DATA CENTER
ETHERNET
M. Keshtgary
OVERVIEW
Residential vs. Data Center Ethernet
 Review of Ethernet Addresses, devices, speeds,
algorithms
 Enhancements to Spanning Tree Protocol
 Virtual LANs
 Data Center Bridging Extensions
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RESIDENTIAL VS. DATA CENTER
ETHERNET
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IEEE 802 ADDRESS FORMAT
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ETHERNET VS IEEE 802.3
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The source address is always a unicast (single node)
address, while the destination address may be unicast,
multicast (group), or broadcast (all nodes).
In Ethernet frames, the 2-byte field following the source
address is a type field. This field specifies the upperlayer protocol to receive the data after Ethernet
processing is complete.
In IEEE 802.3 frames, the 2-byte field following the
source address is a length field, which indicates the
number of bytes of data that follow this field
In IEEE 802.3, the upper-layer protocol must be defined
within the data portion of the frame, if at all
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NAMES, IDS, LOCATORS
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INTERCONNECTION DEVICES
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INTERCONNECTION DEVICES
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ETHERNET SPEEDS
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LINK AGGREGATION CONTROL PROTOCOL
(LACP)
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SPANNING TREE ALGORITHM
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PROBLEMS WITH STP
A topology change can result in 1 minute of
traffic loss with STP and All TCP connections
break
 Does not support VLAN
 Solution is Rapid Spanning Tree Protocol (RSTP)
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RAPID SPANNING TREE PROTOCOL (RSTP)
IEEE 802.1w-2001 incorporated in IEEE 802.1D2004
 One tree for all VLANs => Common spanning
tree
 Many trees => Multiple spanning tree (MST)
protocol
 IEEE 802.1s-2002 incorporated in IEEE 802.1Q2005
 One or more VLANs per tree.
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RSTP
RSTP fixes STP problems by:
 1. Being time + event driven instead of just event
driven
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Once converged, STP sends BPDUs only on change
 RSTP sends Hellos every 2 seconds. Quick failure
detection.
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2. Differentiating between edge ports (servers)
and non-edge ports (switches). No loops ever on
edge ports
 3. Differentiating between point-to-point links
(full duplex) and shared links (half-duplex).
RSTP only on full-duplex
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RSTP (CONT)
Merging three port states (Disabled, blocking,
listening) in to one (discarding).
 5. Adding 4 new flags in BPDU, that allow
sending a proposal and accepting or not accepting
the received proposal
 RSTP is backward compatible with STP. RSTPunaware bridge drop RSTP and RSTP is
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RSTP EXAMPLE
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MSTP (MULTIPLE SPANNING TREE)
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IS-IS PROTOCOL
Intermediate System to Intermediate
System (IS-IS) is a routing protocol designed to
move information efficiently within a computer
network, a group of physically connected
computers or similar devices.
 It accomplishes this by determining the best
route for datagrams through a packet-switched
network.
 The protocol was defined in ISO/IEC 10589:2002
as an international standard within the Open
Systems Interconnection (OSI) reference design
 IS-IS Protocol is link state
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IS-IS PROTOCOL
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SHORTEST PATH BRIDGING
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WHAT IS A LAN?
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WHAT IS A VIRTUAL LAN
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VIRTUAL LAN
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TYPES OF VIRTUAL LANS
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IEEE 802.1Q-2011 TAG
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LINK LAYER DISCOVERY PROTOCOL
(LLDP)
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DATA CENTER BRIDGING
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ETHERNET FLOW CONTROL: PAUSE
FRAME
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PRIORITY-BASED FLOW CONTROL (PFC)

Ref: J. L. White, “Technical Overview of Data Center Networks,” SNIA, 2013,
http://www.snia.org/sites/default/education/tutorials/2012/fall/networking/JosephWhi
te_Technical%20Overview%20of%20Data%20Center%20Networks.pdf
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ENHANCED TRANSMISSION SELECTION
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ETS (CONT)
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QUANTIZED CONGESTION NOTIFICATION
(QCN)
Ref: I. Pepelnjak, “DCB Congestion Notification (802.1Qau),”
http://blog.ipspace.net/2010/11/data-center-bridging-dcbcongestion.html
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DCBX
Data Center Bridging eXchange, IEEE 802.1Qaz2011
 Uses LLDP to negotiate quality metrics and
capabilities for Priority-based Flow Control,
Enhanced Transmission Selection, and Quantized
Congestion Notification
 New TLV’s
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Priority group definition
Group bandwidth allocation
PFC enablement per priority
QCN enablement
DCB protocol profiles
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SUMMARY
Ethernet’s use of IDs as addresses makes it very
easy to move systems in the data center => Keep
traffic on the same Ethernet
 Spanning tree is wasteful of resources and slow.
 Ethernet now uses shortest path bridging
(similar to OSPF)
 VLANs allow different non-trusting entities to
share an Ethernet network
 Data center bridging extensions reduce the
packet loss by enhanced transmission selection
and Priority-based flow control
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