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Addressing. The ‘What’ and ‘Where’ of Communication. Addressing. Addressing is necessary for any communication To talk: Appearance, name, … To call: Telephone numbers To mail: Postal address To visit: Postal address + directions To E-Mail: E-Mail addresses

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addressing

Addressing

The ‘What’ and ‘Where’ of Communication

addressing1
Addressing
  • Addressing is necessary for any communication
    • To talk: Appearance, name, …
    • To call: Telephone numbers
    • To mail: Postal address
    • To visit: Postal address + directions
    • To E-Mail: E-Mail addresses
    • To instant message: ICQ#, AIM ID, etc.
  • These ‘addresses’ allow us to uniquely identify the entity with which we wish to communicate
addressing a la shoch
Addressing a la Shoch
  • Name/Identifier: What
    • Names normally identify the entity
    • If an entity moves, the name/identity will remain the same
  • Address: Where
    • Addresses identify the location of the entity
    • If an entity moves, the address will change
  • Route: How to get there
    • Routes identify the path to get to an entity
    • If an entity moves, the route will change
addressing2
Addressing
  • Addressing deals with how to define an entity’s location (uniquely)
  • Addressing is necessary for message delivery
    • An address is the start and end point for the route
      • However, routing is another subject
    • Where do we want the message to go?
addresses
Addresses
  • We have already seen MAC addresses (for Ethernet and some other LANs):
    • e.g. 02-60-8C-08-E1-0C
    • 6 octet address
    • Globally unique
    • Defined statically by the hardware manufacturer
  • Most people are familiar with the IP addresses used by TCP/IP networks:
    • e.g. 137.207.32.2
    • 4 octet address
    • Not necessarily globally unique
    • Defined dynamically by DHCP servers or negotiated by the operating system
ip addressing

IP Addressing

A Closer Look

ip addresses
IP Addresses
  • TCP/IP networks use IP for the network layer protocol
  • IP defines 4 octet addresses
    • 4 billion possible addresses
  • Usually written in the form A.B.C.D
    • A, B, C, and D are each 1 octet (0-255), normally written in decimal notation
    • Thus, IP addresses fall in the range:

0.0.0.0 – 255.255.255.255

ip addresses1
IP Addresses
  • Originally intended for separate internets (interconnected LANs)
    • Thus, the 32 bit size was not a concern
    • 48 bits is generally considered a fairly safe size for globally unique addressing
    • Computers connected to ARPANET (and later incarnations) were just given consecutive addresses

1.0.0.0, 1.0.0.1, 1.0.0.2, …

ip addresses2
IP Addresses
  • Any computer connected to a TCP/IP network (e.g. the Internet) must have an IP address
  • Further, any network interface card (NIC) using TCP/IP to access an network (e.g. the Internet) must have a different IP address
ip addresses3
IP Addresses
  • Even though there are 4 billion possible IP addresses, they are running out
  • Here’s why:
    • Some of the bits are dedicated to header information (discussed later)
      • ½ the addresses for each lost bit
    • Addresses are categorized, and some of the categories are running out of addresses (while others are not)
non classed addresses
Non-Classed Addresses
  • Part of the address represented the network the computer resided on, and part represented the computer itself
    • Network: 7 bits (up to 128 networks)
    • Computer: 24 bits (up to 1.6 million computers on each network)
  • Since there were very few networks on ARPANET originally, this wasn’t a problem
address classes
Address Classes
  • When private organizations started joining the Internet, the needs became obvious
    • Some (fewer) networks have multitudes of computers (thousands)
      • e.g. The @Home network
    • Some (many) networks have very few computers (a few hundred or less)
      • e.g. The Windsor Police Department
address classes1
Address Classes
  • Quickly, the addresses were separated into 3 classes (plus room for more classes if needed):
    • Class A: Fewer networks, many nodes
    • Class B: Medium networks, medium nodes
    • Class C: Many networks, fewer nodes
ip address classes
IP Address Classes

Class A:

bit index:

0

1-7

8-31

0

network

host (machine)

Class B:

bit index:

0

1

2-15

16-31

1

0

network

host

Class C:

bit index:

0

1

2

3-23

24-31

1

1

0

network

host

ip address classes1
IP Address Classes
  • Class A:
    • Range: 1.0.0.0 – 126.0.0.0
    • Networks: 128 max, Machines: 65537-1.6 million
    • e.g. huge networks, such as large military/government organizations (e.g. FBI), the @Home network, etc…
  • Class B:
    • Range: 128.1.0.0 – 191.255.0.0
    • Networks: 16384 max, Machines: 257-65536
    • e.g. Internet service providers (ISPs) (dial-up)
  • Class C:
    • Range: 192.1.0.0 – 223.255.255.0
    • Networks: 2 million max, Machines: 1-256
    • e.g. Small businesses
ip address classes2
IP Address Classes
  • The IP address classes are self-identifying
    • Which means that given the address, you can determine what class an address is
      • Actually, using only the first number
    • Examples:
      • 137.207.32.2 (server.uwindsor.ca)
        • 137 -> Class B
      • 24.0.0.1 (@Home DHCP server)
        • 24 -> Class A
other ip address classes
Other IP Address Classes

Class D:

bit index:

0 1 2 3

4-31

1 1 1 0

Multicast group address

  • These addresses are used to represent multicast groups
    • Discussed later

Class E:

bit index:

0 1 2 3 4

5-31

1 1 1 1 0

Reserved for future use

  • These addresses were left open to be used and divided into classes as needed
special ip addresses
Special IP Addresses
  • 0.0.0.0: Used to indicate that this machine is without an assigned IP
    • Used during bootstrapping (e.g. requesting an IP from a DHCP server)
  • <all 0s (binary)><hostID>: Used to send messages to some machine on this network
  • 255.255.255.255: Used to send broadcast messages across this machine’s network
  • <netID><all 1s (binary)>: Used to send broadcast messages to the specified network
  • 127.0.0.1: Used to send messages back to this machine (called loopback or localhost)
ip addressing comments
IP Addressing Comments
  • In IP addressing:
    • 0’s usually represent ‘this’
    • 1’s usually represent ‘all’
  • Broadcasting, although discussed here in terms of addressing, will be discussed further
loopback
Loopback
  • The 127.0.0.1 address, does not normally exist on the network
    • Either as the source address or destination address of a packet
  • The address is used internally by NICs
    • When a NIC receives a message addressed with 127.0.0.1 to be transmitted, it passes the message directly to the receiver hardware
    • The receiver hardware returns the message to the operating system exactly as if the message were received from the network
      • However, the message never entered the network medium
internal ip addresses
Internal IP Addresses
  • Depending on the address class needed by an organization, a range of internal addresses is available:
    • Class A: 10.0.0.0 – 10.255.255.255
    • Class B: 172.16.0.0 – 172.31.255.255
    • Class C: 192.168.0.0 – 192.168.255.255
  • IP routers outside a private (connection-shared) network, will not forward datagrams designated for addresses in these ranges
multi homed machines
Multi-homed Machines
  • There is no restriction preventing machines from participating in multiple networks
    • A machine could have multiple NICs
    • Each NIC would have its own MAC address
    • On TCP/IP networks, each of these NICs would be given a different IP address
multi homed machines1

M

M

M

M

M

M

Multi-homed Machines

192.168.0.1

192.168.0.2

192.168.0.3

192.168.0.8

192.168.0.4

Class C private network

M

M

M

M

M

M

M

192.168.0.7

M

192.168.0.6

192.168.0.5

172.16.3.16

172.16.3.15

172.16.3.14

172.16.3.17

M

M

172.16.3.18

Class B private network

172.16.0.1

172.16.0.2

172.16.0.3

172.16.0.4

multi homed machines2
Multi-homed Machines

192.168.0.1

192.168.0.2

192.168.0.3

192.168.0.8

192.168.0.4

Class C private network

192.168.0.7

192.168.0.6

192.168.0.5

172.16.3.16

172.16.3.15

172.16.3.14

172.16.3.17

172.16.3.18

Class B private network

172.16.0.1

172.16.0.2

172.16.0.3

172.16.0.4

routers
Routers
  • Routers are multi-homed machines
    • They have a number of network ports, each of which represents a different path
  • Routers use tables that relate destinations to network paths
    • Internet routers relate destination network addresses with one of their network ports
    • When a datagram arrives at a router:
      • Its destination address is used to determine the network address
      • The network address is used to look up the destination port in the routing table
network addresses
Network Addresses
  • An IP address can be used to calculate the address of the network
  • The machine address is passed through a filter (called a subnet filter):
    • This filter extracts the bits of the address that represent the network and sets the bits that represent the machine to zero
    • The filter determines which part of the address represent the network address, by using the subnet mask
subnet mask
Subnet Mask
  • The subnet mask is a binary number, that has 0s in the machine portion of the address, and 1s in the network portion
  • Most networks of each type use a constant subnet mask
    • Class A: 255.0.0.0

(Binary: 11111111000000000000000000000000)

    • Class B: 255.255.0.0

(Binary: 11111111111111110000000000000000)

    • Class C: 255.255.255.0

(Binary: 11111111111111111111111100000000)

using subnet masks
Using Subnet Masks
  • Example:
    • Address: 137.207.32.2
    • Subnet Mask: 255.255.0.0

Address: 10001001110011110010000000000010

Mask: 11111111111111110000000000000000

Net Address: 10001001110011110000000000000000

  • Network address: 137.207.0.0
routing in action
Routing in Action

Internet

Network N1 (Class B)

Address: 137.207.0.0

P4

P1

P2

P3

Network N2 (Class C)

Address: 194.201.61.0

Network N3 (Class A)

Address: 24.0.0.0

slide30

IPv6

Next Generation Addressing in TCP/IP Networks

slide31
IPv6
  • Due to the limited nature of existing IP addressing (IPv4), a new version of IP addressing was developed
  • This new scheme uses 16 octets for addresses, instead of 4 octets
  • Written using hex notation:

3A57:0000:0000:9CD5:3412:912D:6738:1928

ipv6 features
IPv6 Features
  • 16 octet addresses (128 bits)
  • Larger numbers of address classes
    • More accurate control of network/machine counts
  • Variable-sized headers
    • Optional information can be placed into the header when needed
    • Reduces header size in most cases
  • Extendible protocol
    • IPv6 allows for new header information to be added to support different protocols
ipv6 features1
IPv6 Features
  • Automatically reconfigurable
    • Addresses can be automatically reassigned dynamically
    • e.g. when a certain number of nodes join the network, a different address class may be desired
  • Autoconfigurable
    • The use of autoconfiguration (such as DHCP) allows dynamic private addressing and dynamic public addressing
ipv6 datagram format
IPv6 Datagram Format

optional

header

extension headers

data

ipv6 header format
IPv6 Header Format

0 4 12 31

version

traffic class

flow label

32 48 56 63

payload length

next header

hop limit

64 96 128

source address

destination address

ipv6 integration
IPv6 Integration
  • Will IPv6 replace IP addresses?
    • Who knows?
  • Currently, temporary solutions have made IPv4 addresses capable of lasting longer than originally predicted
  • If and when IPv6 is to be integrated, the process must be a transition
    • Closing the entire Internet down to convert hardware and software to IPv6 not going to happen
    • Some stations may take longer to transition than other stations
      • e.g. Bob’s Internet Shack vs. the Telus Network
ipv6 integration1
IPv6 Integration
  • NAT (network address translators) provide one example of such a temporary solution
  • NATs provide three benefits:
    • NATs provide IP masquerading
      • Messages using these addresses pass through a network address translator (NAT) to be transformed into external IPs
    • NATs provide IP sharing
      • ISPs for example, have many customers, but significantly less at any given time are logged onto their system
        • IP addresses can be assigned dynamically to these customers when they log in
    • NATs provide schemes to allow networks to use either IPv4 or IPv6
      • Addresses would be converted as they pass through a NAT
ipv6 integration2
IPv6 Integration
  • Another method that may be used for the transition between IPv4 and IPv6 is address inclusion:
    • IPv4 addresses could be embedded into IPv6 addresses
      • Translation between the two types of addresses is possible without any other information
    • Some problems exist with this approach, but in general it simplifies communication between IPv6 networks and IPv4
special ipv6 addresses
Special IPv6 Addresses
  • 0:0:0:0:0:0:0:0 Used to indicate that this machine is without an assigned IP
    • Used during bootstrapping (e.g. requesting an IP from a DHCP server)
  • 0:0:0:0:0:0:0:1 Used to send messages back to this machine (called loopback)
    • These two addresses are not valid on the actual network medium (same as with IPv4)
  • 00:… Reserved (including IPv4 and IPX address inclusion)
  • FF:… Multicast addresses
slide40

IPX

Internetwork Packet Exchange Addresses

slide41
IPX
  • IPX was originally created to replace IP
  • In reality, it is used primarily on LANs
  • In conjunction with the SPX protocol, formed one of the two protocol suites used in Netware networks
    • SPX is to TCP, what IPX is to IP
  • Still can be (although rarely is) used today in Windows networks
ipx addresses
IPX Addresses
  • IPX uses a 2 component address (like IP):
    • The network portion (4 octets)
    • The machine portion (6 octets)
  • Unlike IP, these sizes are constant
    • So there are no IPX address classes
  • IPX uses sizes large enough to accommodate all categories of networks
ipx addresses1
IPX Addresses
  • The network portion of an IPX address is 4 octets (32 bits)
    • This allows for 4.29*109 networks (4 billion)
    • This is almost enough for everyone on earth to have their own network
  • The machine portion of an IPX address is 6 octets (48 bits)
    • This allows for 2.81*1014 machines on each network (281,475 trillion)
ipx addresses2
IPX Addresses
  • The scalability of IPX addresses is not their only benefit
  • The constant size of the network and machine address portions simplifies extracting each portion
    • As a result, machines that process IPX networks can process IPX datagrams more quickly
      • Such as network nodes, routers, etc.
ipx addresses3
IPX Addresses
  • Why 48 bits for the machine portion?
    • 48 bits allows for way too many machines, more than will be needed for many years
      • By the time machine IDs run out, network hardware and software will have been obsolete by many years!
    • Using 48 bits allows hardware to use the machine’s MAC address as the machine portion
      • This makes auto-configuration (dynamic IPX address assignment) easier/faster
ipx addresses4
IPX Addresses
  • If IPX has been around since the NetWare days, why don’t we use it for the Internet, instead of IP?
    • Good question! Why don’t we?
    • Frankly, IPX has a bad reputation, because initially it was used with SPX and other bandwidth-munching protocols
    • IPX can be used in conjunction with TCP (TCP/IPX), and it would make an excellent replacement for TCP/IP
      • However, standards organizations (e.g. ISO) want to use the protocols they develop, and not ones developed by corporations, such as Novell
fragmentation reassembly
Fragmentation & Reassembly
  • Packets can arrive out of order in connectionless networks
  • Packets must be reordered during reassembly
  • During fragmentation, the portion of data that each fragment represents must be identified
    • Since the length of a packet’s data can always be determined, all that is necessary is to use the offset of the start of the packet’s data in the larger data chunk
fragmentation reassembly1
Fragmentation & Reassembly

0 1500 3000 4500 6000 6800

Logical Data Chunk

Length:1500

Length:1500

Length:1500

Length:1500

Length:800

Offset:0

Offset:1500

Offset:3000

Offset:4500

Offset:6000

Packet 1

Packet 2

Packet 3

Packet 4

P5

fragmentation reassembly2
Fragmentation & Reassembly
  • Why do we use the data offset, and not just a sequence of numbers to determine packet order?
    • Sometimes, packets can be fragmented at one location, and must be re-fragmented at another location (such as while passing through a network incompatible with larger frame sizes)
    • These situations would require renumbering of all packets in the sequence, which is not always possible
fragmentation reassembly3
Fragmentation & Reassembly

Length:1500

Length:1500

Length:1500

Length:1500

Length:800

Offset:0

Offset:1500

Offset:3000

Offset:4500

Offset:6000

Packet 1

Packet 2

Packet 3

Packet 4

P5

Packet 1

Packet 2

P3a

P3b

Packet 4

P5

Length:1000

Length:500

Offset:3000

Offset:4000

fragmentation reassembly4
Fragmentation & Reassembly
  • Re-fragmentation (at gateways, routers, …) is expensive
    • The re-fragmenting node must process each packet, fragmenting it into smaller packets
    • Another reassembling node must collect these packets and assemble them into larger packets
    • Each of these operations involved memory processing, which is expensive when applied to many packets per second
fragmentation reassembly5
Fragmentation & Reassembly
  • Re-fragmentation (particularly in routers) should be avoided at all costs
    • To virtually eliminate re-fragmentation in a network, the maximum transmission unit (MTU) should be determined and used as the packet size
    • A network’s MTU is the largest size that can be used for packets that will not result in any re-fragmentation by any routers, or other multi-homed nodes
    • Schemes for determining the MTU dynamically have been developed, but are beyond the scope of this course
ip datagrams
IP Datagrams
  • IP datagrams are packets sent over IP networks using connectionless messaging
  • Datagrams can be used directly within network-capable programs by sending datagrams via UDP (user datagram protocol)
  • Datagrams are used transparently by TCP to provide connection-based transport
ip datagram routing
IP Datagram Routing
  • When an IP-enabled router receives a datagram, it:
    • Receives a datagram through one of its ports
    • Deletes the datagram, if the hop count (TTL in IPv4, Hop limit in IPv6) has a non-positive value
    • If the hop count is positive, it is decremented and processing continues
    • Determine the destination address’ network address
    • Uses the destination network address to find an entry in the routing table
    • Uses the routing table entry to determine to which port the datagram should be sent
    • Sends the datagram through the correct port
header checksums
Header Checksums
  • Networks sometimes result in corrupt data
  • Information in the header is equally susceptible to this corruption
  • However, header information, when corrupt, can cause more serious difficulties
    • For example, the destination address may have a few bits changed, or the hop count, etc.
    • Corruption like this, is not always easy to detect and fix
    • Corrupt data (determined by another checksum) can be fixed by re-issuing the datagram
    • Header checksums are used to ease identification of header corruption