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Suman Pandey
• D. Passmore, and J. Freeman, “The Virtual
  LAN Technology Report”,
  http://www.3com.com/nsc/200374.html, March,
• IEEE 802.1Q, “IEEE Standard for Local and
  Metropolitan Area Networks: Virtual Bridge
  Local Area Networks”, 1998
• Meng Guo , Subrata Mazumdar , “Discovery of
  Spanning Trees in Virtual Bridged LAN” , The
  Quarterly Newsletter of SNMP Technology,
  Comment, and Events, Volume 9, Number 1,
  December, 2001
• General Concepts of VLAN
  –   What is VLAN ?
  –   Why use VLAN's?
  –   Different way to assign VLAN Membership.
  –   Spanning Tree in VLAN
  –   Frame processing and 802.1Q standard
  –   Different kind of logical VLAN architecture
• Implementation Details of VLAN for Topology
  – Different Vendor specific Solutions
  – SPECTRUM VLAN manager implementation
  – MIB used
General Concepts of VLAN

    Paper: The Virtual LAN
     Technology Report
              What is VLAN ?
• vendor-specific solution
  and strategy, so defining
  it is an issue.
• VLAN's allow a network
  manager to logically
  segment a LAN into
  different broadcast
• multiple physical LAN
  segments independent of
  physical location and can
  communicate as if they
  were on a common LAN
           Why use VLAN's?
•   Performance
•   Formation of Virtual Workgroups
•   Simplified Administration
•   Reduced Cost
•   Security
         VLAN Membership
• Membership by Port   port     vlan
                       1        1
• Membership by MAC
                       2        1
  Address              3        2
• Membership by IP     4        1
  Subnet Address
                       disadvantage of this
                         method is that it
                         does not allow for
                         user mobility.
         VLAN Membership
• Membership by Port            MAC Address          vlan
• Membership by MAC             1212354145121        1
  Address                       2389234873743        1
                                3045834758445        2
• Membership by IP Subnet
                                5483573475843        1
                       Advantage :
                       • no reconfiguration needed
                       Disadvantage :
                       • VLAN membership must be
                          assigned initially.
                       • performance degradation as
                          members of different VLANs coexist
                          on a single switch port
         VLAN Membership
• Membership by Port          IP Subnet       vlan
                              23.2.24         1
• Membership by MAC
                              26.21.35        2
• Membership by IP
  Subnet Address       • Good for application-based VLAN
                       • User can move workstations
                       • eliminate the need for frame tagging
                       Disadvantage :
                       • Performance/ looking for L3 address in
                       • Less effective with protocols such as
                          IPX™, DECnet®, or AppleTalk®
                       • “unroutable” protocols such as NetBIOS
Frame Processing in VLAN env
Role of Bridges
• bridge on receiving data determines to which
  VLAN the data belongs either by implicit or
  explicit tagging [802.1Q].
• The bridge also keeps track of VLAN members
  in a filtering database which it uses to determine
  where the data is to be sent
• all the bridges in the VLAN should contain the
  same information in their respective filtering
Active Topology of Network with
            Filtering Database
• Membership information for a VLAN is stored in
  a filtering database
  – Static Entries
     • Static Filtering Entries: for every port whether frames to be
       sent to a specific MAC address or group address and on a
       specific VLAN should be forwarded or discarded, or follow
       dynamic entry
     • Static Registration Entries: whether frames to be sent to a
       specific VLAN are to be tagged or untagged and which ports
       are registered for that VLAN
  – Dynamic Entries (learnt by bridges)
     • Dynamic Filtering Entries:
     • Group Registration Entries: follows GVRP protocol.
     • Dynamic Registration Entries:
          Tagging [802.1Q]
• Ethernet Frame Tag Header:

• Token Ring and Fiber Distributed Data
  Interface (FDDI) tag header:

VLAN architecture going forward
Infrastructural VLAN   Service-Based VLAN
     Other Details of the Report
•   DHCP with VLAN
•   ATM with VLAN
•   VLAN Migration Strategy
•   Automatic configuration of VLAN
  Implementation Details of
VLAN for Topology Discovery
  Paper: Discovery of Spanning
  Trees in Virtual Bridged LAN
 Different Vendor specific Solutions
• Avaya's VLANMaster application - only works with
  Avaya’s Cajun switches.
• Aprisma's SPECTRUM VLAN Manager It uses the
  Cabletron Discovery Protocol (CDP) to find all CDP
  compatible 802.1Q switches in a domain
• Cisco's VlanDirector uses Cisco Discovery Protocol
  (CDP) VlanDirector cannot manage any devices that do
  not run CDP.
• 3COM's Enterprise VLAN Manager
• Granite open source C API/SDK to provision VLAN
  configurations using SNMP for Riverstone products.
             MIB Information
MIB used
• RFC1213-MIB
• Q-BRIDGE-MIB (RFC 2674).
Bridge MIB Used
• dot1dStpPort
• dot1qPvid
• dot1dStpPortState
• dot1dStpPortDesignatedRoot
• dot1dStpPortDesignatedBridge
• dot1dStpPortDesignatedPort
  Discovery of Spanning Trees and
• Deduce the target Virtual Bridged LAN from an arbitrary
  IP address in the Virtual Bridged LAN
• Automatically discover all the bridges in the target Virtual
  Bridged LAN
• Collect spanning tree and VLAN related MIB variables
  from the discovered brides using SNMP
• Construct the spanning trees in the Virtual Bridged LAN
  and associate the spanning trees with VLANs.
             Implementation Detail

They have used Avaya's        Collecting Spanning Tree Related
Cajun switches, and the STP   Information
is stored in PROMINET-MIB
             Implementation Detail

Construction of Per-VLAN
Spanning Tree              Spanning Tree of VLAN 12

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