COMS/CSEE 4140 Networking Laboratory Lecture 02

Salman Abdul Baset Spring 2008

Previous lecture…

 Introduction to the lab equipment  A simple TCP/IP example  Overview of important networking concepts 2

Previous lecture…

Web request Web page

Web client Web server

 A user on host argon.netlab.edu (“Argon”) makes web access to URL http://neon.netlab.edu/index.html.  What actually happens in the network? 3

Agenda

 Administrivia  MICE access, lab groups.

 Data Link Protocols  Address Resolution Protocol (ARP)  Internet Protocol (IP) 4

Terminology

 Frame  Data link layer terminology for a data unit  Includes error correction  Packet  Network layer and above  PDU  Protocol specific 5

TCP/IP Suite and OSI Reference Model

• The TCP/IP protocol stack does not define the lower layers of a complete protocol stack Application Layer •How does the TCP/IP protocol stack interface with the data link layer?

Transport Layer Network Layer (Data) Link Layer Logical Link Control (LLC) Media Access Control (MAC) Sublayer in Local Area Networks 6

Data Link Layer

 The main tasks of the data link layer are:  Transfer data from the network layer of one machine to the network layer of another machine  Convert the raw bit stream of the physical layer into groups of bits (“ frames ”) Network Layer Data Link Layer Physical Layer Network Layer Data Link Layer Physical Layer 7

Two types of networks at the data link layer

  Broadcast Networks : All stations share a single communication channel Point-to-Point Networks: directly connected Pairs of hosts (or routers) are Broadcast Network Point-to-Point Network  Typically, local area networks (LANs) are broadcast and wide area networks (WANs) are point-to-point 8

Local Area Networks

     Local area networks (LANs) connect computers within a building or a enterprise network Almost all LANs are broadcast networks Typical topologies of LANs are bus or ring or star We will work with Ethernet LANs. Ethernet has a bus or star topology.

Comparing topologies: workstation vs. cable failure?

Ring LAN Star LAN 9 Bus LAN

MAC and LLC

    In any broadcast network, the stations must ensure that only one station transmits at a time on the shared communication channel The protocol that determines who can transmit on a broadcast channel are called Medium Access Control (MAC) protocol

to Network Layer

The MAC protocol are implemented in the MAC sublayer which is the lower sublayer of the data link layer Logical Link Control Medium Access Control The higher portion of the data link layer is often called Logical Link

to Physical Layer

Control (LLC) 10

IEEE 802 Standards

 IEEE 802 is a family of standards for LANs, which defines an LLC and several MAC sublayers IEEE 802 standard 802.1

IEEE Reference Model Higher Layer 802.2

Logical Link Control Data Link Layer Medium Access Control Physical Layer Physical Layer 11

Ethernet and IEEE 802.3: Any Difference?

 There are two types of Ethernet frames in use, with subtle differences: 

“Ethernet” (Ethernet II, DIX)

  An industry standards from 1982 that is based on the first implementation of CSMA/CD by Xerox.

Predominant version of CSMA/CD in the US.



802.3:

  IEEE’s version of CSMA/CD from 1985.

Interoperates with 802.2 (LLC) as higher layer.



Difference for our purposes:

802.3 use different methods to encapsulate an IP datagram.

Ethernet and 12

Ethernet II, DIX Encapsulation (RFC 894)

802.3 MAC

destination address 6 source address 6 type 2 0800 2 0806 2 0835 2 data 46-1500 IP datagram 38-1492 ARP request/reply PAD 28 10 RARP request/reply PAD 28 10 CRC 4

13

IEEE 802.2/802.3 Encapsulation (RFC 1042)

802.3 MAC 802.2 LLC 802.2 SNAP

destination address 6 source address 6 length DSAP AA SSAP AA 2 1 1 cntl 03 org code 0 1 3 type 2

-

destination address, source address:

MAC addresses are 48 bit -

length

: frame length in number of bytes -

DSAP, SSAP

: always set to 0xaa -

Ctrl:

set to 3 -

org code:

-

type field

set to 0 identifies the content of the -

CRC:

data field cylic redundancy check

0800 2 0806 2 0835 2 data 38-1492 IP datagram 38-1492 ARP request/reply PAD 28 28 10 RARP request/reply PAD 10 CRC 4

14

Ethernet

 Speed: 10 Mbps -10 Gbps  Standard: 802.3, Ethernet II (DIX)  Most popular physical layers for Ethernet:        10Base5 10Base2 10Base-T 100Base-TX 100Base-FX 1000Base-FX 10000Base-FX Thick Ethernet: 10 Mbps coax cable Thin Ethernet: 10 Mbps coax cable 10 Mbps Twisted Pair 100 Mbps over Category 5 twisted pair 100 Mbps over Fiber Optics 1Gbps over Fiber Optics 10Gbps over Fiber Optics (for wide area links) 15

Bus Topology

 10Base5 and 10Base2 Ethernets have a bus topology

Ethernet

16

Star Topology

 Starting with 10Base-T, stations are connected to a hub in a star configuration

Hub

17

Ethernet Hubs vs. Ethernet Switches

 An

Ethernet switch

frames   is a packet switch for Ethernet Buffering of frames prevents collisions. Each port is isolated and builds its own collision domain  An

Ethernet Hub

 does not perform buffering: Collisions occur if two frames arrive at the same time.

Hub Switch

CSMA/CD CSMA/CD CSMA/CD CSMA/CD CSMA/CD CSMA/CD CSMA/CD CSMA/CD CSMA/CD CSMA/CD CSMA/CD CSMA/CD CSMA/CD CSMA/CD CSMA/CD CSMA/CD Input Buffers Output Buffers 18

Point-to-Point (serial) links

 Many data link connections are point-to-point serial links:   Dial-in or DSL access connects hosts to access routers Routers are connected by high-speed point-to-point links

Access Router Modems

Dial-Up Access  Here, IP hosts and routers are connected by a serial cable

Router

 Data link layer protocols for point-to-point links are simple:   Main role is encapsulation of IP datagrams No media access control needed

Router Router

Point-to-Point Links

Router

19

Data Link Protocols for Point-to Point links



SLIP (Serial Line IP) (RFC 1055)

  First protocol for sending IP datagrams over dial-up links (from 1988) Encapsulation, not much else 

PPP (Point-to-Point Protocol) (RFC 1661)

• • Successor to SLIP (1992), with added functionality Used for dial-in and for high-speed routers 

HDLC (High-Level Data Link) (ISO)

• • • Widely used and influential standard (1979) Default protocol for serial links on Cisco routers Actually, PPP is based on a variant of HDLC 20



PPP - IP encapsulation

The frame format of PPP is similar to HDLC and the 802.2 LLC frame format:

flag addr ctrl protocol data CRC flag 7E

1

FF

1

03

1 2 <= 1500 2

7E

1

0021 IP datagram C021 link control data 8021 network control data

   PPP assumes a duplex circuit Note: PPP does not use addresses Usual maximum frame size is 1500 21

Additional PPP functionality

 In addition to encapsulation, PPP supports:   multiple network layer protocols (protocol multiplexing) Link configuration      Link quality testing Error detection Option negotiation Address notification Authentication  The above functions are supported by helper protocols:    LCP PAP, CHAP NCP 22

PPP Support protocols



Link management:

The link control protocol (LCP) is responsible for establishing, configuring, and negotiating a data-link connection. LCP also monitors the link quality and is used to terminate the link.



Authentication:

Authentication is optional. PPP supports two authentication protocols: Password Authentication Protocol (PAP) and Challenge Handshake Authentication Protocol (CHAP).



Network protocol configuration:

used as network layer.

PPP has network control protocols (NCPs) for numerous network layer protocols. The IP control protocol (IPCP) negotiates IP address assignments and other parameters when IP is 23

Agenda

 Administrivia  Data Link Protocols  Address Resolution Protocol (ARP)  Internet Protocol (IP) 24

Overview

ICMP

ARP

TCP IP Network Access Media UDP Transport Layer IGMP Network Layer

RARP

Link Layer 25

ARP (RFC 826) and RARP (RFC 903)

   Note:   The Internet is based on IP addresses Data link protocols (Ethernet, FDDI, ATM) may have different (MAC) addresses The ARP and RARP protocols perform the translation between IP addresses and MAC layer addresses We will discuss ARP for broadcast LANs, particularly Ethernet LANs

IP address (32 bit) ARP RARP Ethernet MAC address (48 bit)

26

Processing of IP packets by network device drivers

IP Output IP Input Put on IP input queue

Yes Yes loopback Driver

IP destination = multicast or broadcast ?

No

IP destination of packet = local IP address ?

Put on IP input queue

Ethernet Driver IP datagram

No: get MAC address with ARP

ARP

ARP Packet demultiplex Ethernet Frame Ethernet 27

Topology

Web client

Web request Web page

Web server

 A user on host argon.netlab.edu (“Argon”) makes web access to URL http://neon.netlab.edu/index.html.  What actually happens in the network? 28

Address Translation with ARP

ARP Request: Argon broadcasts an ARP request to all stations on the network:

“What is the hardware address of Router137?”

Argon 128.143.137.144

00:a0:24:71:e4:44 Router137 128.143.137.1

00:e0:f9:23:a8:20

ARP Request:

What is the MAC address of 128.143.71.1?

29

Address Translation with ARP

ARP Reply: Router 137 responds with an ARP Reply which contains the hardware address Argon 128.143.137.144

00:a0:24:71:e4:44 Router137 128.143.137.1

00:e0:f9:23:a8:20

ARP Reply:

The MAC address of 128.143.71.1

is 00:e0:f9:23:a8:20 30

ARP Packet Format

Ethernet II header Destination address 6 Source address 6 Type 0x8060 2 ARP Request or ARP Reply 28 Padding 10 CRC 4 Hardware type (2 bytes) Hardware address length (1 byte) Protocol address length (1 byte) Source hardware address* Protocol type (2 bytes) Operation code (2 bytes) Source protocol address* Target hardware address* Target protocol address* * Note: The length of the address fields is determined by the corresponding address length fields 31

Example



ARP Request from Argon:

Source hardware address: 00:a0:24:71:e4:44 Source protocol address: 128.143.137.144

Target hardware address: 00:00:00:00:00:00 Target protocol address: 128.143.137.1



ARP Reply from Router137:

Source hardware address: 00:e0:f9:23:a8:20 Source protocol address: 128.143.137.1 Target hardware address: 00:a0:24:71:e4:44 Target protocol address: 128.143.137.144

32

ARP Cache

 Since sending an ARP request/reply for each IP datagram is inefficient, hosts maintain a cache (ARP Cache) of current entries. The entries expire after 20 minutes.

 Contents of the ARP Cache: (128.143.71.37) at 00:10:4B:C5:D1:15 [ether] on eth0 (128.143.71.36) at 00:B0:D0:E1:17:D5 [ether] on eth0 (128.143.71.35) at 00:B0:D0:DE:70:E6 [ether] on eth0 (128.143.136.90) at 00:05:3C:06:27:35 [ether] on eth1 (128.143.71.34) at 00:B0:D0:E1:17:DB [ether] on eth0 (128.143.71.33) at 00:B0:D0:E1:17:DF [ether] on eth0 33

Proxy ARP

 Proxy ARP: Host or router responds to ARP Request that arrives from one of its connected networks for a host that is on another of its connected networks. 34

Things to know about ARP

 What happens if an ARP Request is made for a non existing host?

Several ARP requests are made with increasing time intervals between requests. Eventually, ARP gives up.

 On some systems (including Linux) a host periodically sends ARP Requests for all addresses listed in the ARP cache. This refreshes the ARP cache content, but also introduces traffic.

 Gratuitous ARP Requests: for its own IP address:  A host sends an ARP request Useful for detecting if an IP address has already been assigned.

35

Vulnerabilities of ARP

1.

2.

3.

Since ARP does not authenticate requests or replies, ARP Requests and Replies can be forged ARP is stateless: ARP Replies can be sent without a corresponding ARP Request According to the ARP protocol specification, a node receiving an ARP packet (Request or Reply) must update its local ARP cache with the information in the source fields, if the receiving node already has an entry for the IP address of the source in its ARP cache. (This applies for ARP Request packets and for ARP Reply packets) Typical exploitation of these vulnerabilities:  A forged ARP Request or Reply can be used to update the ARP cache of a remote system with a forged entry ( ARP Poisoning )  This can be used to redirect IP traffic to other hosts 36

Agenda

 Administrivia  Data Link Protocols  Address Resolution Protocol (ARP)  Internet Protocol (IP) 37

IP Addresses

 Structure of an IP address  Classful IP addresses  Limitations and problems with classful IP addresses  Subnetting  CIDR  IP Version 6 addresses 38

IP Addresses

32 bits version (4 bits) header length Type of Service/TOS (8 bits) Identification (16 bits) TTL Time-to-Live (8 bits) Protocol (8 bits) flags (3 bits) Total Length (in bytes) Source IP address (32 bits) (16 bits) Fragment Offset (13 bits) Header Checksum (16 bits) Destination IP address (32 bits)

Ethernet Header

IP Header

TCP Header Ethernet frame Application data Ethernet Trailer 39

IP Addresses

0x4 128 10 0x5 9d08 32 bits 0x00 010 2 0x06 128.143.137.144

128.143.71.21

44 10 0000000000000 2 8bff

Ethernet Header

IP Header

TCP Header Ethernet frame Application data Ethernet Trailer 40

What is an IP Address?

  An IP address is a unique global address for a network interface Exceptions:  Dynamically assigned IP addresses (  DHCP, Lab 7)  IP addresses in private networks (  NAT, Lab 7)  An IP address: - is a

32 bit long

identifier - encodes a network number (

network prefix

) and a

host number

41

Network prefix and host number

 The network prefix identifies a network and the host number identifies a specific host (actually, interface on the network).

network prefix host number



How do we know how long the network prefix is?

 Before 1993: The network prefix is implicitly defined (

class based addressing

)

or

 After 1993: The network prefix is indicated by a

netmask.

42

Dotted Decimal Notation

  IP addresses are written in a so-called

dotted decimal

notation

Each byte is identified by a decimal number in the range [0..255]: 

Example: 10000000

1 st Byte

= 128 10001111

2 nd Byte

= 143 10001001

3 rd Byte

= 137 10010000

4 th Byte

= 144

43

128.143.137.144

Example



Example

: ellington.cs.virginia.edu

128.143

137.144

   Network address is: Host number is: Netmask is:

128.143.0.0 (or 128.143) 137.144

255.255.0.0

(or

ffff0000)

 Prefix or CIDR notation:

128.143.137.144/16

 Network prefix is 16 bits long 44

  

Special IP Addresses

Reserved or (by convention) special addresses: Loopback interfaces

 all addresses 127.0.0.1-127.255.255.255 are reserved for loopback interfaces   Most systems use 127.0.0.1 as loopback address loopback interface is associated with name “localhost”

IP address of a network

  Host number is set to all zeros, e.g., 128.143.0.0

Broadcast address

Host number is all ones, e.g., 128.143.255.255   Broadcast goes to all hosts on the network Often ignored due to security concerns

Test / Experimental addresses

Certain address ranges are reserved for “experimental use”. Packets should get dropped if they contain this destination address (see RFC 1918): 10.0.0.0 - 10.255.255.255

172.16.0.0

- 172.31.255.255

 192.168.0.0

- 192.168.255.255

Convention (but not a reserved address)

Default gateway has host number set to ‘1’, e.g., e.g., 192.0.1.1 45

Special IPv4 Addresses ( RFC 3330)

Addresses CIDR Equivalent Purpose RFC Class # of addresses

0.0.0.0 - 0.255.255.255

0.0.0.0/8 Zero Addresses

RFC 1700 A 16,777,216 10.0.0.0 - 10.255.255.255

10.0.0.0/8 Private IP addresses

127.0.0.0 - 127.255.255.255

127.0.0.0/8

169.254.0.0 - 169.254.255.255

169.254.0.0/16

172.16.0.0 - 172.31.255.255

172.16.0.0/12 Localhost Loopback Address Zeroconf

192.0.2.0 - 192.0.2.255

192.88.99.0 - 192.88.99.255

192.168.0.0 - 192.168.255.255

198.18.0.0 - 198.19.255.255

224.0.0.0 - 239.255.255.255

240.0.0.0 - 255.255.255.255

192.0.2.0/24 192.88.99.0/24 192.168.0.0/16 198.18.0.0/15 224.0.0.0/4 240.0.0.0/4 Private IP addresses Documentation and Examples IPv6 to IPv4 relay Anycast Private IP addresses Network Device Benchmark Multicast Reserved

RFC 1918 RFC 1700 RFC 3330 RFC 1918 RFC 3330 RFC 3068 RFC 1918 RFC 2544 RFC 3171 RFC 1700 A A B B C C C C D E 16,777,216 16,777,216 65,536 1,048,576 256 256 65,536 131,072 268,435,456 46 268,435,456

Subnetting



Problem

managed : Organizations have multiple networks which are independently   Solution 1: Allocate a separate network address for each network  Difficult to manage  From the outside of the organization, each network must be addressable.

Solution 2:

Add another level of hierarchy to the IP addressing structure University Network Engineering School Medical School Library

Subnetting

47

Address Assignment with Subnetting

  Each part of the organization is allocated a range of IP addresses (subnets or subnetworks) Addresses in each subnet can be administered locally

128.143.0.0/16

University Network

128.143.71.0/24 128.143.136.0/24

Engineering School Medical School

128.143.56.0/24

Library

128.143.121.0/24

48

 

Basic Idea of Subnetting

Split the host number portion of an IP address into a

subnet number

and a (smaller)

host number

.

Result is a 3-layer hierarchy

network prefix host number network prefix subnet number host number



extended network prefix

Then:    Subnets can be freely assigned within the organization Internally, subnets are treated as separate networks Subnet structure is not visible outside the organization 49



Subnetmask

Routers and hosts use an

extended network prefix

(

subnetmask)

to identify the start of the host numbers

128.143

137.144

network prefix host number

128.143

137 144

network prefix extended network prefix subnet number host number

1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 0 0 0 0 0 0 0 0

subnetmask 50

Advantages of Subnetting

 With subnetting, IP addresses use a 3-layer hierarchy:    Network Subnet Host  Reduces router complexity. Since external routers do not know about subnetting, the complexity of routing tables at external routers is reduced.

 Note: Length of the subnet mask need not be identical at all subnetworks.

51

Example: Subnetmask

  128.143.0.0/16 is the IP address of the network 128.143.137.0/24 is the IP address of the subnet   128.143.137.144 is the IP address of the host 255.255.255.0 (or ffffff00) is the subnetmask of the host    When subnetting is used, one generally speaks of a “subnetmask” (instead of a netmask) and a “subnet” (instead of a network) Use of subnetting or length of the subnetmask if decided by the network administrator Consistency of subnetmasks is responsibility of administrator 52

No Subnetting

 All hosts think that the other hosts are on the same network 128.143.137.32/16 subnetmask: 255.255.0.0

128.143.137.144/16 subnetmask: 255.255.0.0

128.143.71.21/16 subnetmask: 255.255.0.0

128.143.71.201/16 subnetmask: 255.255.0.0

128.143.70.0/16 53

With Subnetting

 Hosts with same extended network prefix belong to the same network 128.143.137.32/24 subnetmask: 255.255.255.0

128.143.137.144/24 subnetmask: 255.255.255.0

128.143.71.21/24 subnetmask: 255.255.255.0

128.143.71.201/24 subnetmask: 255.255.255.0

128.143.137.0/24 Subnet 128.143.0.0/16 128.143.71.0/24 Subnet 54

With Subnetting

 Different subnetmasks lead to different views of the size of the scope of the network 128.143.137.32/26 subnetmask: 255.255.255.192

128.143.137.144/26 subnetmask: 255.255.255.192

128.143.71.21/24 subnetmask: 255.255.255.0

128.143.71.201/16 subnetmask: 255.255.0.0

128.143.137.0/26 Subnet 128.143.137.128/26 Subnet 128.143.0.0/16 192: 11000000 144: 10010000 128: 10000000 128.143.71.0/24 Subnet 55

Classful IP Adresses (Until 1993)

 When Internet addresses were standardized (early 1980s), the Internet address space was divided up into classes:   

Class A:

Network prefix is 8 bits long

Class B:

Network prefix is 16 bits long

Class C:

Network prefix is 24 bits long  Each IP address contained a key which identifies the class:   

Class A:

IP address starts with “0”

Class B:

IP address starts with “10”

Class C:

IP address starts with “110” 56

The old way: Internet Address Classes

Class A Class B Class C bit # 0

0

1 Network Prefix 8 bits 7 8 bit # 0

1 0

1 2

network id

15 16 Network Prefix 16 bits bit # 0 1 2 3

network id

Host Number 24 bits

host

Host Number 16 bits 23 24

host

31 31 31 Network Prefix 24 bits Host Number 8 bits 57

The old way: Internet Address Classes

Class D bit # 0 1 2 3

0

4

multicast group id

31 Class E bit # 0 1 2 3 4

1 0

5

(reserved for future use)

31  We will learn about multicast addresses later in this course.

58

Problems with Classful IP



Addresses

By the early 1990s, the original classful address scheme had a number of problems 

Flat address space.

Routing tables on the backbone Internet need to have an entry for each network address. When Class C networks were widely used, this created a problem. By the 1993, the size of the routing tables started to outgrow the capacity of routers.

Other problems:



Too few network addresses for large networks

  Class A and Class B addresses were gone

Limited flexibility for network addresses:

  Class A and B addresses are overkill (>64,000 addresses) Class C address is insufficient (requires 40 Class C addresses) 59

Allocation of Classful Addresses

60

CIDR - Classless Interdomain Routing

   IP backbone routers have one routing table entry for each network address:   With subnetting, a backbone router only needs to know one entry for each Class A, B, or C networks This is acceptable for Class A and Class B networks   2 7 2 14 = 128 Class A networks = 16,384 Class B networks  But this is not acceptable for Class C networks  2 21 = 2,097,152 Class C networks In 1993, the size of the routing tables started to outgrow the capacity of routers Consequence: The Class-based assignment of IP addresses had to be abandoned 61

CIDR - Classless Interdomain Routing



Goals:

  New interpretation of the IP address space Restructure IP address assignments to increase efficiency  Permits route aggregation to minimize route table entries  CIDR (Classless Interdomain routing)    abandons the notion of classes

Key Concept:

The length of the network prefix in the IP addresses is kept arbitrary Consequence: an IP address Size of the network prefix must be provided with 62

CIDR Notation

 CIDR notation of an IP address: 

192.0.2.0/18

"18" is the prefix length. It states that the first 18 bits are the network prefix of the address (and 14 bits are available for specific host addresses)  CIDR notation can replace the use of subnetmasks (but is more general)  IP address 128.143.137.144 and subnetmask 255.255.255.0 becomes 128.143.137.144/24  CIDR notation allows to drop traling zeros of network addresses:

192.0.2.0/18

can be written as

192.0.2/18

63

CIDR address blocks

  CIDR notation can nicely express blocks of addresses Blocks are used when allocating IP addresses for a company and for routing tables (route aggregation)

CIDR Block Prefix # of Host Addresses /27 32 /26 /25 /24 /23 /22 /21 /20 /19 /18 /17 /16 /15 /14 /13 64 128 256 512 1,024 2,048 4,096 8,192 16,384 32,768 65,536 131,072 262,144 524,288

64

CIDR and Address assignments

 Backbone ISPs obtain large block of IP addresses space and then reallocate portions of their address blocks to their customers.

Example:

  Assume that an ISP owns the address block 206.0.64.0/18 , which represents 16,384 (2 14 ) IP addresses Suppose a client requires 800 host addresses  With classful addresses: need to assign a class B address (and waste ~64,700 addresses) or four individual Class Cs (and introducing 4 new routes into the global Internet routing tables)  With CIDR: Assign a /22 block, e.g., 206.0.68.0/22, and allocated a block of 1,024 (2 10 ) IP addresses.

65

 

CIDR and Routing

Aggregation of routing table entries:  128.143.0.0/16 and 128.144.0.0/16 are represented as 128.142.0.0/15 Longest prefix match: Routing table lookup finds the routing entry that matches the longest prefix What is the outgoing interface for 128.143.137.0/24 ?

Route aggregation can be exploited when IP address blocks are assigned in an hierarchical fashion Prefix 128.0.0.0/4 128.128.0.0/9 128.143.128.0/17 Interface interface #5 interface #2 interface #1 Routing table 66

CIDR and Routing Information

Company X :

206.0.68.0/22 ISP X owns: 206.0.64.0/18 204.188.0.0/15 209.88.232.0/21 Internet Backbone

ISP y :

209.88.237.0/24

Organization z1 :

209.88.237.192/26

Organization z2 :

209.88.237.0/26 67

CIDR and Routing Information

Backbone routers do not know anything about Company X, ISP Y, or Organizations z1, z2.

Company X :

ISP X does not know about Organizations z1, z2.

ISP X owns: the prefix: 206.0.64.0/18 209.88.237.0/26 to Organizations z1 to Organizations z2 209.88.232.0/21 Internet ISP X sends everything which Backbone 206.0.68.0/22 to Company X, 209.88.237.0/24 to ISP y

ISP y :

209.88.237.0/24 Backbone sends everything which matches the prefixes 206.0.64.0/18, 204.188.0.0/15, 209.88.232.0/21 to ISP X.

Organization z1 :

209.88.237.192/26

Organization z2 :

209.88.237.0/26 68

IPv6 - IP Version 6



IP Version 6

 Is the successor to the currently used IPv4   Specification completed in 1994 Makes improvements to IPv4 (no revolutionary changes)  One (not the only !) feature of IPv6 is a significant increase in of the IP address to

128 bits (16 bytes)

 IPv6 will solve – for the foreseeable future – the problems with IP addressing  10 24 addresses per square inch on the surface of the Earth.

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IPv6 Header

version (4 bits) Traffic Class (8 bits) Payload Length (16 bits) 32 bits Flow Label (24 bits) Next Header (8 bits) Hop Limits (8 bits) Source IP address (128 bits) Destination IP address (128 bits)

Ethernet Header

IPv6 Header

TCP Header Ethernet frame Application data Ethernet Trailer 70



IPv6 vs. IPv4: Address Comparison

IPv4

2 32 has a maximum of  4 billion addresses 

IPv6 2 128

has a maximum of

= (2 32 ) 4



4 billion x 4 billion x 4 billion x 4 billion addresses

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Notation of IPv6 addresses



Convention

: The 128-bit IPv6 address is written as eight 16-bit integers (using hexadecimal digits for each integer)

CEDF:BP76:3245:4464:FACE:2E50:3025:DF12

   

Short notation:

Abbreviations of leading zeroes:

CEDF:BP76:0000:0000:009E:0000:3025:DF12



CEDF:BP76:0:0:9E :0:3025:DF12

“:0000:0000:0000” can be written as “::”

CEDF:BP76:0:0:FACE:0:3025:DF12



CEDF:BP76::FACE:0:3025:DF1 2

IPv6 addresses derived from IPv4 addresses have 96 leading zero bits. Convention allows to use IPv4 notation for the last 32 bits.

::80:8F:89:90



::128.143.137.144

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IPv6 Provider-Based Addresses



010

The first IPv6 addresses will be allocated to a provider based plan

Registry ID Provider ID ID ID Interface ID

  Registry

The following fields have a variable length (recommeded length in “()”)

: identifies the agency that registered the address  Type: Set to “010” for provider-based addresses Provider : Id of Internet access provider

(16 bits)

   Subscriber: Id of the organization at provider

(24 bits)

Subnetwork : Id of subnet within organization

(32 bits)

Interface : identifies an interface at a node

(48 bits)

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Line cards

Cisco CRS-1 1-Port OC-768c (40 Gb/s) Cisco CRS-1 4-Port 10 GbE 74

Lab this week…

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