1. Ethernet Errors and Problems
IST 228\Ch6:Virtual LANs (VLANs)
Ethernet Errors and Problems
Frame size errors
Short frame
Long frame
Jabber
Collision Errors
What percent collision rate is acceptable?
Late collision?
Why late collisions occur? How to prevent them?
Solutions to prevent collisions?
Broadcasts
How much broadcast traffic is acceptable?
How to reduce the amount of broadcast traffic?

2. Ethernet Security Problems
IST 228\Ch6:Virtual LANs (VLANs)
Ethernet Security Problems
By default, all users can see all network devices located on a physical LAN.
Anyone can observe all network traffic by plugging a network analyzer into a hub.

3. Solution(s)? Securing Switch Ports limiting device connections
IST 228\Ch6:Virtual LANs (VLANs)
Solution(s)?
Securing Switch Ports
limiting device connections
1900s2(config)#mac-address-table permanent <MAC Address> e0/7
limiting communication
1900s2(config)#mac-address-table restricted static <MAC Address> e0/6 e0/12
limiting the number of devices
1900s2(config)#interface e/10
1900s2(config-if)#port secure max-mac-count 5

4. Solution(s)? Switching Methods Cut-Through Store-and-Forward Switches
IST 228\Ch6:Virtual LANs (VLANs)
Solution(s)?
Switching Methods
Cut-Through
Store-and-Forward Switches
Fragment-Free Switching
Adaptive Cut-Through
1900s2(config)#switching-mode store-and-forward

5. Solution(s)? Use bridges Use switches
IST 228\Ch6:Virtual LANs (VLANs)
Solution(s)?
Use bridges
Use switches
Use routers to segment a network (Collapsed Backbone Approach)
Advantages
Disadvantages

6. IST 228\Ch6:Virtual LANs (VLANs)
A VLAN is a logical grouping of network devices connected to defined ports on switches.
Each VLAN is a broadcast domain within a layer-2 switched network, created by assigning ports on switches to different subnetworks.

7. Benefits Simplified Network Management Broadcast Control Security
IST 228\Ch6:Virtual LANs (VLANs)
Benefits
Simplified Network Management
Broadcast Control
Security
Flexibility and Scalability
20% to 40% of the workforce is on move every year.
Implementing changes and moves constitutes 23% of the total network administration cost.

8. VLAN Membership Static VLANs Dynamic VLANs the most secure
IST 228\Ch6:Virtual LANs (VLANs)
VLAN Membership
Static VLANs
the most secure
Dynamic VLANs
use an intelligent software to assign ports.

9. Creating VLANs on Cisco Catalyst 1900
IST 228\Ch6:Virtual LANs (VLANs)
Creating VLANs on Cisco Catalyst 1900
1900s2>enable
1900s2#configure terminal
1900s2(config)#vlan 2 name engineering
1900s2(config)#vlan 3 name marketing
: :
1900s2(config)#exit
1900s2#show vlan

10. Assigning Ports to VLANs
IST 228\Ch6:Virtual LANs (VLANs)
Assigning Ports to VLANs
1900s2(config)#interface e0/2
1900s2(config)#vlan-membership static 2
1900s2(config)#exit
1900s2(config)#interface e0/3
: :
1900s2#show vlan
Use the show vlan [#] command to gather information about a specific vlan.

11. Link Types and Configuration
IST 228\Ch6:Virtual LANs (VLANs)
Link Types and Configuration
Access Links
A device attached to an access link is unaware of a VLAN membership.
Access-link devices cannot communicate with devices outside their VLAN unless...
Trunk links
Switch-to-switch, switch-to-server, or switch-to-router 100- or 1000Mbps links that can carry traffic from multiple VLANs.
Five different states you can set for a trunk link:
Auto
Desirable
Nonegotiate
Off On

12. IST 228\Ch6:Virtual LANs (VLANs)
Trunk Links

13. Configuration of Trunk links
IST 228\Ch6:Virtual LANs (VLANs)
Configuration of Trunk links
1900s2#configure terminal
1900s2(config)#interface f0/26
1900s2(config-if)#trunk on
By default, all VLANs are enabled to be routed over this newly configured trunk link.
1900s2(config-if)#no trunk-vlan 2
You cleared VLAN 7 from the trunk.
1900s2#show trunk a allowed-vlans

14. VLAN Trunk Protocol (VTP)
IST 228\Ch6:Virtual LANs (VLANs)
VLAN Trunk Protocol (VTP)
Layer 2 messaging protocol
Manages all changes to the VLANs across networks.
Any changes made to a VLAN by an administrator are automatically propagated by VTP to all VTP-enabled devices.
No need for VTP if there is only a single switch or if all switches are in the same VLAN.

15. Using VTP VTP devices are organized into domains.
IST 228\Ch6:Virtual LANs (VLANs)
Using VTP
VTP devices are organized into domains.
Each domain must have at least one VTP server.
Each switch can only be in one domain.
1900s2(config)#VTP domain <domain name>
Three different modes
Server
Client
Transparent
1900s2(config)#VTP client
VTP Pruning: Reduces the number of VTP updates that traverse a link. By default, VTP pruning is disabled on all switches.
1900s2(config)#vtp pruning enable
1900s2(config)#delete vtp

16. Nonswitching Hubs and VLANs
IST 228\Ch6:Virtual LANs (VLANs)
Nonswitching Hubs and VLANs
Considerations to keep in mind when implementing hubs on a network that employs VLANs:
If you insert a hub into a port on a switch and then connect several devices to the hub, all the system attached to that hub will be in the same VLAN
If you must move a single workstation that is attached to a hub with several workstations, you will have to physically attach the device to another hub or switch ports in order to change its VLAN assignment
The more hosts attached at individual switch ports, the greater the microsegmentation and flexibility the VLAN can offer

17. Routers and VLANs Routers are used with VLANs
IST 228\Ch6:Virtual LANs (VLANs)
Routers and VLANs
Routers are used with VLANs
to communicate each other
to increase security

18. VLAN Identification Inter-Switch Link (ISL) IEEE 802.1Q LAN emulation
IST 228\Ch6:Virtual LANs (VLANs)
VLAN Identification
Inter-Switch Link (ISL)
IEEE 802.1Q
LAN emulation
(FDDI)