CISCO ICND 100-101 V2 Notes

Here’s my notes based on the requirements of the exam. You can find the requirements here: http://www.cisco.com/web/learning/exams/docs/100-101_icnd1.pdf

1.0 Purpose & Functions of Various Network Devices such as Routers, switches, Bridges and Hubs

1.1 – Recognize the purpose and functions of various network devices such as routers, switches, bridges and hubs:

HUB

A hub is the the oldest of the ethernet technologies. It operates at layer 1 of the OSI model. Hubs operate at layer one they have no idea about layer 2 mac addresses. Because they have no idea about Layer 2 devices all ports are part of the same collision and Broadcast domain. A down side of not knowing anything about layer addresses means that hubs don’t have any provisions to stop loops or choose a new path should a router go down. Hubs operate at 1/2 duplex and at a maximum of 100MB/sec. They have been primarily been replaced with Switches.

Bridges / Repeater

Bridges are layer two devices that can make layer two decisions. They don’t cared about higher layer information. Bridges break up collision domains but do not break up Broadcast domains. Bridges have been mostly been replaced by switches.

Switches

Switches are mostly full duplex and can range between 10/10/1000 and even 10000/Mbs! They use ASIC processors which allow them to check packets in almost real time and make forwarding decisions based on Layer 2 addresses. Switches similar to bridges break up collision domains. They are much smarter devices than hubs because they have loop prevention and dynamic path redirection through (STP/RSTP). Switches also now feature things like VLANs, and QOS just to name a few!

Router

Routers allow you move traffic between network (Physical and Logical). Routers break up collision domains and broadcast domains. They operate at layer 3 and can make decisions on protocols that operate at layer 3 addressing. Routers can dynamically create routing tables and prevent routing loops using protocols like OPSF, EIGRP, and RIP. Typically Routers are very processor intensive because unlike Switches that use ASICS specifically programmed for switching, Router have more generic processors/software that does the routing.

Layer 3 Switch

Layer 3 switches have all the benefits of a switch and router combined into one device. The switch can perform layer 3 routing at near wire speeds thanks to it’s ability to use ASICS instead of the general processor and software that routers use. Routing (layer 3 options) are not enabled by default on layer 3 switches.

1.2 Select the components required to meet a given network specification

There will be several types of questions Cisco could ask on this.

Price and Performance

Hubs and switches at first look look similar and do similar roles. It’s good to know what each device does and the price points of each device.

Device functions

Knowing the functions of the device is very important for being able to select component for a given network. For example knowing that a layer 3 switch would improve routing speed and rack density (by removing routers).

1.3 Identify common applications and their impact on the network

There are several applications you will need to know. You will need to know about what they do, what their port number is and if they are TCP, UDP or use both! It’s also a good idea to know if it uses broadcasts or multicast traffic. What layer does it operate at? Knowing what the acronyms mean can help you remember what they do!

Here is a good reference for port #s

DHCP (Dynamic Host Configuration Protocol)

This protocol helps you to dynamically configure hosts network addresses. You can configure things like IP address, Subnet Mask, Default gateway and the ip address of DNS servers.

DHPC uses 4 phases typically called “DORA”

• Discover (client sends out broadcast to discover DHCP server)
• Offer (Server sends unicast offer)
• Request (If the client okays the offer, it will send a broadcast request to the DHCP server)
• Acknowledgement (The server will send an ACK back to the client if the address is still available)

Ports Used

• Server – UDP 67
• Client – UDP 68

Because DHCP uses broadcasts if you need to get an IP address from a DHCP in another network you will need to configure DHCP relay on the gateway to forward the broadcast (as unicast) on to the DHCP server.

HTTP (Web Server)

Web servers typically operate at TCP port 80 and If logins are needed HTTPS runs on TCP port 443. There are several types of Web Servers, Apache and IIS are the two most popular. HTTP servers typically use Unicast type communication.

DNS (Dynamic Name server)

DNS is a server service that uses a database to store names and their related IP addresses. DNS is very important because humans find it much easier to use names over IP addresses. DNS is crucial in most enterprises because things like Active Directory need DNS to function. DNS operates primarily using UDP Port 53 however things like zone transfers use TCP.

There are several types of records in DNS:

• MX (Mail Exchange record of the email server)
• A (Host name that has a corresponding IP address)

FTP

FTP runs on TCP ports 20 (data transfer) and 21 (FTP Control). This protocol transports credentials and files un-encrypted from source to destination. Because of the lack of security FTP tends to be fast than other file transfer protocols.

TFP

TFPT is used by hardware devices to upload configs etc. It uses UDP to make transfers quick because of the lack of TCP overhead. TFTP operates at my favourite port “UDP 69”. Much like FTP this protocol is un-encrypted. Unlike FTP it can’t authenticate.

SSH (Secure Shell)

This can be used for many things. Secure logins, File transfers and port forwarding! Typically on the CCNA route it’s a way to gain secure access to the terminal from a remote computer. SSH runs on TCP and UDP port 22.

SMTP (Simple Mail Transport Protocol)

SMTP is used to send email. SMTP uses TCP Ports (25, 26, 587, 2525) and UDP port (26).

POP (Post Office Protocol)

Pop operates over many different ports:

TCP:

• 109 (Pop2)
• 110 (Pop3)
• 995 (TLS/SSL)

POP is allows for clients to connect to the mail server to download emails.

1.4  Describe the purpose and basic operation of the protocols in the in the OSI and TCP/IP models

I’ve written a complete guide to the OSI and TCP models in great detail

1.5 Predict the data flow between two hosts across a network

Cisco is wanting you to know how the different network object types effect layers 1,2 and 3. It would be greatly beneficially to use a program like packet tracer  and follow packets around to see what is happening.

It’s important to know things like flow:

• How does the packets flow physically (Broadcast or not)
• Does the device do anything to the MAC address in the header when forwarding the packet?
• Does the device do anything to the IP address in the header when forwarding the packet?

Some things you might see:

• Hub – Broadcasts out ALL ports even the port it came in on
• Switch – If the switch doesn’t know the mac address it will flood the frame out all ports except the port the request came in on.