TCP/IP Basis
高雄大學資訊工程學系
嚴力行
Source
OSI Model
Destination
Presentation
Session
Transport
Network
Data-Link
Physical
SEGMENT
PACKET
FRAME
BITS
0101010101010101010
DECAPSULATION
Application
ENCAPSULATION
DATA
Application
Presentation
Session
Transport
Network
Data-Link
Physical
1
TCP/IP Model
涵蓋了OSI模型中的Application,
Presentation, 和Session三層
Socket API
TCP 或 UDP
IP
LAN, WAN 或其它網路
Application Layer Examples
2
IPv4 Addressing
• An IP address is a 32-bit sequence of 1s and 0s.
• To make the IP address easier to use, the
address is usually written as four decimal
numbers separated by periods.
• This way of writing the address is called the
dotted decimal format.
IP Address Structure
• Network number + Host number
• Network numbers are assigned by the NIC
(Network Information Center) to avoid
conflicts.
• All the hosts in a network (可以不透過
router而互相通訊的區域) must have the
same network number.
3
IP Addresses: Self Identification
Class
1
2
3 Range of host
01234567890123456789012345678901 addresses
1.0.0.0 to
127.255.255.255
A
0Network
Host
B
10
C
110
D
1110
Multicast address
224.0.0.0 to
239.255.255.255
E
11110
Reserved for future use
240.0.0.0 to
247.255.255.255
Network
128.0.0.0 to
191.255.255.255
Host
Network
Host
192.0.0.0 to
223.255.255.255
Classes of IP Network Addresses
4
Special IP Addresses
All 1s mean “all”; All 0s mean “this”
00000000000000000000000000000000 This host
netid
A host on this network
00
00
Host
11111111111111111111111111111111
Network
127
Broadcast on the
local network
11
11 Broadcast on a
distant network
(anything)
Loopback
Host Address vs. Network Address
• Host address is assigned to a specific
interface
Network
Host
Host number
cannot be all 0’s
• Network address refers to a whole network
– Not assigned to an interface
Network
00
00 Host number is all 0’s
For a k-bit host number, total 2k -2 addresses are assignable
(excluding all 0’s and all 1’s)
5
One Host Address for One Host?
• A host can have more than one interfaces
• Each interface should be configured an
independent host address
140.126.0.0
140.126.1.2
140.124.0.0
140.124.8.3
IP Addressing Problems
• 32-bit IP address space is not enough
• Organizing the address space by
classes wastes millions of them
– a class B address is far too large for most
organizations
• the routing table explosion
– every router in the Internet would need a
table with half a million entries, if that much
class C networks are in use
6
Subnet Addressing
•ack like a single network to the outside world
•split into several parts for internal use
Subnet 140.127.1.0
class B
140.127.0.0
140.127.1.1
140.127.1.2
140.127.2.1
140.127.2.2
G
Subnet 140.127.2.0
Subnets
A Class B Network
IP address
Subnet mask
Network
11
Host Part
Subnet
11 11
Host
11 00
00
• The standard does not restrict subnet
masks to select contiguous bits of the
address.
7
Introduction to Subnetting
• Host bits must are reassigned (or
“borrowed”) as network bits.
• The starting point is always the leftmost
host bit.
5 bits borrowed allows 25-2 or 30 subnets
(sN 全為0或
的無法使用)
全為 或1的無法使用
的無法使用
Determining Subnet Mask Size
Class C address 197.15.22.131 with a subnet
mask of 255.255.255.224 (3 bits borrowed)
11000101 00001111 00010110 100
Network Field
SN
00011
Host
Field
The address 197.15.22.131 would be on the
subnet 197.15.22.128.
8
Establishing the Subnet Mask
Address
• Determines which part of an IP address is the
network field and which part is the host field.
• Follow these steps to determine the subnet mask:
1. Express the subnetwork IP address in binary form.
2. Replace the network and subnet portion of the
address with all 1s.
3. Replace the host portion of the address with all 0s.
4. Convert the binary expression back to dotteddecimal notation.
Subnet Mask
Subnet mask in decimal = 255.255.240.0
= IP address / 20
9
Network Growth Problem
• Problem
– Immense administrative overhead
• Every time a new network is installed the
system administrator has to contact NIC to get
a new network number.
• Then this number must be announced
worldwide.
– Large routing table
• Solution: To minimize network numbers by
sharing one network number among multiple
physical networks
Classless InterDomain Routing
(CIDR)
• To solve the IP address depletion problem
and the routing table explosion problem
• RFC 1519
• The basic idea behind CIDR is to allocate
the remaining class C networks in
variable-sized (2x) blocks
10
Example
• X University needs 2048 addresses and is
assigned the addresses 194.24.0.0 through
194.24.7.255, along with mask 255.255.248.0.
• Y University needs 4096 addresses and is
assigned the addresses 194.24.16.0 through
194.24.31.255, along with mask 255.255.240.0.
• Z University needs 1024 addresses and is
assigned the addresses 194.24.8.0 through
194.24.11.255, along with mask 255.255.252.0.
Example
Routing table with entries
28 Class
C networks
base address
194.24.0.0
194.24.16.0
194.24.8.0
mask
255.255.248.0
255.255.240.0
255.255.252.0
248=(11111000)2
240=(11110000)2
252=(11111100)2
Destination address with 194.24.17.4 17=(00010001)2
Dest. IP & mask
194.24.17.4 & 255.255.248.0 = 194.24.16.0
194.24.17.4 & 255.255.240.0 = 194.24.16.0 ← match
194.24.17.4 & 255.255.252.0 = 194.24.16.0
11
Classless InterDomain Routing
(CIDR)
• The world was partitioned into zones, each given a
portion of the class C address space:
–
–
–
–
Addresses 194.0.0.0 to 195.255.255.255 for Europe
Addresses 196.0.0.0 to 197.255.255.255 for Others
Addresses 198.0.0.0 to 199.255.255.255 for North America
Addresses 200.0.0.0 to 201.255.255.255 for Central and South
America
– Addresses 202.0.0.0 to 203.255.255.255 for Asia and Pacific
– Addresses 204.0.0.0 to 207.255.255.255 for Others
– Addresses 208.0.0.0 to 223.255.255.255 reserved for future use
Internet Addressing: Host
Names
•
•
Mnemonic address made up of two parts:
– Domain name
• Assigned by a registrar
• Example: aw.com
• Top level domain: Classification of domain owner
– By usage – Example: .com = commercial
– By country – Example: .au = Australia
– Subdomains and individual host names
• Assigned by domain owner
• Example: r2d2.compsci.nowhereu.edu
Translation between mnemonic addresses and IP addresses handled
by name servers (DNS server)
12
Public and Private IP Addresses
• No two interfaces that connect to a public
network can have the same IP address
because public IP addresses are global
and standardized.
• However, private networks that are not
connected to the Internet may use any
host addresses, as long as each host
within the private network is unique.
Private Addresses and NAT
• three blocks of IP addresses are set aside for
private, internal use.
Class
A
B
C
Private Address Range
10.0.0.0 to 10.255.255.255
172.16.0.0 to 172.16.255.255
192.168.0.0 to 192.168.255.255
• Connecting a network using private addresses
to the Internet requires translation of the private
addresses to public addresses using Network
Address Translation (NAT).
13
NAT Translation Example
NAT Router
Internet
Src = 192.168.1.2
Dst. = …
Src = 218.168.153.6
Dst. = …
Private Network
NAT Router
Internet
Src. = …
Dst. = 192.168.1.2
Src. = …
Dst = 218.168.153.6
Dynamic Host Configuration
Protocol (DHCP)
• DHCP allows a host to obtain an IP
address (public or private) using a defined
range of IP addresses on a DHCP server.
• As hosts come online, contact the DHCP
server, and request an address.
14
DHCP與NAT在家庭網路的使用
4. PC1取得IP address的方式與Router相同
Private Network
192.168.1.1
PC1
PC2
Switch
Router
ADSL
Modem
To the
Internet
PC3
192.168.1.2
218.168.153.6
1. Router透過PPPoE建立與ISP的 link layer
並取得public IP address
2. Router啟動DHCP與NAT服務
3. PC3使用DHCP取得 private IP address
IP分享器
Private Network
Switch
Router
ADSL
Modem
To the
Internet
+ DHCP
+ NAT
IP分享器
15
無線IP分享器
Private Network
Switch
AP
Router
Modem
To the
Internet
+ DHCP
+ NAT
無線IP分享器
Transmission Control Protocol
(TCP)
• The protocols that use TCP include:
– FTP (File Transfer Protocol)
– HTTP (Hypertext Transfer Protocol)
– SMTP (Simple Mail Transfer Protocol)
– Telnet
16
UDP
• The protocols that use UDP include:
– TFTP (Trivial File Transfer Protocol)
– SNMP (Simple Network Management
Protocol)
– DHCP (Dynamic Host Control Protocol)
– DNS (Domain Name System)
TCP and UDP Port Numbers
• Both TCP and UDP use port (socket) numbers
to pass information to the upper layers.
– Numbers below 1024 are considered well-known
ports numbers.
– Numbers above 1024 are dynamically assigned
ports numbers.
– Registered port numbers are those registered for
vendor-specific applications. Most of these are
above 1024.
17
Some Well-Known Port Numbers
IPv6: Introduction
• The main problem of IPv4 is its relatively
small address space
• IPv6 extends IP address to 128 bits
18
IPv6 Address Hexadecimal
Notation
• Similar to IEEE 802 MAC addresses
• Colon hexadecimal notation
805B:2D9D:DC28:0:0:FC57:D4C8:1FFF
• Zero compression
– Contiguous zeros are replaced by doubled
colons (can appear only once)
805B:2D9D:DC28::FC57:D4C8:1FFF
Two zero words here
IPv6 Mixed Notation
• IPv4 address can be embedded in an IPv6
address
• It is useful to show the IPv4 portion of the
address in dotted-decimal format
805B:2D9D:DC28::FC57:212.200.31.255
• 0:0:0:0:0:0:212.200.31.255
becomes ::212.200.31.255
19
IPv6/IPv4 Address Embedding
• IPv4-compatible IPv6 addresses
Special address assigned
to IPv6-capable devices
0
32-Bit IPv4 Address
8
101
Used only for devices that
are actually IPv6-aware
IPv6 Address In
Mixed Notation
64
0
32
219
96
00000000 00000000 00000000 00000000 00000000
00000000 00000000 00000000 00000000 00000000
0
75
便於轉換成IPv4位址
32
Prefix IPv4 Address
With 80 Zero Bit
24
16
45
0
0
128
00000000
00000000
101
45
75
219
0
101
45
75
219
0
::101.45.75.219
Compressed
IPv6 Address
IPv6/IPv4 Address Embedding
• IPv4-mapped IPv6 addresses
Regular IPv4 addresses
that have been mapped
into IPv6 address space
0
32-Bit IPv4 Address
8
222
1
For devices that are not
IPv6-capable
IPv6 Address In
Mixed Notation
64
Compressed
IPv6 Address
0
90
96
00000000 00000000 00000000 00000000 00000000
00000000 00000000 00000000 00000000 00000000
0
41
32
由IPv4位址轉換來的
32
Prefix IPv4 Address
With 64 Zero Bit
and 14 One Bit
24
16
0
0
128
11111111
11111111
222
1
41
90
FFFF
222
1
41
90
0
::FFFF:101.45.75.219
20
IPv6 Address Prefix Length
Representation
• IPv6 addresses are divided into a number of
network ID bits followed by a number of host ID
bits
• The network identifier is called the prefix, and
the number of bits used is prefix length
• The prefix is represented by adding a slash after
the address and then putting the prefix length
after the slash
805B:2D9D:DC28::FC57:D4C8:1FFF / 48
21