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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