Compare and Contrast SPB and TRILL

Table of Contents

Section 1: Simplifying Network .................1.. .

. Virtualization

Section 2: Background and Basics...........2

of TRILL

Section 3: Background and Basics ..........2

of SPB

Section 4: Technology Compare and.......3

Contrast

Section 5: Additional Features .................6

Making SPB

“Enterprise-friendly”

Section 6: Summary........................................9

Section 1: Simplifying Network Virtualization

In today’s world of data center consolidation, the move to server virtualization

has happened more quickly than most would have imagined. The primary

benefit of virtualization is a reduction in the number of servers, enabling direct

cost savings for server hardware, space, power, cooling, etc. Virtualization of the

server infrastructure also has a direct impact on the underlying network. Virtual

machine mobility adds requirements to the network in terms of extending Layer

2 VLANs between racks within a data center or between different geographic

data centers. These moves typically require network configuration changes and

in many cases the traffic may use a non-optimal path between data centers.

As enterprises begin to build their own private cloud computing environments,

network virtualization is a key component to overall success. To realize the

benefits of cloud computing, such as application access anywhere and anytime,

along with the ability to add resources and services transparently, the need

to create a virtualized data center backbone becomes apparent. This cloud

computing environment will stress the network in different ways and the

ability to be proactive in network infrastructure connectivity will require a new

paradigm for data center design.

Figure 11: Infrastructure Requirements for the private cloud

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1Tolly Enterprises: Evaluation of Energy Consumption and Projected Costs for a Converged LAN Campus, Data Center, and WAN

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Network virtualization is required to support the growing needs of the data center in terms of cloud computing,

workload mobility (e.g. virtual machine mobility), increased control of traffic flows, efficient use of bandwidth,

and to reduce the amount of network equipment needed. The key is to virtualize the network without adding

complexity – this is the goal of both Shortest Path Bridging (SPB) and Transparent Interconnect of Lots of Links

(TRILL). The desire is to create a more robust Layer 2 topology by eliminating Spanning Tree while supporting both

multipath forwarding and localized failure resolution. Both of these emerging technologies – SPB and

TRILL – promise to do just that. This document seeks to highlight the similarities and differences between these

new emerging standards.

Section 2: Background and Basics of TRILL

TRILL is an IETF proposed standard that was originally introduced to the IEEE in 2006, but was not pursued by

the 802.1 group. Several networking companies, including Cisco, Brocade and Juniper, have begun participating in

the IETF TRILL initiative and have announced intentions to support this technology.

TRILL leverages IS-IS as a topology management protocol and introduces the need for new IS-IS control packets. A

new header format has also been created for TRILL. This new header, which sits behind the standard MAC header,

establishes communications between TRILL nodes. There is also a new TTL (Time to Live) field that is needed to

minimize the impact of loops within the TRILL network. This TTL is mainly needed to support the formation of the

non-congruent trees for Unicast, Multicast, and Broadcast traffic. TRILL builds one or more rooted Spanning Trees

to support flooding of Unknowns, Broadcasts, and Multicasts. This implies that Unicast traffic may take different

paths through the network than Broadcast / Multicast traffic, even though all traffic may be going from the same

source to the same destination.

TRILL can support up to 4,000 VLANs and introduces a new protocol to advertise End Station Address Information

(ESADI). TRILL supports customer MAC Addresses and VLAN IDs (802.1Q). Because there is no abstraction

and no simple way to map VLANs into different services, TRILL lacks the ability to have granular control of

traffic. Also, due to TRILL’s newly introduced encapsulation formats, none of the existing IP- or Ethernet-based

OA&M functionalities apply. For effective troubleshooting of TRILL-based networks, there is a need to develop a

completely new set of OA&M tools.

Section 3: Background and Basics of SPB

SPB was originally introduced to the IEEE as Provider Link State Bridging (PLSB), a technology developed by

Nortel. PLSB was itself an evolution of another Nortel developed technology, namely 802.1ah (Provider Backbone

Bridging). Shortest Path Bridging is now an IEEE draft (802.1aq) that will eventually be included in the 802.1Q

standard. Several networking companies, including Avaya, Alcatel, Hauwei and Cisco, are participating in the IEEE

SPB initiative and have announced support for Shortest Path Bridging technology. This technology is intended to

serve as both an Enterprise and a Carrier solution. For enterprises, the first area of implementation will be the Data

Center and Campus Core solutions; for Carriers SPB is viewed as an alternative and/or extension to H-VPLS. SPB

is a proven technology, having been deployed for several years in the Carrier market; this provides SPB with an

inherent and immediate advantage over TRILL, which is a totally new technology with no roots of evolution.

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Within SPB there are two models for multipath bridging: Shortest Path Bridging VLAN (SPBV) and Shortest Path

Bridging Mac-in-Mac (SPBM). Both variants use IS-IS as the link state topology protocol and both compute

shortest path trees between nodes. SPBV uses a Shortest Path VLAN ID (SPVID) to designate nodal reachability.

SPBM uses a Backbone MAC (BMAC) and Backbone VLAN ID (BVID) combination to designate nodal reachability.

Both SPBV and SPBM provide interoperability with Spanning Tree. For the purposes of this document, SPBM will

be the technology used for all comparisons.

The 802.1aq SPB standard reuses the PBB 802.1ah data path, and therefore fully supports the IEEE

802.1ag-based OA&M functionality. Thus, there is a full set of Ethernet-based network operations and debugging

functionality already available. The 802.1ah frame format provides a service identifier (I-SID) which is completely

separated from the Backbone MAC addresses and the VLAN IDs – this enables simplified data center virtualization.

The goal is to fully separate the connectivity services layer from the physical network infrastructure, removing all

the interdependencies of protocols and the physical network. The I-SID abstracts the service from the network – by

mapping a VLAN or multiple VLANs to an I-SID at the service access point, SPB automatically builds a shortest

path through the network to fully extend LAN connectivity, which is exactly the requirement for the support of

server virtualization and the virtualized data center backbone. The I-SID also provides a mechanism for granular

traffic control. By mapping services (applications) into specific I-SIDs, the user can now create mission-specific

end-to-end networks and control access to those services much easier.

In Avaya’s implementation, the mapping together of end-point services is known as a “Virtual Service Network”

(VSN), and multiple VSNs will exist in a typical enterprise network.

Section 4: Technology Compare and Contrast

Characteristic SPB TRILLStandards Body Definition IEEE (802.1aq) IETF

Multi-Pathing Support Yes Yes

Eliminates Need for Spanning Tree and Blocked Links

Yes Yes

Interoperability with Spanning Tree Yes Yes

Loop Prevention RPFC TTL-based (due to non-congruent trees) & RPFC

Uses IS-IS as the Layer 2 Routing Protocol Yes Yes

IS-IS Interoperability Uses existing IS-IS with TLV extensions (interops with third-party IS-IS routing

solutions)

New type of IS-IS instance with new PDU types

Dynamically Changes Network Paths for Traffic Flows

Yes Yes

Cut-through Switching Possible Possible but difficult due to options field in header

Virtualization Support Service Instance using I-SID (16Mio) VLAN only (4k)

Low-Touch Configuration Yes; need to configure VLAN to Service Instance Mapping

Yes

Election Processes Pre-provisioned Designated Forwarder, Root Bridge, IS-IS nicknames per Rbridge

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Characteristic SPB TRILLLookup and Forwarding Traditional Ethernet switching in tandem

nodes; IEEE 802.1ah in BCB and BEB. No MAC swapping ala router (IEEE

802.1ah capable hardware required)

New header with triple lookup required on every Rbridge node (new ASIC)

Encapsulation Mac-in-Mac TRILL Header

Unicast Traffic Path Shortest Path based on IS-IS calculations

Shortest Path based on IS-IS calculations

Broadcast/Multicast Traffic Path Between two end nodes same as Unicast and bi-directionally congruent – tree is

source node based

Depends on Selected Root Bridge unicast and broadcast/multicast paths can be completely different (can cause out-of-sequence packets when switching

from BR/MC path to Unicast path)

Egress Processing for Multicast Not Required Required due to MAC header change egress port

Customer MAC learning Packet-based learning at edge of SPB network

Packet-based at edge access ports+ ESADI protocol

Out of Sequence Packets (possible) No Possible when a Dest MAC transitions from unknown MAC to known

Service Aggregation Yes (multiple VLANs can be mapped into a Service Instance)

No

Traffic Management Assigns traffic to shortest paths at the head end. Link based metrics for path

calculations.

Assigns shortest path for Unicast with Layer 2 header swap at each Rbridge.

Link based metrics for path calculations.

OA&M IEEE 802.1ag, ITU Y.1731 performance and jitter management

N/A

Ease of Troubleshooting Easier to see entire path through the network. Full set of IEEE/ITU based

Ethernet OAM tools

Need to inspect traffic on a hop-by-hop basis to know the path. No OAM tools

available.

New hardware required Built on 802.1ah, 802.1ad, 802.1ag which is supported in many hardware

platforms

TRILL requires new hardware and as of now there is no OA&M hardware support

Layer 3 and IP VPN Extensions IP/SPB Draft No integration

Scalability 10,000+ with multi-level IS-IS 10,000+ claimed

Convergence Source Node based Tree Calculations (number of trees calculated is based on

number of nodes)

Separate EASDI instance/VLAN – each port announces all VLANs via TRILL hello, up to 4,096 hellos can be sent

per port. Dynamic Root Bridge Election, Dynamic Designated Forwarder Election

System ID Node names use provisioned system IDs Potential Nickname collisions when joining TRILL networks together

TRILL and SPB Lookup/Forwarding Comparison

Figure 2 depicts packet lookup and forwarding within a TRILL and SPB network respectively. As shown in the

TRILL example, TRILL header lookups with MAC swap, TTL decrement and Frame Check Sequence recalculation

occur at every node because forwarding is done on a hop-by-hop basis. This adds to the overall network complexity

and can complicate troubleshooting. Because there is no simple way to determine the selected path for a

particular flow, troubleshooting must be done hop–by-hop at each node. The SPB implementation eliminates the

complexity by using simple MAC forwarding table lookup and assigns the traffic to a shortest path to the desired

egress point. This simplifies troubleshooting in this environment because the entire flow can be easily identified

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by source and destination address. The fact that SPB provides congruent paths for all traffic also makes the job of

troubleshooting different traffic types much easier.

Figure 2

A major difference between SPB and TRILL is in the way they each handle traffic forwarding. 802.1aq uses

a simple and elegant method to utilize the multiple paths through the network. After IS-IS builds the network

topology, SPB creates the shortest paths based on link metrics and then assigns the traffic (Unicast and Multicast)

to that path. Therefore it is very easy to predict the traffic flows through the meshed network since they are

calculated once for the entire path. With 802.1aq, a network analyzer can easily identify the route network traffic

is taking in either direction by looking at the source address, destination address and VLAN ID. The service

identifier (I-SID) in 802.1aq will also scope the flow down to the specific service.

In contrast, TRILL uses two different mechanisms to forward packets based on traffic type. For Unicast traffic

where the egress Rbridge is known, TRILL uses the IS-IS link state database to assign traffic to the most optimal

path (similar to SPB). However, for Multicast, Broadcasts, and Unknowns, TRILL uses distribution trees and an

Rbridge as the root for forwarding. In many cases, these paths will not be congruent and makes TRILL susceptible

to out-of-order packets when the MAC state transitions from unknown to known. This also makes it more difficult

to know the exact path through the network when looking from any given Switch/Port based on traffic type.

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Shortest Path Trees

Figure 3

Section 5: Additional Features Making SPB “Enterprise-friendly”

Enterprise data centers are designed to support Layer 2 VLANs and Layer 3 routing. In the Avaya model, dual-

homing is standard for servers, switches, and appliances with the use of Switch Clustering (using Split Multi-Link

Trunking technology). Typically, it takes significant effort to create solutions that are as resilient as possible while

maintaining the performance and scalability expected by users.

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Moving to a virtualized model should be easy for enterprises to accomplish, and provide a significant return on

investment, since these criteria will directly affect the success or failure of a new technology. After reviewing

the needs of many enterprises, Avaya discovered certain areas could be augmented to make virtualization more

useable. These additional features from Avaya, over and above the IEEE 802.1aq standard, provide the added

value that makes the move to SPB even more enticing. In accordance with its heritage of technology innovation,

Avaya has added these features to its network virtualization offer, and delivers a compelling solution that meets the

needs of the enterprise data center.

SPB UNI Dual-homing Support

The Avaya best practice for Ethernet connectivity employs a dual-homed active/active configuration. The Server

NICs are teamed and connected into an Avaya Switch Cluster. In turn, the compute access layer Switch Cluster

is connected in the same active/active manner to the data center core. This solution eliminates the need for

Spanning Tree, blocked links, and unpredictable failover/recovery times during network outages or maintenance

windows. In order to make a smooth transition from today’s network architecture to a virtualized data center

backbone using SPB, it is critical to support UNI (user network interface) dual-homing. The migration to SPB can

be achieved in a phased approach because end devices with dual-homed attachments do not require configuration

changes. Using this feature as SPB migrates from the data center into the campus, allows dual-homed closets to

remain untouched as the campus core is virtualized.

.

Figure 4

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IP/SPB Inter-ISID Routing

Routing traffic between VLANs is commonly used in traditional 802.1Q environments, and this capability is

replicated in a SPB environment by enabling Inter-ISID routing. This allows the network to use SPB nodes as

default gateways/routers for extended VLANs without having to terminate the I-SID, the Virtual Service Network, at

an edge node. This is particularly interesting in a data center deployment where the top-of-rack devices are also

SPB capable, but are purely Layer 2 devices. In this scenario, the first routing hop is provided at the aggregation

layer, which lies deep in the network.

IP/SPB Layer 3 VRF Extensions

Whether it is an airport authority supporting multiple airlines on its infrastructure or a government IT department

in charge of supporting various agencies, they all need to provide traffic separation on top of one shared network

infrastructure. Typically these deployments start with VRF separation, but in most cases those VRFs need to be

extended across the network infrastructure. The IETF IP/SPB-Unbehagen draft describes an extension to SPB

that leverages IS-IS to not only build Layer 2 domains, but also provide a very flexible Layer 3 VRF extension

capability. This integrated model eliminates the need for BGP4 or any other additional protocols to support Layer 3

virtualization. Typically Layer 3 VRFs can now be provided at any SPB node in the network in parallel to the Layer

2 VLAN extension solution. IS-IS carries the VRF-specific route entries in its link state updates, and in this model

VRF separation is provided by the I-SID mechanism.

Figure 5 highlights SPB and its extensions provided by Avaya.

Figure 5

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Section 6: Summary

Business requirements, especially in the next-generation data center, will drive the need for network virtualization.

As the network progressively becomes more critical to the enterprise and its ability to do business, an always-on,

scalable, and efficient infrastructure and architecture is necessary. A key goal is to expand the network capabilities

while at the same time reducing its complexity.

The value propositions include:

• Ability to provide plug & play services with less complexity than legacy protocols

• Operational savings through simplification, based on a new integrated model

• Increased network uptime through use of one proven and robust link state protocol for all services

• Separates the network infrastructure from the connectivity services layer

• Consistent network behavior and predictability through support of one protocol for all network services

• Optimal network bandwidth utilization through usage of all available links

• Maximal network topology design flexibility through usage of link state based protocol

The return on investment (ROI) for deployment of a new technology must be attractive enough to move forward.

Shortest Path Bridging provides the value of network virtualization with the overall ease of deployment and

on-going maintenance. TRILL provides some of the same basic values as SPB; however, TRILL is more complex

and doesn’t provide the additional feature augmentation that Avaya brings with SPB. There are substantial

differences between the two technologies. SPB delivers simplicity and elegance over the life of the network, along

with the additional Layer 3 features that enterprises need.

Avaya continues to deliver unique technological innovation to the market, and network virtualization is a prime

example. By coupling IEEE 802.1aq SPB with the additional features enterprises find important – namely Layer

3 routing, extension of virtual routers (VRFs), and the need for dual-home access – Avaya creates substantial

differentiation for SPB over TRILL.

© 2011 Avaya Inc. All Rights Reserved. Avaya and the Avaya Logo are trademarks of Avaya Inc. and are registered in the United States and other countries. All trademarks identified by ®, TM or SM are registered marks, trademarks, and service marks, respectively, of Avaya Inc. All other trademarks are the property of their respective owners. Avaya may also have trademark rights in other terms used herein.References to Avaya include the Nortel Enterprise business, which was acquired as of December 18, 2009.06/11 • DN4634-01

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