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Virtual LAN by Namrata Vichare (Reasons for a VLAN (Reduce CPU overhead…
Virtual LAN
by Namrata Vichare
Same Broadcast Domain
Reasons for a VLAN
Reduce CPU overhead as there are less devices in each BD
Reduce Security risks (how?)
Flexible designs (e.g. by departments)
Fast problem solving (Why?)
Reduce STP load by limiting a VLAN to a single access switch
Multiswitch VLAN
Without Trunking
n VLANS - n links
With Trunking
1 link- part of all VLANs which keeps the traffic separate
VLAN Trunking Protocols (VTP)
IEEE 802.1Q
Tag frame with ID (Extra 4 byte header)
Type | Priority | Flag | VLAN ID
VLAN ID = 12 bits
0 & 4095 reserved. Total available IDs = 4094
Normal Range 1-1005
1002–1005 can' be deleted & can't be used as access VLANs today
VLAN 1 can't be deleted, but can be used
Extended Range 1006 - 4094
Native VLAN (Default VLAN)
Functions
Capability of passing frames in at least 1 VLAN, providing basic reachability
Support devices that do not support Trunking
ISL(Inter-Switch Link)
Cisco developed
Forwarding Data Between VLANs
L2 switch
No forwarding traffic b/w different VLANs
How to resolve this?
Use a multilayer switch/ router
Router
Forwarding traffic b/w without trunking: n VLANS - n links
Forwarding traffic b/w VLANs with trunking: 1 link for all VLANs
Router-on-a-stick
Problem
Performance
physical link puts upper limit on how many bits can be routed
cheap routers = less powerful, can't keep up with the traffic volumes
Solution: Layer 3 Switches
Multilayer(Layer 3) Switch (L3 & L2)
VLAN Configuration
Type of trunking
IEEE 802.1Q
ISL
if switches support both protocols, ISL is used
negotiate which 1 to use
use Dynamic Trunking Protocol for this
Cisco recommended: disable trunk negotiation on most ports for better security
Administrative modes
Always trunk
trunk
always not trunk
access
negotiate
dynamic desirable
Initiates negotiation messages & responds to negotiation messages to dynamically choose whether to start using trunking
dynamic auto
Passively waits to receive trunk negotiation messages, at which point the switch will respond & negotiate whether to use trunking
If both switches are in this mode, neither switch will initiate the trunk negotiation process, & this will result in no trunking
will help DTP to decide whether to trunk or not
Operational Mode
What is currently happening on the interface
Status: Access
Not trunking
Status: Trunk
Trunking
Commands
Global Config mode
vlan
vlan_id
Creates VLAN and puts CLI into VLAN config mode
VLAN config mode
name
vlan_name
names the VLAN
shutdown
disables the VLAN
no shutdown
enables the VLAN
shutdown vlan
vlan-id
disables that VLAN
vtp
mode {server | client | transparent
| off}
defines
vtp
mode
Interface config mode
switchport
mode {access | dynamic
{auto | desirable} | trunk}
configures the trunking
administrative mode on the interface
switchport access vlan
vlan-id
statically configures
interface into that 1 VLAN
switchport trunk encapsulation
{dot1q |
isl | negotiate}
defines which type of trunking to use assuming it is configured or negotiated
switchport trunk native vlan
vlan-id
defines native VLAN for a trunk port
switchport nonegotiate
disables the negotiation
of VLAN trunking
switchport voice vlan
vlan-id
defines Voice VLAN on a port
switch uses 802.1Q tagging for frames in this VLAN
switchport trunk allowed vlan {add | all
| except | remove}
vlan-list
defines the list of
allowed VLANs
Exec Commands
show interfaces
interface-id
switchport
Lists information about any interface regarding
administrative settings & operational state
show interfaces
interface-id
trunk
Lists information about all operational trunks
show vlan [brief | id
vlan-id
| name
vlan-name
| summary]
Lists information about the VLAN
show vlan
[
vlan
]
Displays VLAN information
show vtp status
Lists VTP configuration & status information
Cisco Proprietary VLAN Trunking Protocol
Configuring standard & Extended Range VLANs
VTP Transparent mode
Disabled
Server switches
can configure VLANs in the std range(1-1005)
Learn new VLANs from other switches & seeing their VLANs deleted by other switches
Client Switches
Can't configure VLANs
show running-config
does not list any
vlan
commands
For ICND1 Labs
switch to VTP transparent mode
ignore VTP configuration
Implementing Interfaces connected to phones
Data & Voice VLAN concepts
IP Telephony
Branch of Networking in which telephones use IP packets to send/receive voice
Phones started using Ethernet/Wi-Fi
Cisco Product:Cisco Unified Communication
Manager
Problems during migration
non-IP had UTP cabling not supporting 100/1000 Mbps
had 1 UTP cable from wiring closet to desk, but now 2 devices(PC and Phone) needed a cable
more switch ports & installing a new cable = expensive
Solution
PC- patch cable- Phone (having embedded switch) - Ethernet UTP cable- Wiring closet (having Ethernet Switch)
Before IP telephony
Phone used UTP cabling to connect to some voice device(voice switch or Private Branch Exchange[PBX])
Data VLAN
Same idea & configuration as the access VLAN on an access port
defined as the VLAN on that link for forwarding traffic for the device connected to the phone on the desk (typically the user’s PC)
Voice VLAN
The VLAN defined on the link for forwarding the phone’s traffic.
command options