The Layer 2 gadgets use Ethernet outline header data to send bundles without having directing tables. Normally, the Ethernet outline header doesn’t contain any data about virtual neighborhood (VLAN), in this way, when Ethernet outlines show up in a trunk, The virtual neighborhood (VLAN) data should add to the casing.
This technique called labeling. The norm for VLAN labeling is IEEE 802.1Q. The 802.1Q header incorporates a 32-bits label embedded inside the first Ethernet outline header, indicating the VLAN to which the casing has a place.
At the point when the switch gets an Ethernet outline on a port in access mode and allocated a VLAN, the switch embeds a virtual neighborhood (VLAN) tag into the got outline header, works out the FCS once more, and conveys the labeled casing to the storage compartment port. The figure beneath outlines the various fields of VLAN tag:
- Type-Type field is 16 pieces field additionally called the label convention ID (TPID) esteem. The incentive for Ethernet hexadecimal 0x8100.
- Client need It has a 3-bit esteem that supports administration execution.
- Accepted Format Identifier (CFI)- This is a 1-bit identifier that empowers Token Ring edges to be conveyed across Ethernet joins.
- VLAN ID (VID)- It is a 12-digit VLAN ID number that backings up to 4096 VLAN IDs.
Local VLANs and 802.1Q Tagging
Labeled Frames on the Native virtual neighborhood (VLAN)
A few gadgets that help trunking, embed a VLAN tag to local VLAN traffic. Assuming a port arranged on 802.1Q trunk get a labeled edge with VID and equivalent to the local VLAN, it drops the edge.
So while arranging a switch port on Cisco switch, design gadgets that they send untagged edges on the local VLAN. Other merchant gadgets, switches, non-Cisco switches, and servers support labeled casings on the local VLANs.
Untagged Frames on the Native VLAN
At the point when a trunk port gets untagged casings, it advances these untagged edges to the local VLAN. Assuming there are no gadgets related with the local VLAN and there could be no other trunk ports, then, at that point, the switch dropped the casing. During designing a 802.1Q trunk port, the local VLAN Id is alloted as a default Port VLAN ID.
All untagged traffic coming all through the 802.1Q port is sent in view of the PVID. For instance, assuming that VLAN 10 is a local VLAN. Thus, every untagged information is shipped off VLAN 10 which PVID is 10. In the event that the local has not been arranged, the PVID an incentive for local VLAN is 1. Since the default local VLAN is 1.
Voice VLAN Tagging
To Voice over IP Support, a different voice VLAN is required. Port that interfaces the Cisco IP telephone can be designed to utilize two separate VLANs. One for voice and one more for information traffic.
The connection between IP telephone and switch work like the storage compartment to convey both voice and information VLAN traffic. The Cisco IP Phone has a three-port 10/100 switch. These ports give committed associations with these gadgets:
Port-1 – This port interfaces the IP telephone to the switch or other VoIP (Voice Over Internet Protocol) gadgets.
Port-2 – This port is an interior 10/100 point of interaction that conveys the IP telephone traffic.
Port-3 – This is an entrance port that interfaces with a PC or other gadget.
On the switch, the switch port is designed to send CDP (Cisco Discovery Protocol) parcels and educate an appended IP telephone to send voice traffic to the switch in one of the accompanying ways, contingent upon the sort of traffic:
- In a voice VLAN labeling with a Layer 2 class of administration need esteem.
- In; an entrance VLAN labeling with a Layer 2 class of administration need esteem.
- In an entrance VLAN, untagged without a Layer 2 class of administration need esteem.
