In IOS, if we assign a switchport to a non-existent VLAN, the switch will kindly create the missing VLAN for us. NX-OS does not do that – if a switchport is assigned to a missing VLAN, the interface will be placed in the down state. Let’s look at it…
Here’s an example of an IOS switch which doesn’t have VLAN 2 defined:
IOS_SWITCH(config-if)# sw ac vl 2 % Access VLAN does not exist. Creating vlan 2 IOS_SWITCH(config-if)#
It created the VLAN, assigned it to the interface and took the time to tell us about it.
Let’s compare that with the behavior on NX-OS:
switch(config-if)# sh vlan
VLAN Name Status Ports
---- -------------------------------- --------- -------------------------------
1 default active Eth1/2, Eth1/3, Eth1/4, Eth1/5
Eth1/6, Eth1/7, Eth1/8, Eth1/9
Eth1/10, Eth1/11, Eth1/12
Eth1/13, Eth1/14, Eth1/15
Eth1/16, Eth1/17, Eth1/18
Eth1/19, Eth1/20, Eth2/1, Eth2/2
Eth2/3, Eth2/4, Eth2/5, Eth2/6
Remote SPAN VLANs
-------------------------------------------------------------------------------
Primary Secondary Type Ports
------- --------- --------------- -------------------------------------------
No VLAN 2 anywhere to be seen – let’s try adding eth1/1 to VLAN 2 now:
switch(config)# int eth1/1 switch(config-if)# sw ac vl 2
Now look at the VLANs on the Nexus (again):
switch(config-if)# sh vlan
VLAN Name Status Ports
---- -------------------------------- --------- -------------------------------
1 default active Eth1/2, Eth1/3, Eth1/4, Eth1/5
Eth1/6, Eth1/7, Eth1/8, Eth1/9
Eth1/10, Eth1/11, Eth1/12
Eth1/13, Eth1/14, Eth1/15
Eth1/16, Eth1/17, Eth1/18
Eth1/19, Eth1/20, Eth2/1, Eth2/2
Eth2/3, Eth2/4, Eth2/5, Eth2/6
Remote SPAN VLANs
-------------------------------------------------------------------------------
Primary Secondary Type Ports
------- --------- --------------- -------------------------------------------
switch(config-if)#
switch(config-if)# sh int eth1/1 switch
Name: Ethernet1/1
Switchport: Enabled
Switchport Monitor: Not enabled
Operational Mode: access
switch(config-if)# sh run int eth1/1
version 4.0(1a)N1(1)
interface Ethernet1/1
speed 1000
switchport access vlan 2
switch(config-if)#
Be aware of this behavior in NX-OS – it doesn’t like IOS-style VLAN shorthand!
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Tags: 5000, access vlan, automatic, cisco, config, ethernet, example, ios, nexus, nexus 5000, nexus 5010, nexus 5020, nx-os, switch access vlan, training, tutorial, virtual lan, vlan