TRILL vs.

SPB

Mikael Holmberg
Senior Principal Corporate Systems Engineer EMEA
mikael@extremenetworks.com
Introduction Data Center Switching Evolving!

Host A

Host B

Host C

Spanning Tree Challenges

STP introduced Blocked Ports leading to Inefficient Paths
STP has slow convergence (in seconds) and is disruptive
Less Aggregate Bandwidth
MAC address tables dont scale
Instability with Multicast Optimization
Could IP help?... Yes but.
 Optimum Forwarding

In the following 6 Bridge Network: B C

Optimum forwarding would use all 8
links E F

A D

Loop avoidance protocols reduce B C

available links F
E
Traffic limited to only one path
(STP, ERPS, EAPS) A D

3
 Multi-Pathing

B C

E F

A D

4
 Multi-Pathing

Bridges limit traffic to one path

B5 B6 B7

B1 B2 B3 B4

5
 Multi-Pathing

You want something that would support multi-path for higher

throughput

RB5 RB6 RB7

RB1 RB2 RB3 RB4

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Path Computation
 (IS-IS) UNICAST PATH CALCULATION

TRILL uses the Dijkstra Algorithm,

to calculate the best path route 8 8 8
based on link cost to every node in E F G H
the network 8 12 12 14
10 10
Each node makes an independent 10
decision on where to send a packet I 12 A B 12 J
based on the packets destination 8 10 10 8
egress node
12 12
F to H: K C 10 D L
F-G-H = path cost 16 10 10
8 12 12 8
F to N:
F-I-K-N = path cost 28 M N 8
O 8
P
8

8
 (IS-IS) MULTIPATH CALCULATION

A link state algorithm allows multipath

forwarding
Multipath forwarding allows the ingress 8 8 8
node to forward packets along multiple E F G H
paths to reach the destination, so long 8 12 14
12
as they are all considered to be the best 10 10
path 10
I 12 A B 12 J
The ingress node uses a hashing
algorithm to select the next hop peer. 8 10 10 8
The hashing algorithm operates on the 12 12
encapsulated packet header so that K C 10 D L
individual flows always follow the same 10 10
path 8 12 12 8
This can lead to bi-directional traffic
flows taking different paths based on the M N 8
O 8
P
8
hash
I to L:
I-A-B-J-L= cost 42
I-K-C-C-L= cost 42
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(IS-IS) PER HOP MULTIPATH CALCULATION

Each hop along the path performs

its own next hop look-up
8 8 8
independently of the previous hops E F G H
At each hop along the path, there 12 14
8 12
may be multiple paths that were not 10 10
10
available to the previous hops I 12 A B J
12
This provides another level of load
8 10 10 8
sharing not available to Layer 2
networks K
12
C D
12
L
10
This is not currently supported in 10 10
Service Provider Bridging (SPB). 8 12 12 8
M to B: M N O P
Shortest path is via C 8 8 8

C to B:
C-A-B = path cost 20
C-D-B = path cost 20
10
 Multi-Destination Trees (TRILL)

VLAN X VLAN X VLAN X

Broadcast, Multicast and Unknown
Unicast packets are forwarded 8 8 8
using Multicast Distribution Tress E F G H

RBridges compute a single shared 8 12 12 14

10 10
tree based on LSP database for all 10
multi-destination traffic I 12 A B 12 J

Multiple trees can be computed to 8 10 10 8

load-share across multiple equal 12 12
cost links K C 10 D L
10 10
RBridge with highest priority 8 12 12 10
becomes the TREE Root and all
distribution trees are rooted from M N 8
O 8
P
8
here
VLAN X VLAN X

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 Multicast Distribution Trees (TRILL)

VLAN X attached at F,E,H,M and O

RBridge F has been configured with the highest priority Root Distribution Tree
Rbridge forwards packets with VLAN tags to only those tree adjacencies that
have downstream matching Access VLANs
RBridges K, G, and L are not required to forward traffic to some or all of the
distribution tree adjacencies.
This effectively prunes the distribution tree and reduces packet replication and
unnecessary traffic forwarding.

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TRILL
 TRILL: Transparent Interconnection of Lots
of Links

IETF standard for L2 scalability

Inventor of STP is inventor of TRILL Radia J. Perlman
Many RFCs:
RFC 5556: Problem & Applicability Statement
RFC 6325: Routing Bridges (RBridges): Base Protocol Specification
RFC 6326: TRILL use of IS-IS
RFC 6327: Routing Bridges Adjacency
RFC 6439: Routing Bridges Appointed Forwarders
 WHY IS-IS ?

The IS-IS (Intermediate System to Intermediate System) link

state routing protocol was chosen for SPB over OSPF
(Open Shortest Path First), the only other plausible
candidate, for the following reasons:
IS-IS runs directly at Layer 2. Thus no IP addresses are
needed, as they are for OSPF, and IS-IS can run with
zero configuration.
IS-IS uses a TLV (type, length, value) encoding which
makes it easy to define and carry new types of data.

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Introduction Best of the Both Worlds!

L2 Switching TRILL L3 Routing

Plan & Play

Minimal Configuration
Minimal Configuration Fast Convergence

Plug & Play

Plug & Play Multiple Paths

Fast Convergence
Flat Addressing Load Balancing

Multiple Paths
Slow Convergence Hierarchical

Load Balancing
Forwarding
Single Path Hierarchical
Multiple Multicast
Single Multicast Tree Forwarding
Trees
Constrained Scalability Highly Scalable
Highly Scalable
 TRILL: Transparent Interconnection of Lots
of Links

TRILL Header (8 bytes including TRILL Ethertype)

OP- Egress RBridge Ingress RBridge
V R M Length
Hop Count
Nickname Nickname
Options

M (1-bit): Multi-destination bit (0 = Unicast, 1 = Multi-destination)

Hop Count (6-bit): Mitigates Loop issues
Nicknames (16-bit): Dynamically assigned through nickname acquisition
protocol

Dynamic Nickname Acquisition Protocol

Nicknames are manually configured or dynamically assigned

Dynamic nicknames based on hashing parameters (System ID, time, date etc.)
RBridge Nicknames advertised using Link State PDUs (LSP)
Priority of the nickname is advertised in the LSP
Nicknames are persistent across reboots
 TRILL Basic Interworking

TRILL Campus

VLAN X

VLAN Y

RBridges exchanges TRILL IS-IS Hello frames

Hellos establish IS-IS connectivity on RBridge port
RBridges elect Designated RBridge (DRB) for each link
RBridges exchanges LSP to have a global link state database
Includes information such as VLAN, Nicknames, link cost etc.
Calculates optimal paths for unicast and multi-destination traffic
DRB specifies the Appointed Forwarder for each VLAN
Appointed Forwarders encapsulate/decapsulates TRILL data frames
 TRILL Packet Encapsulation (Unicast
Frames)
RBridge1 RBridge2 RBridge3

Host X Host Y
MAC A MAC B MAC C MAC D MAC E MAC F

MAC C MAC E Host X MAC

Host X MAC
MAC B MAC D Host Y MAC
Host Y MAC
Outer VLAN Outer VLAN
VLAN VLAN
RBridge3 Payload
Payload RBridge3
Nickname
Nickname
FCS RBridge1 FCS
RBridge1
Nickname
Nickname
Hop Count
Outer Ethernet Header Hop Count

TRILL Header Host X MAC Host X MAC

Original Frame with Host Y MAC Host Y MAC

Inner Ethernet Header,
Payload & new FCS Inner VLAN Inner VLAN

Payload Payload

FCS FCS
SPB
 What is SPB? (1)

IEEE protocol builds on 802.1 standards

A new control plane for Q-in-Q and M-in-M
Leverage existing inexpensive ASICs
Q-in-Q mode called SPBV
M-in-M mode called SPBM
Backward compatible to 802.1
802.1ag, Y.1731, Data Center Bridging protocols
Multiple loop free shortest paths routing
Excellent use of mesh connectivity
Currently 16 equal cost paths.
Optimum multicast head end or tandem replication

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 What is SPB? (2)

Light weight form of traffic engineering

Head end assignment of traffic to 16 shortest paths.
Deterministic routing - offline tools predict exact routes.
Scales to ~1000 or so devices
Uses IS-IS already proven well beyond 1000.
Huge improvement over the STP scales.
Good convergence with minimal complexity
sub second (modern processor, well designed)
below 100ms (use of hardware multicast for updates)
Includes multicast flow when replication point dies.

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 What is SPB? (3)

Service membership advertised in same protocol as

Topology
Minimizes complexity, near plug-and-play
Support E-LINE/E-LAN/E-TREE
Just variations on membership attributes
Address learning restricted to edge (M-in-M)
FDB is computed and populated just like a router.
Unicast and Multicast handled at same time.
Computations guarantee unicast/multicast:
Symmetry (same in both directions)
Congruence (unicast/multicast follow same route)
Tune-ability (currently 16 equal costs paths)

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 SPBM Packet Encapsulation
BEB A BCB B BEB C
VLAN X VLAN X
CVLAN=20 ISID=100 CVLAN=20 ISID=100
Destination C Destination A

Data ISID ISID ISID Data

Ethertype Ethertype
Ethertype Ethertype Ethertype
CTAG CTAG
BTAG BTAG BTAG
SRC MAC SRC MAC
BSA BSA BSA DST MAC
DST MAC

BDA BDA BDA

SPB Header Data Data Data

Ethertype Ethertype Ethertype

CTAG CTAG CTAG

Original Frame with
Inner Ethernet SRC MAC SRC MAC SRC MAC
Header, Payload etc.
DST MAC DST MAC DST MAC
Comparison to MLAG, SPB, VPLS/MPLS
 M-LAG for Active-Active Paths
Efficient Bandwidth Usage

LAG allows combining of ports effectively Core Network

increasing the bandwidth. Up to 64 ports
in a LAG Group.
Inter-
M-LAG allows combining of ports on two Switch
Connection
switches to form a single logical (ISC)

connection to another network device

Active-active paths. No STP port blocking
Fast Failover
For both Layer-2 and Layer-3
deployments MLAG MLAG
Group 1 Group 2
Interoperates across tiers
Works with servers, switches, storage,
and other network appliances

Data Center

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 Virtual Private LAN Service (VPLS) RFC
4761/4762

Emulated
LAN

L2 Ethernet VPN providing multi-point communication over IP/MPLS networks

All tenants sites appear to be on the same LAN regardless of location
VPLS provides VLAN extensions over IP/MPLS networks
Each tenant VLAN is mapped to a virtual switch instance or VPN ID

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 Shortest Path Bridging (SPB) IEEE
802.1aq

Equal Cost Multi-Path (ECMP) solution (up to 16 trees)

Large L2 bridging topologies (up to 16 million) based on IS-IS as link
state control protocol
Service & Infrastructure separation

Core/Backbone VLANs
(4096 VLANs)

Service Instance IDs

(16 million)

Tenant VLANs
(4096 VLANs)

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 IEEE Standards Evolution to scale L2
Fabrics

Payload

VLAN ID (12 bit)

Source Address

Payload Destination Address

Payload VLAN ID (12 bit) Service ID (24 bit)

Payload VLAN ID (12 bit) SVLAN ID (12 bit) B VLAN ID (12 bit)

Source Address Source Address Source Address Source Address

Destination Address Destination Address Destination Address Destination Address

IEEE 802.1 IEEE 802.1Q IEEE 802.1ad IEEE 802.1aq

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 Comparison

TRILL MLAG SPB VPLS

Standard Body IETF Vendor-specific IEEE IETF
New (Variant of
Technology New Matured Matured
PBB)
Yes
Minimal B-VID needs to be
Yes Yes No
Configuration configured for
each ECMP

Yes Yes
Yes
16 active links with Yes 16 active links with
ECMP 16 ECMP LSPs
true hop-by-hop 2 active links ingress ECMP
can be achieved
ECMP decisions decisions

Loop Yes Yes

Yes Yes
Prevention TTL and RPC RPC only
Virtualization Higher scale Higher scale
4K networks 4K networks
Scale with mac-in-mac with VPN ID