ajout VLAN (part1) brouillon

16. VLAN (Part 1).md

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+---
+id: 16. VLAN (Part 1)
+aliases: []
+tags: []
+---
+
+# VLAN (Part 1)
+
+## What is a [[LAN]]?
+
+Previously i said that a LAN is a group of devices (PCs, servers, routers, switches) in a single
+location (home office, etc.)
+
+A more specific definition: A LAN is a single [[broadcast domain]], including all devices in that
+broadcast domain.
+
+## Broadcast domains
+
+A broadcast domain is the group of devices which will receive a broadcast frame (destination [[MAC]]
+FFFF.FFFF.FFFF) sent by any one of the members.
+
+Perfomance: lots of unnecessary broadcast traffic can reduce network performance
+Security : Even within the same office you want to limit who has access to what. You can apply
+security policies on a [[router]]/[[firewall]]
+
+Because this is one LAN, PCs can reach each other directly, without traffic passing through the router
+So even if you configure security policies, they won't have any effect.
+
+Although we separated the three departments into three subnets ([[OSI|Layer 3]]), they are still in
+the same broadcast domain ([[OSI|Layer 2]])
+
+## What is a [[VLAN]]
+
+A [[switch]] will not forward traffic between VLANs, including broadcast/unknown unicast traffic
+
+- VLANs are configured on switches on a **per-interface** basis.
+- logically separate end hosts at Layer 2.
+
+The switch does not perform inter-Vlan routing. It must send the traffic through the router
+
+### VLAN configuration
+
+to display all the VLAN's available you can do the command 
+
+```Cisco
+SW1#show vlan brief
+```
+
+By default all interfaces are set to VLAN 1
+
+But VLANs1, 10002-1005 exist by default and *cannot be deleted*
+
+to assign interfaces to a VLAN
+
+```Cisco
+SW1(config)#interface range g1/0 - 3
+SW1(config)#switchport mode access
+SW1(config)#switchport access vlan 10
+% Access VLAN does not exist. Creating vlan 10
+```
+
+An access port is a switchport which belongs to asingle VLAN, and usually connects to end hosts
+like PCs
+
+Switchports which carry multiple VLANs are called 'trunk ports'  (More information on trunks in 
+the next lesson)
+
+You can change the name of the VLAN with the command :
+
+```Cisco
+SW1(config)#vlan 10
+SW1(config-vlan)#name ENGINEERING
+```
+
+This Commang creates a VLAN.
+(In this case it was already automatically created when we assigned the interfaces)
+
+## Review
+
+- What is a (LAN)?
+- Broadcast domains
+- What is a Vlan
+- What is the purpose of VLANs?
+- How to configure VLANs on Cisco switches
+