Transcript VLAN

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
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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?
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Performance
Formation of Virtual Workgroups
Simplified Administration
Reduced Cost
Security
VLAN Membership
• Membership by Port
• Membership by MAC
Address
• Membership by IP
Subnet Address
port
vlan
1
1
2
1
3
2
4
1
disadvantage of this
method is that it
does not allow for
user mobility.
VLAN Membership
• Membership by Port
• Membership by MAC
Address
• Membership by IP Subnet
Address
MAC Address
vlan
1212354145121
1
2389234873743
1
3045834758445
2
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
• Membership by MAC
Address
• Membership by IP
Subnet Address
IP Subnet
vlan
23.2.24
1
26.21.35
2
Advantage:
• 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
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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
They have used Avaya's
Cajun switches, and the STP
is stored in PROMINET-MIB
2
Collecting Spanning Tree Related
Information
Implementation Detail
3
Construction of Per-VLAN
Spanning Tree
4
Spanning Tree of VLAN 12