Switch Virtual LANs

Posted on July 23, 2009. Filed under: CCNA, ICND1 break down | Tags: , , , , |


By default, all ports attached to a Layer 2 switch operate in the same broadcast domain. This is the limitation of Layer 2 switches, because it can lead to the transmission of unnecessary broadcasts.VLAN logically divide the physical network into smaller, logical networks, so that each of these smaller, logical group acts like an individual broadcast domain. When a member of one VLAN sends a broadcast, only the other members of the same VLAN will receive the broadcast.

Using VLANs, you can configure ports on the switch for segmentation, flexibility, and security.

Access Links are the links or ports assigned to a particular VLAN. An access link can only carry one VLAN.

Trunk Links are capable of carrying multiple VLANs.

The switch decide which ports belong to which VLANs by configuring their VLAN membership.

VLAN memebership

  • Static VLAN memebership — administrator statically assign a particular VLAN to a particular port.
  • Dynamic VLAN memebership — through VLAN membership policy server, a server contains the mapping of MAC address to corresponding VLANs.

Frame Tagging: the method of identify which VLAN a frame came from and which VLAN it will go to. There are two methods of frame tagging:

  • Inter Switch Link (ISL) is a Cisco proprietary standard.
  • 802.1q is an industry standard, also associate Native VLAN (No tag)

Here is a simplified example of VLAN Frame tagging.

Configure VLANs on a cisco Switch

Basic commands:

To show all VLAN status in brief

show vlan brief

To create a VLAN

vlan vlanid

After creating the VLAN, we exit the VLAN database by using the the command “end” to update this database.

To set the ascii name for the VLAN

name WORD

Example:

Switch(config)#vlan 2
Switch(config-vlan)#name raliegh
Switch(config-vlan)#end

To set access mode characteristics of the interface, and associate this interface to a particular VLAN

Switchport access vlan vlanid
Example:

Switch(config)#interface fa0/7
Switch(config-if)#switchport access vlan 2

The following commands are tested in packet tracer 5.1 with a 3560-24PS  Multilayer Switch.

Switch>enable
Switch#show vlan brief

VLAN Name                             Status    Ports
—- ——————————– ——— ——————————-
1    default                          active    Fa0/1, Fa0/2, Fa0/3, Fa0/4
Fa0/5, Fa0/6, Fa0/7, Fa0/8
Fa0/9, Fa0/10, Fa0/11, Fa0/12
Fa0/13, Fa0/14, Fa0/15, Fa0/16
Fa0/17, Fa0/18, Fa0/19, Fa0/20
Fa0/21, Fa0/22, Fa0/23, Fa0/24
Gig0/1, Gig0/2
1002 fddi-default                     active
1003 token-ring-default               active
1004 fddinet-default                  active
1005 trnet-default                    active
Switch#config terminal
Enter configuration commands, one per line.  End with CNTL/Z.
Switch(config)#vlan 2
Switch(config-vlan)#name raliegh
Switch(config-vlan)#end
%SYS-5-CONFIG_I: Configured from console by console
Switch#show vlan brief

VLAN Name                             Status    Ports
—- ——————————– ——— ——————————-
1    default                          active    Fa0/1, Fa0/2, Fa0/3, Fa0/4
Fa0/5, Fa0/6, Fa0/7, Fa0/8
Fa0/9, Fa0/10, Fa0/11, Fa0/12
Fa0/13, Fa0/14, Fa0/15, Fa0/16
Fa0/17, Fa0/18, Fa0/19, Fa0/20
Fa0/21, Fa0/22, Fa0/23, Fa0/24
Gig0/1, Gig0/2
2    raliegh                          active
1002 fddi-default                     active
1003 token-ring-default               active
1004 fddinet-default                  active
1005 trnet-default                    active
Switch#config terminal
Enter configuration commands, one per line.  End with CNTL/Z.
Switch(config)#interface fa0/7
Switch(config-if)#switchport access vlan 2
Switch(config-if)#end
%SYS-5-CONFIG_I: Configured from console by console
Switch#show vlan brief

VLAN Name                             Status    Ports
—- ——————————– ——— ——————————-
1    default                          active    Fa0/1, Fa0/2, Fa0/3, Fa0/4
Fa0/5, Fa0/6, Fa0/8, Fa0/9
Fa0/10, Fa0/11, Fa0/12, Fa0/13
Fa0/14, Fa0/15, Fa0/16, Fa0/17
Fa0/18, Fa0/19, Fa0/20, Fa0/21
Fa0/22, Fa0/23, Fa0/24, Gig0/1
Gig0/2
2    raliegh                          active    Fa0/7
1002 fddi-default                     active
1003 token-ring-default               active
1004 fddinet-default                  active
1005 trnet-default                    active
Switch#

By default, all the switch ports belong to VLAN 1 and VLAN 1 is the default management VLAN. We can assign an ip address to the default management VLAN 1 so that we can remotely manage the switch using Cisco’s defaults.

Switch(config)#interface vlan1
Switch(config-if)#ip address 10.1.1.5 255.255.255.0

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[…] and Routers * MAC address learning and filter/forward decisions * Frame Processing Methods * Virtual LANs * Cisco Three-Layer Switching Model * Introduction to STP * Basic Switch […]

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