Inter-VLAN Routing and Wireless LAN Fundamentals

Inter-VLAN Routing

Inter-VLAN routing is the process of forwarding network traffic from one VLAN to another via a router. As shown in the figure, traffic from PC1 in VLAN10 is routed through the router to reach PC3 in VLAN30.

Traditional Routing

Traditionally, routing the LAN using routers involves multiple interfaces. You must connect each interface to a separate network and configure it to a different subnet.

Router-on-a-Stick Configuration

"Router-on-a-stick" is a configuration where a single physical interface routes traffic between multiple VLANs on a network.

Subinterfaces

Subinterfaces are multiple virtual interfaces associated with a single physical interface. These software interfaces are configured on a router independently with an IP address and VLAN assignment to operate on a specific VLAN.

Multilayer Switch Routing

To enable a multilayer switch to perform routing functions, you must configure the VLAN on the switch interfaces with corresponding IP addresses that match the subnet associated with the VLAN.

The Routing Process

The routing process requires the source device to determine if the destination device is local or remote. The source device performs this by comparing the source and destination addresses with the subnet mask of the interface.

Interface Setup

In global configuration mode, switch to the interface configuration mode for the specific port you want to configure. After assigning IP addresses to each physical interface, the router can perform routing.

Verification Commands

The commands show running-config and show interface [interface-id] switchport are useful for identifying VLAN assignments and port configuration problems, such as an incorrectly configured IP address. The show ip interface command is also highly useful.

Wireless LAN (WLAN) Standards

802.11 Wireless LANs extend the 802.3 Ethernet infrastructure to provide additional connectivity options. The 802.11 WLAN is an IEEE standard that defines how to use radio frequency (RF) in unlicensed Industrial, Scientific, and Medical (ISM) bands for the physical and MAC sub-layers.

WLAN Organizations

The three key organizations that influence WLAN standards worldwide are:

• ITU-R
• IEEE
• Wi-Fi Alliance

Access Point Functionality

In essence, an access point converts TCP/IP data packets from their encapsulation in the air (802.11 frame format) to the 802.3 Ethernet wired network format. The router provides a gateway to connect to other network infrastructures.