VLAN are denoted using VLAN ID’s (VLAN Identifiers). The VLAN ID’s are numerical values ranging from 1 – 4096 and are classified as below,
- Normal Range ID: 1 – 1005
- Token Ring and FDDI VLANS: 1002 – 1005
- Extended Range ID: 1006 – 4094
Since we have 12 bits assigned for VLAN Identifier field in the 802.1Q VLAN header we cannot extend the VLAN range more than 4096. VLAN ID 1 and 4096 are reserved and cannot be used for forwarding traffic.
Following steps walk through the process of creating a VLAN on the switch
- Create a VLAN
- Name the VLAN (optional)
- Assign ports to the VLAN
VLAN Layer 3 Interface
Layer 3 (L3) switches are capable of doing routing. Inter-VLAN routing is process of passing traffice between two different VLANS. Since traffic here is routed and not switched broadcast traffic will not be forwarded between VLANS.
L3 interface is a logical interface with the VLAN ID
We can use “show ip interface” command to view the L3 interfaces configured
Configuring VLAN on FTOS based switches
FTOS based systems use the command “interface vlan X” to create VLAN where X is the VLAN ID. The command “untagged switchport X” where X is the port number is used to assign a port to VLAN
Tagged Vs Untagged
VLAN information is present inside the 802.1Q cladding of the frame. A frame is said to be tagged with a VLAN ID if the 802.1Q header information is present in the frame. Tagged frames are sent to devices which has the intelligence to understand the VLAN information.
Untagged frames implies that the VLAN information is removed by the switch before transmitting the frame out of the port and the 802.1Q cladding is not present.
