The IP Header - I4 * Lehrstuhl fuer Informatik * RWTH Aachen

Lehrstuhl für Informatik 4
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On the Way to Today's Internet
Goal:
• Interconnection of computers and networks using uniform protocols
• A particularly important initiative was initiated by the ARPA
(Advanced Research Project Agency, with military interests)
• The participation of the military was the only sensible way to implement such
an ambitious and extremely expensive project
• The OSI specification was still in developing phase
Result: ARPANET (predecessor of today's Internet)
Chapter 3.2: The Internet Protocol IP
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ARPANET
Design objective for ARPANET
• The operability of the network should remain
intact even after a largest disaster possible,
e.g. a nuclear war, thus high connectivity and
connectionless transmission
• Network computer and host computer are
separated
ARPA
Advanced Research
Projects Agency
ARPANET
Subnet
Chapter 3.2: The Internet Protocol IP
1969
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ARPANET
A node consists of
• an IMP
• a host
A subnet consists of:
• Interface Message Processors
(IMPs), which are connected by
leased transmission circuits
• High connectivity (in order to
guarantee the demanded
reliability)
Host-host Protocol
Host
Host-IMP
Protocol
IMP
Source IMP to
destination IMP protocol
MP
I
IMP tocol
pro
Subnet
Several protocols for the
communication between
IMP-IMP, host-IMP,…
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The Beginning of ARPANET
Stanford Research
Institutes (SRI)
XDS
940
IMP
IMP
IBM
360/75
DEK
PDP-10
IMP
University of
California Santa
Barbara (UCSB)
University
of Utah
IMP
XDS
1-7
California
University of California
Los Angeles (UCLA)
Chapter 3.2: The Internet Protocol IP
ARPANET
(December 1969)
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Evolution by ARPANET
Very fast evolution of ARPANET within shortest time:
SRI
SRI
Utah
Illinois
WITH
Utah
Illinois
USC
Stanford
Harvard
Aberdeen
WITH
UCSB
UCSB
UCLA
Harvard
ARPANET in April 1972
Chapter 3.2: The Internet Protocol IP
UCLA
USC
CMU
ARPANET in September 1972
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Interworking
Problem: Interworking!
Simultaneously to the ARPANET further (smaller) networks were developed.
All the LANs, MANs, WANs
• had different protocols, media,…
• could not be interconnected at first and were not be able to communicate
with each another.
Therefore:
Development of uniform protocols on the transport- and network level
(without a too accurate definition of these levels, in particular without
exact coordination with the respective OSI levels).
Result: TCP/IP networks.
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TCP/IP
Developed 1974:
Transmission Control Protocol/Internet Protocol (TCP/IP)
Requirements:
• Fault tolerance
• Maximal possible reliability and availability
• Flexibility (i.e. suitability for applications with very different
requirements)
The result:
• Network protocol IP; (Internet Protocol; connectionless)
• End-to-end protocols TCP (Transmission Control Protocol; connection-oriented)
and UDP (User Datagram Protocol; connectionless)
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TCP/IP and the OSI Reference Model
Application Layer
Application Layer
Presentation Layer
Session Layer
Transport Layer
Transport Layer (TCP/UDP)
Network Layer
Internet Layer (IP)
Data Link Layer
Host-to-Network Layer
Physical Layer
ISO/OSI
Chapter 3.2: The Internet Protocol IP
TCP/IP
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From the ARPANET to the Internet
• 1983 TCP/IP became the official protocol of ARPANET. ARPANET was
connected with many other USA networks.
• Intercontinental connecting with networks in Europe, Asia, Pacific.
• The total network evolved this way to a world-wide available network (called
“Internet”) and gradually lost its early militarily dominated character.
• No central administrated network, but a world-wide union from many
individual, different networks under local control (and financing).
• 1990 the Internet consisted of 3,000 networks with 200,000 computers. That
was however only the beginning of a rapid evolution.
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Internet
What does it mean: “a computer is connected to the Internet”?
- Use of the TCP/IP protocol suite
- Accessibility over an IP address
- Ability to send IP packets
In its early period, the Internet was limited to the following
applications:
E-mail
electronic mail (partly because the US post was not very reliable
and the different time zones made telephone accessibility of the
telephone partner more difficult)
Remote login
running jobs on external computers
File transfer
exchange of data between computers
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Evolution of the Internet
• Until 1990: the Internet was comparatively small, only used by universities
and research institutions.
• 1990: The WWW (World Wide Web) - first developed by the CERN for the
simplification of communication within the field of high-energy physics became, together with HTML and Netscape browsers, a from nobody
foreseen “killer application”; this was the breakthrough for the acceptance of
the Internet.
• Emergence of so-called Internet Service Providers (ISP), i.e. companies,
which make their computers available as access points to the Internet.
• Millions of new (predominantly non-academic) users!
• New applications, e.g. E-Commerce
• 1995: Backbones, ten thousands LANs, millions attached computers,
exponentially rising number of users
• 1998: The number of attached computers is doubled approx. all 6 months
• 1999: The transferred data volume is doubled in less than 4 months
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Evolution of the Internet
1.01.1981
1.01.1982
1.01.1983
1.01.1984
1.01.1985
1.01.1986
1.01.1987
1.01.1988
1.01.1989
1.01.1990
1.01.1991
1.01.1992
1.01.1993
1.01.1994
1.01.1995
1.01.1996
1.01.1997
1.01.1998
1.01.1999
1.01.2000
1.01.2001
1.01.2002
1.01.2003
200.000.000
180.000.000
160.000.000
140.000.000
120.000.000
100.000.000
80.000.000
60.000.000
40.000.000
20.000.000
0
• At mid of 2005: (estimated) 350 million of hosts attached to the Internet
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Evolution in Europe
Date
Chapter 3.2: The Internet Protocol IP
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Internet and Intranet
Internet
•
Communication via the TCP/IP protocols
•
Local operators control and finance
•
Global coordination by some organizations
•
Internet Providers provide access points for private individuals
Intranet
•
Enterprise-internal communication with the same protocols and applications
as in the Internet.
Computers are sealed off from the global Internet (data security)
Heterogeneous network structures from different branches can be
integrated with TCP/IP easily
Use of applications like in the WWW for internal data exchange
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The TCP/IP Protocol Suite
HTTP
Protocols
Telnet
SMTP
DNS
Ethernet
ICMP
Token Ring
Chapter 3.2: The Internet Protocol IP
SNMP
TFTP
IP
Token Bus
ARP
Application
Layer
Transport
Layer
UDP
TCP
IGMP
Networks
FTP
RARP
Wireless LAN
Internet
Layer
Host-tonetwork Layer
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Sandglass Model
E-Mail, File Transfer,
Video Conferencing, …
HTTP, SMTP, FTP, …
Because of the small number of central
protocols but the large number of
applications and communication
networks, the TCP/IP protocol stack
(and applications/networks) can be
represented like a sandglass.
Twisted Pair, Optical Fiber,
Radio, …
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Internet Layer
Raw division into three tasks:
• Data transfer over a global network
• Route decision at the sub-nodes
• Control of the network or transmission status
Routing Protocols
Transfer Protocols:
IPv4, IPv6
Routing Tables
“Control” Protocols:
ICMP, ARP, RARP, IGMP
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IP – Internet Protocol
IP: connectionless, unreliable transmission of datagrams/packets (“Best Effort”)
• Transparent end-to-end communication between the hosts
• Routing, interoperability between different network types
• IP addressing (IPv4):
→
→
→
→
Uses logical 32-bit addresses
Hierarchical addressing
3 network classes
4 address formats (including multicast)
• Fragmenting and reassembling of packets
• Maximum packet size: 64 kByte (in practice: 1500 byte)
• At present commonly used: Version 4 of IP protocol: IPv4
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IP Packet
32 Bits (4 Bytes)
Version IHL
Type of
Service
Identification
Time to Live
Protocol
Total Length
DM
FF
Fragment Offset
Header Checksum
IP Header,
usually 20 Bytes
Source Address
Destination Address
Options (variable, 0-40 Byte)
DATA (variable)
Chapter 3.2: The Internet Protocol IP
Padding
Header
Data
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The IP Header (1)
• Version: IP version number (for simultaneous use of several IP versions)
• IHL: IP Header Length (in words of 32 bit; between 5 and 15, depending upon
options)
• Type of Service: Indication of the desired service: Combination of reliability (e.g.
file transfer) and speed (e.g. audio)
3 bit priority
(0 = normal data,
7 = control packet)
Precedence
D T R unused
Delay
Reliability
Throughput
• Total Length: Length of the entire packet (in byte, ≤ 216-1 = 65535 bytes)
• Identification: definite marking of a packet
• Time to Live (TTL): Lifetime of packets is limited to maximal 255 Hops (endless
circling of packets in the network is prevented). In principle, also the processing
time in routers is to be considered, which does not happen in practice. The
counter is reduced with each hop, with 0 the packet is discarded.
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The IP Header (2)
• DF: Don't Fragment. All routers must forward packets up to a size of 576 byte,
everything beyond that is optional. Larger packets with set DF-bit therefore cannot
take each possible way in the network.
• MF: More Fragments. “1” - further fragments follow. “0” - last fragment of a
datagram)
• Fragment Offset: Sequence number of the fragments of a packet (213 = 8192
possible fragments). The offset states, at which place of a packet (counted in
multiples of 8 byte) a fragment belongs. From this a maximum length of 8192 * 8
byte = 65536 byte results for a packet.
• Protocol: Which transport protocol is used in the data part (UDP, TCP,…)? To
which transport process the packet is to be passed on?
• Header Checksum: 1’s complement of the sum of the 16-bit half words of the
header. Must be computed with each hop (since TTL changes)
• Source Address/Destination address: Network and host numbers of sending and
receiving computer. This information is used by routers for the routing decision.
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Fragmentation
• A too large or too small packet length prevents a good performance. Additionally
there are often size restrictions (buffer, protocols with length specifications,
standards, allowed access time to a channel,…)
• The data length must be a multiple of 8 byte. Exception: the last fragment, there
only the remaining data are packed, padding to 8 byte units does not take place.
• If the “DF”-bit is set, the fragmentation is prevented.
Ident. Flags Offset
777
x00
Data
0
0
1200 bytes
IP header
777
x01
0
0
777
x01
64
511
512
777 x00 128
Chapter 3.2: The Internet Protocol IP
1023
1024
1200
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The IP Header (3)
Options: Prepare for future protocol extensions. Coverage: Multiple of 4 byte,
therefore possibly padding is necessary. At present, 5 options are defined,
however none is supported by common routers:
• Security: How secret is the transported information? (Application e.g. in
military: Avoidance of crossing of certain countries/networks.)
• Strict Source Routing: Complete path defined from the source to the
destination host by providing the IP addresses of all routers which are
crossed. (Use by system managers e.g. in case of damaged routing
tables or for time measurements)
• Loose Source Routing: The carried list of routers must be passed in
indicated order. Additional routers are permitted.
• Record Route: Recording of the IP addresses of the routers passed.
(Maximally 9 IP addresses possible, nowadays too few.)
• Time Stamp: Records router addresses (32 bits) as well as a time stamp
for each router (32 bits). Application e.g. in fault management.
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IP Addressing
• Unique IP address for each host and router.
• IP addresses are 32 bits long and are used in the Source Address as well as in
Destination Address field of IP packets.
• The IP address is structured hierarchical and refers to a certain network, i.e.
machines with connection to several networks have several IP addresses.
• Structure of the address: Network address for physical network (e.g. 137.226.0.0)
and host address for a machine in the addressed network (e.g. 137.226.12.221)
32 bits
126 networks with
224 host each
(starting from 1.0.0.0)
Class
A
0
B
10
C
110
D
1110
Multicast address
E
1111
Reserved for future use
Network
16383 networks with
216 hosts each
(starting from 128.0.0.0)
Host
Network
Host
Network
Chapter 3.2: The Internet Protocol IP
Host
2097151 networks
(LANs) with
256 hosts each
(starting from 192.0.0.0)
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IP Addresses
137.226.12.0
137.226.112.0
137.226.12.1
137.226.112.1
Router
137.226.12.21
137.226.112.78
Binary format
10001001 11100010 00001100 00010101
Dotted Decimal Notation
137.226.12.21
•
Each node has (at least) one world-wide unique IP address
•
Router or gateways, which link several networks with one another, have for each
network an assigned IP address
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IP Addresses and Routing
a
Ziel-IP
Anschluss
Netzwerkinterface
12.x.x.x
194.52.124.x
b
137.226.x.x
142.117.x.x
a
142.117.x.x
direkt
a
194.52.124.x
direkt
b
x.x.x.x
default
a
b
142.117.0.0
194.52.124.0
137.226.0.0
Chapter 3.2: The Internet Protocol IP
12.0.0.0
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IP Addressing - Examples
The representation of the 32-bit addresses is divided into 4 sections of each 8 bits:
137.226.12.174
10001001
11100010
Class B address
of RWTH Aachen
Class B address
00001100
Subnet
(Computer science 4)
10101110
Terminal
“Shadow”
Special addresses:
0 0 0 .............................................................. 0 0 0
This host
0 0 ................. 0 0
Host in this network
Host
1 1 1 .............................................................. 1 1 1
Network
127
1 1 1 ................................. 1 1 1
arbitrary
Chapter 3.2: The Internet Protocol IP
Broadcast in own local area network
Broadcast in the remote network
Loop, no sending to the network
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Address Space
6,25%
6,25%
12,50%
50,00%
Klasse
Class A
Klasse
Class B
Class C
Klasse
Class D
Klasse
Class E
Klasse
25,00%
Chapter 3.2: The Internet Protocol IP
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IP Addresses are scarce…
Problems
• Nobody had thought about such a strong growth of the Internet
(otherwise one would have defined longer addresses from the beginning).
• Too many Class A address blocks were assigned in the first Internet years.
• Inefficient use of the address space.
Example: if 500 devices in an enterprise are to be attached, a Class B address
block is needed, but by this unnecessarily more than 65.000 host addresses are
blocked.
Solution approach
Extension of the address space within IPv6 against the actual version IPv4
⇒ IP version 6 has 128 bit for addresses
⇒ 7 x 1023 IP addresses per square meter of the earth's surface (including the
oceans!)
⇒ one address per molecule on earth's surface!
But: The success of IPv6 is not by any means safe! (The introduction of IPv6 is
tremendously difficult: Interoperability, costs, migration strategies,….)
Chapter 3.2: The Internet Protocol IP
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IP Subnets
Problem: Class C-networks are very small, Class B-networks often already too
large. Therefore exists the possibility of dividing an through the IP-address
identified network into so-called subnets.
Examples for subnets: subnet mask 255.255.255.0
Ethernet A 128.10.1.0
All traffic
for 128.10.0.0
Rest
of the
Internet
128.10.1.3
Router
128.10.1.8
Ethernet
A
Host
Ethernet
A
Host
Ethernet
A
Host
128.10.2.1
Ethernet B 128.10.2.0
128.10.2.3
Ethernet
B
Host
Chapter 3.2: The Internet Protocol IP
128.10.1.70 128.10.1.26
128.10.2.133 128.10.2.18
Ethernet
B
Host
Ethernet
B
Host
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IP Subnets
• Within an IP network address block, several physical networks can be
addressed
• Some bits of the host address part are used as network ID
• A Subnet mask identifies the „abused” bits
Class B
address
Subnet
Mask
Network
Host
11111111111111111111110000000000
10
Network
Subnet
Host
• All hosts of a network should use the same subnet mask
• Routers can determine through combination of an IP address and a subnet
mask, into which subnet a packet must be sent.
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IP Subnets - Computation of the Destination
The entrance router of the RWTH, which receives the IP packet, does not know,
where host “12.21” is located.
.
12
.
21
137.
226
0111
1000
10001001
11100010
00001100
IP address
AND
255.
255.
00010101
255.
0
1111 1111 1111 1111 1111 1111 0000 0000
Subnet mask
137.
226.
12.
0
1000 1001 1110 0010 0000 1100 0000 0000
Network of the addressed host
The router computes the subnet “137.226.12” and sends the packet to the router,
which links this subnet.
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Example of a Subnet
Assigned network address for the RWTH:
137.226.0.0
137.226.12.0 Info IV
137.226.8.0
137.226.112.0
254 hosts per subnet:
• Hosts have the addresses
1 – 254
• 0 is reserved for the subnet
• 255 is reserved for broadcast
in the subnet
137.227.10.0
Subnet mask for each subnet = 255.255.255.0
Other format for writing of addresses in subnets:
137.226.12.221/24
Number of bits for “(sub)network address”
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More flexible Addressing
Problem: static categorization of IP addresses - how to use the very small class C
networks efficiently?
Remedy: Classless Inter-Domain Routing (CIDR)
Weakening of the rigid categorization by replacing the static classes by network
prefixes of variable length
• Example: 137.250.3/17: The first 17 bits of the IP address are used for the
network identification
• Used together with routing: Backbone router, e.g. on transatlantic links only
considers the first 13 bits; thus small routing tables, little cost of routing decision
• Routers of an ISP considers e.g. only the first 15 bits
• Routers in company networks consider e.g. the first 25 bits
Chapter 3.2: The Internet Protocol IP
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NAT – Network Address Translation
• Each internal computer in the Intranet needs an own IP address to communicate
with the others. For this purpose, “private” address blocks are reserved, which
everyone may use within its own networks and which are never routed in the
Internet:
• 10.0.0.0 - 10.255.255.255
• 172.16.0.0 - 172.31.255.255
• 192.168.0.0 – 192.168.255.255
• When using addresses of those range, the internal computers can communicate
with each other
• But: packets with those addresses are not forwarded by a router. Thus: routers,
which are attached to the “external world” need a global address
• Assign a few IP addresses to a company which are known by a “NAT box” which
usually is installed with the router
• When data are leaving the own network, an address translation takes place: the
NAT box exchanges the private address with a globally valid one
• Side effect: hiding of the internal network structure (security)
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NAT Variants
NAT is available in several “variants”, known under different names:
Basic NAT (also: Static NAT)
• Each private IP address is translated into one certain external IP
• Either, you need as much external addresses as private ones, otherwise no retranslation is possible when a reply arrives
• Or, you manage a pool of external IP addresses and assign one dynamically when
a request is sent out
192.168.0.2
Private IP
Currently
mapped:
137.226.12.32
192.168.0.2
137.226.12.32
192.168.0.3
137.226.12.33
192.168.0.5
137.226.12.33
192.168.0.4
137.226.12.34
---
137.226.12.34
192.168.0.5
137.226.12.35
---
137.226.12.35
Private IP
Map to
192.168.0.2
192.168.0.3
192.168.0.2
192.168.0.3
Internet
Internet
router with
NAT box
192.168.0.4
192.168.0.5
Chapter 3.2: The Internet Protocol IP
router with
NAT box
192.168.0.4
192.168.0.5
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NAT Variants
Disadvantages of static NAT:
• With static mapping, you need as much official IP addresses as you have
computers
• With dynamic mapping, you need less official IP addresses, but for times of high
traffic you nevertheless need nearly as much addresses as local computers
• Those approaches help to hide the network structure, but not to save addresses
Hiding NAT (also: NAPT: Network Address Port Translation, Masquerading)
• Translate several local addresses into the same external address
• Now: some more details are necessary to deliver a response
router with
NAT box
192.168.0.2 192.168.0.3
destination?
to: 137.226.12.32
Internet
192.168.0.4
192.168.0.5
Private IP
Map to
192.168.0.2
137.226.12.32
192.168.0.3
137.226.12.32
192.168.0.4
137.226.12.32
192.168.0.5
137.226.12.32
Chapter 3.2: The Internet Protocol IP
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NAPT – Network Address Port Translation
Protocol Port (local) IP (local) Port (global) IP (global)
IP (destination)
Port
(destination)
TCP
1066
10.0.0.1 1066
198.60.42.12 137.226.12.221
21
TCP
1500
10.0.0.7 1500
198.60.42.12 207.17.4.21
80
Chapter 3.2: The Internet Protocol IP
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Problems with NAPT
NAPT works well with communication initiated from the Intranet. But: how could
someone from outside give a request to the Intranet (e.g. to the webserver)?
• NAPT box needs to be a bit more “intelligent”
• Some static information has to be stored, e.g. “each incoming request with port 80
has to be mapped to the private address of the webserver”
• Still problems with applications like e.g. ICQ
• Thus, only more IP addresses really help to solve the problem
Chapter 3.2: The Internet Protocol IP
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The new IP - IPv6
IPv6 (December 1995, RFC 1883)
Publication of the standard (January 1995, RFC 1752)
Specification for IPng (December 1994, RFC 1726)
First requirements for IPng (December 1993, RFC 1550)
.
Simpler structure of the headers
More automatism
Simpler configuration
Performance improvements
Migration strategies
More security
Larger address space
IPv4 (September 1981, RFC 791)
Chapter 3.2: The Internet Protocol IP
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Lehrstuhl für Informatik 4
Kommunikation und verteilte Systeme
IPv6
Why changing the protocol, when IPv4 works well?
• Dramatically increasing need for new IP addresses
• Improved support of real time applications
• Security mechanisms (Authentication and data protection)
• Differentiation of types of service, in particular for real time applications
• Support of mobility (hosts can go on journeys without address change)
• Simplification of the protocol in order to ensure a faster processing
• Reduction of the extent of the routing tables
• Option for further development of the protocol
Chapter 3.2: The Internet Protocol IP
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Lehrstuhl für Informatik 4
Kommunikation und verteilte Systeme
IPv6 - Characteristics
• Address size
– 128-bit addresses (8 groups of each 4 hexadecimal numbers)
• Improved option mechanism
– Simplifies and accelerates the processing of IPv6 packets in routers
• Auto-configuration of addresses
– Dynamic allocation of IPv6-addresses
• Improvement of the address flexibility
– Anycast address: Reach any one out of several
• Support of the reservation of resources
– Marking of packets for special traffic
• Security mechanisms
– Authentication and Privacy
• Simpler header structure:
– IHL: redundant, no variable length of header by new option mechanism
– Protocol, fragmentation fields: redundant, moved into the options
– Checksum: Already done by layer 2 and 4
Chapter 3.2: The Internet Protocol IP
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Lehrstuhl für Informatik 4
Kommunikation und verteilte Systeme
IPv6 Main Header
• Version: IP version number
• Priority: 4 bits for priority. 1 - News, 4 ftp, 6 - telnet, 8 to 15 - real time traffic
• Flow label: virtual connection with certain
characteristics/requirements
• PayloadLen: packet length after the 40byte header
• Next Header: 8-bit selector. Indicates the
type of the following extension header (or
the transport header)
• HopLimit: At each node decremented by
one. At zero the packet is discarded
• Source Address: The address of the
original sender of the packet
• Destination Address: The address of the
receiver (not necessarily the final
destination, if there is an optional routing
header)
• Next Header/Data: if an extension header
is specified, it follows after the main
header. Otherwise, the data are following
Chapter 3.2: The Internet Protocol IP
1
4
Version
(4)
16
8
Priority
(4)
24
32
Flow label (24)
PayloadLen (16)
Next Header (8)
HopLimit (8)
Source Address (128)
Destination Address (128)
Next Header/Data
The prefix of an address characterizes
geographical areas, providers, local internal
areas,…
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Lehrstuhl für Informatik 4
Kommunikation und verteilte Systeme
IPv6 Extension Headers
Optional data follows in extension headers. There are 6 headers defined:
• Hop by Hop (information for single links)
All routers have to examine this field. Momentarily only the support of
Jumbograms (packets exceeding the normal IP packet length) is defined (length
specification).
• Routing (definition of a full or partly specified route)
• Fragmentation (administration of fragments)
Difference to IPv4: Only the source can do fragmentation. Routers for which a
packet is too large, only send an error message back to the source.
• Authentication (of the sender)
• Ciphered data
• Destination options (additional information for the destination)
Chapter 3.2: The Internet Protocol IP
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Lehrstuhl für Informatik 4
Kommunikation und verteilte Systeme
IPv4 vs. IPv6: Header
4
VerEn
sion
8
IHL
16
Type
TypeOF
of
Service
service
Identification
Time to
Live
32
Totally
Total Length
length
Fragment offset
Protocol
Header Checksum
4
8
16
VerEn PrioPrio
sion rity
32
Flow
Flow Label
label
PayloadLen
Next
NEXT
Header
headers
Hop
Hop Limit
limit
SOURCE
Source ADDRESS
Address
SOURCE
Source ADDRESS
Address
SOURCE
Source ADDRESS
Address
Destination
DestinationADDRESS
Address
SOURCE
Source ADDRESS
Address
Options
Option (variable)/Padding
(variable)/Padding
SOURCE
Source ADDRESS
Address
DATA
Data
Destination
DestinationADDRESS
Address
Destination
DestinationADDRESS
Address
The IPv6 header is longer, but this is only
caused by the longer addresses.
Otherwise it is “better sorted” and thus
faster to process by routers.
Chapter 3.2: The Internet Protocol IP
Destination
DestinationADDRESS
Address
Destination
DestinationADDRESS
Address
NEXT
Next Header
header/DATA
/ Data
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Kommunikation und verteilte Systeme
Coexistence of IPv4 and IPv6
IPv6 cannot be introduced “over night”… for some time both IP variants will be used in
parallel.
• New network interface card drivers support both versions of IP, thus they are able to
communicate with the newer version
• But: how to enable two modern IPv6-based hosts to communicate if only an IPv4based network is in between?
1. Header Conversion
Router translates an incoming IPv6 packet into a IPv4
packet, receiving router retranslates
payload
IPv6
header
payload
IPv4
header
But: reconstruction
of e.g. flow label???
payload
IPv6
header
Internet
mostly IPv4
IPv6 network
Routers which “speak” IPv4 and IPv6 in parallel
Chapter 3.2: The Internet Protocol IP
IPv6 network
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Lehrstuhl für Informatik 4
Kommunikation und verteilte Systeme
Coexistence of IPv4 and IPv6
2. Tunneling
Router at the entry to the IPv4-based network encapsulate an incoming IPv6 packet
into a new IPv4 packet with destination address of the next router also supporting IPv6
payload
IPv6
header
payload
IPv6
header
IPv4
header
payload
IPv6
header
Internet
mostly IPv4
IPv6 network
IPv6 “tunnel” through IPv4
IPv6 network
• More overhead because of two headers for one packet, but no information
loss due to header conversion
Tunneling is a general concept also used for multicast, VPN, etc: it simply
means “pack a whole packet as it is into a new packet of different protocol”
Chapter 3.2: The Internet Protocol IP
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Lehrstuhl für Informatik 4
Kommunikation und verteilte Systeme
Virtual Private Network (VPN)
•
•
•
•
By a Virtual Private Network (VPN) a network infrastructure is understood, in
which distributed components belonging to one logical private network
communicate with one another over a public network (e.g. Internet)
VPNs are used frequently for the connection of geographically distributed
organizations (Intranet in the Internet)
VPNs ensure authenticated access and permit the protection of sensitive data in
distributed networks by encryption of data
The logical connection between private components over a public network is
achieved again by tunneling an IPv4 connection with e.g. IPsecure
VPN
Chapter 3.2: The Internet Protocol IP
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Lehrstuhl für Informatik 4
Kommunikation und verteilte Systeme
Tunneling Mechanism
Tunneling here:
Encapsulate packets into
encrypted IP packets, e.g. by
using IPsecure. Packets
directed to the remote network
part by this remain unchanged,
but are the payload of an
encrypted packet.
Chapter 3.2: The Internet Protocol IP
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