LAN Switching Commands

Show interface trunk
SW1#show interface trunk
Port Mode Encapsulation Status Native vlan
Fa0/11 desirable 802.1q trunking 1
Fa0/12 desirable 802.1q trunking 1
Port Vlans allowed on trunk
Fa0/11 1-4094
Fa0/12 1-4094
Port Vlans allowed and active in management domain
Fa0/11 1
Fa0/12 1
Port Vlans in spanning tree forwarding state and not pruned
Fa0/11 1
Fa0/12 none
This command displays all ports that are actively trunking, their trunking mode, the encapsulation type, and the native VLAN. It also displays the VLANs that are allowed to have traffic go across the trunk. CCNA candidates should note that this is the command that displays the trunking protocol in use – either 802.1Q (“dot1q) or ISL.
Show mac-address-table
SW1#show mac-address-table
Mac Address Table
-------------------------------------------
Vlan Mac Address Type Ports
---- ----------- -------- -----
All 000f.90e2.25c0 STATIC CPU
All 0100.0ccc.cccc STATIC CPU
All 0100.0ccc.cccd STATIC CPU
All 0100.0cdd.dddd STATIC CPU
1 000b.be2c.518b DYNAMIC Fa0/11
Total Mac Addresses for this criterion:5

Show spanning-tree vlan (VLAN_NUMBER)
SW2#show spanning-tree vlan 23
VLAN0023
Spanning tree enabled protocol ieee
Root ID Priority 32791
Address 000b.be2c.5180
This bridge is the root
Hello Time 2 sec Max Age 20 sec Forward Delay 15 sec
Bridge ID Priority 32791 (priority 32768 sys-id-ext 23)
Address 000b.be2c.5180
Hello Time 2 sec Max Age 20 sec Forward Delay 15 sec
Aging Time 15
Interface Role Sts Cost Prio.Nbr Type
---------------- ---- --- --------- -------- --------------------------
Fa0/3 Desg FWD 100 128.3 Shr
Fa0/11 Desg FWD 19 128.11 P2p
Fa0/12 Desg FWD 19 128.12 P2p
Show vlan brief
SW1#show vlan brief
VLAN Name Status Ports
---- -------------------------------- --------- ---------------------------
1 default active Fa0/1, Fa0/3, Fa0/4, Fa0/5
Fa0/6, Fa0/7, Fa0/8, Fa0/9
Fa0/10
23 VLAN0023 active Fa0/2
1002 fddi-default act/unsup
1003 token-ring-default act/unsup
1004 fddinet-default act/unsup
1005 trnet-default act/unsup
Quickly learn what ports are in what VLAN with this command. Note the default VLAN is VLAN 1, which is also the native VLAN.
Show vtp status
SW2#show vtp status
VTP Version : 2
Configuration Revision : 2
Maximum VLANs supported locally : 64
Number of existing VLANs : 6
VTP Operating Mode : Server
VTP Domain Name : CCNA
VTP Pruning Mode : Enabled
VTP V2 Mode : Disabled
VTP Traps Generation : Disabled
MD5 digest : 0xE2 0xCC 0x1A 0xB8 0x8E 0x80 0x6F 0xF4
Configuration last modified by 0.0.0.0 at 3-1-93 00:52:40
Local updater ID is 0.0.0.0 (no valid interface found)
The main concerns here is that this is the command that shows you the VTP operating mode of this device (server, client, or transparent), the VTP domain name, and whether pruning is enabled.

Spanning-tree vlan (VLAN_NUMBER) root primary
SW1#conf t
Enter configuration commands, one per line. End with CNTL/Z.
SW1(config)#spanning vlan 23 root primary
SW1(config)#^Z
SW1#show spanning vlan 23
VLAN0023
Spanning tree enabled protocol ieee
Root ID Priority 20503
Address 000f.90e2.25c0
This bridge is the root
Hello Time 2 sec Max Age 20 sec Forward Delay 15 sec
This one-line command can make a non-root bridge become the root bridge. In this example, SW1 was configured with the command. Where SW2 was the root bridge in the previous command example, SW1 is now the root bridge. Note the priority change from the default of 32768.
Vtp domain
Vtp password
Vtp pruning
SW1#conf t
Enter configuration commands, one per line. End with CNTL/Z.
SW1(config)#vtp domain CCNA
Changing VTP domain name from NULL to CCNA
SW1(config)#vtp password CISCO
Setting device VLAN database password to CISCO
SW1(config)#vtp pruning