Network Basics

Network devices

Router: Device that routes packets between networks (layer 3)

Switch: Device that moves packets based on L2 switching (Layer 2)

Ethernet (RJ-45 is generally the interfaces between devices) however SFP interfaces are becoming a mandatory depending on use case and location within network such as in the core.

Many devices can have both layer 2 and 3 these devices are generally called multilayer switches.

Networking devices will have physical interfaces that will allow configuration, but most users will end up interacting with their equipment either over ssh or some API based way.

Binary

Binary is a number system using 2 as a base. This is in contrast of our number system that uses 10 as a base.

Base 10 being 0-9 then you add another digit and start over.

Base 2 being 0-1 then adding a digit and starting over.

Example:

9 goes to 10 and 19 goes to 20

1 goes to 10 (2) and 11(3) goes to 100 (4) with 101 being 5.

Some examples of binary numbers are:

00000001 (1)

00000010 (2)

00000011 (3)

00000101 (5)

00101000 (40)

10001100 (140)

11111111 (255)

IP Address

Octets of bits. Either 0 or 1 that add up in decimal to 255 in each octet.

Examples:

11111111.11111111.11111111.11111111: 255.255.255.255

11111111.11111111.11111111.11111110: 255.255.255.254

11111111.11111111.11111111.10101110: 255.255.255.174

11111111.11111111.11111110.10101100: 255.255.254.172

11000000.10101000.00000001.00001000: 192.168.1.8

Subnet Address

The ip address alone does not do anything. The subnet address used in conjunction with the ip address is what we use. The subnet address is what tells you where the network and host portions are located.

A /24 or 255.255.255.0 (24 bits as 1s from the left)

Subnetting

Supernetting

Reading

00000000.00000000

00000011.11111111

>

vs

00000000

<

Frames/Packets

Broadcast Domains

Unicast

Multicast

MAC addresses table

ARP

Address resolution protocol

Device sends a broadcast message with its IP and MAC with the designation IP of the device it is looking for. Destination devices will receive this message as a broadcast, the devices with the incorrect IP will drop it and the intended recipient with the correct IP will send it's MAC address in a message as a response.

CISCO PRESS

IOS versioning

CLI

Navigating the CLI 

Basic Commands/Setup

Int range

NX-OS vs IOS

NX-OS has slightly different command and syntax structure.

On boot Nexus devices will come to a login page.

The command differences I will have for differences I am aware of on each of the pages. 

For example, when configuring OSPF you don't add the network command under the global config. You navigate to the interface you want to configure with OSPF and you add it to the OSPF process ID and area. This will be on the OSPF page under NX-OS (Nexus) Configuration.

SSH setup

SSH requires a domain name and a hostname to be configured on the switch as well as an RSA key to be generated.

Commands for this process would show as follows:

(conf) #ip domain name "domain-name"

(conf) #hostname "hostname"

(conf) #crypto key generate rsa "key length"

Domain name can have .com or .net

key length can vary, and it will give you options you have based on your IOS image.

Device will give notification that ssh version 1.99 (2) has been enabled. SSH version can be chosen explicitly with the following:

(conf) #ip ssh version "2"

Virtual lines/terminal interfaces for accessing and managing are called VTY lines. These need to be configured next.

(conf-line) #line vty "0-15"

Here we will configure ssh as the only usable access to these VT lines. This is also where you would configure login for local users or an outside source such as a aaa server. Here we will use local.

(conf-line) #transport input ssh

(conf-line) #login local

We will now configure a local user that we can now use to login to the device over SSH. You can also configure a specific enable secret for users as well as privilege.

(conf) #username "name" secret "5" "password"

(conf) #username "name" privilege "0-15"