C
D
Spanning tree forwarding
• Shortest path forwarding
– Each bridge only sends
frames on its own Shortest
Path Tree (SPT)
– Automatic SPT management
– Controlled by IS-IS
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A
B
C
D
SPB forwarding
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Interworking with RSTP and
MSTP
• Common Spanning Tree (CST)
• Internal Spanning Tree (IST)
• Common and Internal Spanning Tree
SPT Region
IST
SPT Region
CST
IST
MST Region
RSTP bridges
MST Region
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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
IEEE 802.1aq
SPBB
SPB
Enterprise Network
• Reliability
• Bandwidth efficiency
• Unknown or managed
addresses
• Plug & Play
• Easy to operate
• Unknown addresses
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Metro Core Network
Access Network
MAC learning
in data plane
MAC learning
in control plane
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• Reliability
• Auto-discovery
• Load sharing
• Managed addresses
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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
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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
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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
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VLAN assignment
VLAN
IEEE 802.1aq implements
identified by
VID VID
Base
allocated to
MSTI
CIST
supported by
supported by
SPT Set
MSTI
ID
Base
VID
VID*
B-SA
Group B-DA
Non-learning
SPBB
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ID
SPVID
Nonlearning
Learning
SPBB
Base VID
Learning
Nonlearning
PBB-TE
Learning
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IST
CST
ID
ID
Base VID
Nonlearning
SPBB
Learning
Base VID
Learning
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Tree implementation
• By Port Roles
• By Filtering Entries
Root Bridge
Source Bridge
Designated,
Forwarding
Root,
Forwarding
Alternate,
Blocking
• SPT is formed from the Root
Bridge
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• Source rooted SPTs applied in
802.1aq
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MAC learning
• MAC learning in the data plane (Learning)
IS-IS
IS-IS
IS-IS
FDB
FDB
FDB
Bridge
Bridge
Bridge
Frames
Frames
• MAC learning in the control plane (Non-learning)
Control Messages
IS-IS
Addresses
Addresses
Bridge
IS-IS
Addresses
FDB
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FDB
FDB
Bridge
Control Messages
IS-IS
Bridge
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SPB
• SPB (802.1Q compliant)
– Uses VID for source identification, don’t own the CMAC
– 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
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SPB Concepts
SPB Region Identifier!= Base VID
SPT Region
Payload
Payload
45
SA
DA
45
SA
DA
Base VID 22
SPVID = 22
SPVID = 45
Payload
22
SA
DA
SPVID = 66
Payload
CST
IST
SPVID = 71
Payload
Payload VID
22
SA
DA
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=6
41
SA
DA
SPVID = 44
22
SA
DA
SPVID = 41
Payload
Payload
41
SA
DA
22
SA
DA
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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
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SPBB Operation
IS-IS
IS-IS
BEB
Backbone Edge
Bridge BEB
IS-IS
IS-IS
IS-IS
Shortest path between any
two points is both the same
and symmetrical for unicast
and multicast
Backbone Core
Bridge BCB
BCB
IS-IS
IS-IS
BCB
BEB “A”
BEB
PBBN
IS-IS
IS-IS
BEB
BEB
Shortest Path Tree from “A”
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SPBB Shortest Path Tree
to/from “A”
IS-IS
IS-IS
BEB
Backbone Edge
Bridge BEB
IS-IS
IS-IS
IS-IS
Shortest path between any
two points is both the same
and symmetrical for unicast
and multicast
Backbone Core
Bridge BCB
BCB
IS-IS
IS-IS
BCB
BEB “A”
BEB
PBBN
IS-IS
IS-IS
BEB
BEB
All pairs shortest path
computation
performed in parallel
Uses the full mesh network
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SPBB Multicast Groups
I-SID 5
I-SID 5
IS-IS
IS-IS
MMAC for 5
from A
BEB
Backbone Edge
Bridge BEB
IS-IS
IS-IS
IS-IS
Backbone Core
Bridge BCB
BCB
BCB
BEB “A”
I-SID 5
IS-IS
IS-IS
BEB
PBBN
IS-IS
IS-IS
BEB
BEB
I-SIDs define efficient subsets
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Forward and Reverse path
Congruency
1
1
Bridge2
Bridge3
1
1
1
Bridge4
Bridge1
2
Bridge5
1
Bridge6
• Necessary if MAC learning is in the data plane
• Not necessary if MAC learning is in the control plane
• 1/13/2009
Going to be assuredJanuary
by both
SPB and SPBB
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Unicast and Multicast
Congruency
unicast
1
1
Bridge2
Bridge3
1
multicast
1
1
Bridge4
Bridge1
2
Bridge5
1
Bridge6
• Necessary for MAC learning in data plane
• Necessary for the proper operation of OAM
• 1/13/2009
Going to be assuredJanuary
by both
SPB and SPBB
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20
Implementation of
Congruency
• 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}
1
1
Bridge2
Bridge3
1
1
1
Bridge4
Bridge1
2
Bridge5
1
Bridge6
Januaryboth
Interim for
New Orleans
• 1/13/2009
Same algorithm is used
unicast and multicast
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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
1
1
Bridge2
Bridge3
1
1
1
Bridge4
Bridge1
2
Bridge5
1
Bridge6
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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
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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
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Agreement
– Digest of LSP database
– Info on the CIST
Agreement
• Tree Agreement Protocol
(TAP)
• Two-way Agreement =
three-way handshake
• No per tree handshake
• BPDUs contain
Proposal
Handshake: MSTP extension
• Proposal-Agreement
– Explicit on the CIST
– Computed for SPTs
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Handshake: Filtering entry
manipulations
Wait for LSP update
• 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
Unicast computation
Install Unicast and
remove ‘unsafe’
Multicast FDB entries
Update Digest and
send it to neighbors
Multicast computation
Install ‘safe’
Multicast FDB entries
Wait for Digest synch
Install ‘unsafe’
Multicast FDB entries
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Two Options
• BPDUs
• Link State
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SPB IS-IS TLVS
IS-IS Reachability TLV
8
c) SPB Link Metric Sub TLV
a)Hello PDU BASE-VID TLV
Res
M-T ID
S
16
12
4
Reserved
Number of-VIDs
For
the
CIST
B
SPT SET
Base VID
Res
M-T ID
16
16
Bridge Identifier
64
SPT Set
4
SP-VID
12
VID
Nickname
Nickname Priority
12
Reserved
16
16
SPB-Link Metric
24
Port Identifier
16
For the SPT
For the ST
12
4
Res
4
SPT Set
S
4
8
0
M-T ID
Res
Reserved
8
8
Algorithm
Reserved
O
S
8
Algorithm
Reserved
b)SPB Instance TLV
20
32
Per Adjacency
Nickname Flags
Per Bridge
Per Bridge
d) SPB Multicast Group TLV
Res
M-T ID
S
Reserved
Number of VIDs
SPT Set
VID
Number of records
Source MAC
Destination MMAC
16
8
8
4
12
8
48
48
Per Bridge
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SPBB IS-IS TLVS
IS-IS Reachability TLV
8
c) SPB Link Metric Sub TLV
a)Hello PDU BASE-VID TLV
Res
M-T ID
S
16
12
4
Reserved
Number of-VIDs
For
the
CIST
B
SPT SET
Base VID
Res
M-T ID
16
16
Bridge Identifier
64
SPT Set
4
SP-VID
12
VID
Nickname
Nickname Priority
12
Reserved
16
16
SPB-Link Metric
24
Port Identifier
16
12
4
Res
4
SPT Set
S
4
8
0
M-T ID
Res
Reserved
8
8
Algorithm
Reserved
O
S
8
Algorithm
Reserved
b)SPB Instance TLV
20
32
Per Adjacency
Nickname Flags
Per Bridge
Per Bridge
e) SPBB I-SID & Unicast
MAC TLV
Res
S
M-T ID
Reserved
Number of VIDs
SPT Set
VID
8
4
12
MAC Address
TYP
Res
Number of I-SIDs
T R
16
8
Res
I-SID
48
8
8
8
24
Per Bridge
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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
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SPVID Allocation
VID space
0
4096
SPVID Set 1
SPVID Set 2
Configure Sets an let the allocation be from the set
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SPVID Allocation
VID space
4096
0
SPVID Pool
SPVID Region
VIDs
VIDs
Configure an SPVID pool and sets come from the pool
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IEEE 802.1aq Project
Where are we now?
•
Topology Distribution
–
•
Loop Prevention
–
•
Optional Forwarding change Ingress Check
Leverage link State
Multicast Source Tree identification
•
•
Convergence time/algorithms
MSTP/RSTP/STP backwards/forwards interoperability & coexistence
Provisioning
–
–
–
•
SPVID or B-VID&Source DA
MRP and Link State
Path Computation
–
•
•
Documenting options
Proposals in works
SPBB
–
•
Documenting compliance
SPVID allocation
–
•
TAP or SPBB Multicast Loop Prevention
Loop Mitigation
–
•
Only IS-IS need TLVs
IS-IS
Tree types (Shared Trees or Tree per source, etc)
MIBs
Mis-provisioning
Proposal in works
Documented Clause 13
TBD
Seems complete
CFM
–
–
Document Both
TBD
SPB CFM
SPBB CFM
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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
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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.
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Glossary
B-MAC Backbone MAC
BEB Backbone Edge Bridge
BCB Backbone Core Bridge
C-VID Customer VID
CFM Connectivity Fault Management
CST Common Spanning Tree
ELINE Ethernet Point to Point Service
ELAN Ethernet LAN Service
ETREE Ethernet Hub and Spoke Service
FDB Filtering Data Base
I-SID (802.1ah) Service Identifier
IGP Interior Gateway Protocol (Typically link state)
IS-IS Intermediate System to Intermediate System
(IGP)
IST Internal Spanning Tree
LAN Local Area Network
MAC Media Access Control
MACinMAC see PBB
MEP Maintenance End point
1/13/2009
MIP Maintenance Intermediate point
MMAC Multicast MAC
MSTP Multiple Spanning tree protocol
MMRP Multiple MAC Registration Protocol
OAM Operations, Administration and
Maintenance
PB Provider Bridges IEEE 802.1ad
PBB Provider Backbone Bridging IEEE 802.1ah
PBB-TE PBB Traffic Engineering IEEE
802.1Qay
QinQ see PB
S-VID Service VID
SPB Shortest Path Bridging IEEE 802.1aq
SPBB Shortest Path Backbone Bridging
SPT Shortest Path Tree
STP Spanning tree protocol
RSTP Rapid Spanning tree protocol
TTL Time To Live
VID VLAN Identifier
VLAN Virtual LAN
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