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Chapter Eleven

An Introduction to TCP/IP

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Objectives

  • To compare TCP/IP’s layered structure to OSI
  • To review the structure of an IP address
  • TCP/IP Protocols

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TCP/IP and Layers

  • TCP/IP has four layers
  • Process/Application
  • Host-to-Host
  • Internet
  • Network Access

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Mapping TCP/IP Layers to OSI

For the most part, map cleanly to OSI layers

Process Application
Host to Host
Internet
Network Access
Application
Presentation
Session
Transport
Network
Data Link
Physical

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Reviewing IP Address Structure

  • IPv4 uses a 32-bit address.
  • IPv6 uses a 128-bit address.
  • IPv4 addresses are broken down into classes.
  • One address identifies both the network and host address.
  • A subnet mask separates the network portion from the host portion of the address.

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Structure of an IP address

  • Subnet mask can be used to tell the network address and host address
  • Subnet mask covers the network address with 1s and host address with 0s.

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IP Address Classes

  • Class A
  • 1 octet for network, 3 for host
  • Class B
  • 2 octets for network, 2 for host
  • Class C
  • 3 octets for network, 1 for host
  • Class D – multicasts
  • Class E – experimental

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Default subnet Mask

  • The default subnet mask for class A address is 255.0.0.0

  • The default subnet mask for class B address is 255.255.0.0

  • The default subnet mask for class C address is 255.255.255.0

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Structure of an IP address

  • The number of hosts and the number of networks can be found by a simple formula:

  • where x equals the number of bits available for hosts or networks and y equals the number of hosts or network available

  • Neither a network address nor a host address can be all 1s or all 0s.
  • All 1s is a broadcast address.
  • All 0s is the address of the wire.

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TCP/IP Protocol Suite

  • TCP/IP is one of the largest suites and there are many protocols that make up the entire set
  • FTP/TFTP UDP
  • HTTP/HTTPS DNS
  • Telnet IP
  • SMTP/POP BootP
  • SNMP DHCP
  • IMAP4 ICMP
  • NFS ARP/RARP
  • TCP

FTP/TFTP

  • File Transfer Protocol/Trivial File Transfer Protocol
  • Both function to transfer complete files over the network
  • FTP is a connection-oriented protocol
  • Port 20 for user data and Port 21 for control data
  • TFTP is a connectionless protocol and is primarily targeted at moving smaller files
  • Port 69 for user data, no control data passed

HTTP and HTTPS

  • Hypertext Transfer Protocol and Hypertext Transfer Protocol Secure
  • Used for interpreting and moving hypermedia over a network
  • Any form of communication that allows a dynamic link to another location is hypermedia; all web pages are hypermedia
  • HTTP uses Port 80; HTTPS uses Port 443.
  • HTTPS uses the secure socket layer (SSL) and encryption algorithms in order to increase security.

Telnet

  • Creates a virtual terminal on the network
  • Allows a user to take control of a device remotely
  • Uses Port 23
  • User data does not actually move from device to device. The user is manipulating the selected device remotely. What is moving is keyboard and display information
  • Used by many routers and switches for configuration

SMTP and POP

  • The protocols of email
  • Simple Mail Transfer Protocol for outgoing
  • Post Office Protocol for incoming
  • SMTP uses Port 25
  • POP3 uses Port 110 (older POP2 uses 109)

Architecture and Services

  • Three major components:
  • user agents
  • mail servers
  • simple mail transfer protocol: SMTP
  • User Agent
  • a.k.a. mail reader
  • composing, editing, reading mail messages
  • e.g., Eudora, Outlook, elm, Netscape Messenger
  • outgoing, incoming messages stored on server

mail

server

mail

server

user

agent

user

agent

user

agent

user

agent

user

agent

user

agent

user

agent

user

agent

user

agent

mail

server

mail

server

mail

server

user

agent

user

agent

user

agent

user

agent

user

agent

user

agent

mail

server

mail

server

mail

server

user

agent

user

agent

user

agent

SMTP

SMTP

SMTP

SMTP

The User Agent

  • Mail Servers
  • mailbox contains incoming messages for user
  • message queue of outgoing (to be sent) mail messages
  • SMTP protocol between mail servers to send email messages
  • client: sending mail server
  • server: receiving mail server

mail

server

mail

server

mail

server

mail

server

mail

server

user

user

user

mail

server

mail

server

mail

server

user

agent

user

agent

user

agent

SMTP

SMTP

SMTP

SMTP

user mailbox

outgoing

message queue

Scenario: Alice sends message to Bob

1) Alice uses UA to compose

message and

“

to

”

[email protected]

2) Alice

'

s UA sends message

to her mail server; message

placed in message queue

3) Client side of SMTP opens

TCP connection with Bob

'

s

mail server

4) SMTP client sends Alice

'

s

message over the TCP

connection

5) Bob

'

s mail server places the

message in Bob

'

s mailbox

6) Bob invokes his user agent

to read message

user

agent

user

agent

user

agent

mail

server

mail

server

mail

server

server

server

server

user

agent

user

agent

user

agent

1

2

3

4

5

6

IMAP4

  • Internet Message Access Protocol, Version 4
  • A more advanced protocol for sending email messages
  • Allows users to create and maintain folders on the remote server
  • Uses Port 220

SNMP

  • Simple Network Management Protocol
  • Allows network administrators to gather information about the network and to perform routine maintenance functions remotely
  • To use SNMP, the user needs manager and agent.
  • SNMP manager runs on the administrator machine and provide an interface for administrator
  • the agent can be a device, a piece of software, or simply a statistic that the administrator is gathering.
  • Both manager and agent must have SNMP protocol installed.
  • Uses Port 161 for general messages and 162 for trap messages

SNMP

  • The way that SNMP works I that:
  • An administrator identifies the target information to be collected along with the agents that should do the collecting
  • Manager send queries to various agents, then subsequently monitor and store their responses into a management information base (MIB).
  • When a network administrator wants a report, he/she just needs to use the management software to open the MIB

Host-to-Host Protocols

  • TCP
  • TCP is connection-oriented. TCP has the following responsibilities:
  • Logical connection maintenance
  • Data transfer
  • Flow control
  • Reliability
  • Multiplexing
  • UDP is connectionless transport layer protocol

Domain Name Service (DNS)

People:

many identifiers:

v

SSN, name, passport #

Internet hosts, routers:

v

IP address (32 bit)

-

used for addressing

datagrams

v

“

name

”

, e.g.,

ww.yahoo.com

-

used by

humans

Q:

map between IP

addresses and name ?

Domain Name System:

1

distributed database

implemented in hierarchy of

many

name servers

2

application

-

layer protocol

1) Application program calls resolver

2) resolver sends UDP to local DNS server

3) Local DNS server looks up the name and returns the IP address to the resolver

4) the resolver return the IP address to caller

Internet Names

  • The Internet is divided into over 200 top-level domains
  • Domain names are assigned by the Internet Corporation for Assigned Names and Numbers (ICANN) www.icann.org
  • Hierarchical starting from the right
  • host.subnet.organization.type
  • Names can be in either upper or lower case.

Top Level Domain Names

  • .com Commercial business
  • .edu Educational
  • .gov Government
  • .mil Military
  • .net Gateway or host (business)
  • .org Other (typically non-profit)
  • .info Informational web sites
  • .biz Business related
  • .pro Professions
  • Outside the US
  • Top level domain is country name
  • .au : Australia
  • .za : South Africa, etc

DNS

  • Every domain has a resource record associated to it.
  • When a resolver gives a domain name to DNS, what it gets back is the resource records associated with it.
  • Primary function of DNS is to map domain names onto resource record.

Root DNS Servers

com DNS servers

org DNS servers

edu DNS servers

poly.edu

DNS servers

indstate.edu

DNS servers

yahoo.com

DNS servers

amazon.com

DNS servers

pbs.org

DNS servers

Root DNS Servers

com DNS servers

org DNS servers

edu DNS servers

poly.edu

DNS servers

yahoo.com

DNS servers

amazon.com

DNS servers

pbs.org

DNS servers

Distributed, Hierarchical Name Server

  • Client wants IP for www.amazon.com
  • Client checks its own computer first to see if the resource resides locally.
  • Client queries a DNS server. This query can be one of two types

Root DNS Servers

com DNS servers

org DNS servers

edu DNS servers

poly.edu

DNS servers

indstate.edu

DNS servers

yahoo.com

DNS servers

amazon.com

DNS servers

pbs.org

DNS servers

Root DNS Servers

com DNS servers

org DNS servers

edu DNS servers

poly.edu

DNS servers

yahoo.com

DNS servers

amazon.com

DNS servers

pbs.org

DNS servers

Distributed, Hierarchical Name Server

  • Two types of queries:

  • A recursive query tell the DNS server to check its own resources first and return the information to the client. If a server support recursive query, the server can forward the request to other DNS servers or to the root server.

  • An iterative or nonrecursive query tells the DNS server to return whatever information it has alone with its list of other servers that the client might be able to query.

Internet Layer Protocols

  • There are a number of different protocols that operate in this layer
  • IP
  • BootP
  • DHCP
  • ICMP

IP (Internet Protocol)

  • IP is a protocol that allows the process of routing
  • There are six basic services that IP provides
  • Addressing
  • Routing
  • Fragmentation
  • Options
  • Packet timeouts
  • Type of service

BootP

  • In early networks, it was common to see networks based on thin client that does not have disk drives and local OS.
  • When a machine begins its boot process, the NIC issues a boot message packet to broadcast address 255.255.255.255 on port 67 with its own address 0.0.0.0.
  • If there is a BootP server on local network, the server will reply with a bootreply packet on port 68 that contain information bounded to NIC.
  • If there is no BootP server, it is the essential that the router will forward the request to the appropriate entity.
  • If there is no reply, the client will not be able to boot.

DHCP

  • DHCP is an extension of BootP and allows for dynamic configuration of network address.
  • The enhancement of DHCP is DHCP lease. The lease can be for as long or as short as the administrator wishes them to be.
  • Once the lease has been configured, the client machine can keep the IP address for that amount of time.
  • When the lease reaches 50% of its maturity, the client will begin sending message to DHCP server to renew the lease or reassign a new address
  • At approximately 75% of maturity, the client begins broadcasting to all hosts, looking for any DHCP server to give it a new IP address.

ICMP

  • ICMP is a protocol that was first announced in RFC792 and is one of TCP/IP’s best troubleshooting aid.
  • ICMP delivers out-of-band message that are related to network performance and malfunction. These messages can report the following conditions:
  • Announce network errors
  • Announce network congestion
  • Assist troubleshooting (such as ping using ICMP protocol)
  • Announce timeouts