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					 VLAN

Suman Pandey
              References
• D. Passmore, and J. Freeman, “The Virtual
  LAN Technology Report”,
  http://www.3com.com/nsc/200374.html, March,
  1997
• 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
                       Outline
• 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
  Discovery
  – 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
  domains.
• 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
  Address
                       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
  Address
• Membership by IP
                       Advantage:
  Subnet Address       • Good for application-based VLAN
                          strategy
                       • User can move workstations
                       • eliminate the need for frame tagging
                       Disadvantage :
                       • Performance/ looking for L3 address in
                          packet.
                       • 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
  databases
Active Topology of Network with
            Bridges
            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:

• TCI
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
• BRIDGE-MIB (RFC 1493)
• Q-BRIDGE-MIB (RFC 2674).
Bridge MIB Used
• dot1dStpPort
• dot1qPvid
• dot1dStpPortState
• dot1dStpPortDesignatedRoot
• dot1dStpPortDesignatedBridge
• dot1dStpPortDesignatedPort
  Discovery of Spanning Trees and
               VLANs
Steps
• 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
  1
                                2

They have used Avaya's        Collecting Spanning Tree Related
Cajun switches, and the STP   Information
is stored in PROMINET-MIB
             Implementation Detail
  3
                             4


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

				
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