Chapter 3 - VLANs

VLANs Logical grouping of devices or users Configuration done at switch via software Not standardized – proprietary software from vendor

VLANs Logically segment the physical LAN infrastructure into different subnets (or broadcast domains for Ethernet)

Differences Between Traditional Switched LAN and VLANs VLANs work at Layer 2 and Layer 3 of OSI Communications between VLANs is done by routers VLANs provide a method of controlling network broadcasts Administrators assign users to VLANs VLANs increase network security – defines who can communicate with whom Group switch ports and their connected users into logically defined workgroups

Transport of VLANs Across the Backbone Ability to transport VLAN information between interconnected switches and routers that reside on the backbone –Remove physical boundaries between users –Increase configuration flexibility – users move –Provide mechanism for interoperability between backbone components

VLAN transportation Backbone commonly acts as collection point for large volumes of traffic Carries end user information and ID between switches, routers and directly attached servers

Routers in the VLAN Traditionally provide firewalls, broadcast management etc. Provide connected routes between different VLANs Cost effectively integrate external routers into switching architecture by using one or more high speed backbone connection like: –Fast Ethernet, or ATM connection Increasing the throughput between switches and routers Consolidating number of physical router ports required fro communication between VLANs

Frame Use in the VLAN Switches core component of VLAN communication Each switch makes forwarding and filtering decisions based on the frame –Based on VLAN metrics Approaches for logically grouping users into distinct VLANs: –Frame filtering –Frame tagging (identification)

Frame Filtering

Frame Tagging Uniquely assigns a VLAN ID to each frame VLAN IDs assigned by switch administrator Chosen by IEEE for its scalability Gaining recognition as the standard trunking mechanism IEEE 802.1q states that Frame Tagging is the way to implement VLANs

Frame Tagging Continued Places a unique identifier in the header of each frame as it is forwarded throughout the network When the frame exits the network backbone – switch removes the identifier before the frame is transmitted to its target Frame identification functions at Layer 2 and requires little administrative overhead

Ports, VLANs and Broadcasts VLANs make up a switched network – logically segmented Ports assigned to the same VLAN share broadcasts Three VLAN implementation –Port-centric –Static –Dynamic

Port-Centric All nodes connected to ports in the same VLAN are assigned same VLAN ID VLAN Membership by port make administrator’s job easier and more efficient because: Users assigned by port VLANs easily administered Increased security Packets do not LEAK into other domains

Port-Centric VLANs

Static VLANs Ports on switch that is statically assigned to a VLAN Require administrator to make changes Secure Easy to configure Straightforward to monitor Works well in which moves are controlled and managed

STATIC VLANs

Dynamic VLANs Ports on switch automatically determine their VLAN assignments Based on MAC addresses, logical addressing or protocol type of data packet Less administration with in the wiring closet when a user moves or new one added Centralized notification when an unrecognized user is added to the network More administration is required to initially set up database within the VLAN management software

Dynamic VLANs

VLAN Additions, Moves and Changes Companies continually reorganizing –These moves/changes are network manager’s biggest headaches and one of the largest expenses related to managing a network VLANs provide effective measures for controlling changes and reducing costs Users in a VLAN can share the same network address space i.e. IP subnet VLANs require less rewiring, configuration and debugging

Movement of Users

VLANs Help Control Broadcast Activity Most effective measures is to properly segment with firewalls that help prevent problems on segment from damaging other parts of the network Firewall segmentation provides reliability and minimizes overhead broadcast traffic No routers between switches broadcasts (layer 2) are sent to every switched port – referred to as a FLAT network(one broadcast domain across the whole network) Flat Network –Provides low latency & high throughput –Easy to administer

VLANs Controlling Broadcast Activity FLAT Network – Disadvantages –Increases vulnerability to broadcast traffic across all switches, ports, backbone links and users VLANs effectively extend firewalls from routers to the switch fabric and protecting against potentially dangerous broadcast problems Creating firewalls –Assign switch ports or users to specific VLAN groups both within single switches and across multiple connected switches

VLANs and Broadcast Activity

How do VLANs Improve Network Security Restrict number of users in a VLAN group Prevent another user from joining without first receiving approval from the VLAN network management application Configure all unused ports to a default low- service VLAN

Tightening Network Security

VLANS Save Money Connect existing HUBS to switches Each hub segment connected to a switch can be assigned only ONE VLAN Stations that share a hub segment are in the same VLAN If a station need to be assigned a new VLAN that station must move to the new hub with the appropriate VLAN

Using Existing Hubs

Summary Switch is designed to physically segment a LAN into individual domains LAN typically configured according to the physical infrastructure it connects LANs that use LAN switching devices - VLAN technology is cost effective and an efficient way of grouping network users into virtual workgroups regardless of their physical placment

Summary Continued VLANs work at Layer 2 and Layer 3 of the OSI VLAN architecture must allow transportation of VLAN information between interconnected switches and routers on the corporate backbone Most common approach for logically grouping users into distinct VLANS are frame filtering, frame tagging, and frame identfication

Summary Continued Types of VLANS –Port-centric –Static –Dynamic VLANs provide benefits –Reduce administration costs – moves, additions changes –Controlled broadcast activity –Workgroup and network security –Save money by using existing hubs

QUIZ

THE END!!!