1. Switching and VLANs

2. Switching Tasks Switching operation VLANs Trunking
Verify VLAN connectivity
Verify spanning-tree operations
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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
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4. A VLAN = A broadcast domain = Logical network (subnet)
VLAN Overview
Segmentation
Flexibility
Security
3rd floor
2nd floor
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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
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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
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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
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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. 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
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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

9. 802.1Q Frame

10. VLAN Configuration Guidelines
Maximum number of VLANs is switch-dependent
VLAN1 is One of the factory default VLANs
Usually there is a one-to-one association between VLANs and subnets
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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.

11. VLAN Configuration Steps
Create VLANs
Assign VLAN to ports
Configure trunks as necessary
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Purpose: Show the four basic steps for configuring VLANs.
Emphasize:

12. 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
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Note:

13. Defining a Trunk
On = Set trunk on and negotiate with other side
Result =Trunk on if other side is on, desirable, or auto
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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

14. switchport mode dynamic desirable
Defining a Trunk
Desirable = Negotiate with other side
Result =Trunk on if other side is on, desirable, or auto
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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

15. switchport mode dynamic auto
Defining a Trunk
Auto = Default setting
Result =Trunk on if other side is on or desirable
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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

16. 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
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Trunk A = fasthethernet 0/26
Trunk B = fastetherent 0/27

17. 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
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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.

18. wg_sw_a#show vlan [vlan#]
Verifying a VLAN
wg_sw_a#show vlan [vlan#]
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19. Assigning Switch Ports to a VLAN
Switch1(config-if)#
switchport access vlan 2
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Purpose:
Emphasize: By default, all ports are in VLAN 1.