This document provides an overview of switch functionality within networking, explaining the roles and advantages of switches compared to routers, including their ability to create multiple collision domains, independent bandwidth for each port, and low latency. It details the processes of address learning, forwarding decisions, and loop avoidance, emphasizing the importance of Spanning Tree Protocol (STP) to prevent loops in redundant link scenarios. Additionally, it covers different switching modes, such as cut-through, fragment-free, and store-and-forward, and outlines the basic configuration tasks for Catalyst 1900 and 2950 switches.

1. SwitchingSwitching
&&
VLANsVLANs

2. Switching BasicsSwitching Basics
 Switch act as a multiport bridge and itsSwitch act as a multiport bridge and its
basic duty is to break collision domain.basic duty is to break collision domain.
 Layer 2 switches and bridges are fasterLayer 2 switches and bridges are faster
than routers because they don’t take upthan routers because they don’t take up
time looking at the Network layer headertime looking at the Network layer header
information.information.
 Switches look at frame’s hardwareSwitches look at frame’s hardware
addresses before deciding to eitheraddresses before deciding to either
forward the frame or drop it.forward the frame or drop it.

3. Switching BasicsSwitching Basics
 Switches create private dedicated collisionSwitches create private dedicated collision
domain.domain.
 They provide independent bandwidth onThey provide independent bandwidth on
each port.each port.
 Layer 2 switching provide the following:Layer 2 switching provide the following:
 Hardware based bridging (Application SpecificHardware based bridging (Application Specific
Integrated Circuit – ASIC)Integrated Circuit – ASIC)
 Wire SpeedWire Speed
 Low latencyLow latency
 Low cost.Low cost.

4. Switching BasicsSwitching Basics
 Switches do not do any modification toSwitches do not do any modification to
the data packet.the data packet.
 They only read the frame encapsulatingThey only read the frame encapsulating
the packet.the packet.
 This makes the switching processThis makes the switching process
considerably faster and less error-pronconsiderably faster and less error-pron
than routing process.than routing process.

5. Switches create private domainSwitches create private domain

6. Bridging Vs. LAN SwitchingBridging Vs. LAN Switching
 Bridges are software based, while switchesBridges are software based, while switches
are hardware based because switches useare hardware based because switches use
ASIC chips to help make filtering decisions.ASIC chips to help make filtering decisions.
 A switch is basically a multiport bridge.A switch is basically a multiport bridge.
 Bridges can only have one spanning treeBridges can only have one spanning tree
instance per bridge, while switches can haveinstance per bridge, while switches can have
many.many.
 Switches have more number of ports.Switches have more number of ports.

7. Bridges and SwitchesBridges and Switches
 Both poses multiple COLLISION DOMAINBoth poses multiple COLLISION DOMAIN
but one BROADCAST DOMAIN.but one BROADCAST DOMAIN.
 Both learn MAC addresses by examiningBoth learn MAC addresses by examining
the source address of each frame received.the source address of each frame received.
 Both make forwarding decisions based onBoth make forwarding decisions based on
layer 2 addresses.layer 2 addresses.

8. Functions of SwitchFunctions of Switch
 Address LearningAddress Learning ::
 Layer 2 switches remember the source hardwareLayer 2 switches remember the source hardware
address of each frame received on an interface .address of each frame received on an interface .
 Switches enter this information into a MACSwitches enter this information into a MAC
database called a forward/filter table.database called a forward/filter table.
 Forward/Filter DecisionForward/Filter Decision ::
 When a frame is received on an interface, theWhen a frame is received on an interface, the
switch looks at the destination hardware addressswitch looks at the destination hardware address
and fields the exit interface in the MAC database.and fields the exit interface in the MAC database.
 The frame is only forwarded out the specifiedThe frame is only forwarded out the specified
destination port.destination port.

9. Functions of SwitchFunctions of Switch
 Loop AvoidanceLoop Avoidance::
 If multiple connections between switchesIf multiple connections between switches
are created for redundancy purpose,are created for redundancy purpose,
network loops can occur.network loops can occur.
 Spanning Tree Protocol (STP) is used toSpanning Tree Protocol (STP) is used to
stop network loops while still permittingstop network loops while still permitting
redundancy.redundancy.

10. Address LearningAddress Learning
 When switch is first powered on, the MACWhen switch is first powered on, the MAC
forward/filter table is empty.forward/filter table is empty.
 When an interface receives a frame, the switchWhen an interface receives a frame, the switch
places the frame’s source address in MACplaces the frame’s source address in MAC
forward/filter table, allowing it to rememberforward/filter table, allowing it to remember
which interface the sending device is located on.which interface the sending device is located on.
 Switch then floods the network with this frameSwitch then floods the network with this frame
out of every port except the source port becauseout of every port except the source port because
it has no idea where the destination deviceit has no idea where the destination device
actually located.actually located.

11. Address LearningAddress Learning
 If a device answers this flooded frame andIf a device answers this flooded frame and
sends a frame back, then:sends a frame back, then:
 Switch takes the source address from that frameSwitch takes the source address from that frame
and place the mac address in the database asand place the mac address in the database as
well.well.
 Switch associates this address with the interfaceSwitch associates this address with the interface
that received the frame.that received the frame.
 Since the switch now has both the relevantSince the switch now has both the relevant
MAC address in its filtering table, the twoMAC address in its filtering table, the two
devices can now make a point-t0-pontdevices can now make a point-t0-pont
connectionconnection

14. Forward/Filter DecisionsForward/Filter Decisions
 When a frame arrives at a switchWhen a frame arrives at a switch
interface, the destination hardwareinterface, the destination hardware
address in compared to the MACaddress in compared to the MAC
forward/filter table.forward/filter table.
 If the destination hardware is known andIf the destination hardware is known and
listed in the database, the frame is onlylisted in the database, the frame is only
sent out the correct exit interface.sent out the correct exit interface.
 This preserves bandwidth and is called asThis preserves bandwidth and is called as
frame filtering.frame filtering.

15. Forward/Filter DecisionsForward/Filter Decisions
 If destination hardware address is notIf destination hardware address is not
listed in the MAC database, then thelisted in the MAC database, then the
frame is flooded out all active interfacesframe is flooded out all active interfaces
except the interface the frame wasexcept the interface the frame was
received on.received on.
 If a device answers the flooded frame, theIf a device answers the flooded frame, the
MAC database is updated with the deviceMAC database is updated with the device
interface.interface.

16. Loop AvoidanceLoop Avoidance
 Redundant links between switches are aRedundant links between switches are a
good idea because they help preventgood idea because they help prevent
complete network failure in the event onecomplete network failure in the event one
link stops working.link stops working.
 But in a redundant link frames can beBut in a redundant link frames can be
flooded down all redundant linksflooded down all redundant links
simultaneously, resulting in network loops.simultaneously, resulting in network loops.

17. Redundant links may invite followingRedundant links may invite following
set of problems:set of problems:
 If no loop avoidance schemes are put in place,If no loop avoidance schemes are put in place,
the switches will flood broadcast endlessly.the switches will flood broadcast endlessly.
Following figure illustrates it:Following figure illustrates it:
Broadcast Storm

18.  A device can receive multiple copies of the sameA device can receive multiple copies of the same
frame, since that frame can arrive from multipleframe, since that frame can arrive from multiple
segments simultaneously. Following figuresegments simultaneously. Following figure
demonstrates it best.demonstrates it best.
 The server in this figureThe server in this figure
sends a unicast frame tosends a unicast frame to
router C.router C.
 Since it’s a unicast frame,Since it’s a unicast frame,
switch A forwards the frameswitch A forwards the frame
and switch B provides theand switch B provides the
same service – it forwards thesame service – it forwards the
broadcast.broadcast.
 This is not good because now route C will receive unicastThis is not good because now route C will receive unicast
frame twice, causing additional overhead on the network.frame twice, causing additional overhead on the network.

19.  The MAC address filter table will be totallyThe MAC address filter table will be totally
confused about the devices locationconfused about the devices location
because the switch can receive the framebecause the switch can receive the frame
from more than one links.from more than one links.
 Multiple loops could be generated. ThisMultiple loops could be generated. This
mean a loop can occur within other loop.mean a loop can occur within other loop.

20. Spanning Tree ProtocolSpanning Tree Protocol
 Its main task is to stop routing loops fromIts main task is to stop routing loops from
occurring on layer 2. (Bridges or Switches)occurring on layer 2. (Bridges or Switches)
 It monitors the network to find all links makingIt monitors the network to find all links making
sure that no loops occur by shutting down thesure that no loops occur by shutting down the
redundant link.redundant link.
 It uses Spanning Tree Algorithm (STA), toIt uses Spanning Tree Algorithm (STA), to
first create a topology database, then searchfirst create a topology database, then search
out and destroy redundant links.out and destroy redundant links.
 With STP running, frames are only forwardedWith STP running, frames are only forwarded
on the STP, picked links.on the STP, picked links.

21. LAN Switch TypesLAN Switch Types
 LAN Switch Types decide how a frame isLAN Switch Types decide how a frame is
handled when it’s received on a switch port.handled when it’s received on a switch port.
 Latency: The time switch takes for a frame toLatency: The time switch takes for a frame to
be sent out an exit port once the switchbe sent out an exit port once the switch
receives the frame.receives the frame.
 There are three switching modes:There are three switching modes:
 Cut – through (Fast Forward)Cut – through (Fast Forward)
 Fragment Free (Modified cut-through)Fragment Free (Modified cut-through)
 Store-and-forwardStore-and-forward

22.  Cut-through (Fast Forward)Cut-through (Fast Forward) ::
 In this mode, the switch only waits for theIn this mode, the switch only waits for the
destination hardware address to be received beforedestination hardware address to be received before
it looks up the destination address in the MAC filterit looks up the destination address in the MAC filter
table.table.
 Fragment Free (Modified cut-through)Fragment Free (Modified cut-through) ::
 In this mode, the switch checks the first 64 bytes ofIn this mode, the switch checks the first 64 bytes of
a frame before forwarding it for fragmentation.a frame before forwarding it for fragmentation.
 This is the default mode for catalyst 1900 seriesThis is the default mode for catalyst 1900 series
switch.switch.
 Store-and-forwardStore-and-forward ::
 In this mode, the complete frame is received on theIn this mode, the complete frame is received on the
switch’s buffer, a CRC is run and then the switchswitch’s buffer, a CRC is run and then the switch
looks up the destination address in the MAClooks up the destination address in the MAC
forward/filter table.forward/filter table.

23. Different switching modes within a frameDifferent switching modes within a frame

24. Cut - ThroughCut - Through
 With cut-through switching method, the LAN switchWith cut-through switching method, the LAN switch
reads only the destination.reads only the destination.
 That is it looks at the first six bytes following theThat is it looks at the first six bytes following the
preamble.preamble.
 It then:It then:
 Looks up the hardware destination address in the MACLooks up the hardware destination address in the MAC
switching table.switching table.
 Determines the outgoing interface.Determines the outgoing interface.
 Proceeds to forward the frame towards its destination.Proceeds to forward the frame towards its destination.
 A cut-through switch helps in reducing latency,A cut-through switch helps in reducing latency,
because its begins to forward the frame as soon as itbecause its begins to forward the frame as soon as it
reads the destination address and determines thereads the destination address and determines the
outgoing interface.outgoing interface.

25. Fragment Free (ModifiedFragment Free (Modified
Cut – Through)Cut – Through)
 It is a modified form of cut-through switching inIt is a modified form of cut-through switching in
which the switch waits for the collision window (64which the switch waits for the collision window (64
bytes) to pass before forwarding.bytes) to pass before forwarding.
 This is because if a packet has a collision error, itThis is because if a packet has a collision error, it
almost always occurs within the first 64 bytes.almost always occurs within the first 64 bytes.
 This means each frame will be checked into theThis means each frame will be checked into the
data field to make sure no fragmentation hasdata field to make sure no fragmentation has
occurred.occurred.
 Fragment Free mode provides better error checkingFragment Free mode provides better error checking
than the cut-through mode with practically nothan the cut-through mode with practically no
increase in latency.increase in latency.
 It is the default switching mode for 1900 switches.It is the default switching mode for 1900 switches.

26. Store – and – ForwardStore – and – Forward
 It is CISCO’s primary LAN switching method.It is CISCO’s primary LAN switching method.
 In this method, the LAN switch copies the entireIn this method, the LAN switch copies the entire
frame onto its onboard buffers and then computesframe onto its onboard buffers and then computes
the CRC (Cyclic Redundancy Check).the CRC (Cyclic Redundancy Check).
 Since it copies the entire frame, latency through theSince it copies the entire frame, latency through the
switch varies with frame length.switch varies with frame length.
 The frame is discarded if it contains a CRC error:The frame is discarded if it contains a CRC error:
 If it is too short (Less then 64 bytes including the CRC)If it is too short (Less then 64 bytes including the CRC)
 If it is too long (More than 1518 bytes, including the CRC)If it is too long (More than 1518 bytes, including the CRC)
 If the frame doesn’t contain any error, the LANIf the frame doesn’t contain any error, the LAN
switch looks up the destination hardware address inswitch looks up the destination hardware address in
its MAC forward/filter table to find the correctits MAC forward/filter table to find the correct
outgoing interface.outgoing interface.

27. Spanning Tree TermsSpanning Tree Terms
 STP:STP:
 It is a bridge protocol that uses the STA to findIt is a bridge protocol that uses the STA to find
redundant links dynamically.redundant links dynamically.
 It creates a spanning tree topology database.It creates a spanning tree topology database.
 Bridges exchange BPDU messages with otherBridges exchange BPDU messages with other
bridgesbridges

28. Configuring 1900 & 2950 catalystConfiguring 1900 & 2950 catalyst
switchesswitches
 We will cover following list of tasks:We will cover following list of tasks:
 Setting the passwordSetting the password
 Setting the hostnameSetting the hostname
 Configuring the ip address and subnet masksConfiguring the ip address and subnet masks
 Setting a description on the interfaceSetting a description on the interface
 Erasing the switch configurationErasing the switch configuration
 Configuring VLANsConfiguring VLANs
 Adding VLAN membership to switch port.Adding VLAN membership to switch port.
 Creating VTP domain.Creating VTP domain.
 Configuring trunking.Configuring trunking.

29. Setting the passwordSetting the password
 1900 Series:1900 Series:
 It uses same command to set both user levelIt uses same command to set both user level
password as well as privileged password, butpassword as well as privileged password, but
with different level numbers.with different level numbers.
 Level is 1 for user level and 15 for privilegeLevel is 1 for user level and 15 for privilege
level.level.
 Password length should be from 4 to 8Password length should be from 4 to 8
characters.characters.
 Setting user password:Setting user password:
 switch(config)#switch(config)# enable password level 1 ciscoenable password level 1 cisco
 Setting privileged level passwordSetting privileged level password
 switch(config)#switch(config)# enable password level 15 ciscoenable password level 15 cisco

30. Setting the passwordSetting the password
 2950 Series:2950 Series:
 To set user mode password for the 2950 switch,To set user mode password for the 2950 switch,
we configure the line just as we would do on awe configure the line just as we would do on a
router.router.
 Console:Console:
 switch(configswitch(config))## line console 0line console 0
switch(config-lineswitch(config-line))## passwordpassword ciscocisco
switch(config-lineswitch(config-line))## loginlogin
 Telnet:Telnet:
 switch(configswitch(config))## line vty 0 15line vty 0 15
switch(config-lineswitch(config-line))## passwordpassword ciscocisco
switch(config-line)#switch(config-line)# loginlogin
 Enable secret password is set in the same wayEnable secret password is set in the same way
as we would do for a router.as we would do for a router.
 switch(config)#switch(config)# enable secretenable secret ciscocisco

31. Setting hostnameSetting hostname
 The hostname on a switch is only locallyThe hostname on a switch is only locally
significant.significant.
 This means it doesn’t have any function onThis means it doesn’t have any function on
the network or with the name resolution.the network or with the name resolution.
(Though it has an exception with PPP(Though it has an exception with PPP
authentication)authentication)
 1900 Series:1900 Series:
 switch(configswitch(config))## hostnamehostname LAN1LAN1
 2950 Series:2950 Series:
 switch(config)#switch(config)# hostnamehostname LAN1LAN1

32. Setting IP informationSetting IP information
 Generally a switch doesn’t need any ipGenerally a switch doesn’t need any ip
address at all to manager a LAN.address at all to manager a LAN.
 There are exceptions though.There are exceptions though.
 We have got two reasons where weWe have got two reasons where we
probably do want to set IP addressprobably do want to set IP address
information on the switch.information on the switch.
 To manage the switch via TELNET or otherTo manage the switch via TELNET or other
management software.management software.
 To configure the switch with different VLANsTo configure the switch with different VLANs
and other network functions.and other network functions.

33. Setting IP informationSetting IP information
 1900 Switch:1900 Switch:
 By default no ip address or default gatewayBy default no ip address or default gateway
information is set.information is set.
 We can verify this by using the commandWe can verify this by using the command sh ipsh ip atat
privileged mode.privileged mode.
 Switch#sh ipSwitch#sh ip
 IP address and default gateway are set throughIP address and default gateway are set through
GCM.GCM.
 Switch(config)#Switch(config)# ip address 172.16.10.16 255.255.255.0ip address 172.16.10.16 255.255.255.0
Switch(config)#Switch(config)# ip default-gateway 172.16.10.1ip default-gateway 172.16.10.1

34. Setting IP informationSetting IP information
 2950 Switch :2950 Switch :
 In 2950 switch , we consider a default VLAN with theIn 2950 switch , we consider a default VLAN with the
switch.switch.
 This VLAN is called as VLAN1.This VLAN is called as VLAN1.
 Every port on switch is a member of VLAN1 byEvery port on switch is a member of VLAN1 by
default.default.
 We always set ip address for VLAN1.We always set ip address for VLAN1.
 Switch(config)#Switch(config)# interface vlan1interface vlan1
Switch(config-if)#Switch(config-if)# ip address 172.16.10.17 255.255.255.0ip address 172.16.10.17 255.255.255.0
Switch(config-if)#Switch(config-if)#exitexit
Switch(config)#Switch(config)# ip default-gateway 172.16.10.1ip default-gateway 172.16.10.1

35. Configuring Interface DescriptionConfiguring Interface Description
 We can administratively set a name for eachWe can administratively set a name for each
interface on the switches.interface on the switches.
 These descriptions are only locally significant.These descriptions are only locally significant.
 1900 Switch:1900 Switch:
 Description command is used from interfaceDescription command is used from interface
configuration mode.configuration mode.
 Spaces can't be used within description.Spaces can't be used within description.
 Switch(config)#Switch(config)# int e0/1int e0/1
Switch(config-if)#Switch(config-if)# description Finance_VLANdescription Finance_VLAN
Switch(config)#Switch(config)# int f0/26int f0/26
Switch(config-if)#Switch(config-if)# description trunk_to_building_4description trunk_to_building_4

36. Configuring Interface DescriptionConfiguring Interface Description
 2950 Switch:2950 Switch:
 Description command is used from interfaceDescription command is used from interface
configuration mode.configuration mode.
 Spaces can be used within description.Spaces can be used within description.
 Switch(config)#Switch(config)# int fastEthernet 0/1int fastEthernet 0/1
Switch(config-if)#Switch(config-if)# description Sales Printerdescription Sales Printer
Switch(config)#Switch(config)# int f0/12int f0/12
Switch(config-if)#Switch(config-if)# description trunk_to_building_4description trunk_to_building_4

37. Erasing the Switch ConfigurationErasing the Switch Configuration
 1900 Switch:1900 Switch:
 We can’t see the content of NVRAM.We can’t see the content of NVRAM.
 We can only view RAM’s content.We can only view RAM’s content.
 When we make changes to switch’s runningWhen we make changes to switch’s running
configuration, it automatically copies it to the NVconfiguration, it automatically copies it to the NV
RAM.RAM.
 Following syntax helps us in deleting NVRAM’sFollowing syntax helps us in deleting NVRAM’s
contents.contents.
 Switch#Switch# delete nvramdelete nvram

38. Erasing the Switch ConfigurationErasing the Switch Configuration
 2950 Switch:2950 Switch:
 Concepts of startup config and running configConcepts of startup config and running config
holds exactly same as they do with routers overholds exactly same as they do with routers over
here.here.
 Following syntax helps us in deleting NVRAM’sFollowing syntax helps us in deleting NVRAM’s
contents.contents.
 Switch#Switch# erase startup-configerase startup-config

39. Virtual LANs (VLANs)Virtual LANs (VLANs)
 A VLAN is a logical grouping of networkA VLAN is a logical grouping of network
users and resources connected tousers and resources connected to
administratively defined ports on a switch.administratively defined ports on a switch.
 VLANs allow us to break broadcastVLANs allow us to break broadcast
domain in a pure switched internetwork.domain in a pure switched internetwork.
 VLANs allow us to create smallerVLANs allow us to create smaller
broadcast domains within a layer 2broadcast domains within a layer 2
switched based internetwork.switched based internetwork.

40. How VLANs simplify networkHow VLANs simplify network
management?management?
 Network adds, moves and changes are achievedNetwork adds, moves and changes are achieved
by configuring a port into the appropriate VLAN.by configuring a port into the appropriate VLAN.
 A group of users needing high security can be putA group of users needing high security can be put
into a VLAN so that no users outside of the VLANinto a VLAN so that no users outside of the VLAN
can communicate with them.can communicate with them.
 VLANs are independent from their physical orVLANs are independent from their physical or
logical locations.logical locations.
 VLANs can enhance network security.VLANs can enhance network security.
 VLANs increase no. of broadcast domains andVLANs increase no. of broadcast domains and
decrease the size of each broadcast domain.decrease the size of each broadcast domain.

41. Broadcast ControlBroadcast Control
 All devices in a VLAN are member of sameAll devices in a VLAN are member of same
broadcast domain and receive all broadcasts.broadcast domain and receive all broadcasts.
 The broadcasts, by default, are filtered fromThe broadcasts, by default, are filtered from
all ports on a switch that are not member ofall ports on a switch that are not member of
the same VLAN.the same VLAN.
 This is one of the prime benefit that we getThis is one of the prime benefit that we get
with a VLAN based switched network,with a VLAN based switched network,
otherwise we would have faced seriousotherwise we would have faced serious
problem if all our users were in sameproblem if all our users were in same
broadcast domain.broadcast domain.

42. SecuritySecurity
 In a flat network anyone connecting to the physical networkIn a flat network anyone connecting to the physical network
could access the network resources located that physicalcould access the network resources located that physical
LAN.LAN.
 In order to observe any/all traffic happening in that networkIn order to observe any/all traffic happening in that network
one has to simply plug a network analyzer into the hub.one has to simply plug a network analyzer into the hub.
 Users can join any workgroup by just plugging theirUsers can join any workgroup by just plugging their
workstations into the existing hub.workstations into the existing hub.
 By building VLANs and creating multiple broadcast groups,By building VLANs and creating multiple broadcast groups,
administrators can now have control over each port andadministrators can now have control over each port and
user.user.
 Since VLANs can be created in accordance with theSince VLANs can be created in accordance with the
network resources a user requires, a switch can benetwork resources a user requires, a switch can be
configured to inform a network management station of anyconfigured to inform a network management station of any
unauthorized access to network resources.unauthorized access to network resources.
 During inter VLAN communication, we can implementDuring inter VLAN communication, we can implement
restrictions on a router to achieve it.restrictions on a router to achieve it.

43. Flexibility and ScalabilityFlexibility and Scalability
 By assigning switch ports or users to VLANBy assigning switch ports or users to VLAN
groups on a switch or group of switches, wegroups on a switch or group of switches, we
gain flexibility to add only the users we wantgain flexibility to add only the users we want
into that broadcast domain regardless ofinto that broadcast domain regardless of
their physical location.their physical location.
 When a VLAN becomes to big, we canWhen a VLAN becomes to big, we can
create more VLANs to keep broadcasts fromcreate more VLANs to keep broadcasts from
consuming too much bandwidth.consuming too much bandwidth.

44. Physical LAN connected to a RouterPhysical LAN connected to a Router

45. Switches removing physical boundarySwitches removing physical boundary

46. Static VLANStatic VLAN
 These VLANs are created by administrators.These VLANs are created by administrators.
 An administrator creates static VLANs and thenAn administrator creates static VLANs and then
assigns switch port to each VLAN.assigns switch port to each VLAN.
 Static VLANs are:Static VLANs are:
 Most secureMost secure
 Comparatively easy to set up and monitor.Comparatively easy to set up and monitor.
 Works well in a network where the movement ofWorks well in a network where the movement of
users within the network is controlled.users within the network is controlled.
 Switch port that is assigned a VLANSwitch port that is assigned a VLAN
association to always maintains the associationassociation to always maintains the association
until an administrator changes that portuntil an administrator changes that port

47. Dynamic VLANDynamic VLAN
 When network administrator assigns, all the hostWhen network administrator assigns, all the host
device's hardware addresses into a database, thedevice's hardware addresses into a database, the
switches can be configured to assign VLANsswitches can be configured to assign VLANs
dynamically whenever a host is plugged into adynamically whenever a host is plugged into a
switch.switch.
 These are called as dynamic VLANs.These are called as dynamic VLANs.
 A dynamic VLAN determines node’s VLANA dynamic VLAN determines node’s VLAN
assignment automatically.assignment automatically.
 Using intelligent management software, we canUsing intelligent management software, we can
base VLAN assignment on hardware addressbase VLAN assignment on hardware address
(MAC address), protocols, or even applications to(MAC address), protocols, or even applications to
create dynamic VLANs.create dynamic VLANs.

48. Dynamic VLANDynamic VLAN
 Suppose MAC addresses have been entered intoSuppose MAC addresses have been entered into
centralized VLAN management application.centralized VLAN management application.
 If a node is then attached to an unassigned switchIf a node is then attached to an unassigned switch
port, the VLAN management database can look upport, the VLAN management database can look up
the hardware address and assign and configure thethe hardware address and assign and configure the
switch port to the correct VLAN.switch port to the correct VLAN.
 Its make management and configuration easierIts make management and configuration easier
because if a user moves, the switch will assign thembecause if a user moves, the switch will assign them
to the correct VLAN automatically.to the correct VLAN automatically.
 CISCO allows us to use the VLAN ManagementCISCO allows us to use the VLAN Management
Policy Server (VMPS) service to set up a database ofPolicy Server (VMPS) service to set up a database of
MAC addresses that can be used for dynamicMAC addresses that can be used for dynamic
addressing of VLANs.addressing of VLANs.
 A VMPS database maps MAC addresses to VLANs.A VMPS database maps MAC addresses to VLANs.

49. VLAN linksVLAN links
 Frames are handled differently accordingFrames are handled differently according
to the type of link they are traversing in ato the type of link they are traversing in a
switch.switch.
 Following two links are available in aFollowing two links are available in a
switched network:switched network:
 Access LinkAccess Link
 Trunk LinkTrunk Link

50. Access LinkAccess Link
 This type of link is only part of one VLAN, and it’sThis type of link is only part of one VLAN, and it’s
referred to as the native VLAN of the port.referred to as the native VLAN of the port.
 Any device attached to an access link is unawareAny device attached to an access link is unaware
of a VLAN membership. The device just assumesof a VLAN membership. The device just assumes
it’s part of a broadcast domain, but it has noit’s part of a broadcast domain, but it has no
understanding of the physical network.understanding of the physical network.
 Switches remove any VLAN information from theSwitches remove any VLAN information from the
frame before it’s sent to an access-link device.frame before it’s sent to an access-link device.
 Access-link devices cannot communicate withAccess-link devices cannot communicate with
devices outside their VLAN unless the packet isdevices outside their VLAN unless the packet is
routed.routed.

51. Trunk LinkTrunk Link
 A trunk line is a 100 or 1000 Mbps point-to-point linkA trunk line is a 100 or 1000 Mbps point-to-point link
between:between:
 Two switchesTwo switches
 A switch and a routerA switch and a router
 A switch and a serverA switch and a server
 Trunk lines carry traffic of VLANs from 1 to 1005 at a time.Trunk lines carry traffic of VLANs from 1 to 1005 at a time.
 Trunking allows us to make a single port part of multipleTrunking allows us to make a single port part of multiple
VLANs at the same time.VLANs at the same time.
 We can actually set things up to have a server in twoWe can actually set things up to have a server in two
broadcast domains simultaneously, so that users don’t havebroadcast domains simultaneously, so that users don’t have
to cross the router to log in and access it.to cross the router to log in and access it.
 Another advantage of trunking is when we are connectingAnother advantage of trunking is when we are connecting
switches.switches.
 Trunk links can carry some or all VLAN information acrossTrunk links can carry some or all VLAN information across
the link, but if the links between switches aren’t trunked,the link, but if the links between switches aren’t trunked,
only VLAN 1 information will be switched across the link byonly VLAN 1 information will be switched across the link by
default.default.

52. Access and Trunk LinksAccess and Trunk Links
in a switched networkin a switched network

53. Creating & Verifying VLANs 1900Creating & Verifying VLANs 1900
switchswitch
 Creating VLANs:Creating VLANs:
 Mode: GCMMode: GCM
 Syntax:Syntax:
Switch(config)# VLANSwitch(config)# VLAN VLAN numberVLAN number namename
VLAN nameVLAN name
E.g. switch(config)# VLANE.g. switch(config)# VLAN 22 namename salessales
 Verifying VLANs:Verifying VLANs:
 Mode: PrivilegedMode: Privileged
 Syntax:Syntax:
Switch# show VLANSwitch# show VLAN

54. Creating & Verifying VLANsCreating & Verifying VLANs
2950 switch2950 switch Creating VLANs:Creating VLANs:
 Mode: Privileged and switch configMode: Privileged and switch config
 Syntax:Syntax:
Switch# VLAN databaseSwitch# VLAN database
Switch(VLAN)# VLANSwitch(VLAN)# VLAN VLAN numberVLAN number namename VLAN nameVLAN name
Switch(VLAN)# applySwitch(VLAN)# apply
E.g. Switch(VLAN)# VLANE.g. Switch(VLAN)# VLAN 22 namename salessales
Switch(VLAN)# VLANSwitch(VLAN)# VLAN 33 namename mktmkt
Switch(VLAN)# applySwitch(VLAN)# apply
 Verifying VLANs:Verifying VLANs:
 Mode privilegedMode privileged
 Syntax:Syntax:
Switch# show VLAN briefSwitch# show VLAN brief

55. Assigning switch ports to VLANs 1900Assigning switch ports to VLANs 1900
switchswitch
 Mode: Interface SpecificMode: Interface Specific
 Syntax:Syntax:
Switch(config)# intSwitch(config)# int interface no.interface no.
Switch(config – if)# VLAN-membership staticSwitch(config – if)# VLAN-membership static
VLAN no.VLAN no.
Example 1: Switch(config)# int e0/2Example 1: Switch(config)# int e0/2
Switch(config – if)# VLAN-membership static 2Switch(config – if)# VLAN-membership static 2
Example 2: Switch(config)# int e0/3Example 2: Switch(config)# int e0/3
Switch(config – if)# VLAN-membership static 3Switch(config – if)# VLAN-membership static 3
Example 3: Switch(config)# int e0/4Example 3: Switch(config)# int e0/4
Switch(config – if)# VLAN-membership static 2Switch(config – if)# VLAN-membership static 2

56. Assigning switch ports to VLANs 2950Assigning switch ports to VLANs 2950
switchswitch
 Mode: Interface SpecificMode: Interface Specific
 Syntax:Syntax:
Switch(config)# intSwitch(config)# int interface no.interface no.
Switch(config – if)#switchport access VLANSwitch(config – if)#switchport access VLAN VLANVLAN
no.no.
Example 1: Switch(config)# int f0/2Example 1: Switch(config)# int f0/2
Switch(config – if)# switchport access VLAN 2Switch(config – if)# switchport access VLAN 2
Example 2: Switch(config)# int f0/3Example 2: Switch(config)# int f0/3
Switch(config – if)# switchport access VLAN 3Switch(config – if)# switchport access VLAN 3
Example 3: Switch(config)# int f0/4Example 3: Switch(config)# int f0/4
Switch(config – if)# switchport access VLAN 2Switch(config – if)# switchport access VLAN 2

57. Frame TaggingFrame Tagging
 Switch fabric: It is a group of switches sharing theSwitch fabric: It is a group of switches sharing the
same VLAN information.same VLAN information.
 Frame tagging is a frame identification method, whichFrame tagging is a frame identification method, which
uniquely assigns a user-defined ID to each frame.uniquely assigns a user-defined ID to each frame.
 It is also called asIt is also called as VLAN idVLAN id oror colorcolor..
 How does it work?How does it work?
 Each switch that the frame reaches must first identify theEach switch that the frame reaches must first identify the
VLAN ID from the frame tag.VLAN ID from the frame tag.
 Then it finds out what to do with the frame by looking at theThen it finds out what to do with the frame by looking at the
information in the filter table.information in the filter table.
 If the frame reaches a switch that has another trunked link,If the frame reaches a switch that has another trunked link,
the frame will be forwarded out the trunk-link port.the frame will be forwarded out the trunk-link port.
 Once the frame reaches an exit to an access link matchingOnce the frame reaches an exit to an access link matching
the frames VLAN ID, the switch removes the VLAN identifierthe frames VLAN ID, the switch removes the VLAN identifier
so that the destination device receive the frames withoutso that the destination device receive the frames without
having to understand their VLAN identification.having to understand their VLAN identification.