Compare and Contrast SPB and TRILL
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Compare and Contrast
SPB and TRILL
Table of Contents Section 1: Simplifying Network Virtualization
Section 1: Simplifying Network ................1 In today’s world of data center consolidation, the move to server virtualization
has happened more quickly than most would have imagined. The primary
Virtualization
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
Section 2: Background and Basics........... 2
server infrastructure also has a direct impact on the underlying network. Virtual
of TRILL machine mobility adds requirements to the network in terms of extending Layer
2 VLANs between racks within a data center or between different geographic
Section 3: Background and Basics .......... 2 data centers. These moves typically require network configuration changes and
of SPB in many cases the traffic may use a non-optimal path between data centers.
Section 4: Technology Compare and.......3 As enterprises begin to build their own private cloud computing environments,
network virtualization is a key component to overall success. To realize the
Contrast
benefits of cloud computing, such as application access anywhere and anytime,
along with the ability to add resources and services transparently, the need
Section 5: Additional Features .................6
to create a virtualized data center backbone becomes apparent. This cloud
Making SPB computing environment will stress the network in different ways and the
“Enterprise-friendly” ability to be proactive in network infrastructure connectivity will require a new
paradigm for data center design.
Section 6: Summary........................................9
Figure 11: Infrastructure Requirements for the private cloud
1
Tolly Enterprises: Evaluation of Energy Consumption and
Projected Costs for a Converged LAN Campus, Data Center,
and WAN
WHITE PAPER 1
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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 TRILL
Standards Body Definition IEEE (802.1aq) IETF
Multi-Pathing Support Yes Yes
Eliminates Need for Spanning Tree and Yes Yes
Blocked Links
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 New type of IS-IS instance with new
(interops with third-party IS-IS routing PDU types
solutions)
Dynamically Changes Network Paths for Yes Yes
Traffic Flows
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 Yes
Instance Mapping
Election Processes Pre-provisioned Designated Forwarder, Root Bridge, IS-IS
nicknames per Rbridge
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Characteristic SPB TRILL
Lookup and Forwarding Traditional Ethernet switching in tandem New header with triple lookup required
nodes; IEEE 802.1ah in BCB and BEB. on every Rbridge node (new ASIC)
No MAC swapping ala router (IEEE
802.1ah capable hardware required)
Encapsulation Mac-in-Mac TRILL Header
Unicast Traffic Path Shortest Path based on IS-IS Shortest Path based on IS-IS
calculations calculations
Broadcast/Multicast Traffic Path Between two end nodes same as Unicast Depends on Selected Root Bridge
and bi-directionally congruent – tree is unicast and broadcast/multicast paths
source node based 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 Packet-based at edge access ports+
network 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 No
into a Service Instance)
Traffic Management Assigns traffic to shortest paths at the Assigns shortest path for Unicast with
head end. Link based metrics for path Layer 2 header swap at each Rbridge.
calculations. Link based metrics for path calculations.
OA&M IEEE 802.1ag, ITU Y.1731 performance N/A
and jitter management
Ease of Troubleshooting Easier to see entire path through the Need to inspect traffic on a hop-by-hop
network. Full set of IEEE/ITU based basis to know the path. No OAM tools
Ethernet OAM tools available.
New hardware required Built on 802.1ah, 802.1ad, 802.1ag TRILL requires new hardware and as of
which is supported in many hardware now there is no OA&M hardware support
platforms
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 Separate EASDI instance/VLAN – each
(number of trees calculated is based on port announces all VLANs via TRILL
number of nodes) 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.
9About Avaya Avaya is a global leader in enterprise communications systems. The company provides unified communications, contact centers, and related services directly and through its channel partners to leading businesses and organizations around the world. Enterprises of all sizes depend on Avaya for state-of-the-art communications that improve efficiency, collaboration, customer service and competitiveness. For more information please visit www.avaya.com. © 2010 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. avaya.com 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. 11/10 • DN4634
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