Basics Introducing Virtual LANs (VLANs) in CCNA

What is a VLAN?

As I said, a VLAN is a virtual LAN. In technical terms, a VLAN is a broadcast domain created by switches. Normally, it is a router creating that broadcast domain. With VLAN’s, a switch can create the broadcast domain.

This works by, you, the administrator, putting some switch ports in a VLAN other than 1, the default VLAN. All ports in a single VLAN are in a single broadcast domain.

Are VLANs required?

It is important to point out that you don’t have to configure a VLAN until your network gets so large and has so much traffic that you need one. Many times, people are simply using VLAN’s because the network they are working on was already using them.

Another important fact is that, on a Cisco switch, VLAN’s are enabled by default and ALL devices are already in a VLAN. The VLAN that all devices are already in is VLAN 1. So, by default, you can just use all the ports on a switch and all devices will be able to talk to one another.

When do I need a VLAN?

You need to consider using VLAN’s in any of the following situations:

• You have more than 200 devices on your LAN
• You have a lot of broadcast traffic on your LAN
• Groups of users need more security or are being slowed down by too many broadcasts?
• Groups of users need to be on the same broadcast domain because they are running the same applications. An example would be a company that has VoIP phones. The users using the phone could be on a different VLAN, not with the regular users.
• Or, just to make a single switch into multiple virtual switches.

How can devices on different VLAN’s communicate?

Devices on different VLAN’s can communicate with a router or a Layer 3 switch. As each VLAN is its own subnet, a router or Layer 3 switch must be used to route between the subnets.

What is a trunk port?

When there is a link between two switches or a router and a switch that carries the traffic of more than one VLAN, that port is a trunk port.

A trunk port must run a special trunking protocol. The protocol used would be Cisco’s proprietary Inter-switch link (ISL) or the IEEE standard 802.1q.

Setting Up Passwords on Cisco Router

Setting password to protect Console Port
To configure the console password, follow these steps.
Router#config □ t
Router(config)# line □ console □ 0
Router(config-line)# password □ CISCO
Router(config-line)# login
How to password protect Auxilary (AUX Port) Port
To configure the auxilary password, follow these steps.
Router#config □ t
Router(config)#line □ aux □ 0
Router(config-line)#password □ cisco
Router(config-line)#login
How to password protect VTY Ports (Telnet Ports)

Configuring the VTY password is very similar to doing the Console and Aux ones. The only difference is that there are 5 VTY virtual ports, which are named 0, 1, 2, 3, and 4. You can use the shortcut 0 4 (a zero, a space, and 4) to set all 5 passwords at the same time. To configure the VTY password, follow these steps.

Router#config □ t
Router(config)#line □ vty □ 0 □ 4
Router(config-line)#password □ cisco
Router(config-line)#login
How to password protect Privileged Mode
The Enable Password is the old form of the password for “Privileged Mode”. Here the password is stored un-encrypted.
Router#config □ t
Router(config)#enable □ password □ cisco
Enable Secret provides better security since password is kept encrypted.
Router#config □ t
Router(config)#enable □ secret □ cisco

Idea of “The IEEE standardized protocol”-Part-4

EIGRP: Enhanced Interior Gateway Routing Protocol. An advanced version of IGRP developed by Cisco. Provides superior convergence properties and operating efficiency and combines the advantage of link-state protocols with those of distance vector protocols.

encoding: The conventions for how a device varies the electrical or optical signals sent over a cable to imply a particular binary code. For instance, a modem might encode a binary 1 or 0 by using one frequency to mean 1 and another to mean 0.

EtherChannel: Developed and copyrighted by Cisco Systems. A logical aggregation of multiple Ethernet interfaces used to form a single higher-bandwidth routing or bridging endpoint.

feasible successor: To converge quickly, EIGRP keeps track of possible alternative next-hop routers for each route’s feasible successor is a neighboring that can be used as a replacement next-hop router for a particular route when it fails.

FECN: Forward Explicit Congestion Notification. The bit in the Frame Relay header that signals to anything receiving the frame (switches and DTEs) that congestion is occurring in the same direction as the frame.

filter:  generally, a process or a device thet screens network traffic for certain characteristics,such as source address ,destination address,or protocol,and determines whether to forward or discard that traffic based on the established criteria.

forward:  To send a frame toward its ultimate destination by way of an internetworking device.

Forward Delay timer:   A timer that sets the amount of time an interface spends in the STP listening and learning  states. In other words, an interface stays in each of these two states for the Forward Delay amount of time.

forwarding state:  A Spanning Tree Protocol port state in which the bridge or switch processes frames (input or output) on the interface, with the exception of STP messages.

framing:  The conventions for how the bits sent according to OSI Layer 1 are interpreted by Layer 2.for instance, after an electrical signal has been received and converted to binary, framing identifies the information fields inside the data.

FTP:  File Transfer Protocol. An application protocol, part of the TCP/IP protocol stack,used to transfer files between network nodes FTP is defined in RFC 959.

function group:  An ISDN term that generically refers to set of functions that a piece of hardware or software must perform. Because the ITU wanted several options for the customer,it defined multiple different function groups. See also reference point.

HDLC:  High-Level Data Link Control. A bit-oriented synchronous data link layer protocol developed by the International Organization for Standardization (ISO).Derived from synchronous data link control (SDLC) HDLC specifies a data encapsulation method on synchronous  serial links using frame characters and checksums.