Configure VLANs
Virtual LAN (VLAN) is a concept that allows devices to be logically partitioned at layer 2 (data link layer). Layer 3 devices typically share a broadcast domain, but the concept of VLANs can be used to divide the broadcast domain with switches.
Layer2 Switch VLAN Config:
| Command | Description |
|---|---|
| (config)# [no] vlan 23 | To [delete vlan or] create vlan and enter config-vlan mode |
| (config-vlan)# name TelephoneSanitizer | Name this vlan TelephoneSanitizer |
| (config)# int g1/1 | NULL |
| (config-if)# switchport mode access | Make frames out this port untagged |
| (config-if)# switchport access vlan 23 | NULL |
| (config)# int g1/2 | NULL |
| (config-if)# switchport mode trunk | Make frames out this port tagged by default |
| (config-if)# switchport trunk encapsulation dot1q | Sometimes the default is ciscos old isl. |
| (config-if)# switchport trunk native vlan 256 | Except for vlan 256, which is still untagged. |
| (config-if)# switchport nonegotiate | Disable DTP |
Layer3 Switch VLAN Config:
| Command | Description |
|---|---|
| (config)# interface VLAN 23 | enter interface config mode |
| (config-if)# IP address 1.2.3.4 255.255.255.0 | set device IP in VLAN 23 |
| (config-if)# no shutdown | virtual interfaces are disabled by default |
| (config-if)# int g | NULL |
| (config)# no VLAN 23 | delete VLAN 23 |
Router (on a Stick) VLAN Config:
| Command | Description |
|---|---|
| (config)# interface g1/1.10 | Create subinterface g1/1.10 on g1/1 |
| (config-subif)# encapsulation dot1q 10 | enable IEEE 802.1Q VLAN tagging with VLAN 10 on the subinterface |
| (config-subif)# ip address 10.0.10.1 255.255.255.0 | NULL |
| # show vlans | Show VLANs and their trunk interfaces |
Troubleshoot VLANs on a Switch:
| Command | Description |
|---|---|
| # show vlan [{id 23, name TelephoneSanitizer}] [brief] | Show VLAN settings for all switch ports |
| # show interfaces g1/1 switchport | Verify mode and VLAN of g1/1 |
| # show interfaces g1/1 trunk | Show trunk settings and state |
| # show run interface VLAN 1 | A quick way to search the running config. |
| # show interface status | Show trunk mode/access VLAN |
| # show dtp interface g1/1 | Show current DTP mode for g1/1 |
VTP:
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