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52. LAN ARCHITECTURES

  • You have studied various NETWORK technologies: ROUTING, SWITCHING, STP, ETHERCHANNEL, OSPF, FHRPs, SWITCH SECURITY FEATURES, etc.
    • Now, let’s look at some BASIC NETWORK DESIGN / ARCHITECTURE
  • There are standard “BEST PRACTICES” for NETWORK DESIGN
    • However there are a few UNIVERSAL “CORRECT ANSWERS”
    • The answer to MOST general questions about NETWORK DESIGN is “IT DEPENDS”
  • In the early stages of your NETWORKING career, you probably won’t be asked to DESIGN NETWORKS yourself
  • However, to understand the NETWORKS you will be CONFIGURING and TROUBLESHOOTING, it’s important to know some BASICS of NETWORK DESIGN

COMMON TERMINOLOGIES

  • STAR
    • When several DEVICES all connect to ONE CENTRAL DEVICE, we can draw them in a “STAR” shape like below, so this is often called a “STAR TOPOLOGY”

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  • FULL MESH
    • When each DEVICE is connected to each OTHER DEVICE

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  • PARTIAL MESH
    • When SOME DEVICES are connected to each other but not ALL

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2-TIER AND 3-TIER LAN ARCHITECTURE

  • The TWO-TIER LAN DESIGN consists of TWO Hierarchical Layers:
    • ACCESS LAYER
    • DISTRIBUTION LAYER
  • Also called a “COLLAPSED CORE” DESIGN because it omits a layer that is found in the THREE TIER DESIGN : THE CORE LAYER
  • ACCESS LAYER
    • The LAYER that END HOSTS connect to (PCs, Printers, Cameras, etc)
    • Typically, ACCESS LAYER SWITCHES have lots of PORTS for END HOSTS to connect to
    • QoS MARKING is typically done here
    • Security Services like PORT SECURITY, DAI, etc are typically performed here
    • SWITCHPORTS might be PoE-Enabled for Wireless APs, IP Phones, etc.
  • DISTRIBUTION LAYER
    • Aggregates connections from the ACCESS LAYER SWITCHES
    • Typically is the border between LAYER 2 and LAYER 3
    • Connects to services such as Internet, WAN, etc
    • Sometimes called AGGREGATION LAYER

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THREE-TIER CAMPUS LAN DESIGN

  • In large NETWORKS with many DISTRIBUTION LAYER SWITCHES (for example in separate buildings), the number of connections required between DISTRIBUTION LAYER SWITCHES grows rapidly

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  • To help SCALE large LAN NETWORKS, you can add a CORE LAYER.

** Cisco recommends adding a CORE LAYER if there are more than THREE DISTRIBUTION LAYERS in a single location

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  • The THREE-TIER LAN DESIGN consists of THREE HIERARCHICAL LAYERS:

    • ACCESS LAYER
    • DISTRIBUTION LAYER
    • CORE LAYER

  • CORE LAYER:

    • Connects DISTRIBUTION LAYERS together in large LAN NETWORKS
    • The focus is SPEED (”FAST TRANSPORT”)
    • CPU-INTENSIVE OPERATIONS, such as SECURITY, QoS Markings / Classification, etc. should be avoided at this LAYER
    • Connections are all LAYER 3. NO SPANNING-TREE!
    • Should maintain connectivity throughout the LAN even if DEVICES FAIL

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SPINE-LEAF ARCHITECTURE (DATA CENTER)

  • CISCO ACI ARCHITECTURE (Application Centric Infrastructure) uses this architecture
  • DATA CENTERS are dedicated spaces / buildings used to STORE COMPUTER SYSTEMS such as SERVERS and NETWORK DEVICES
  • Traditional DATA CENTER designs used a THREE-TIER ARCHITECTURE (ACCESS-DISTRIBUTION-CORE) like we just covered
  • This worked well when most TRAFFIC in the DATA CENTER was NORTH-SOUTH

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  • With the precedence of VIRTUAL SERVERS, applications are often deployed in a DISTRIBUTED manner (across multiple physical SERVERS) which increases the amount of EAST-WEST TRAFFIC in the DATA CENTER
  • The traditional THREE-TIER ARCHITECTURE led to bottlenecks in the BANDWIDTH as well as VARIABILITY in the SERVER-TO-SERVER latency depending on the PATH the TRAFFIC takes
  • To SOLVE this, SPINE-LEAF ARCHITECTURE (also called CLOS ARCHITECTURE) has become prominent in DATA CENTERS

RULES FOR SPINE-LEAF ARCHITECTURE

  • Every LEAF SWITCH is connected to every SPINE SWITCH
  • Every SPINE SWITCH is connected to every LEAF SWITCH
  • LEAF SWITCHES do NOT connect to other LEAF SWITCHES
  • SPINE SWITCHES do NOT connect to other SPINE SWITCHES
  • END HOSTS (Servers, etc) ONLY connect to LEAF SWITCHES

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  • The PATH taken by TRAFFIC is randomly chosen to balance the TRAFFIC LOAD among the SPINE SWITCHES
  • Each SERVER is separated by the same number of “HOPS” (except those connected to the same LEAF) providing CONSISTENT LATENCY for EAST-WEST TRAFFIC

SOHO (SMALL OFFICE / HOME OFFICE)

  • SMALL OFFICE / HOME OFFICE (SOHO) refers to the office of a small company, or a small home office with few DEVICES

    • Doesn’t have to be an actual home “office”; if your home has a NETWORK connected to the INTERNET it is considered a SOHO NETWORK

  • SOHO NETWORKS don’t have complex needs, so all NETWORKING functions are typically provided by a SINGLE DEVICE, often called a “HOME ROUTER” or “WIRELESS ROUTER”

  • The one DEVICE can serve as a:

    • ROUTER
    • SWITCH
    • FIREWALL
    • WIRELESS ACCESS POINT
    • MODEM

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