bitmindframes

Bitmindframes cisco study guides

INTERVLAN ROUTING
A VLAN is a broadcast domain and unique ip subnet
Switches operate at layer2 (Data link Layer)
VLANS cannot communicate without L3 (Network Layer)
The L3 communication is called inter-vlan routing
Inter-vlan routing is a process of forwarding network traffic from one vlan to another using a router
The Subnets of your network facilitate the routing process.
Router interfaces can be connected to separate vlans.
Devices on vlans send traffic through the router(L3) to other vlans.

Traditionally vlan routing required multiple interfaces.
Each interface was connected to a separate switch port & configured with a different subnet
The switch port is connected to the router in access mode.

Subinterfaces
Virtual interfaces & trunk links overcome the physical limitations of a router.

Subinterface configuration
Configuring subinterfaces is similar to interfaces, except you must create the subinterface & assign it to a vlan.
Create it by adding a decimal # to the interface: fa0/1.10
Any decimal number may be used but it is best practice to make the subinterface match the vlan.
Before assigning an IP address to a subinterface, the encapsulation method & vlan ID must be assigned.

-subif)#encapsulation dot1q vlan#
Subinterfaces do not need no shutdown, when the physical interface is enabled all sub interfaces are enabled.

Router table output
The routing table associates routes with subinterfaces, rather than physical interfaces.
A major advantage of trunk links is that they reduce the number of router & switch ports
This saves money and configuration complexity.
Consequently with sub interfaces we increase scalability.

Here is a topology showing vlan 10 and vlan 20 (layer 2) communicating through a router (layer 3)
switch(config)#interface FastEthernet 0/0
switch(config-if)#switchport trunk encapsulation dot1q
switch(config-if)#switchport mode trunk

Tags: study, 802.1q, vtp, router, cisco, guides