3. Internet Protocol:
Connectionless Datagram Delivery
최양희
서울대학교 컴퓨터공학부
MMlab
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Introduction
ƒ Internet architecture and philosophy
Application Services
Reliable Transport Service
Connectionless Packet Delivery
Service
IP packet delivery service
•
•
•
•
•
Unreliable: lost, duplicated, delayed, or delivered out of order
Best-effort
Connectionless
Variable size datagrams
Data forwarding only (routing, error, and control by other
protocols)
2005 Yanghee Choi
MMlab
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IP Features
ƒ Interconnecting end systems across multiple
networks
ƒ Implemented everywhere (end system, router)
ƒ High level protocol data encapsulated in IP Protocol
Data Unit (PDU)
ƒ IP version 4 (rfc 791, in 1981)
ƒ IP version 6 (IPv6) (rfc 2460, in 1998)
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Router Features
ƒ Coping with the differences among networks
• Addressing schemes
• Maximum packet size
• Hardware and software interfaces
• No assumption on network reliability
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IP datagram
HEADER
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DATA
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IP encapsulation
IP Header
Frame Header
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IP Data
Frame Data
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Transmission across
Internet
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IP Datagram Forwarding
ƒ Delivers datagrams to destination subnetwork
ƒ Routers maintain a routing table of next hops
ƒ Next hop field does not appear in the datagram
Net 1
Table at R2
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R1
Net 2
Destination
Net 1
Net 2
Net 3
Net 4
R2
Net 3
R3
Net 4
Next Hop
Forward to R1
Deliver Direct
Deliver Direct
Forward to R3
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Routing Table
ƒ IF ((Mask[I] & Destination_Address) = Destination [I])
Forward to NextHop [I]
30.0.0.7
Net 1
30.0.0.0
40.0.0.8
R1
Net 2
40.0.0.0
40.0.0.7
Destination
30.0.0.0
40.0.0.0
128.1.0.0
192.4.10.0
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R2
128.1.0.9
Net 3
128.1.0.0
128.1.0.8
Mask
255.0.0.0
255.0.0.0
255.255.0.0
255.255.255.0
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R3
Net 4
192.4.0.0
192.4.10.9
Next Hop
40.0.0.7
Deliver Direct
Deliver Direct
128.1.0.9
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IPv4 Datagram Format
0
4
8
VERS HLEN
16
24
19
SERVICE
TYPE
31
TOTAL LENGTH
IDENTIFICATION
FLAGS
TIME TO LIVE PROTOCOL
FRAGMENT OFFSET
HEADER CHECKSUM
SOURCE IP ADDRESS
DESTINATION IP ADDRESS
IP OPTIONS (IF ANY)
PADDING
DATA
...
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MMlab
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IP Format
ƒ Version (4 bits)
ƒ Internet Header Length (4 bits) : in 32-bit words
Min header is 5 words
ƒ Type of Service (8 bits)
Precedence, delay, reliability, throughput
ƒ Total Length (16 bits)
header + data in bytes, less than 64KB
ƒ Identifier (16 bits)
uniquely identifies the datagram during its life
ƒ Flags (3 bits)
More flag, No fragmentation
ƒ Fragment offset (13 bits) in units of 8 bytes
ƒ Time to live (8 bits) in router hops
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MMlab
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IP Format (cont’d)
ƒ Protocol (8 bits)
Next level protocol to receive the data
ƒ Header Checksum (16 bits)
One’s complement sum of all 16-bit words in the header
ƒ Source Address (32 bits)
Original source. Does not change along the path
ƒ Destination Address (32 bits)
Final destination. Does not change among the path
ƒ Options (variable)
ƒ Padding (variable)
Makes header length a multiple of 4 bytes, zero is inserted
ƒ Data (variable)
Data + header < 65,535 bytes
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Service Type
0
1
2
PRECEDENCE
3
4
5
D
T
R
6
7
UNUSED
D
low delay
T
high throughput
R
high reliability
Precedence=importance of datagram
===> hint to routing algorithm
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DiffServ
0
5
CODEPOINT
6
7
Unused
64 different services
xxx000 for original definition
precedence 6 or 7 for routing traffic
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MMlab
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Fragmentation
ƒ Datagram Size, Network MTU, and Fragmentation
• MTU (maximum Transfer Unit): fixed upper bound on the amount
data that can be transferred in one physical frame
e.g.) Ethernet: 1500 octets, FDDI: 4470 octets
• Fragmentation: dividing large datagrams into smaller pieces when
the datagram needs to traverse a network that has a small MTU
• Fragments must be reassembled at the destination
• If any fragments are lost, the datagram cannot be reassembled.
• Reassembly timer : if expired, discard the received packets
ƒ Fragmentation control
• IDENTIFICATION : identical to the fragments
• FLAGS: Don’t Fragment bit, More Fragments bit,
• FRAGMENT OFFSET : by 8 octets
ƒ No sequence number
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Fragmentation
HOST
A
HOST
B
Net 1
MTU=1500
R1
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Net 2
MTU=620
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Net 3
MTU=1500
R2
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Fragments
Datagram
Header
Data1
600 octets
Data2
Data3
600 octets 200 octets
Fragment 1
Data1
Header
600 octets
Fragment 1 (offset 0)
Fragment 2
Data2
Header
600 octets
Fragment 2 (offset 600)
Fragment 3
Data3
Header
200 octets
Fragment 3 (offset 1200)
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Internet Datagram Options
ƒ Included primarily for network testing or debugging
ƒ Type(code)- Length-Value
ƒ Option code (1 octet)
0
1
2
COPY OPTION CLASS
3
4
5
6
7
OPTION NUMBER
ƒ Copy = 1
option copied to all fragments
=0
copied to the first fragment only
ƒ Class = 0
Datagram or network control
=1
Resv’d
=2
Debugging and measurement
=3
Resv’d
ƒ Option length (1 octet)
ƒ Value : variable length
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MMlab
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IP Options
ƒ Loose Source Routing
ƒ Record Route
ƒ Strict Source Routing
ƒ Internet Timestamp etc.
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Record Route Option
0
8
16
24
31
CODE LENGTH POINTER
FIRST IP ADDRESS
SECOND IP ADDRESS
……...
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Strict Source Route Option
0
8
16
24
31
CODE LENGTH POINTER
IP ADDRESS OF FIRST HOP
IP ADDRESS OF SECOND HOP
……...
Addresses overwritten by visited routers
(= record route)
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MMlab
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Timestamp Option
0
8
16
24
31
CODE LENGTH POINTER OFLOW FLAGS
FIRST IP ADDRESS
FIRST TIMESTAMP
……...
In msec since midnight
OFLOW : count of routers that couldn’t supply timestamps
because the option was too small
FLAGS : record timestamps only (0), etc.
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IPv6
ƒ
ƒ
ƒ
ƒ
ƒ
ƒ
ƒ
Expanded Addressing Capabilities
Flexible header format
Improved Support for Extensions and Options
Support for resource allocation
Provision for protocol extension
Flow Labeling Capability
Authentication and Privacy Capabilities
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IPv6 Addresses
ƒ
ƒ
ƒ
ƒ
ƒ
ƒ
ƒ
ƒ
128-bit long. Fixed size
3.4 X 10~38 addresses
Assigned to individual interfaces
Allows multiple interfaces per host
Allows multiple addresses per interface
Allows unicast, multicast, anycast
Allows provider based, site-local, link-local
85% of the space is unassigned
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MMlab
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Colon-Hex Notation
ƒ Dot-Decimal 147.47.114.115
ƒ Colon-Hex
FEDC:0000:0000:0000:3232:0000:0000:ACFE
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IPv6 Prefix Allocation
Allocation
Prefix
Allocation
Prefix
Reserved
Unassigned
NSAP
IPX
Unassigned
Unassigned
Unassigned
Global Unicast
Unassigned
Unassigned
Unassigned
0000 0000
0000 0001
0000 001
0000 010
0000 011
0000 1
0001
001
010
011
100
Unassigned
Unassigned
Unassigned
Unassigned
Unassigned
Unassigned
Unassigned
Unassigned
Link-Local
Site-Local
Multicast
101
110
1110
1111 0
1111 10
1111 110
1111 1110
1111 1110 0
1111 1110 10
1111 1110 11
1111 1111
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IPv6 Address Formats
Top-Level Aggregation (ISP or exchange)
Next-Level Aggregation (subscriber site)
Site-Level Aggregation (subnet)
001 TLA id RES
3
13
8
NLA id
SLA id INTERFACE id
24
16
64
Aggregatable global unicast address
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Local Address
1111111010
Interface ID
Link Local address : Not forwarded outside the link
1111111011
Interface ID
Site Local address : Not forwarded outside the subnetwork
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IPv4 Addresses
32
0000…………………………………………...…………………..0000 IPv4 address
0000…………………………………………...…………………..FFFF IPv4 address
IPv4-compatible IPv6 address
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Anycast Address
Routed to the nearest interface in the group
Allocated in the unicast address space
Subnet-router anycast address :
delivered to one router in the subnetwork
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Multicast Addresses
ƒ Flag bit :
T=0 Permanent (well-known) multicast address
T=1 Transient
ƒ Scope
1
Node-local
2
Link-local
5
Site-local
8
Organization-local
E
Global
ƒ Group ID
Predefined 1
All nodes
2
Routers
1:0
DHCP servers
11111111 Flag Scope
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Group ID
MMlab
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IPv6 PDU General Form
40 octets
IPv6
header
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0 or more
Extension
header
…..
MMlab
Extension Transport-level
header
PDU
32
IPv6 Header
4
8
16
Version traffic class
Payload length
24
Flow label
31
Next header Hop limit
Source
Address
40 octets
0
Destination
Address
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IPv6 Header
ƒ
ƒ
ƒ
ƒ
ƒ
ƒ
ƒ
ƒ
ƒ
Version = 6
Traffic Class (8 bits)
Flow Label (20 bits)
Payload length (16 bits) : in octets except the IPv6 header
Next Header (8 bits) : identifies the type of header following the
IPv6 header
Hop Limit (8 bits) : remaining number of allowable hops for this
packet
Source Address (128 bits)
Destination Address (128 bits) : may not be the ultimate
destination, if routing header is present
40 octets in length
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Flow Label
ƒ A Flow is uniquely identified by source address and
20-bit flow label.
ƒ A flow may comprise single or multiple TCP
connections.
ƒ A single application may generate a single or multiple
flows (multimedia conferencing).
ƒ At router, the same flow has the same path, resource
allocation, discard requirements, accounting, and
security attributes.
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Header Order
ƒ IPv6 header : mandatory
ƒ Hop-by-Hop Options header
ƒ Destination Options header
to be processed by destinations in the IPv6 header and Routing
header
ƒ Routing header : extended routing (source routing)
ƒ Fragment header
ƒ Authentication header
ƒ Encapsulating Security Payload header
ƒ Destination Options header
to be processed by destination in the IPv6 header
ƒ upper-layer header (TCP, application etc.)
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IPv6 Fragmentation
ƒ End-to-end
ƒ Does not accommodate route changes
ƒ Use Path MTU Discovery to determine minimum
MTU in the path
ƒ Minimum MTU is 1280 octets
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IPv6 Transition (ngtrans)
IPv4/IPv6
DualStack
IPv4
IPv6
IPv6
IPv4
IPv6-in-IPv4 tunneling
IPv4
IPv4/IPv6
Translation
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IPv6
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