vlans.md 1.8 KB


title: Vlans categories: [cheatsheets]

tags: [networking]

Virtual LANS (VLANs)

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

Normally:

1 Switch with 3 Ports, one every Port there are multiple Stations (each Port is one separated network)

VLAN:

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)

Membership

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

Truncation

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

Priorities

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)