VLANs

Basic VLANs info. Cisco series 1900 routers support up to 16 VLANs.

Create

#vlan vlan_id

Deleting a VLAN

#no vlan vlan_id

Show all VLANs summary and port assignment

r1-basic#sh vlan-switch

VLAN Name                             Status    Ports
---- -------------------------------- --------- -------------------------------
1    default                          active    Gi0/1/0, Gi0/1/1, Gi0/1/2
                                                Gi0/1/3
1002 fddi-default                     act/unsup
1003 token-ring-default               act/unsup
1004 fddinet-default                  act/unsup
1005 trnet-default                    act/unsup

VLAN Type  SAID       MTU   Parent RingNo BridgeNo Stp  BrdgMode Trans1 Trans2
---- ----- ---------- ----- ------ ------ -------- ---- -------- ------ ------
1    enet  100001     1500  -      -      -        -    -        1002   1003
1002 fddi  101002     1500  -      -      -        -    -        1      1003
1003 tr    101003     1500  1005   0      -        -    srb      1      1002
1004 fdnet 101004     1500  -      -      1        ibm  -        0      0
1005 trnet 101005     1500  -      -      1        ibm  -        0      0

Verify trunk interfaces

r1-basic#show interfaces trunk

Access port configuration

interface GigabitEthernet1/0/2
description Access Port to Cisco Access Point
switchport access vlan 10
no ip address
end

interface range

interface range gi 0/1/0 - 3

Trunk port configuration

For 802.1Q trunking, one VLAN is not tagged. This VLAN is called native VLAN. The native VLAN is used for untagged traffic when the port is in 802.1Q trunking mode. While configuring 802.1Q trunking, it is very important to keep in mind that the native VLAN must be configured the same on each side of the trunk link. It is a common mistake not to match the native VLANs while configuring 802.1Q trunking between the router and the switch.

In this example 802.1Q encapsulation is used

interface GigabitEthernet1/0/1
description Trunk Port to Cisco WLC
switchport trunk encapsulation dot1q
switchport trunk native vlan 99
switchport trunk allowed vlan add 10,20,99
switchport mode trunk
switchport nonegotiate
no shutdown

The following list shows options for the switchport mode command.

trunk - configures the port into permanent 802.1Q trunk mode and negotiates with the connected device to convert the link to trunk mode.

access - disables port trunk mode and negotiates with the connected device to convert the link to nontrunk.

nonegotiate - the port is a trunk and does not do DTP negotiation with the other side of the link.

dynamic desirable - triggers the port to negotiate the link from nontrunk to trunk mode. The port negotiates to a trunk port if the connected device is in trunk state, desirable state, or auto state. Otherwise, the port becomes a nontrunk port.

dynamic auto - enables a port to become a trunk only if the connected device has the state set to trunk or desirable. Otherwise, the port becomes a nontrunk port.

Verifying a Trunk

******* (requires live capture) ************

Switch#show interfaces GigabitEthernet1/0/1 switchport

Switch#show interfaces GigabitEthernet1/0/1 trunk