Configuring VLANs

© 2002, Cisco Systems, Inc. All rights reserved.
© 2002, Cisco Systems, Inc. All rights reserved.
2
Configuring VLANs
Objectives
Upon completing this lesson, you will be able to:
Use Cisco IOS commands to configure VLANs, VTP, IEEE 802.1Q trunking, and ISL trunking, given a functioning access layer switch
Execute an add, move, or change on an access-layer switch, given a new network requirement
Use show commands to identify anomalies in VLAN, VTP, IEEE 802.1Q trunking, ISL trunking, and spanning-tree operation within a VLAN, given an operational access layer switch
Use debug commands to identify events and anomalies in VLAN, VTP, IEEE 802.1Q trunking, ISL trunking, and spanning-tree operation, given an operational access layer switch
VTP domain name
VTP mode (server/client/transparent)—VTP server mode is the default
VTP pruning
VTP password
VTP trap
Use caution when adding a new switch to an existing domain. Add a new switch in client mode to prevent the new switch from propagating incorrect VLAN information.
Use the delete vtp command to reset the VTP revision number.
VTP Configuration Guidelines
wg_sw_1900#configure terminal
Enter configuration commands, one per line. End with CNTL/Z
wg_sw_1900(config)#vtp transparent
wg_sw_1900(config)#vtp domain switchlab
wg_sw_1900(config)#vtp [server | transparent | client] [domain domain-name] [trap {enable | disable}] [password password] [pruning {enable | disable}]
Creating a VTP Domain
Catalyst 1900
Catalyst 2950
wg_sw_2950#vlan database
wg_sw_2950(vlan)#vtp [ server | client | transparent ]
wg_sw_2950(vlan)#vtp domain domain-name
wg_sw_2950(vlan)#vtp password password
wg_sw_2950(vlan)#vtp pruning
wg_sw_2950(vlan)#snmp-server enable traps vtp
wg_sw_2950(vlan)#exit
VTP Configuration Example
wg_sw_1900(config)#vtp transparent
wg_sw_1900(config)#vtp domain switchlab pruning enable
wg_sw_1900(config)#exit
wg_sw_1900#show vtp
VTP version: 1
Configuration revision: 4
Maximum VLANs supported locally: 1005
Number of existing VLANs: 6
VTP domain name : switchlab
VTP password :
VTP operating mode : Transparent
VTP pruning mode : Enabled
VTP traps generation : Enabled
Configuration last modified by: 0.0.0.0 at 00-00-0000
00:00:00
wg_sw_1900#config terminal
wg_sw_1900(config)#interface f0/26
wg_sw_1900(config-if)#trunk on desirable
wg_sw_1900(config-if)#exit
wg_sw_1900(config)#exit
wg_sw_1900#show trunk A
DISL state: On, Trunking: On, Encapsulation type: ISL
802.1Q Trunking Limitations
Make sure the native VLAN for an 802.1Q trunk is the same on both ends of the trunk link.
Make sure your network is loop-free before disabling STP.
Configuring
802.1Q Trunking
wg_sw_a(config-if)#switchport mode trunk
Configures the port as a VLAN trunk
wg_sw_1900#conf terminal
Enter configuration commands, one per line. End with CNTL/Z
wg_sw_1900(config)#interface f0/26
wg_sw_1900(config-if)#trunk on
First Trunk Port (Port A)
wg_sw_1900(config-if)#trunk [on | off | desirable | auto | nonegotiate]
on = Set trunk on and negotiate with other side
off = Set trunk off and negotiate with other side
desirable = Negotiate with other side;
trunk on if other side is on, desirable, or auto
auto = Will be a trunk only if the other side is on or desirable
nonnegotiate = Set trunk on and will not negotiate
Configuring ISL Trunking
Note: The Catalyst 1900 only supports ISL encapsulation.
VLAN Configuration Guidelines
Maximum number of VLANs is switch-dependent.
Catalyst desktop switches support 64 VLANs with a separate spanning tree per VLAN.
VLAN1 is the factory default Ethernet VLAN.
CDP and VTP advertisements are sent on VLAN1.
The Catalyst switch IP address is in the management VLAN (VLAN1 by default).
To add or delete VLANs, the switch must be in VTP server or transparent mode.
wg_sw_1900(config)# vlan vlan# [name vlan-name]
Adding a VLAN
wg_sw_1900#configure terminal
Enter configuration commands, one per line. End with CNTL/Z
wg_sw_1900(config)#vlan 9 name switchlab2
Catalyst 1900
Catalyst 2950
wg_sw_2950#vlan database
wg_sw_2950(vlan)# vlan vlan# [name vlan-name]
wg_sw_2950#vlan database
wg_sw_ 2950(vlan)#vlan 9 name switchlab2
wg_sw_ 2950(vlan)#exit
wg_sw_a(config)#vlan vlan# name vlan-name
wg_sw_a#configure terminal
Enter configuration commands, one per line. End with CNTL/Z
wg_sw_a(config)#vlan 9 name switchlab90
wg_sw_a#show vlan 9

VLAN Name Status Ports
------------------------------------------------
9 switchlab90 Enabled
------------------------------------------------
Modifying a VLAN Name
wg_sw_1900(config-if)#vlan-membership {static {vlan#} | dynamic}
Assigning Switch Ports to a VLAN
wg_sw_1900#conf terminal
Enter configuration commands, one per line. End with CNTL/Z
wg_sw_1900(config)#interface ethernet 0/8
wg_sw_1900(config-if)#vlan-membership static 9
Catalyst 1900
Catalyst 2950
wg_sw_2950(config-if)#switchport access vlan vlan#
Verifying the VTP Configuration
for the Catalyst 1900
wg_sw_1900#show vtp
VTP version: 1
Configuration revision: 4
Maximum VLANs supported locally: 1005
Number of existing VLANs: 6
VTP domain name : switchlab
VTP password :
VTP operating mode : Transparent
VTP pruning mode : Enabled
VTP traps generation : Enabled
Configuration last modified by: 10.1.1.40 at 00-00-0000 00:00:00
wg_sw_1900#show vtp
Verifying the VTP Configuration
for the Catalyst 2950
wg_sw_2950#show vtp status
wg_sw_2950#show vtp status
VTP Version : 2 <--- indicates v2-capable
Configuration Revision : 4
Maximum VLANs supported locally : 68
Number of existing VLANs : 6
VTP Operating Mode : Server
VTP Domain Name : switchlab
VTP Pruning Mode : Enabled
VTP V2 Mode : Disabled <--- indicates v2 disabled; v1 set
VTP Traps Generation : Disabled <--- catalyst 2950 default
MD5 digest : 0x3D 0x02 0xD4 0x3A 0xC4 0x46 0xA1 0x03
Configuration last modified by 10.1.1.40 at 5-4-02 22:25:
wg_sw_1900#show trunk a
DISL state: On, Trunking: On, Encapsulation type: ISL
wg_sw_1900#show trunk [A | B]
Verifying a Trunk
Catalyst 1900
Catalyst 2950
wg_sw_2950#show interface interface switchport
wg_sw_2950#show interface fa0/2 switchport
Name: Fa0/2
Switchport: Enabled
Administrative mode: trunk
Operational Mode: trunk
. . .

wg_sw_1900#show vlan 9

VLAN Name Status Ports
-------------------------------------------------
9 switchlab2 Enabled
-------------------------------------------------

VLAN Type SAID MTU Parent RingNo BridgeNo Stp Trans1 Trans2
---------------------------------------------------------------------------
9 Ethernet 100009 1500 0 1 1 Unkn 0 0
---------------------------------------------------------------------------
wg_sw_1900#show vlan [vlan#]
Verifying a VLAN
Catalyst 1900
Catalyst 2950
wg_sw_2950#show vlan [id vlan#]
wg_sw_1900#show vlan-membership

Port VLAN Membership Type Port VLAN Membership Type
--------------------------- ------------------------------
1 5 Static 13 1 Static
2 1 Static 14 1 Static
3 1 Static 15 1 Static
4 1 Static 16 1 Static
5 1 Static 17 1 Static
6 1 Static 18 1 Static
7 1 Static 19 1 Static
8 9 Static 20 1 Static
Note: port 1=e0/1, port 2=e0/2 .....
wg_sw_1900#show vlan-membership
Verifying VLAN Membership
on a Catalyst 1900
wg_sw_2950#show vlan brief
VLAN Name Status Ports
---- ------------------------ --------- -----------------------
1 default active 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
5 VLAN5 active Fa0/3
9 VLAN9 active Fa0/22, Fa0/23
1002 fddi-default active
1003 token-ring-default active
1004 fddinet-default active
1005 trnet-default active
wg_sw_2950#show vlan brief
Verifying VLAN Membership
on a Catalyst 2950
wg_sw_2950#show interfaces interface switchport
wg_sw_1900#show spantree 1

VLAN1 is executing the IEEE compatible Spanning Tree Protocol
Bridge Identifier has priority 32768, address 0050.F037.DA00
Configured hello time 2, max age 20, forward delay 15
Current root has priority 0, address 00D0.588F.B600
Root port is FastEthernet 0/26, cost of root path is 10
Topology change flag not set, detected flag not set
Topology changes 53, last topology change occurred 0d00h17m14s ago
Times: hold 1, topology change 8960
hello 2, max age 20, forward delay 15
Timers: hello 2, topology change 35, notification 2
Port Ethernet 0/1 of VLAN1 is Forwarding
Port path cost 100, Port priority 128
Designated root has priority 0, address 00D0.588F.B600
Designated bridge has priority 32768, address 0050.F037.DA00
Designated port is Ethernet 0/1, path cost 10
Timers: message age 20, forward delay 15, hold 1
wg_sw_1900#show spantree [vlan#]
Verifying STP for a VLAN
Catalyst 1900
Catalyst 2950
wg_sw_2950#show spanning-tree vlan [vlan#]
Executing Adds, Moves, and Changes for VLANs
wg_sw_a(config)#vlan database
Enters the vlan database privileged EXEC command to access VLAN configuration mode
Writes VLAN adds, moves, and changes to the vlan.dat file
wg_sw_a(config)#vlan vlan-id mtu mtu-size
Identifies a VLAN and changes the MTU size
Troubleshooting Switched LANs
Problem: One Device Cannot Communicate with Another
Make sure the IP address, subnet mask, and VLAN membership of the switch interface is correct.
If the host is in the same subnet as the switch interface, make sure the switch interface and the switch port to which the host is connected are assigned to the same VLAN.
If the host is in a different subnet, make sure the default gateway on the switch is configured with the address of a router in the same subnet as the switch interface.
Problem: One Device Cannot Communicate with Another (Cont.)
If the port is in listening or learning mode, wait until the port is in forwarding mode and try to connect to the host again.
Make sure the speed and duplex settings on the host and the appropriate switch ports are correct.
If the connected device is an end station, enable spanning-tree PortFast, disable trunking, and disable chaneling on the port.
Make sure the switch is learning the MAC address of
the host.
Problem: A Device Cannot Establish a Connection Across a Trunk Link
Make sure the trunking mode configured on both ends of the link is valid. The trunking mode should be on or desirable on one end and on, desirable, or auto on the other end.
Make sure the trunk encapsulation type configured on both ends of the link is valid.
On IEEE 802.1Q trunks, make sure the native VLAN is the same on both ends of the trunk.
Problem: VTP Not Updating Configuration on Other Switches
Make sure the switches are connected through trunk links. VTP updates are exchanged only over trunk links.
Make sure the VTP domain name is the same on the appropriate switches. VTP updates are only exchanged between switches in the same VTP domain.
Check if the switch is in VTP transparent mode. Only switches in VTP server or VTP client mode update their VLAN configuration based on VTP updates from other switches.
If you are using VTP passwords, you must configure the same password on all switches in the VTP domain.
Summary
Before you create VLANs, you must decide whether to use VTP in your network. With VTP, you can make configuration changes centrally on one or more switches and have those changes automatically communicated to all the other switches in the network.
You will configure IEEE 802.1Q to carry traffic for multiple VLANs over a single link on a multivendor network.
ISL operates in a point-to-point environment to carry traffic for multiple VLANs over a single link.
Most Catalyst desktop switches support a maximum of 64 active VLANs. The Catalyst 1900 supports 1,024 VLANs with the Enterprise Edition software. Depending on the model, the 2950 series can support up to 250 VLANs.
Summary (Cont.)
After creating a VLAN, you can statically assign a port or a number of ports to that VLAN. A port can belong to only one VLAN at a time.
You can verify the VLAN configuration using the show commands.
As network topologies, business requirements, and individual assignments change, VLAN requirements also change.
Misconfiguration of a VLAN is one of the most common errors in switched networks.