Lesson 9: Networking¶

Who is this talk for?¶

Someone with little or no networking knowledge.

ECE/CS 372 at OSU covers this content, more or less

What is a network?¶

“a group or system of interconnected people or things“

To us, a network is:

• Electronic devices
• Sending signals over wire, fiber, or radio
• Communicating data using a standardized protocol

What is a protocol?¶

“A set of agreed upon rules for communication“

• Defines sequence & format of packets being sent

The OSI Model¶

Open Systems Interconnection

• Layers of abstraction

Layer 1: Physical¶

Networking Hardware

• Connector shapes
• Wire, optical fiber, or radio signal specifications

RS-232

Layer 2: Data Link¶

MAC: Media Access Control

• MAC address should be globally unique
• ARP: Address Resolution Protocol (between layer 2 & 3)
• NDP (neighbor discovery protocol) used in IPv6
• Flow control & error checking

Layer 3: Network¶

Packet forwarding and routing

Network and host addressing

• IPv4
• IPv6

Layer 4: Transport¶

Interact directly with program same-order delivery, reliability, flow control, and congestion avoidance

• used by HTTP, HTTPS, SMTP, POP3, IMAP, SSH, FTP, Telnet

• No error checking built in
• No retransmission delays
• VoIP, media, games

Get your hands dirty¶

In a linux terminal run::

ip a

These will display information about your network interfaces.

See also:

ifconfig
iwconfig

Example output:¶

user@host:~$ ip a
...
2: eth2: <NO-CARRIER,BROADCAST,MULTICAST,UP> mtu 1500 qdisc pfifo_fast state DOWN qlen 1000
    link/ether 33:77:00:44:66:33 brd ff:ff:ff:ff:ff:ff
3: wlan1: <BROADCAST,MULTICAST,UP,LOWER_UP> mtu 1500 qdisc mq state UP qlen 1000
    link/ether 24:77:33:44:55:66 brd ff:ff:ff:ff:ff:ff
    inet 192.168.1.55/24 brd 192.168.1.255 scope global wlan1
    inet6 fe80::2677:3ff:fed4:538c/64 scope link
       valid_lft forever preferred_lft forever

Netmask:¶

Available Hosts: 192.168.1.[1-254]

Broadcast address: 192.168.1.255

Netmask Example:¶

Netmask Example:¶

Netmask Example:¶

Available Hosts: 192.168.[64-127].[1-254]

Broadcast Address: 192.168.127.255

Routes¶

user@host:~$ route
Kernal IP routing table
Destination     Gateway         Genmask         Flags Metric Ref    Use Iface
default         foo.osuosl      0.0.0.0         UG    0      0        0 wlan1
link-local      *               255.255.0.0     U     1000   0        0 wlan1
192.168.1.0     *               255.255.255.0   U     2      0        0 wlan1

user@host:~$ route -n
Kernel IP routing table
Destination     Gateway         Genmask         Flags Metric Ref    Use Iface
0.0.0.0         192.168.1.1     0.0.0.0         UG    0      0        0 wlan1
169.254.0.0     0.0.0.0         255.255.0.0     U     1000   0        0 wlan1
192.168.1.0     0.0.0.0         255.255.255.0   U     2      0        0 wlan1

Bootstrapping¶

What happens when your computer connects to a network?

1. Duplex and speed negotiation
2. Static or dynamic configuration is applied

Static Configuration¶

Must in advance know:

• IP Address
• Netmask
• Default Gateway
• DNS Servers (optional in some cases)

Dynamic Configuration¶

All of the statically defined parameters are retrieved over the network via DHCP

But how do you communicate over the network without a network configuration?

Reserved IPv4 Addresses¶

• 127.0.0.1

• 192.168.0.0
• 172.16.0.0
• 10.0.0.0
• 169.254.0.0

Public vs Private Address¶

• lose end-to-end traceability
• hides internal network topology
• allows use of private IP’s over public internet
• conserves limited public IP’s

Network Devices¶

Network Devices¶

Control Layer¶

Connection oriented vs Connectionless

Collisions¶

CSMA CA

All Wireless networks use this Carrier Sense Multiple Access with Collisions Avoidance

CSMA CD

Carrier Sense Multiple Access with Collisions Detection

Why is this important?

http://articles.latimes.com/2007/aug/15/local/me-lax15