VLANs

1. VLANs Semester 3, Chapter 3 Linda Stacy

2. Table of Contents • Virtual LANs (VLANs) Go There! • Segmentation with Switching Architecture Go There! • VLAN Implementation Go There! • Benefits of VLANs Go There!

3. Virtual LANs(VLANs) Table of Contents

4. Existing Shared LAN Configurations • In a typical shared LAN... • Users are grouped physically based on the hub they are plugged into • Routers segment the LAN and provide broadcast firewalls • In VLANs... • you can group users logically by function, department or application in use • configuration is done through proprietary software

5. Segmentation with Switching Architecture Table of Contents

6. Grouping Users • VLANs can logically segment users into different subnets (broadcast domains) • Broadcast frames are only switched between ports on the switch or switches with the same VLAN ID. • Users can be logically group via software based on: • port number • MAC address • protocol being used • application being used

7. Differences between LANs & VLANs • VLANs... • work at Layer 2 & 3 • control network broadcasts • allow users to be assigned by net admin. • provide tighter network security. How?

8. VLANs Across the Backbone • VLAN configuration needs to support backbone transport of data between interconnected routers and switches. • The backbone is the area used for inter-VLAN communication • The backbone should be high-speed links, typically 100Mbps or greater

9. Router’s Role in a VLAN • A router provides connection between different VLANs • For example, you have VLAN1 and VLAN2. • Within the switch, users on separate VLANs cannot talk to each other (benefit of a VLAN!) • However, users on VLAN1 can email users on VLAN2 but they need a router to do it.

10. How Frames are Used in a VLAN • Switches make filtering and forwarding decisions based on data in the frame. • There are two techniques used. • Frame Filtering--examines particular information about each frame (MAC address or layer 3 protocol type) • Frame Tagging--places a unique identifier in the header of each frame as it is forwarded throughout the network backbone.

11. More on Frame Tagging • Frame Tagging... • is specified by IEEE 802.1q which states frame tagging is the preferred way to implement VLANs • uniquely assigns a VLAN ID to each frame before it is forwarded across the backbone. • is understood by switches prior to any broadcasts or transmission to other switches or routers • places a tag in the frame...thus, frame tagging. So what layer? • is removed by the switch after frame exits the backbone and before frame is forwarded to the end station

12. VLAN Implementation Table of Contents

13. Ports, VLANs, and Broadcasts • Three methods for implementing VLANs • Port-Centric • Static • Dynamic • Each switched port can be assigned to a VLAN. This... • ensures ports that do not share the same VLAN do not share broadcasts. • ensures ports that do share the same VLAN will share broadcasts.

14. 3 Port-Centric VLANs Benefits of Port-Centric VLANs • All nodes in the same VLAN are attached to the same router interface. (Note: curriculum says “switched port”) • Makes management easier because... • Users are assigned by router port • VLANs are easy to admin. • provides increased security • packets do not “leak” into other domains

15. Static VLANs • Defined • Static VLANs are when ports on a switch are administratively assigned to a VLAN • Benefits • can be assigned by port, address, or protocol type • secure, easy to configure and monitor • works well in networks where moves are controlled

16. Dynamic VLANs • Defined • Switch ports can automatically determine a user’s VLAN assignment based on either/or: • MAC • logical address • protocol type • When a station is initially connected to an unassigned port, the switch checks an entry in the table and dynamically configures the port with the right VLAN • Benefits • less administration (more upfront) when users are added or move • centralized notification of unauthorized user

17. Benefits of VLANs Table of Contents

18. VLANs Make Changes Easier • Traveling Users • 20% to 40% of work force moves every year • net admin’s biggest headache • largest expense in managing networks. Moves may require... • recabling • readdressing and reconfiguration • VLANs provide a way to control these costs. As long as the user still belongs to the same VLAN... • simply configure the new switch port to that VLAN • router configuration remains intact

19. VLANs Control Broadcasts • Routers provide an effective firewall against broadcasts • Adding VLANs can extend a router’s firewall capabilities to the “switch fabric” • The smaller the VLAN, the smaller the number of users that are effected by broadcasts

20. VLANs Improve Security • Shared LANs are easy to penetrate...simply plug into the shared hub. • VLANs increase security by ... • restricting number of users in a VLAN • preventing user access without authorization • configuring all unused ports to the “Disabled” setting • control access by • addresses • application types • protocol types

21. VLANs Save Money • Hub Replacement & Segmentation • The ports on a non-intelligent hub can only be assigned one VLAN. • Replacing hubs with switches is relatively cheap compared to the benefit gained. • In the graphic, replacing the core hub in an extended star topology with a VLAN capable switch effectively microsegments one shared LAN into six.

22. Table of Contents End Slide Show