L13: Networking Flashcards
Symbolic Addressing:
Domain Name Services
- A technique used to map domain addresses
Flow:
- Look in a local table for a match
- on Unix : /etc/hosts
- If None, as a DNS Server to find one of the domain’s servers
- Ask THAT server to completely resolve the symbolic address
Ethernet:
Hardware Specifications
- Max cable length of 500 meters
- Length can be extended with repeaters
- Bandwidth: About 10 Mbps max transfer rate
- Few fast or several slow slow computers
- Several Cabling Schemes:
- Thick Coaxial
- Thin Coaxial
- Twisted pair 10 Base-T
“Backbone” infrastructure
of the Internet
- Connects Networks, Makes the Internet Global
- Includes many Providers
- Providers cooperate in moving the packets
- Packets may go a round-about way, depending on traffic
- Features:
- High Speed Lines
- routers
- digital formats
Protocols defined
above IP (8)
- TCP
- FTP
- TELNET
- SMTP
- SNMP
- DHCP
- NTP
- UDP
Protocols:
TCP
Transmission Control Protocol
- This is a reliable transport protocol service
- Provides Robust Delivery
- Most applications and many other protocols use TCP
Responsibilities:
- Decomposition of messages into datagrams
- Assume that all arrive and are in good condition
- Use ack/nak and checksums
- Assemble back into proper order
- Uses sequence numbers
Protocols:
FTP
File Transfer Protocol
- Transfers files using TCP
Protocols:
TELNET
- Remote login protocol
Protocols:
SMTP
Simple Mail Transfer Protocol
Protocols:
SNMP
Simple Network Management Protocol
- Helps find and query hosts
Protocols:
DHCP
Dynamic Host Configuration Protocol
- Assign IP addresses at boot
Protocols:
NTP
Network Time Protocol
Protocols:
UDP
User Datagram Protocol
- almost raw IP packets
Possible Issues
with
IP Delivery Service
- Packets shouldn’t be longer than 1500 characters
Packets may:
- be arbitrarily delayed
- “die” and never arrive
- arrive out of sequence
- get data corrupted
Organizations that
Regulate Internet Protocols
Internet Engineering Task Force (IETF)
administers protocol proposals and analysis
Internet Architecture Board (IAB)
approves protocols and allocates addresses
Networking:
Major Topics (12)
- Ethernet LAN technology
- Bridges
- Types of Networks:
- Centralized
- Decentralized
- Distributed
- Symbolic Addressing
- Network Architecture/Backbone
- MANs
- How data is delivered
- Protocols and Protocol Hierarchy
- TCP
- Unix Network Tools
- Ports
- Client-Server Model
Network Protocol Layers:
Layers of a single host
Upper to Lower:
- Application
- Networking Library
- TCP
- IP
- Internet
- Physical
Network Packet Layers
From Outer Layer to Inner Layer
Ethernet Packet
IP Datagram
TCP Packet
Library Wrapper
Data
Networking:
Ports
Overview
- Servers use ports to announce Services
- There are some Standard Ports
- __These are created at boot
- Stored in /etc/services
- A client connects to a specific port
- On the server, you can open a new port at any time
Symbolic Addressing:
Overview
- Simplifies human use
- Authority assigns a symbolic address domain
Format:
org.type
where org denotes the organization
type denotes the type of organization
Organization extends the address to name hosts within its network.
Ex: vancouver.wsu.edu
Symbolic Addresses are mapped to Domain Adresses by DNS
Ethernet:
Bridges:
- Operation
- Attributes
Bridges connect separate ethernets
Operation:
- Bridge has a list of ethernet addresses on each separate net
- Packets are accepted from one side, forwarded to the other
- Bridge is invisible(transparent) to the ethernet cards
Attributes:
- An Adaptive Bridge learns each side’s addresses and forwards only as needed
- Bridges do not propogate electrical noise(or repeaters), & follow collision rules, so can be used to extend an ethernet almost indefinitely
Unix Shell Networking Tools:
netstat
Display which clients are connected
Unix Shell Tools
for Networks (15)
- whois
- ping
- traceroute
- hostname
- nslookup
- netstat
- ftp
- telnet
- rcp
- rlogin
- rsh
- rusers
- rwho
- rwall
Unix Shell Networking Tools:
rwall
Send a message to
everyone on a host
Unix Shell Networking Tools:
rwho
Display who is
logged in on a host
Unix Shell Networking Tools:
Send or recieve
Electronic Mail
Unix Shell Networking Tools:
nslookup
Map a symbolic name
to a
numeric address
Unix Shell Networking Tools:
ping
Time the packets traveling from
your host
to another
Unix Shell Networking Tools:
traceroute
Display path
to another host
Unix Shell Networking Tools:
telnet
Begin a Remote Login Session
Unix Shell Networking Tools:
rcp
Copy files to another
Unix host
Unix Shell Networking Tools:
whois
Display NIC information
about a host
Unix Shell Networking Tools:
hostname
Display your
host’s name
Unix Shell Networking Tools:
rlogin
Remotely login
to another Unix host
Unix Shell Networking Tools:
rsh
Run a shell command
on another unix host
Unix Shell Networking Tools:
rusers
Display User Accounts
on a host
Unix Shell Networking Tools:
ftp
Begin a File Transfer Session
Standard Services
and their Ports (8)
- echo - 7
- discard - 9
- systat - 11
- daytime - 13
- ftp - 21
- telnet - 23
- smtp - 25
- http - 80
Ethernet :
Addressing
- Addresses are 48 bytes long and fixed at factory
- Physical address, stays with a computer where ever it moves
Ethernet:
Packet Layout Sections
- Preamble
- Destination Address
- Source Address
- Frame Type
- Frame Data
- CRC
Ethernet LAN Technology:
Connecting
- Each computer has an Ethernet Card
- The Card is special hardware with a unique address
- In an ethernet LAN, every computer’s card is connected to the same single piece of wire( a cable)
Ethernet LAN Technology:
Messages
- Sender broadcasts a structured chunk of bytes( a packet)
- Packet has address of sender/receiver and body of the message(payload)
- Only the card with the receiver address accepts the message
- If 2 senders attempt broadcast at same time (a collision), they both wait a random length of time and try again
Problems of
Large Scale Networking
- How to connect large numbers of separate networks?
- Networks may have incompatible physical addresses and data
- May be multiple paths from destination to source
- Machines assigned to various functions may change
- No single entity can know where everything is
- Response times cannot be guaranteed
Solution: Internetworking
agreements(protocols) that networks obey in communicating with each other.
The most successful is TCP/IP
Ethernet:
History
- Packet switched LAN technology
- Invented at Xerox PARC in the 1970s
- Now IEEE standard 802.3
How Data is delivered
- A Host breaks messages up into structured chunks called packets
- Packets have an address, read during delivery
- Packets have data, not read during delivery
- IPv4 packet Format is called “Datagrams”, the basic unit of TCP/IP transfer
- IP delivery service guarantees are very weak
- Each packet is on it’s own, so the service is called connectionless
Basic Network
Connection Diagram
-
Gateway
- Maps addresses
- Prevents access (firewall)
-
Internet Service Provider (ISP)
- Provides local access
-
Point of Presence (PoP)
- “on-ramp” to backbone
-
Backbone
- High speed lines, “Interstate”
- Digital formats
- Routers
Diagram:
Client/Server
Programming Model
Work Flow
