ccna exp3 - chapter03 - vlans_dpf

8/3/2019 CCNA Exp3 - Chapter03 - VLANS_dpf

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Cha ter 3 - VLANS

CCNA Exploration 4.0

1



Objectives

• Explain the role of VLANs in a network.

• Ex lain the role of trunkin VLANs in a network.

• Explain the role of trunking VLANs in a network.• Troubleshoot the common software or hardware

configuration problems associated with VLANs on switches

in a network topology.

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Role of VLANS

• One of the contributing technologies to excellent network

performance is the separation of large broadcast domains

into smaller ones with VLANs.• Smaller broadcast domains limit the number of devices

separated into functional groupings, such as database

services for an accounting department and high-speedata trans er or an eng neer ng epartment.




Before VLANS

1 building

•1 building -> OK

• Man buildin -> NOT OK

Many building

– IT department wants to ensure that student computers all share thesame security features and bandwidth controls. How can thenetwork accommodate the shared needs of the geographically

department together? – It would be great to group the people with the resources they use

regardless of their geographic location, and it would make it easier


.



VLAN overview

• A VLAN allows a network administrator to create groups of

logically networked devices that act as if they are on their own independent network

•


access and security policies to particular groups of users.



VLANS details

•

switches.

• The network design above creates three separate


broadcast domains.



Without VLANs – No Broadcast Control

ARP Request

Switch 1172.30.1.21

255.255.255.0172.30.2.12

255.255.255.0

172.30.2.10 172.30.1.23

No VLANs

Same as a single VLAN

. . . . . .

• Without VLANs, the ARP Request would be seen by all hosts.

•


,

cycles.



With VLANs – Broadcast Control

Switch Port: VLAN IDARP Request

Switch 1172.30.1.21

255.255.255.0

VLAN 1

172.30.2.12

255.255.255.0

VLAN 2

172.30.2.10 172.30.1.23

Two VLANs

. . .

VLAN 2

. . .

VLAN 1 1 2 3 4 5 6 .

1 2 1 2 2 1 .

Port

VLAN

wo u ne s




Benefit of VLANS




VLAN ID




VLAN Tagging

No VLAN Tagging

VLAN Tagging

more than one VLAN.




VLAN Tagging

802.10

, -Switch Link (ISL) and IEEE 802.1Q.

• ISL used to be the most common, but is now being replaced by 802.1Qframe ta in .


• Cisco recommends using 802.1Q.

• VLAN Tagging and Trunking will be discussed in the next chapter.



Types of VLAN

• Data VLAN: A data VLAN is a VLAN that is configured to

carry only user-generated traffic.




Types of VLAN

• Default VLAN:

– All switch ports become a member of the default VLAN after theinitial boot up of the switch.

– av ng a e sw c por s par c pa e n e e au ma esthem all part of the same broadcast domain. This allows any deviceconnected to any switch port to communicate with other devices onother switch ports.


– The default VLAN for Cisco switches is VLAN 1. VLAN 1 has all thefeatures of any VLAN, except that you cannot rename it and youcan not delete it.



Types of VLAN

• Management VLAN:

– A management VLAN is any VLAN you configure to access the

.

– VLAN 1 would serve as the management VLAN if you did not

proactively define a unique VLAN to serve as the management


.

– You assign the management VLAN an IP address and subnet

mask. A switch can be managed via HTTP, Telnet, SSH, or SNMP.



Types of VLAN

• Native VLAN:

– A native VLAN is assigned to an 802.1Q trunk port.

– n . run por suppor s ra c com ng rom manyVLANs (tagged traffic) as well as traffic that does notcome from a VLAN (untagged traffic).


– The 802.1Q trunk port places untagged traffic on the

native VLAN. In the figure, the native VLAN is VLAN 99.



Types of VLAN

• Voice VLAN: – It is easy to appreciate why a separate VLAN is needed to support

Voice over IP VoIP

– VoIP traffic requires:

• Assured bandwidth to ensure voice quality

• Transmission priority over other types of network traffic

• Ability to be routed around congested areas on the network

• Delay of less than 150 milliseconds (ms) across the network




Voice VLAN




Types of traffic




Switch port membership




VLAN Trunk




802.1Q tagging

• EtherType field – Set to the hexadecimal value of 0x8100. This value is

called the ta rotocol ID TPID value. With theEtherType field set to the TPID value, the switch receivingthe frame knows to look for information in the tag controlinformation field.

•

– 3 bits of user priority - Used by the 802.1p standard, which specifies how to provide

expedited transmission of Layer 2 frames. A description of the IEEE 802.1p is beyond

the scope of this course; however, you learned a little about it earlier in the discussion

.

– 1 bit of Canonical Format Identifier (CFI) - Enables Token Ring frames to be carried

across Ethernet links easily.

– 12 bits of VLAN ID (VID) - VLAN identification numbers; supports up to 4096 VLAN


IDs.

• FCS field



Native Vlan and 802.1q




Trunking mode

• The trunking modes

available in Fast Ethernet

and Gigabit Ethernet

switchport mode trunk

switchport mode access

switchport mode dynamic desirable

switchport mode dynamic auto


Nonegotiateswitchport nonegotiate



Trunking mode




Configure VLAN and Trunking

• Add VLAN




Assign VLAN to port




Configuring Ranges of VLANs

vlan 3

SydneySwitch(config)#interface range

-

SydneySwitch(config-if)#switchport access vlan 3

SydneySwitch(config-if)#exit




Verify VLAN

• Show vlan

• Show vlan brief

• Show interface vlan 2• Show interface fa0/18 switchport




Delete Vlan

• No vlan

• Delete flash:vlan.dat




Configure Trunk link




Common Problem




Naitve VLAN mismatch




Trunk mode mismatch

• Both side is configured : switchport mode dynamic auto

• -> access

• Solution: switchport mode trunk




Incorrect VLAN list

•

• S3 F0/3: allow vlan 10, 20, 99

• Solution: S1 f0/3: switchport trunk allowed vlan 10, 20, 99




Mistake of VLAN and IP subnets


S



Summary


ccna exp3 - chapter03 - vlans_dpf

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