Network Administration

In 2014, I sat for my CCNA (Cisco Certified Network Admin) exam. It isn't an area I was really interested in, but I needed that certification first in order to get my CCNA-Voice certification, which I was interested in.

While my study notes from the ETEC bootcamp do not apply directly to development, they do provide some pretty good basics for IT infrastructure and how things in general work. Therefore, I am including them in this collection of knowledge.

(All information in this section is from the CCNA Bootcamp provided by ETEC, LLC in Houston, Texas unless otherwise noted.)

Networking Concepts

OSI Model

The most referenced network protocols is the OSI (Open Systems Interconnection) model which describes how data moves throughout the network and is broken down into seven (7) layers:

  • Application Layer 7 (Data)
  • Presentation Layer 6 (Data)
  • Session Layer 5 (Data)
  • Transport Layer 4 (Segments)
  • Network Layer 3 (Packets)
  • Data Link Layer 2 (Frames)
  • Physical Layer 1 (Bits)

Encapsulation - Each layer of the OSI model adds its protocol information

  • Layer 5, 6, 7 - Data
  • Layer 4 produces the Segment (Data plus the source port and the destination port)
  • Layer 3 produces the Packet (Segment plus the source IP and destination IP)
  • Layer 2 produces the Frame (Packet plus the destination MAC and source MAC)
  • Layer 1 converts to Binary and sends it to the destination

Decapsulation - Each layer examines the pieces to see if they belong to it.

  • Layer 1 converts from binary and sends to Layer 2
  • Layer 2 receives the Frame; will strip off the destination and source MAC addresses and send the Packet on
  • Layer 3 receives the Packet; will strip off the source and destination IPs and send the Segment on
  • Layer 4 receives the Segment; will strip off the source and destination ports and send the Data on

Cabling

There are different types of cabling that can be used in a network.

  • Fiber Optic

    • Single strand = long distance
    • Multi-strand = short distance
    • Considerations:
      • Uses light and very fast
      • Not prone to electrical interference
      • Rigid and fragile... not very bendable
      • Cost is high

  • Co-axial

    • Thin = short distance
    • Thick = long distance
    • Considerations:
      • Uses electrical pulses to send signals and subject to electro-magnetic interference.

  • UPT/STP

    • RJ11 = 2 pairs
      • Modems used to convert analog to digital signals (binary)
    • RJ45 = 4 pair signal
    • Considerations:
      • Uses electrical pulses to send signals and subject to electro-magnetic interference.
      • Limited to 100 meters (signal is not readable beyond that)

Network Equipment

Repeater = line or signal reconditioner; does not amplify the signal

  • Half-duplex device (one pair that is shared for all functions)
    • Can only send or receive at one time
    • When one host talks, all others must listen
    • Creates a large collision domain
    • Everyone, including sender, will receive data.

Hub = multi-port repeater (3 or more ports)

  • Also half-duplex device
  • Uses CSMA-CD (Carrier Sensing Multi-Access Collision Detection)
    • Samples the line (see if anyone is using the line) and if true, holds off on using until the line is free
    • Jams the line (to hold the line for use)
    • Transmits the data
    • 99.9% effective so you still see lots of collisions
  • No security; every device connected is in one collision domain and receives all data

Bridge = hub with software; helps cut down on the traffic because it doesn't flood out to everyone

  • Full duplexed device that can break up collision domains
    • Can send and receive at the same time
    • Everyone, except sender, receives data
  • Virtual software that uses some of the CPU to run
  • Operates off of a MAC Table, which contains the MAC address and interface for each device:
    • Record source MAC
    • Lookup destination MAC
    • If not in the MAC table, flood all ports
    • If in the MAC table, send to the right interface

Switch = Hardware that runs on the MAC Table

  • Full duplex device that breaks up collision domains
  • Hardware (not software) that runs on the MAC Table, which is maintained until the power recycles or is manually erased.
  • Can send and receive
  • Every port/interface on the switch is one collision domain

Router = translator between two or more networks

  • IP Address
  • Breaks up broadcast domains
    • A router will never allow a broadcast to go across it; it will be discarded/dropped.

OSI Model Overview (Bringing it all together)

Layer OSI Layer Description TCP/IP DoD Encapsulation / Decapsulation Hardware / Devices Software / Protocols
7 Application Provides network services directly to the user's application and supports end-user processes. Process / Application Data User level applications (Word, Excel, web browsers), Protocols: Telnet, FTP, HTTP, etc.
6 Presentation Presents the data in a uniform format and masks any differences. Process / Application Data Formatting coding schemes: ASCII, EBCDIC, MPEG, GIF, JPEG
5 Session Establishes and manages the session between the two users at different ends of the network. Process / Application Data Protocols: NetBIOS, Mail Slots, Names Pipes, and RPC, POP/25
4 Transport Converts data and responsible for end-to-end delivery of messages. Host-to-Host Segments (data + source port & dest port) Error Checking & Flow Control software; Protocols: TCP (connection-oriented), UDP (connectionless), NETBEUI, SPX
3 Network Responsible for determining path, routing & delivery of packets. Internet Packets (segments + source IP and dest IP) Routers & Layer 3 Switches Protocols: IP (IPv4, IPv6), IPX, AppleTalk, ICMP, RIP, OSPF, BGP, IGRP, EIGRP, NLSP, ARP, RARP, X.25 Ping
2 Data Link Provides transparent network services to the Network layer. Network Access Frames (packets + dest MAC & source MAC) Switches, Bridges, WAPs, NICs Sub Layers: LLC (Logical Link Control) and MAC (Media Access Control), LAN protocols
1 Physical Communicates directly with the physical media. Network Access Bits Cabling, Hubs, Concentrators, Repeaters, NICs, LAN/WAN Interfaces

General Terminology and Information

Layer 2 will "flood"

Layer 3 will "broadcast"

DNS (Domain Naming System) converts a name to an IP address

There are 65,536 ports available.

  • 1-1024 are reserved
    • 80 = HTTP
    • 443 = HTTPS
    • 20/21 = FTP
    • 23 = Telnet
    • 25 = SMTP
    • 110 = POPS
    • 143 = IMAP
  • 1025-65536 are open

The default gateway is the door to get out of the network. It will either be the first or the last usable IP address (usually x.x.x.1).

ARP - converts the IP address to the MAC address.

TCP/IP