title: Vlans
categories: [cheatsheets]
Vlans can splits different Hosts in the local network.
- Basically: Switches only forward Frames inbetween same vLan
- Therefore you can have multiple LANs within one Network without the need of multiple Switches and Cables
Whats Important:
- belonging of Stations
- Configuration
- Communication between the Switches
- IEEE Standards
1 Switch with 3 Ports, one every Port there are multiple Stations (each Port is one separated network)
1 Switch with X Ports, having multiple Stations, randomly at the switch, having multiple VLANS that are port-independent
- Works over Backbones
- Works with other technologies (IP)
Different techniques:
Split by:
- Port Numbers (Ports on a switch)
- MAC addresses (defined in the switch)
- IP Addresses (-> not really good)
- Multicast IP addresses (one IP multicast = one vlan)
- a combination of the above
This is for the case you have multiple VLAN Switches
-> The switches have a "Trunk Port" over which the Frames are passed from one switch to another
-> Packets are tagged with a vlan ID to identify the correct vlan membership
Frame Tagging (IEEE 802.1q for Frame Tagging)
Another Field in the Frame for the Vlan tag:
[TAG] = [Ether Type][PRI][CFI][VLAN ID]
- Ether Type: (16 Bit) to know that this is a vlan packet
- PRI: (3 Bit) Priority
- CFI: (1 Bit) almost always 0 (for compatibility with token ring)
- VLAN ID: (12 Bit) Number of the corresponding vlan
Quality of Service Classes:
- 0 : Best Effort (BE)
- 1 : Background (BK)
- 2 : - (not specified)
- 3 : Excellent Effort (EE)
- 4 : Controlled Load (CL)
- 5 : Video < 100ms (VI)
- 6 : Voice < 10ms (VO)
- 7 : Network Control (NC)