VLAN Technology Principle

Before VLAN:

→ Network Security is bad.

→ Network efficiency is low. (unnecessary packets → wasting bandwidth and CPU resources)

→ Service expanded capability is bad. (e.g. It can't forward Ethernet frame used for network management with higher priority.

VLAN Tag: +4-byte. (IEEE 802.1Q)

| DA | SA | +TAG | TYPE | DATA | FCS |

[6B] [6B] [4B] [2B] [64-1500B] [4B]

|– TPID (Tag Protocol Identified): fixed value 2-byte (802.1Q tag: 0x8100)

|– TCI (Tag Control Information): 2-byte. {

→ Priority: 3bits. [0-7] → to provide differential forwarding service.

→ CFI (Canonical Format Indicator): 1bit. [token ring/FDDI media access]

→ VLAN ID: 12bits. [0-4095] → it can control the forwarding of Ethernet frame

Implement VLAN in the following way :

→ Based on port: Port VLAN ID (PVID) / port default VLAN configured on every port. If an untagged frame is received, the VLAN ID will be PVID.

→ Based on MAC: mapping relation between MAC and VLAN ID. If an untagged frame is received, VLAN ID will be added according to the mapping relation table.

→ Based on protocol: mapping relation between protocol filed of the Ethernet frame and VLAN ID. If an untagged frame is received, VLAN ID will be added according to the mapping relation table.

→ Based on subnet: add VLAN ID according to IP address information in packet.

Priority order from high to low: subnet → protocol → MAC → port. Based on port is common method.

Ports of switch divided into three types:

→ Access : only permit VLAN ID to pass the port, the VLAN ID is the same with PVID of the port; if the frame received from peer device is untagged, the switch will add PVID to the frame by force; the frame sent by Access port is always untagged frame; the default port of switches are access, PVID is 1 by default. VLAN 1 is created by system and can not be deleted.

→ Trunk : VLAN ID can be the same with PVID and also can be different; if ( VLAN ID != exist in permitted list ) { discarded; else if { VLAN ID == PVID {sent to another device after removing away the tag (*PVID each port is unique); else if ( VLAN ID != PVID ) {forwarded without modification}}}

→ Hybrid : if (VLAN tag == none) {same function with access port; else if (not (!) configure untagged VLAN) {trunk;} }

[ e0/1]port link-type hybrid [ e0/2]port link-type hybrid [ e0/24]port link-type hybrid

[ ]port hybrid pvid vlan 2 [ ]port hybrid pvid vlan 3 [ ]port hybrid pvid vlan 99

[ ]port hybrid vlan 2 untagged [ ]port hybrid vlan 3 untagged [ ]port hyb vlan 2 to 3 untagg

[ ]port hybrid vlan 99 untagged [ ]port hybrid vlan 99 untagged

GVRP (GARP VLAN Registration Protocol) → create VLAN automatically

[]gvrp

[]int e0/1

[ ]port link-type trunk

[ ]port trunk permit vlan all

[ ]gvrp