2. Implementing Ethernet Virtual
LANs
So far we saw a switch receives a frame and makes a
Forwarding decision and forwards it.
We haven’t much deal with the VLANs so in this chapter
We will see that.
Section 1 : How vlan works in 1 switch and how to span
Single vlan across multiple switches.
Section 2 : How to configure VLANs and VLAN trunks, and how
To route a frame from one vlan to another vlan
Section 3 : Issues that can arise with vlans
3. Virtual LAN Concepts
LAN - A LAN includes all devices in the same broadcast domain.
It stands for virtual local area network.
VLAN is a network that collects a set of network ports on a switching
device into a single broadcast domain.
VLAN separating the large broad cast domain into small broadcast domains.
If a device in one VLAN sends a broadcast frame all device in that same
VLAN receive and other VLAN device will not receive that.
4. VLAN are most often used over ethernet network.
In one physical switch we can create multiple logical network thus each
VLAN create its own broadcast domain.
By default all the port are in VLAN1.
VLAN1 is management VLAN.
VLAN2 can create 2-1005.
5. Other Reason to use VLANS
To reduce CPU overhead on each device, improving host performance, by
reducing the number of devices that receive each broadcast frame.
To create more flexible designs that groups users by department, or by groups
that work together, instead of by physical location.
To solve problems more quickly, because the failure domain for many
problems is the same set of devices as those in the same broadcast domain.
6.
7. Creating Multi switch VLANs Using
Trunking
Generally we are configuring VLANs on a single switch and simply configuring
each port to tell it the VLAN number to which the port belongs.
But if w have multiple switches, then we need to consider additional concepts
about how to forward traffic between the switches.
When we are using VLANs in networks that have multiple interconnected
switches the switches need to use VLAN Trunking on the links between the
switches.
VLAN trunking causes the switches to use a process called VLAN Tagging, by
which switch that is sending switch adds another header to the frame before
sending it over the trunk.
This exrtra Trunking header includes a VLAN identifier that is VLAND ID field
so that the sending switch can associate the frame with a particular VLAN ID
and receiving switch can then know in what VLAN each frame belongs.
8.
9. Interface Types In Switch
Trunk Port :
Trunk port is a port in a switch which can carry multiple vlan traffic.
Access Port :
Access port is a port in a switch which can carry single vlan traffic only.
10. VLAN Tagging Concepts
The use of Trunking allows switches to forward frames from multiple VLANs over
a single physical connection by adding a small header.
SW1 adds a VLAN header to the original Ethernet frame, with the
VLAN header listing a VLAN ID of 10 in this case
11. CISCO has supported two different
Trunking protocols.
1. Inter-switch Link(ISL)--------CISCO created the ISL it add 30 byte
2. IEEE802.1Q------IEEE it add 4 byte
3. Both ISL and IEEE tags the frame in the trunk but how is what differs.
4. 1.IEEE inserts 4byte or 24 bits 802.1Q Header out of which 12 bit is for VLAN
ID
5. Hence Maximum vlan is 2^12(4096)VLANs.
12.
13. Types of VLAN
1. Static VLAN---→Base on port number
2. Dynamic VLAN-→Base on the MAC address
Static VLAN
Static VLANs are based on port numbers.
Need to configure manually i.e. Assign a port on a switch to a VLAN.
One port can be a member of only one VLAN.
It is also called port Based VLANs.
Static VLAN is a group of ports designated by the switch as belonging to the same
broadcast domain.
VLAN Creation:
Switch(Config)#vlan <no>
Switch(Config-vlan)#name<name>
14. Assigning ports in VLAN:
Switch(Config)#interface<interface type><interface n0.>
Switch(Config-if)#switchport mode access
Switch(Config-if)#switchport access Vlan <no>
Dynamic VLAN:
Generally we don’t use Dynamic VLAN.
Dynamic VLAN’s are based on the MAC address of a PC.
Switch automatically assign the port of multiple VLAN
Each port can be member of multiple VLAN’s
For Dynamic VLAN configuration .a software called VMPS(VLAN
Membership policy server)is needed.
15. Native VLAN
By definition, 802.1Q Simply does not add an 802.1Q header to frames in the
native VLAN.
If my switch receives a frame without vlan tags it then it decides to choose it
as a part of Native VLAN.
Native VLAN can change from one switch to another switch.
16. We can change Native vlan from vlan 1
to other.
Switch(configuration)
Switch>en
Switch#config t
Switch(config)#vlan 666
Switch(config-vlan)#end
Switch(config)#into f0/1
Switch(config-if)#switchport trunk native vlan 666
Remember: For CISCO switches the Native VLAN ID must match on both end
of trunk.
17. To see Native VLAN:
Switch#sh in trunk
Switch#sh in f0/1 switchport
18. VLAN Trunking Protocol
It’s a protocol developed by Cisto to send the vlan information
from ne switch to others, instead of configuring every switch.
VTP Modes:
1.Server:
The server switches can configure VLANs in
the standard range only(1-1005)
2.Client:
The client switches cannot configure VLANs,
however, they receive it from server.
3.Transparent:
If they receive a VTP message it will
update itself with vlan it just passes it to next switch.
19. DTP – Dynamic Trunking Protocol
We can use DTP to dynamically make our port as Trunk port if neighbor is
trunk port.
20. Troubleshooting VLANs and VLAN TRUNKS
This final session will discuss about the issues related to VLAN.
1. Make sure the access vlan is up or active, normally a vlan goes to shut
state when you use shutdown command.
IOU2(config)#vlan 10
IOU2(config-vlan)#shutdown
