1
프로토콜
기술과
성능분석
발
표
:
김재석
발표일
: 2006
년
10
월
11
일
Part Ⅸ : Classless And Sbunet Address Extensions(CIDR)
Part Ⅹ : Protocol Layering
2
PART Ⅸ
Classless
And
Subnet Addresses Extention
Part
Ⅳ
䍉䑒
3
Introduction
Four Extension of the IP Address
Proxy Arp
Subnet Addressing
Anonymous Point
-
to
-
Point Networks
Classless Addressing
Part
Ⅳ
䍉䑒
4
Review Of Relevant Facts
Original address scheme (IPv4)
Divided into two parts : Network + Host
Unique network address (Each Physical Network)
Prefix (Each host on a network)
Advantage
reduce the size of routing table
keep one routing entry per network
Classful addressing
Class A
–
8bit network portion
Class B
–
16bit network portion
Class C
–
24bit network portion
Part
Ⅳ
䍉䑒
5
Minimizing Network Numbers
Reduce the number of network prefixes used
Weakness of Original IP addressing scheme
Growth ( From Mainframe Computer environment)
doubled in size every nine to fifteen months
Management overhead, Huge size of routing table, exhaustion
“
How can the technology accommodate growth without
abandoning the original calssful addressing scheme?
´
Transparent routers
unnumbered point
-
to
-
point links
proxy ARP
subnet addressing
Part
Ⅳ
䍉䑒
6
Proxy ARP
Single network prefix is used for two physical networks
H
1
H
2
H
3
H
4
H
5
H
6
Main Network
Hidden Network
Router running proxy ARP
Two network share single IP network
‘
R
’
keeps the location of hosts completed hidden
Hosts communicate
As if they are directly connected on a single network
TRUST
ARP based on COOPERTION & LEGITIMATION
spoofing warning Implementation
R
Part
Ⅳ
䍉䑒
7
Proxy ARP Cont
Host H
1
needs to communicate with host H
4
NO
OBJ
Action
비고
1
H1
Broadcast ARP REQ
To H4
2
R
Capture ARP REQ, Decide the LOC of H4
3
R
H1
Responds to the ARP REQ (R
’
s Physical Address)
4
H1
Receive ARP Response
Install the mapping ARP Table
5
H1
R(H4)
Sends Datagrams(Use above mapping to R)
6
R
Forward datagrams to H4
H
1
H
2
H
3
H
4
H
5
H
6
R
Part
Ⅳ
䍉䑒
8
Subnet Addressing
Subnet routing, Subnet forwarding, Subnetting
Standard, most general, most widely used
H
1
H
2
R
H
3
H
4
Network 128.10.1.0
Network 128.10.2.0
128.10.1.1
128.10.1.2
128.10.2.1
128.10.2.2
Rest Of The
Internet
(Another AS)
All Traffic to
128.10.0.0
Accepts all traffic for net 128.10.0.0
Chooses a physical network based on the third octet of the address
Part
Ⅳ
䍉䑒
9
Subnet Addressing Cont
Network Portion + Host Portion
Instead of Prefix and suffix
Internet Part
Local Part
Internet Part
Physical
Network
Host
Site, possibly with multiple
physical networks
Physical network and hosts at that
site
Hierarchical addressing
Leads to hierarchical routing
First level (Other Autonomous System) : use the first two octet
Next level : uses an additional octet
Lowest Level
…
.
Telephone System
Scalability
Part
Ⅳ
䍉䑒
10
Flexibility in Subnet Address Assignment
Allow Site Flexibility : assigning subnet address
Network 1
Part
Ⅳ
䍉䑒
To rest of Internet
Network 2
Network 3
Network 4
Network 5
Five Physical network
Three level
Subnet Bits
NO of Subnet
Hosts per
Subnet
0
1
65534
2
2
16382
3
6
8190
4
14
4094
5
30
2046
6
62
1022
7
126
510
Subnet Bits
NO of Subnet
Hosts per
Subnet
8
254
254
9
510
126
10
1022
62
11
2046
30
12
4094
14
13
8190
6
14
16382
2
Class B Subnetting
11
Variable
-
Length Subnets
Most site : Fixed
-
Length Subnets
Some Case Needs
Many networks with few hosts per networks
A few networks with many hosts
Flexibility
mixture of large and small networks
higher utilization of the address space
Address ambiguity
assigned carefully
Part
Ⅳ
䍉䑒
12
Implementation Of Subnets With Masks
Subnet Technology
either fixed or variable length
Standard : 32
-
bit Mask
Subnet prefix : set to
‘
1
’
Host prefix : set to
‘
0
’
Part
Ⅳ
䍉䑒
11111111 11111111 11111111
00000000
Identify Network
Identify Hosts
recommendation
use contiguous subnet mask
routing Table trick
11111111 11111111 00011000
01000000
13
Subnet Mask Representation
In Binary
awkward and prone to errors
Alternative representations
dotted decimal representation (
ex) 255.255.255.0
)
3
-
tuple(
{<network number>,<subnet number>,<host number>}
)
‘
-
1
’
means
“
all ones(1s)
”
ex) 255.255.255.0 {
-
1,
-
1,0}
{128.0,
-
1,0}
Part
Ⅳ
䍉䑒
14
forwarding In The Presence Of Subnets
Subnet forwarding, Subnet routing
Modified standard IP forwarding algorithm
Part
Ⅳ
䍉䑒
乥琠N⡓畢(e琠潦 a摤牥ss 丩
H
R2
R1
Net 3(Subnet of address N)
Net 1(not a Subnet address)
H can send to either
‘
R1
¶
and
µ
R2
¶
Not Shortest Path
To activate optimal forwarding : user subnet forwarding
Modified standard IP forwarding algorithm
The subnet mask should be uniform across all networks
All machines should participate in subnet forwarding
15
The Subnet forwarding Algorithm
Used With subnet searches a table of routes
Routing table entries (network address, next hop address)
network address : Ip address of destination network
N
next hot address : address of a router to which datagrams
destined for
N
should be sent
Subnet Forwarding Algorithm
maintains additional information in the routing table
address mask : extract bits for the destination address for
comparison with the table entry
network address
Next hop address
Part
Ⅳ
䍉䑒
16
Maintenance Of Subnet Masks
How are subnet masks assigned by an administrator?
Each site is free to choose subnet masks for its networks
balance sizes of networks
Numbers of physical networks
Expected growth
Ease of maintenance
nouniform masks
flexibilities but lead to ambiguous route
Part
Ⅳ
䍉䑒
17
Broadcasting To Subnets
{network,
-
1,
-
1}
deliver a copy to all machines that have network as their networks
address even if they on separate physical networks
Reverse path forwarding (RPF)
Router can
’
t merely propagate a broadcast packet that arrives on one
interface to all interfaces that share the subnet prefix
discard the datagram unless it arrived on the inerface used to forward
to the source
{Network, subnet,
-
1)
Part
Ⅳ
䍉䑒
18
Anonymous Point
-
To
-
Point networks
To avoid assigning a prefix to each point
-
to
-
point connection.
Often applied when a pair of routers is connected with a leased
digital circuit.
Unnumbered network
no number on leased line
no host address to the router at each end
no hardware address
interface software
ignore the next hop address
arbitrary value can be used as the next
-
hop address
does not operate like shared
-
media hardware
only one possible destination
–
摯es no琠畳u 灨ys楣al 慤dress
Part
Ⅳ
䍉䑒
19
Anonymous Point
-
To
-
Point networks cont
Part
Ⅳ
䍉䑒
R2
R1
128.10.0.0
128.211.0.0
Leased serial line
128.10.2.250
128.211.0.100
TO REACH HOSTS
ON NETWORK
ROUTE TO
THIS ADDRESS
USING THIS
INTERFACE
128.10.0.0
DELIVER DIRECT
1
default
128.211.0.100
2
1 2
Routing Table of R1
The address of R2’s Ethernet connection
20
Classless Addressing And Supernetting
Attempt to conserve the IP address space
subnet addressing, unnumbered network
not enough to prevent Internet growth from exhausting
defining an entirely new Version of IP with large addresses
temporary solution to accommodate growth
Permit a network prefix to be an arbitrary length
CIDR
-
Classless Inter
-
Domain Routing
classful scheme did not divide network addresses into equal size
Class C : much smaller than demand for class B
not amenable to subnetting
Class B : would be exhausted quickly (ROADS)
Supernetting
Assign a block of class C instead of a single class
Part
Ⅳ
䍉䑒
21
Advantage of Supernetting
Clear the issue of Class B address exhausting
Disadvantage : Increasing of routing information
CIDR clear the issue of increasing of routing Information
(Network address, Count)
Network address : minimum network address of the block
Count : Entire NO of network address of the block
192.5.48.0
ex) (192.5.48.0, 3) 192.5.49.0
192.5.50.0
Part
Ⅳ
䍉䑒
22
CIDR Address Blocks And Bit Masks
ISP assign each subscriber a block of addresses
Uses 32
-
bit address bit mask
Part
Ⅳ
䍉䑒
Dotted Decimal
32
-
bit Binary Equivalent
Lowest
128.211.168.0
10000000 11010011 10101000 00000000
highest
128.211.175.255
10000000 11010011 10101111 11111111
CIDR Mask
11111111 11111111 11111000 00000000
Example of CIDR block of 2048 addresses
continuous 1 bit for prefix,
continuous 0 bit for suffix
23
Address Blocks And CIDR Notation
Identifying CIDR Block requires : address, mask
CIDR Notation (Slash Notation)
ex) 128.211.168.0/21
Part
Ⅳ
䍉䑒
CIDR
Notation
Dotted
Decimal
CIDR Notation
Dotted
Decimal
CIDR Notation
Dotted Decimal
/1
128.0.0.0
/12
255.240.0.0
/23
255.255.254.0
/2
192.0.0.0
/13
255.248.0.0
/24
255.255.255.0
/3
224.0.0.0
/14
255.252.0.0
/25
255.255.255.128
/4
240.0.0.0
/15
255.254.0.0
/26
255.255.255.192
/5
248.0.0.0
/16
255.255.0.0
/27
255.255.255.224
/6
252.0.0.0
/17
255.255.128.0
/28
255.255.255.240
/7
254.0.0.0
/18
255.255.192.0
29
255.255.255.248
/8
255.0.0.0
/19
255.255.224.0
/30
255.255.255.252
/9
255.128.0.0
/20
255.255.240.0
/31
255.255.255.254
10
255.192.0.0
/21
255.255.248.0
/32
255.255.255.255
/11
255.224.0.0
/22
255.255.252.0
Dotted decimal mask values form all possible CIDR prefixes
24
A Classless Addressing Example
Complete flexibility in allocating blocks of various sizes
ISP can assign each customer a block of an appropriate size
128.211.0.0/21 for some customer
128.211.176.212/30 for some customer
Part
Ⅳ
䍉䑒
Dotted Decimal
32
-
bit Binary Equivalent
Lowest
128.211.176.212
10000000 11010011 10110000 11010100
highest
128.211.176.215
10000000 11010011 10110000 11010111
CIDR Block with 128.211.176.211/30
Summary
-
Classless Addressing
Treat IP Address as arbitrary integers
Partitioning addresses into contiguous blocks
25
Data Structure And Algorithms for Classless Lookup
Speed
–
fundamental criterion of Algorithm and data Structure
finding next hop, making changes to values in the table
1.
Hashing And Classful Address
Glassful Addressing :
self
-
identifying, hash table works well
router extracts network portion
N
and using it hashing Key
Classless Addressing :
non self
-
identifying, hashing doesn
’
t works well
Alternative must be used
2. Searching By Mask Length
LPM (Longest Prefix Match) : subscriber
’
s address mask > ISP
’
address
mask
Iterates approaching
–
extremely slow
Default route
–
performs 31 unnecessary lookups
Part
Ⅳ
䍉䑒
26
Data Structure And Algorithms for Classless Lookup
3. Binary trie Structure
Hierarchical data structure
Variants of binary trie
Many systems use
Part
Ⅳ
䍉䑒
32
-
Bit Address
Unique Prefix
00110101 00000000 00000000 00000000
01000110 00000000 00000000 00000000
01010110 00000000 00000000 00000000
01100001 00000000 00000000 00000000
10101010 00000000 00000000 00000000
10110000 00000000 00000000 00000000
10111011 00000000 00000000 00000000
00
0100
0101
011
010
10110
10111
A set of Binary address and the corresponding set of prefixes that uniquely identify each
27
Data Structure And Algorithms for Classless Lookup
Part
Ⅳ
䍉䑒
0
0
0
0
0
0
0
1
1
1
1
1
1
1
A Binary trie for seven binary prefixes listed previous
Prefix 0101
Stop when
reaches an exterior node
no path exists for the specified prefix
28
PATRICIA And Level compressed Tries
Binary Tries Omit details relate to optimization of lookup
“
skipping
”
levels in the trie that do not distinguish among routes
Examine all bits of a destination address at once rather than extracting
bits one at a time
PATRICIA tree
allows each node to specify a value to test long with a number of
bits to skip
Level compressed trie
provides additional optimizations by eliminating one or more levels
In the trie that can be skipped along any path
Trade Off
improve search speed but require more computation
Part
Ⅳ
䍉䑒
29
CIDR Blocks Reserved For Private networks
Reserved prefixes for Private Networks
private addresses
nonroutable addresses
Routers in the internet understand that the addresses are reserved
Part
Ⅳ
䍉䑒
Prefix
Lowest Address
Highest Address
10.0.0.0/8
172.16.0.0/12
192.168.0.0/16
169.254.0.0/16
10.0.0.0
172.16.0.0
192.168.0.0
169.254.0.0
10.255.255.255.255
172.31.255.255
192.168.255.255
169.254.255.255
The prefixes reserved for use with private internets
30
Summary
Five techniques to conserve IP addresses
Transparent Router
Proxy ARP
Subnet addressing
Anonymous point
-
to
-
point connection
CIDR
Part
Ⅳ
䍉䑒
31
PART Ⅹ
Protocol Layering
Part
Ⅳ
䍉䑒
32
Introduction
Structure of the software found in hosts and routers
presents the general principle of layering
easy to understand, build and trace
Part
Ⅳ
P牯瑯c潬⁌oye物湧
The Need for Multiple Protocols
Protocol allow one to
specify or understand communication without knowing the details
Complex data communication
protocol family, protocol suite
-
require a set of cooperative protocols
Why
Hardware failure, Network Congestion
Packet Delay (Loss), Data Corruption
Data Duplication or Inverted Arrival
33
The Conceptual Layers Of Protocol Software
Part
Ⅳ
P牯瑯c潬⁌oye物湧
Sender
Layer n
…
Layer2
Layer1
Receiver
Layer n
«
Layer2
Layer1
Network
The conceptual organization of protocol software in layers
In practice, the protocol software is much more complex.
High
-
Level Protocol Layer
Internet Protocol Layer
Network Interface Layer
Protocol 1
Protocol 1
Protocol 1
Interface 1
Interface 2
Interface 3
IP Module
Conceptual protocol layering Realistic view of software organization
Multiple network interfaces below IP and multiple protocol above it
34
The Conceptual Layers Of Protocol Software Cont
Part
Ⅳ
P牯瑯c潬⁌oye物湧
Message traversing from the sender through two intermediate routers to the receiver.
Intermediate only send the datagram to the IP software layer
Sender
Other
…
IP Layer
Interface
Net 1
IP Layer
Interface
IP Layer
Interface
Receiver
Other
…
IP Layer
Interface
Net 2
Net 3
35
ISO 7
-
Layer Reference Model
Part
Ⅳ
P牯瑯c潬⁌oye物湧
The ISO 7
-
Layer reference model for protocol software
ISO
’
s Reference Model of Open System Inerconnection
ISO Model
Contains 7 Conceptual layers
Application
Presentation
Session
Transport
Network
Data Link
(Hardware Interface)
Physical Hardware
Connection
Layer Functionality
1
2
3
4
5
6
7
36
X.25 And Its Relation To The ISO Model
Recommendation of ITU, most recognized and widely used
Adopted by public data network, like a telephone system
Physical Layer
Standard for the physical interconnection
Procedures used to transfer packets
Data Link Layer
-
How data travels
Network Layer
–
Network or communication subnet layer
Defines the basic unit of transfer,
The concepts of destination addressing and forwarding
Transfer Layer
–
Provide end
-
to
-
end Reliability
Session Layer
±
Remote terminal access
Presentation Layer
-
compress text, convert graphics images into
bit stream
Application Layer
±
application programs (E
-
mail, FTP
«
.)
Part
Ⅳ
P牯瑯c潬⁌oye物湧
37
The TCP/IP 5
-
Layer Reference Model
Five conceptual layers
Part
Ⅳ
P牯瑯c潬⁌oye物湧
Application
Transport
Internet
Network Interface
Hardware
Conceptual Layer
Object Passed
Between Layers
Message or Streams
Transport Protocol Packets
IP Datagrams
Network
–
Specific Frames
Application Layer
–
Invoke application programs
Transport Layer
Provide communication from one application program to another
Regulate flow on information, Reliable transport
Internet Layer
–
handle communication from one machine to another
encapsulation, forwarding algorithm
Network Layer
–
responsible for accepting IP datagrams and
transmitting them over a specific network
38
The Protocol Layering Principle
Layered protocols are designed so that layer N at the destination
receives exactly the same object sent by layer N at the source
Allows the protocol designer
-
to focus attention on one layer at a time,
without worrying about how other layers performs
Part
Ⅳ
P牯瑯c潬⁌oye物湧
Application
Transport
Internet
Network
Interface
Application
Transport
Internet
Network
Interface
Identical
message
Identical
packet
Identical
datagram
Physical Net
Identical frame
Host A
Host B
39
Layering in a TCP/IP Internet Environment
Part
Ⅳ
P牯瑯c潬⁌oye物湧
Application
Transport
Internet
Network
Interface
Application
Transport
Internet
Network
Interface
Identical
message
Identical
packet
Host A
Host B
Internet
Network
Interface
Physical Net 1
Identical
datagram
Identical
datagram
Identical
frame
Physical Net 2
Identical
frame
Router R
The ultimate destination will not receive exactly the same datagtams
as the source sent
-
datagram header contains fields like TTL
…
The Layering principle only applies to datagrams across single
machine transfers.
40
Layering in The Presence Of Network Substructure
Part
Ⅳ
P牯瑯c潬⁌oye物湧
Transport
Internet
Network
Interface
Interanet
Protocol 1
Protocol 1
Protocol 1
Interface 1
Interface 2
Interface 3
IP Module
Point
-
to
-
Point
(Intranet)
Software Organization
Conceptual Layer
41
Two Important Boundaries In The TCP/IP Model
Part
Ⅳ
P牯瑯c潬⁌oye物湧
Protocol address boundary
high
-
level address (IP Address) :
from the internet layer upward
Application Programs
low
-
level address (Physical Address) :
network interface layer
Operating System Boundary
considered part of the operating system
and software that is not
42
Two Important Boundaries In The TCP/IP Model
Part
Ⅳ
P牯瑯c潬⁌oye物湧
Application
Conceptual Layer
Boundary
Transport
Internet
Network
Interface
Hardware
Software outside the operating system
Software inside the operating system
Only IP addresses used
Physical addresses used
43
The Disadvantage Of Layering
Part
Ⅳ
P牯瑯c潬⁌oye物湧
Strict layering can be extremely inefficient
Usually, relax the strict layering scheme
44
The Basic Idea Behind Multiplexing and Demultiflexing
Part
Ⅳ
P牯瑯c潬⁌oye物湧
䥐⁍潤畬u
A剐 M潤畬o
剁剐 M潤畬o
Demultiflexing Based
On Frame Type
Frame Arrived
Multiplexing and Demultiplexing
Communication protocol use throughout the layered hierarchy.
ICMP Protocol
UDP Protocol
TCP Protocol
IP Module
Datagram Arrived
Demultiplexing at the network interface
Demultiplexing of incoming frames based on the type field
found in the frame header
Demultiplexing at the internet layer
IP Software chooses an appropriate procedure
to handle a datagram base on the protocol type field
in the datagram header
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