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Chapter 11
Introduction to TCP/IP
TCP/IP
• DARPA is an extension of the Department of
Defense assigned to fund basic research.
• ARPA was its original name, then it was
renamed DARPA (for Defense) in 1972, then
back to ARPA in 1993, and then back to DARPA
again on March 11 1996.
• ARPA was responsible for funding development
of ARPANET (which grew into the Internet), as
well as the Berkeley version of Unix (BSD) and
TCP/IP.
RFC
• Request for Comments – beginning
development of protocols
• Handled by the IETF
• RFC 791 Internet Protocol released in
1981
TCP/IP Protocol Stack
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4 layers
Process/Application
Host to Host
Internet
Network Access
app/pres/sess
transport
network
datalink/physical
IP
• IP V4 uses a 32 bit address in 4byte
divisions
• Each byte has 256 possibilities
• 0 and 255 reserved for network broadcast
• 127 is a loop back
• 1-254 are used to denote networks or
hosts
IP Addressing
• Logical Address assigned to each host
• IP locates the network of a device
• Once the network is located the network
will find the device by the host portion of
the address
Subnet Mask
• Used to denote which part of the address
Is the network and which is the node
• 1 masks the network
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IP Addressing (Ver. 4)
•First octet denotes class A, B, C, D, E
•Class A,B,C are network classes
•Class D is multicast addresses
•Class E is experimental
– Class A 1-126 16,387,064 hosts
•(254*254*254 hosts)
– Class B 128-191 64,512 hosts
•(254*254 hosts)
– Class C 192-223
•254 hosts per network
Class A
• 1st octet is supplied by INTERNIC
• Must begin with 0
• 1 network 1-126
– Mask 255.0.0.0
– 16 million nodes
– 254x254x254
Class B
• 2 octets assigned by INTERNIC
• Must begin with 10
• 1 network 128-191
– Mask 255.255.0.0
– 16,384 networks
– @65000 nodes
– 254x254
Class C
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•
•
•
•
•
3 octets to define network
Must begin with 110
Network 192-223
Mask 255.255.255.0
254 nodes
2,097,152 networks
Class D
•
•
•
•
Starts with 1110
Range from 224.0.0.1 to 239.255.255.255
Does not use subnet mask
Dynamically allocated by the application or
protocol
Class E
•
•
•
•
Starts with 11110
Range of 224.0.0.1 to 255.255.255.254
Not useable by the public
Account for 6% of IP addresses
Reserved Addresses
• Class A
– 10
– 1 network
• Class B
– 172.16- 172.31
– 16 networks
• Class C
– 192.168.0 – 192.168.255
– 256 networks
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TCP/IP (Internet Protocol - IP)
•Most commonly used protocol suite
•Allows for easy cross-platform
communications
•Scalable and superior functionally over
WANs for connecting different types of
computers and networks
TCP/IP Protocol Suite
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TCP/IP Protocol Suite
•Utilizes small, specialized protocols
more than any other protocol suite.
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Process/Application
•Direct support for end user
–FTP/TFTP
–HTTP/HTTPS
–Telnet
–SMTP/POP
–IMAP4
–SNMP
–NFS
•Most are associated with a front-end utility
or application with which the user interfaces
FTP/TFTP
• FTP (File Transport Protocol)
– Connection oriented protocol for transferring files
over the network
– upper layer protocol that works cooperatively at
the Session, Presentation, and Application layers
(5-7) RFC 454
– provides services for file transfer as well as
directory and file-manipulation services (DIR,
Delete, etc…) via port 20 (data) and 21 (control)
• Command line interface
• TFTP (Trivial file transport protocol)
– Connectionless protocol
– No interface
•HTTP/HTTPS
• HTTP– Protocol of the Internet
• Designed to collect hypermedia over a
network
– Hypermedia – form of communication that allows
a dynamic link to another location
• Uses port 80
• Works in client/server mode
• HTTPS– connections using secure socket
layer protocol
– Encrypts transmissions
– Requires a secure server and login
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Telnet
– a remote terminal emulation protocol, also
operating at all upper layers (5-7)
•Data remains on the remote system
• remote equipment can be operated and configured
–Uses port 23
– mostly used to provide connection between
dissimilar systems (PC and VMS, PC and
router, UNIX and VMS)
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SMTP and POP
• SMTP (Simple Mail Transport Protocol)
–Uses port 25
–used for messaging services in the TCP/IP
suite
– basis for e-mail across the Internet
•POP (Post Office Protocol)
–Uses port 110(POP3) and 109(POP2)
–Distributes mail to the users
•IMAP4
• Internet Message Access Protocol Version 4
• E-mail protocol for retrieving messages that
supports advanced features
– Allows the user to create and maintain folders on
the remote server
– allows the user to perform remote searches of
messages using different parameters
• Uses port 220
•SNMP
• Simple Network Management Protocol
• Manager – interface through which the
administrator can gather information
• Agent– utility that fulfills the request
from the manager
• Stores the information in a file or
database
• Can be configured to send critical
updates or alerts to the manager
NFS
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•
•
•
•
Network File System
Port 2049
Locate and access remote files
Locking mechanism to protect data
Permission checks
•Host to Host Protocols
• Perform all the functions of the
transport layer
– TCP (Transmission Control Protocol)
– UDP (User Datagram Protocol)
– DNS (Domain Name System)
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TCP (Transmission Control Protocol)
•the primary Internet transport protocol (layer 4)
• accepts messages of any length from the upperlayer protocols
• provides transportation to a TCP peer
• Connection oriented (more reliable than IP)
• Port address is used to determine which
connection a packet is destined
• responsible for message fragmentation and reassembly
• uses a sequencing function to ensure correct
packet re-assembly
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UDP (User Datagram Protocol)
– Connectionless Transport layer protocol
– Faster, but less reliable than TCP
–No virtual link
–Flow control and data recovery are provided
by the application
–Used by SNMP, DNS, NFS, TFTP
DNS (Domain Name System)
– Transport layer, name-to-address
resolution protocol
– DNS server keeps a list of system’s
names and their IP addresses.
• Can use a system’s logical name
(microsoft.com) rather than its numerical
address when communicating
The DNS Tree
• The set of IP addresses and names in
DNS is called a namespace
• Structured in a tree structure starting at
the root
• Subsections can be located by branching
down the tree
DNS Tree
Company.com
Sales.Company.com
D1.Sales.Company.com
Marketing.Company.com
D2.Sales.Company.com
Namespace
• Namespace = any bounded area in
which a name can be resolved
Namespace
Fully Qualified Domain Name
• Unique computer name within a DNS
namespace
– Example—sales.www.emcp.com
• Read from left to right
• More specific information is on the left
Public and Private DNS Roots
• Root of a namespace is where the server
starts looking
• The Internet also contains DNS roots, but
these are not owned by any one company
• Private DNS roots are maintained by a
company for their internal use
• Public DNS roots are maintained by
Internet organizations for public use
Public Roots
• A public root is used to access computers on the
Internet
• There are 13 authoritative root servers
– An authoritative DNS server is responsible for their
namespace
• Currently, the top level domains are fall under
– Country code domains
• Us, uk, jp
– Generic domains
• com, org, net, mil, edu, gov
• Soon to be released domains are
int, aero, biz, coop, info, museum, name, pro
– Infrastructure
• .arpa used by IANA exclusively
Maintaining Public Root Servers
• Maintained by the InterNIC organization
• Assigns IP addresses and domain names
• Has licensed other organizations to also
assign names and IP addresses
Name Resolution in DNS
• A resolver (client computer requesting a name)
must contact a DNS server
• The resolver wants the IP address for a specific
name
• The DNS server can respond to the request in
several ways
– Return the IP address
– Send the resolver the IP address of another DNS
server that might have the requested address
Name Resolution Steps
1.
2.
3.
4.
5.
Resolver contacts DNS server with a name to be
resolved.
The DNS server asks a local DNS server for the IP
address of the root server.
The DNS asks the root server for the IP address of the
authoritative server for the requested address.
The DNS server asks the authoritative server for the IP
address.
The DNS server returns the IP address to the resolver.
Types of DNS Queries
• Recursive
– Resolver is given an IP address of a server
that might know the requested address and
the resolver must then make another query
• Iterative
– Resolver expects to get the final IP address
meeting their request
• Both types of queries are common.
Network layer protocols of
TCP/IP suite
– IP
– BootP
– DHCP
– ICMP
– ARP
– RARP
IP (Internet Protocol)
– Network layer protocol that provides source
and destination addressing and routing
– Connectionless datagram protocol (fast,
unreliable)
– Assumes that other protocols used by the
computer ensure reliable delivery of data.
IP services
• Six services
– Addressing
• Logical IP address
– Routing
• Select path through the network using IP and subnet mask
– Fragmentation—
• MTU
– Options–
• source routing, additional security
– Packet timeouts
• TTL
– Type of service
BootP
• Bootstrap Protocol used to boot diskless
workstations
• NIC has a bootprom
• BIOS bootstrap loader program points to boot
prom
• Boot request is issued to 255.255.255.255 on
port 67
– Boot reply on port 68
– Router forwards request if configured with relay agent
DHCP
• Places available IP addresses into a pool
and leases to clients
• 50% maturity client request renewal from
leasing server
• 75% maturity client requests reassignment
from any server
• Can hand out most TCP/IP configuration
parameters
•ICMP (Internet Control
Message Protocol)
– RFC 792
– TCP/IP best troubleshooting aid
– Network layer protocol used to send
control messages (errors and
confirmations)
• Out of band messages separate from the data
–
•Out of Band Messages
• Announce network errors
– host not reachable
• Announce Network Congestion
– Source Quench messages
• Assist Troublshooting
– Ping utility - used to request a response from a
host
• Echo request/reply request message
• timed out
• Round trip time and percentage loss
• Announce timeouts
– Trace Route
•ARP Address Resolution
Protocol
– Network layer protocol used to resolve a
logical (IP) address to a physical (MAC)
address
– When a system begins a conversation
with a host that it does not have a physical
address for, it sends and ARP broadcast
packet requesting the physical address
that corresponds to the logical address.
Then, the Data Link layer can correctly
send the packet through the network.
– RARP- assign IP address to MAC address
Address Resolution
DNS
ARP
RARP
BootP
DHCP
WINS
HOSTS
LMHOSTS
WINS
NETBIOS to IP
Requires WINS server
WINS database is dynamic–
system broadcasts when it boots to the
network
Server extracts information
Hosts and LMHosts
Statically resolve IP addresses
Hosts
DNS to IP
LMHosts
NETBIOS to IP
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TCP/IP Protocol Suite
•RIP (Routing Information Protocol)
– Network layer protocol
– Distance-vector routing protocol used for
route discovery (hops)
•OSPF (Open Shortest Path First)
– Network layer protocol
– Link-state routing protocol used by routers
running TCP/IP to determine the best path
through a network.
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TCP/IP
Figure 6-8
Transmission Control
Protocol (TCP/IP)
Three-Way Handshake:
• Requestor sends a packet specifying the port number
and its initial sequence number (ISN) to server
• Server acknowledges with its ISN, which consists of the
requestor’s ISN, plus 1
• The requester replies with the server’s ISN, plus 1
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TCP/IP
Figure 6-8