1. Switching and VLANs

2. Switching Tasks Switching operation Configure a VLAN
Configure VLAN Trunking Protocol (VTP)
Configure a switch for trunking
Verify VLAN connectivity
Verify spanning-tree operations
Slide 1 of 1
Purpose:
Emphasize:

3. Switching operation
Switches forward frames based on destination MAC address
Switches store MAC addresses in the MAC address table
Switches populate the table from the source MAC address from frames that enter the switch
If the destination MAC address is not in the table the switch forwards the frame out all ports in the same VLAN except the receiving port
By default all ports are in VLAN 1
Slide 1 of 1
Purpose:
Emphasize:

4. A VLAN = A broadcast domain = Logical network (subnet)
VLAN Overview
Segmentation
Flexibility
Security
3rd floor
2nd floor
Slide 1 of 1
Purpose:
Emphasize: A VLAN is a broadcast domain.
Note: In order to have inter-vlan communications, a router is required.
1st floor
SALES HR
ENG
A VLAN = A broadcast domain = Logical network (subnet)

5. VLAN Operations Each logical VLAN is like a separate physical bridge
Switch A
Green
VLAN
Black
Red
Slide 1 of 3
Purpose:
Emphasize:
Each port on the switch can be assigned to a VLAN.
By default, all ports are in VLAN 1, a factory default VLAN.
Each logical VLAN is like a separate physical bridge

6. VLAN Operations Each logical VLAN is like a separate physical bridge
Switch A
Green
VLAN
Black
Red
Switch B
Slide 2 of 3
Purpose:
Emphasize:
To allow VLANs to span across multiple switches, the connection between the switches must belong to mulitple VLANs.
Red
VLAN
Black
VLAN
Green
VLAN
Each logical VLAN is like a separate physical bridge
VLANs can span across multiple switches

7. VLAN Operations Each logical VLAN is like a separate physical bridge
Switch A
Green
VLAN
Black
Red
Switch B
Trunk
Fast Ethernet
Slide 3 of 3
Purpose:
Emphasize:
A trunk is used to connect two switches together.
A trunk carries traffic for multiple VLANs.
Only the fastethernet ports on the 1900 can be configured as trunk port.
Trunking is off by default on the 1900 fastethernet ports (fa 0/26 and fa 0/27).
Note:
The 1900 supports DISL.
At the time of the beta, the core switch (2900xl) doesn’t support DISL.
Red
VLAN
Black
VLAN
Green
VLAN
Each logical VLAN is like a separate physical bridge
VLANs can span across multiple switches
Trunks carries traffic for multiple VLANs

8. VLAN Membership Modes Static VLAN Dynamic VLAN Port e0/4 Port e0/9
Trunk
Port e0/4
Port e0/9
VLAN5
Slide 1 of 1
Purpose:
Emphasize:
Note:
Once a port has been assigned to a VLAN, it can not send or receive traffic from devices in another VLAN without the intervention of a layer 3 device like a router.
The 1900 can’t be configure as the VMPS.
A CiscoWorks 2000 or CWSI management station or a Cat 5000 switch can be configured as the VMPS.
In the future, dynamic VLANs may also offer membership based on other criteria such as protocol or application. Dynamic VLANs are covered in the Managing Cisco Switched Internetworks class.
VLAN10
VMPS
= vlan 10
MAC =

9. 802.1q Tagging
Not intrusive to client stations, client does not see the 8-2.q header
Effective between switches, routers and switches, switches and servers with 802.1q network interface cards
VLAN Tag added by outgoing port
802.1q carries VLAN identifier
Slide 1 of 1
Purpose:
Emphasize:
Note:
The 1900 only supports ISL trunking.
ISL is Cisco Proprietary Q is an IEEE standard.
Other trunk types:
LANE (VLANSs over ATM)
(FDDI trunk)
VLAN Tag stripped by forwarding port

10. 802.1Q Frame

11. VTP Pruning
Reduces unnecessary flooded (broadcast/unknown address) traffic
Example: Station A sends broadcast. Broadcast is only flooded toward any switch with ports assigned to the green VLAN
Port 2 B
Switch 4
Flooded traffic is pruned
Switch 2
Slide 1 of 1
Purpose:
Emphasize: VTP prunning provides optimized flooding. Without VTP prunning, station A’s broadcast will be flooded to all switches whether they have any port in the red vlan or not.
Note:
VLAN 1 can’t be prunned. STP, CDP, VTP updates are sent on VLAN1.
All switches in the switched network must support prunning or prunning will be disabled.
Each trunk port maintains a state variable per vlan indicating if the switch has any port assigned to a particular vlan or not.
Green VLAN
Switch 5
Port 1 A
Switch 6
Switch 3
Switch 1

12. VLAN Configuration Guidelines
Maximum number of VLANs is switch-dependent
VLAN1 is One of the factory default VLANs
CDP and VTP advertisements are sent on VLAN1
Must be in VTP server or transparent mode to create, add, or delete VLANs
Slide 1 of 1
Purpose:
Emphasize:
Note:
In the ICND lab,
All the switches and routers are in VLAN1.
The core server and the core router are in multiple VLANs.
Each workgroup PC is on an unique VLAN.

13. VLAN Configuration Steps
Enable VTP (optional)
Enable trunking
Create VLANs
Assign VLAN to ports
Slide 1 of 1
Purpose: Show the four basic steps for configuring VLANs.
Emphasize:

14. Defining a Trunk Many Options…
On = Set trunk on and negotiate with other side
Result - Trunk on if other side is on, desirable, or auto
Desirable = Negotiate with other side. Result - Trunk on if other side is on, desirable, or auto
Auto = Will be a trunk only if the other side is on or desirable
Non-negotiate = Set trunk on and will not negotiate
Slide 2 of 2
Purpose:
Emphasize:
Note:

15. Defining a Trunk
On = Set trunk on and negotiate with other side
Result =Trunk on if other side is on, desirable, or auto
Slide 1 of 2
Purpose:
Emphasize: The 1900 supports DISL.
Note:
At the time of the beta, the core switch (2900xl) does not support DISL.
If trunking is on at one end, and off at the other end, the link will be down.
Switch1(config-if)#
switchport mode trunk

16. switchport mode dynamic desirable
Defining a Trunk
Desirable = Negotiate with other side
Result =Trunk on if other side is on, desirable, or auto
Slide 1 of 2
Purpose:
Emphasize: The 1900 supports DISL.
Note:
At the time of the beta, the core switch (2900xl) does not support DISL.
If trunking is on at one end, and off at the other end, the link will be down.
Switch1(config-if)#
switchport mode dynamic desirable

17. switchport mode dynamic auto
Defining a Trunk
Auto = Default setting
Result =Trunk on if other side is on or desirable
Slide 1 of 2
Purpose:
Emphasize: The 1900 supports DISL.
Note:
At the time of the beta, the core switch (2900xl) does not support DISL.
If trunking is on at one end, and off at the other end, the link will be down.
Switch1(config-if)#
switchport mode dynamic auto

18. switchport nonegotiate
Defining a Trunk
Non-negotiate = Do not send DTP frames to negotiate with other side
Result =Trunk on if other side set on or non-negotiate
Slide 1 of 2
Purpose:
Emphasize: The 1900 supports DISL.
Note:
At the time of the beta, the core switch (2900xl) does not support DISL.
If trunking is on at one end, and off at the other end, the link will be down.
Switch1(config-if)#
switchport nonegotiate

19. Verifying a Trunk Switch#sh int trunk
wg_sw_a#show interface trunk
Switch#sh int trunk
Port Mode Encapsulation Status Native vlan
Fa0/ on q trunking
Port Vlans allowed on trunk
Fa0/
Port Vlans allowed and active in management domain
Fa0/ ,1002,1003,1004,1005
Port Vlans in spanning tree forwarding state and not pruned
Slide 1 of 2
Purpose:
Emphasize:
Trunk A = fasthethernet 0/26
Trunk B = fastetherent 0/27

20. Adding a VLAN Switch1(config)#
vlan vlan#
Switch1#conf terminal
Enter configuration commands, one per line. End with CNTL/Z
Switch1(config)#vlan 9
Switch1(config-vlan)# name Accounting VLAN
Slide 1 of 2
Purpose:
Emphasize:
Each VLAN has a unique, four-digit number that can be from 1 to To add a VLAN to the VLAN database, the minimum parameter required is the VLAN number.

21. wg_sw_a#show vlan [vlan#]
Verifying a VLAN
wg_sw_a#show vlan [vlan#]
Slide 1 of 2
Purpose:
Emphasize:

22. Assigning Switch Ports to a VLAN
Switch1(config-if)#
switchport access vlan 2
Slide 1 of 2
Purpose:
Emphasize: By default, all ports are in VLAN 1.