Future Internet Technologies

Dr. Dennis Pfisterer

Institut für Telematik, Universität zu Lübeck http://www.itm.uni-luebeck.de/people/pfisterer

Future Internet Technologies

Traditional Internet

•  Packet-Switched Datagram Service

–  Each packet is independent from any other packet

–  Routing is done on a per-packet basis

•  Routing Tables used to select next hop

–  i.e., which link to use •  Best-effort Service

–  No guarantees regarding QoS, in-order delivery, real-time, …

IPv4 Model

–  Header Length in multiples of 32-bit (>5)

•  Type of Service (8 bit) – now obsolete

–  Precedence: 7=High, 0=Normal

–  ToS: 8=min. Delay, 4=max. Throughput, 2=max. Reliability, 0=normal

IPv4 packet format

6-4

0 4 8 16

VersionHdrLen Type of service

Identification

Time to live Protocol

19 31

Total length

Flags Fragment offset

•  Total length (16 bit)

–  Including Header

•  Identification (16 bit)

–  Used for fragmentation

•  Flags (3 bit)

–  D = Don’t fragment, M = More Fragments

•  Fragment offset

–  Offset in multiples of 8 Byte

IPv4 packet format

6-5

0 1 2 - D M

0 4 8 16

Version HdrLen Type of service Identification Time to live Protocol

19 31

Total length Flags Fragment offset

Header checksum Source address Destination address Bits: 20 octets Options + padding Data (! 65536 octets)

•  Time To Live (8 bit)

–  Decremented at each hop, packet dropped if zero is reached

•  Protocol (8bit)

–  Indicates next protocol (upper layer protocol such as UDP=17/TCP=6) •  Header Checksum (16 bit)

–  CRC-16 (complete header)

•  Source- and Destination IP-Address (32 bit) •  Options

–  Security, Source routing, …

IPv4 packet format

6-6

0 4 8 16

Version HdrLen Type of service Identification Time to live Protocol

19 31

Total length Flags Fragment offset

Some Protocol Numbers

7

• See http://www.iana.org/assignments/protocol-numbers/ for reference • Unix lists these well-known numbers in /etc/protocols

•  IP packets are transported over a variety of networks

–  Each network has a maximum transmission unit (MTU) –  Examples

•  Ethernet (1500 bytes) •  ATM (multiples of 48 bytes) •  PPPoE (1480 bytes)

•  X.25 (576 bytes) •  FDDI (4352 bytes)

•  Sender and receiver only know the link’s local MTU

–  The maximum path MTU is unknown

IPv4 Fragmentation

9

•  IP packets may exceed a link’s MTU

•  IP packet size > MTU

–  Must be split into fragments smaller than the current MTU

•  Fragmentation options

–  Transparent fragmentation –  Non-transparent fragmentation

IPv4 Fragmentation

•  Transparent fragmentation

–  Fragmentation and reassembly performed on each link

•  Non-transparent fragmentation

–  Fragmentation at each intermediate station, reassembly at destination

•  IP: Non-transparent fragmentation

IPv4 Fragmentation

11

Ver HL TOS Total length Identification D,M Fragment offset TTL Protocol Header checksum

...

Flags: D = Don’t fragment M = More fragments

Relevant fields in IP packet header:

•  Split up packets into segments smaller than MTU (including IP header, 20-60 bytes)

•  Compute new value for Total Length

•  Set “More Fragments”-bit, except for the last fragment •  Compute “Fragment Offset” value

–  Multiple of 8 bytes, offset of the data in the original packet

•  Re-Compute header checksum

IP Packet Fragmentation

12

Ver HL TOS Total length Identification D,M Fragment offset TTL Protocol Header checksum

...

Flags: D = Don’t fragment M = More fragments

•  Fragmented packet arrives if either

–  “More Fragments" flag is set

–  “Fragment Offset" field is non-zero

•  Store all related packets (final size yet unknown) •  Wait until packet with MF=0 arrives

–  Original IP packet length: Fragment Offset + Total Length

•  Reassemble packet in original order

IPv4 Reassembly

13

Ver HL TOS Total length Identification D,M Fragment offset TTL Protocol Header checksum

...

Flags: D = Don’t fragment M = More fragments

Relevant fields in IP packet header:

•  32-bit " 232 _{# 4.29 Billion addresses (in theory)}

–  Some reserved (e.g., private networks: ~18 million, multicast : ~270 million)

•  Types of Addresses –  Unicast

•  Identifies a single network interface (multiple interfaces: multi-homing) •  May be used as source- and destination address

–  Broadcast

•  Addresses all hosts in a certain scope (e.g., on a link), only as destination –  Multicast

•  Addresses a group of interfaces (hosts)

IPv4 Adressing

31 24 23 16 15 8 7 0

11010100 01111110 11010000 10000111

212 . 126 . 208 . 135 Binary value:

Dotted decimal notation:

•  How to structure the address space?

•  Goals

–  Hierarchical address allocation and routing –  Support for multi- and broadcasting

•  History

–  ARPANET: highest 8 bit as network identifier: 254 networks –  RFC 791, 1981: Classful IP addressing

–  Later: additional levels of hierarchy (1985-1987)

–  1993-Until today: Classless Inter-Domain Routing (CIDR)

Evolution of IPv4 Addressing

•  Address space divided into 5 classes

–  Fixed prefix (1-4 bit) depending on the network class

IPv4: Classful Addressing

17

Class Prefix Address Range Networks Hosts

A 0 001.0.0.0 - 127.255.255.255 128 16M

B 10 128.0.0.0 - 191.255.255.255 16k 65k

C 110 192.0.0.0 - 223.255.255.255 2M 256

D 1110 224.0.0.0 - 239.255.255.255 268M groups

E 1111 240.0.0.0 - 255.255.255.255 reserved

•  Networks assigned by Internet Assigned Numbers Authority (IANA) •  Host identifiers assigned by local authority (e.g., an administrator)

IPv4: Classful Addressing

18

8 bits (128 nets) 24 bits (224 _{# 16M hosts)}

0 network host

16 bits (214 _{nets # 16K hosts) 16 bits (2}16 _{# 65K hosts)}

10 network host

24 bits (221 _{# 2 M nets) 8 bits (256 hosts)} 110 network host

28 bits (228 _groups)

1110 multicast group address

IPv4: Classful Addressing: Special Addresses

19

Network Host Description

net-id All 0 Network Address: Not a source/destination but defines a network (e.g., for routing).

Example: 212.126.208.0 (net-id 212: Class C)

net-id All 1 Broadcast Address: Destination of a packet. Addresses all stations of a network.

Example: 212.126.208.255

All 1 All 1

Network-Broadcast Address: Destination address only. Addresses all hosts of a network. Not forwarded by routers.

Example: 255.255.255.255

127 Arbitrary Loopback Address: Useful for tests, local host.

Example: 127.0.0.1, 127.34.43.1

All 0 host-id _{or all 0} Special address for bootstrapping (e.g., DHCP)

Example: 0.0.0.0

•  Network sizes

–  Class C: 256 hosts ! to few for an organization

–  Class B: 65K hosts ! too much for most organizations –  Class A: 16mio. hosts ! only for large ISPs

•  Problems

–  Fixed class sizes led to IP address exhaustion

–  Many IP addresses were unused but could not be reassigned –  Routers experienced heavy loads

–  Large routing tables: No route aggregation possible

! Sub-networks were created by splitting the host into sub-network/host

IPv4: Subnetting

•  Advantages

–  Subnetworks give additional structure to the host part

–  Routers are agnostic to this structure ! only one routing table entry •  Subnetmasks describe structure of IP addresses –  Information no longer contained in the IP address

IPv4: Subnetting

Address Structure for address block assigned to a network:

network host

Address structure for subnetted network:

network subnet host

Example: Assigned Class B network address block

network host

Example: Subnetting with 8 subnet bits, 8 host bits (256 hosts/subnet)

network subnet host

Binary subnet mask:

11111111 11111111 11111111 00000000

Dotted-decimal subnet mask:

255. 255. 255. 0

•  Subnetting creates sub-networks of equal size

•  Problems

–  Still an inefficient use of IP addresses –  IP address space exhausted in the 1990s –  Nearly no route aggregation possible

(Backbone router would need to store 2mio. entries only for Class C networks)

•  Solution

–  Classless Inter-Domain Routing (CIDR)

IPv4: Subnetting

Classless Inter-Domain Routing (CIDR)

•  Replaces fixed <network, sub-network, host>

structure

•  Arbitrary network/host size (2

_{, 2}

₎

•  Networks are specified using /N syntax

–  Example: 212.126.208.0/24

•  Allows upstream path aggregation

–  Smaller routing tables

Classless Inter-Domain Routing (CIDR)

Example: Classless Inter-Domain Routing (CIDR)

Router R0 - Routing table Route Interf. Next hop 200.10.0.0/17 s1 R1 200.10.128.0/18 s2 R2

... ... ...

Router R1 - Routing table Route Interf. Next hop 200.10.0.0/21 s1 R11 200.10.8.0/22 s2 R12 200.10.12.0/23 s3 R13 200.10.14.0/24 s4 R14

... ... ...

•  Routing decision based on prefixes

–  Prefix length not evident from IP address (use of CIDR /xx syntax mandatory)

–  Address allocation based on topology (ISP ! reseller ! customer)

–  Must be signaled out of band (e.g., BGP)

•  Routing tables entries may contain overlapping

entries

–  A longer prefix is more specific

–  Routing uses longest prefix match to select outgoing link

CIDR: Properties

•  Entries: 192.168.20.16/28 & 192.168.0.0/16

•  IP-Address to match: 192.168.20.19

•  Both network masks “match” ! /28 is used

CIDR: Longest Prefix Match (Examples)

27

IP / Netmask IP / Netmask [binary notation]

192.168.20.16/28 /28 11111111 11111111 11111111 11110000 Entry 11000000 10101000 00010100 00010000 192.168.20.19 IP 11000000 10101000 00010100 00010011 192.168.0.0/16 /16 11111111 11111111 00000000 00000000 Entry 11000000 10101000 00000000 00000000 192.168.20.19 IP 11000000 10101000 00010100 00010011

•  CIDR provides better address space utilization

–  Without CIDR: address space exhaustion in the 1990s –  Still, the 232 _{limit sustains}

–  Prediction: Last IP addresses assigned 2012 [potaroo.net]

•  Current countermeasures

–  Network address translation (NAT)

–  Dynamic Host Configuration Protocol (DHCP) –  HTTP Name-based virtual hosting

–  Network renumbering (reclaim IP address blocks space allocated in the early days of the Internet)

–  Use of IPv6

CIDR: Limitations

•  [potaroo.net] IPv4 Address Report, http://

www.potaroo.net/tools/ipv4/index.html

Literature