1. Addressing and Routing Topics discussed in this section:
Chapter
Addressing and Routing
An IPv4 address is a 32-bit address that uniquely and universally defines the connection of a device (for example, a computer or a router) to the Internet.
Topics discussed in this section:
Address Space
Notations
Classful Addressing
Classless Addressing
Network Address Translation (NAT)

2. The IPv4 addresses are unique and universal
Two devices in the Internet can never have the same address at the same time.
An address may be assigned to a device for a time period and then taken away and assigned to another device.
If a device operating at the network layer (e.g. router) has m connections to the Internet, it needs to have m IP address.
The IPv4 addresses are unique and universal

3. IPv4 IPV4 has an address space: is the total number of
addresses used by the protocol.
If a protocol uses N bits to define an address, the address space is 2N .
IPv4 uses 32-bit addresses:
The address space=232 =4,294,967,296 ( more than 4 billion)
This means, if there were no restrictions, more than 4 billion devices could be connected to the Internet.
IPv6 uses 128 bit-addresses

4. IPv4 Addresses: Notations
There are two prevalent notations to show an IPv4 address
Binary notation
Address is displayed as 32 bits.
Each octet is often referred to as byte.
IPv4 address referred to as 32-bit address or 4- byte address
Dotted-decimal notation:
More compact and easier to read
Written in decimal form with a decimal point( dot) separating the bytes
Example:
Each decimal value range from 0 to 255

5. Address Allocation How are the block allocated?
The address allocation is given to global authority called
Internet Assigned Number Authority (IANA)
IANA does not allocate addresses to individual organizations
It assigns a large block of addresses to an ISP

6. Example
Change the following IPv4 addresses from binary notation to dotted-decimal notation.
Solution
We replace each group of 8 bits with its equivalent decimal number (see Appendix B) and add dots for separation.

7. Example
Change the following IPv4 addresses from dotted-decimal notation to binary notation.
Solution
We replace each decimal number with its binary equivalent (see Appendix B).

8. Example Find the error, if any, in the following IPv4 addresses.
Solution
a. There must be no leading zero (045).
b. There can be no more than four numbers.
c. Each number needs to be less than or equal to 255.
d. A mixture of binary notation and dotted-decimal notation is not allowed.

9. We can find the class of an address in
Classfull addressing
In classfull addressing, the address space is divided into five classes: A, B, C, D, and E
We can find the class of an address in
Binary notation: the first few bits define the class
Decimal-dotted notation: the first byte define the class

10. Classfull addressing
In classfull addressing, the address space is divided into 5 classes: A, B, C, D, and E.
Addresses in Classes A, B and C are uniast ddresses
A host needs to have at least one unicast address to be able to send packet (Source).
Addresses in Class D are for multicast address
Used only for destination
Addresses in class E are reserved

11. Example 19.4 Find the class of each address.b c d
Solution
a. The first bit is 0. This is a class A address.
b. The first 2 bits are 1; the third bit is 0. This is a class C address.
c. The first byte is 14; the class is A.
d. The first byte is 252; the class is E.

12. Classfull Addressing Classes and Blocks
Net Id and Host Id
The address is divided into Netid and Hostid.
These part are of varying lengths, depending on the class.
Dose not apply to classes D and E

13. Classfull Addressing Classes and Blocks

14. number of blocks with each block having a fixed size
Classes and Blocks
Class A address
designed for large organizations with a large number of attached hosts or routers. (most of the addresses were wasted and not used)
Class B address
designed for midsize organizations with ten of thousands of attached hosts or routers( too large for many organizations)
Class C address
designed for small organizations with a small number of attached hosts or routers (too small for many organizations)
Class D address
designed for multicasting. (waste of addresses)
Class E address
reserved for future use (waste of addresses)
One problem is that each class is divided into fixed
number of blocks with each block having a fixed size

15. Mask (default mask)
Help us to find the NetId and HostId
Mask: 32-bit made of 1s followed by 0s.
Dose not apply to classes D and E.
CIDR(Classless Interdomain Routing): used to show the mask in the form /n (n=8,16,24)
Classfull addressing, which is almost obsolete, is replaced with classless addressing.

16. Classfull Addressing Network address
The network address is an address that define the network itself to the reset of the internet
The network address has the following properties:
All hostid bytes are 0’s
It is the first address in the block
It cannot be assigned to a host
Given the network address, we can find the class of the address

17. Find the network address for the following
Example
Find the network address for the following
The class is B
The first 2 bytes defines the Netid. We can find the network address by replacing the hostid bytes (17.85) with 0s
Therefore, the network address is
The class is A. Only the first byte defines the Netid. We can find the network address by replacing the hostid bytes ( ) with 0s.
Therefore, the network address is

18. Figure 19.3 A block of 16 addresses granted to a small organization

19. In IPv4 addressing, a block of addresses can be defined as x.y.z.t /n
x.y.z.t defines one of the addresses and the /n defines the mask
The first address in the block can be found by setting the rightmost 32 − n bits to 0s
The last address in the block can be found by setting the rightmost 32 − n bits to 1s.

20. Example
A block of addresses is granted to a small organization. We know that one of the addresses is /28.
What is the first and the last address in the block
Find the number of addresses?
Solution
The binary representation of the given address is
If we set 32−28 = 4 rightmost bits to 0, we get
If we set 32−28 = 4 rightmost bits to 1, we get
The number of addresses is −28 = 16

21. Example
Another way to find the first address, the last address, and the number of addresses is to represent the mask as a 32-bit binary number. In the previous Example the /28 can be represented as
Find
a. The first address
b. The last address
c. The number of addresses.

22. Solution
The first address can be found by ANDing the given addresses with the mask
The last address can be found by ORing the given addresses with the complement of the mask
The number of addresses can be found by complementing the mask, interpreting it as a decimal number, and adding 1 to it

23. A network configuration for the block 205.16.37.32/28
The first address in a block is normally not assigned to any device; it is used as the network address that represents the organization to the rest of the world
The Last address in a block is normally not assigned to any device; it is used as the Broadcast address

24. Configuration and addresses in a subnetted network
Each address in the block can be considered as a two-level hierarchical structure
the leftmost n bits define the network
the rightmost 32 − n bits define the host.

25. Three-level hierarchy in an IPv4 address

26. Example
An ISP is granted a block of addresses starting with /16 (65,536 addresses). The ISP needs to distribute these addresses to three groups of customers as follows
a. The first group has 64 customers; each needs 256 addresses.
b. The 2nd group has 128 customers; each needs 128 addresses.
c. The 3rd group has 128 customers; each needs 64 addresses.
Design the subblocks and find out how many addresses are still available after these allocations.

27. Solution
Group 1
For this group, each customer needs 256 addresses. This means that 8 bits are needed to define each host. The prefix length is 32 − 8 = 24
Group 2
For this group, each customer needs 128 addresses. This means that 7 bits are needed to define each host. The prefix length is 32 − 7 = 25

28. Group 3
For this group, each customer needs 64 addresses. This means that 6 bits are needed to each host. The prefix length is 32 − 6 = 26
Number of granted addresses to the ISP: 65,536
Number of allocated addresses by the ISP: 40,960
Number of available addresses: 24,576

29. Classfull Addressing Subnetting
If an organization was granted a large block in classes A or B
It could divide the addresses into several contiguous groups and assign each group to smaller networks ( subnets)
It increases the number of 1s in the mask
To make a subnet mask , we change some of the leftmost 0s in mask to 1s
The number of subnets is determine by the number of extra1s.
If the number of extra 1 is n, the number of subnets is 2n

30. Example Class B address For 4 subnets : (need 2-extra bits )
mask : or /16
For 4 subnets : (need 2-extra bits )
Subnet mask: or /18
For 8 subnets: (need 3-extra bits )
subnet mask : or /19

31. Example
A router receives a packet with destination address
Show how it finds the network and the sub_network address to route the packet.
Assume the subnet mask is /19
The router follows steps:
The router looks at the first byte of the address to find the class. It is class B
The mask for class B is (/16)The router ANDs this mask with the address to get the network address :
The router applies the subnet mask (/19) to the address, : ı
The subnet address is
The router looks in its routing table to find how to route the packet to this destination

32. Supernetting Huge demand for midsize blocks.
Although class A and B addresses are almost depleted, class C addresses are still available( size of block= 256 address did not satisfy the needs).
In super netting, an organization can combine several class C blocks to create a larger range of addresses.
Several networks are combined to create a super network ( super net).
e.g. Organization needs 1000 address can be granted 4 contiguous class C blocks to create one super network.

33. Subnetting Collision domain Broadcast domain
Are the connected physical network segments where collisions can occur
Broadcast domain
A group of collision domains that are connected by layer 2 devices

34. Collision domains = # of hosts connected to a switch or bridge + # of router links Broadcast domains = # of router links, since only routers will create broadcast domains

35. A BRIDGE will create a collision domain while the HUB will not

36. Network Address Translation NAT
The Internet Authorities have reserved 3 sets of addresses as a private addresses
Network Address Translation
NAT enables a user to have a large set of addresses internally and one address or small set of address externally.
A NAT box located where the LAN meets the Internet makes all necessary IP address translations
Any organization can use an addresses out of this set without permission from internet authorities.
Provides a type of firewall by hiding internal IP addresses

37. Network Address Translation
Private addresses are unique inside the organization , but they are not unique globally
No router will forward a packet that has one of these addresses as the destination addresses
The site must have one connection to the global internet through the router that runs NAT software
The router has uses one private address and one global address
The internet sees only NAT router with global address

38. NAting
NAT router replaces the source address in the outgoing packets with the global NAT address ( )
Router replaces the destination address (the NAT router global address) in the incoming packets with appropriate private address

39. private network must start (initiate ) the communication
NAT address translation
Note
private network must start (initiate ) the communication

40. NAT address translation Using pool of IP addresses
Restriction
Since the NAT router has only one global address, only one private network host can
To remove the previous restriction, the NAT router uses a pool of global addresses access the same external host
For example
instead of using one global address , the NAT router can uses 4 addresses ( , , , ).
In this case 4 private network hosts can communicate the same external host at the same time because each pair of addresses defines a connection

41. Pool of IP addresses

42. Pool of IP addresses There are still some drawbacks:
No than four private network hosts can communicate the same destination
No private network host can access two external server programs (e.g. HTTP (port 80 )and FTP) at the same time
To allow many to many relationship use 5- coloum translation table

43. NAT address translation
Using both IP addresses and Port number
Five-column translation table

46. IPv6 ADDRESSES IPv6 address in binary and hexadecimal colon notation
Despite all short-term solutions, address depletion is still a long-term problem for the Internet. This and other problems in the IP protocol itself have been the motivation for IPv6.
An IPv6 address is 128 bits long
IPv6 address in binary and hexadecimal colon notation

47. Abbreviated IPv6 addresses

48. Example Expand the address 0:15::1:12:1213 to its original. Solution
We first need to align the left side of the double colon to the left of the original pattern and the right side of the double colon to the right of the original pattern to find how many 0s we need to replace the double colon.
This means that the original address is.

49. Routing

50. Forwarding means to place the packet in its route to its destination.
Forwarding requires a host or a router to have a routing table.
When host has a packet to send or when a router has received a packet to be forwarded, it looks at this table to find the route to the final des
Topics discussed in this section
Forwarding Techniques
Forwarding Process
Routing Table

51. Route method vs Next-hop method

52. Host-specific vs Network-specific method

53. Host-specific routing

54. Default method

55. Simplified forwarding module in classless address
In classless addressing, we need at least 4 columns in a routing table

56. Example Make a routing table for router R1, using the following configuration

57. Example Show the forwarding process if a packet arrives at R1 with the destination address
Routing table for R1

58. Solution The router performs the following steps
The first mask (/26) is applied to the destination address
The result is , which does not match the corresponding network address
The second mask (/25) is applied to the destination address.
The result is ,which matches the corresponding network address. The next-hop address and the interface number m0 are passed to ARP for further processing

59. The router performs the following steps
Example Show the forwarding process if a packet arrives at R1 in with the destination address
The router performs the following steps
The first mask (/26) is applied to the destination address
The result is , which does not match the corresponding network address
The second mask (/25) is applied to the destination address
The result is , which does not match the corresponding network address (row 2)
The third mask (/24) is applied to the destination address
The result is , which matches the corresponding network address. The destination address of the packet and the interface number m3

60. CLASSFUL ADDRESSING ROUTING TABLE
Example, the router receives a packet for destination
For each row, the mask is applied to the destination address until a match with the destination address is found. In this example, the router sends the packet through interface m0 (host specific).
Example, the router receives a packet for destination For each row, the mask is applied to the destination address until a match with the next-hop address is found. In this example, the router sends the packet through interface m2 (network specific).
Example, the router receives a packet for destination For each row, the mask is applied to the destination address, but no match is found. In this example, the router sends the packet through the default interface m0.

61. Autonomous systems Autonomous System (AS)
Group of networks and routers under the authority of a single administration.
Routers inside an autonomous system is referred to as interior routing (Intradomain).
Routing between autonomous systems is referred to as exterior routing (Interdomain)
Solid lines show the communication between routers that use interior routing protocols.
Broken lines show the communication between routers that use an exterior routing protocols.

62. Example Show the forwarding process if a packet arrives at R1 with the destination address
This time all masks are applied, one by one, to the destination address, but no matching network address is found. When it reaches the end of the table, the module gives the next-hop address and interface number m2 to ARP. This is probably an out going package that needs to be sent, via the default router, to some place else in the Internet.

63. Packet go from source to destination via routers.
Routing
Packet go from source to destination via routers.
Router consults the routing table.
Routing table can be
Static: does not change automatically (manual entries)
Dynamic: updated automatically when there is change in the Internet
Routing protocols are needed to create the routing tables dynamically.
A routing protocol is a combination of rules and procedures that
Lets routers in the internet inform one another of changes.
Allows routers to share whatever they know about the internet or their neighborhood.

64. Interior and Exterior routing protocols
Each AS can choose one or more intradomain (interior) routing protocol to handle routing inside the AS such as RIP and OSPF
One interdomain (exterior) routing protocol is usually chosen to handle routing between ASs ; BGP

65. Metric of different protocols
Metric is the cost assigned for passing through a network.
The total metric of a particular router is equal to the sum of the metrics of networks that comprise the route.
A router chooses the route with smallest metric.
The metric assigned to each network depends on the type of protocol
RIP (Routing Information Protocol) “Shortest distance”
Cost of passing each network is same; it is one hop count.
If a packet passes through 10 networks to reach the destination, the total cost is 10 hop counts.
OSPF(Open Shortest Path First)
Administrator can assign cost for passing a network based on type of service required such as :throughput, delay,..etc.
OSPF allows each router to have more than one routing table based on required type of service
BGP(Border Gateway Protocol)
Criterion is the policy, which is set by the administrator

66. Routing Algorithm classification
Routing algorithms can be
distance vector algorithms
router knows physically-connected neighbors, link costs to neighbors, iterative process of computation, exchange of partial information with neighbors.
The least cost between any two nodes is the route with minimum distance
RIP is an implementation of this approach
link state algorithms
all routers have complete topology, link cost information
OSPF is an implementation of this approach

67. Distance Vector Routing
Each node( router) maintains a set of triples (table): Destination, Cost, Next Hop)
Node knows the cost to each neighbor (the distance between itself and its immediate neighbors)
Directly connected neighbors exchange updates
periodically (on the order of several seconds -30s)
whenever table changes (called triggered update)
Each update is a list of pairs: Destination, Cost
Update local table if receive a “better” rout (smaller cost)

68. Distance vector routing
infinite ∞ ( unreachable).
Think the node as the cities and the lines as the roads connecting them

69. Distance vector routing
Sharing: Updating in distance vector routing

70. Distance vector routing
The least cost route between any two nodes is the route with min distance.
Each node maintains a table which contains
Destination, Cost, Next hop

71. Distance vector routing
Each router shares its entire routing table with its neighbors
Sharing
Periodically update :on the order of several seconds -30s-
Triggered update: The change can result from the following
A node receives a table from a neighbor, resulting in changes in its own table after updating.
A node detects some failure in the neighboring links which results in a distance change to infinity ∞
Each update is a list of pairs
Destination, Cost(two column routing table)

72. Routing Information Protocol
RIP implement Distance vector routing with some considerations
Destination in the routing table is a network (first column defines network address)
Metric(distance) is Hop count : is the number of networks that a packet encounters to reach its final destination
Infinity is defined as value of 16
Therefore, the Max limited of hops is 15
suitable for small networks (local area environments)
Router sends update message to neighbors every 30 sec.
If router does not receive update message from neighbor X within this limit, it assumes the link to X has failed and sets the corresponding minimum cost to 16 (infinity)
In distance vector routing, each node shares its routing table with its immediate neighbors periodically and when there is a change

73. RIP
Routing table
Has one entry for each destination network of which the router is aware
Each entry has destination network address, the shortest distance to reach the destination in hop count, and next router to which the packet should be delivered to reach its final destination

74. Example Internetwork

75. ARP:

76. Initial routing tables in a small AS
When a router is added to a network, it initializes a routing table for itself, using its configuration file
The table consists only the directly attached networks and the hop counts, which are initialized to 1
The next-hop field, which identifies the next router, is empty

77. Final routing tables
Each routing table is updated upon receipt of RIP messages using the RIP updating algorithm

78. RIP Updating Algorithm
Receive: a response RIP message(significant portion of its routing table)
Add one hop to the hop count for each advertised destination
Repeat the following steps for each advertised destination
If (destination not in the routing table)
Add the advertised information to the table
Else
If (next-hop field is the same)
Replace entry in the table with the advertised one.
If (advertised hop count smaller than one in the table)
Replace entry in the routing table

79. Example of updating a routing table

80. Example Domain using RIP

81. Link State Routing Analogous to a city map
Each node in the domain has the entire topology of the domain
Analogous to a city map

82. Link State Routing
Link-state routing works by having the routers tell every router on the network about state of its neighbors.
Sharing knowledge about the neighborhood
Each router sends the state of its neighborhood to every other router in the area.
Sharing with every other router
By flooding, a process whereby a router sends its information to all its neighbors (through all its output ports).
Each neighbor sends the packet to all its neighbors, and so on.
Every router that receives the packet sends copies to each of its neighbors. Eventually, every router (without exception) has received a copy of the same information
Sharing when there is a change; Only to its neighbors
The node can use Dijkstra Algorithm to build a routing table
Metric
Administrator can assign the cost to each route.
Based on type of service (minimum delay, maximum throughput, ..)

83. Link state routing

84. OSPF OSPF Based on Link state Routing OSPF divides an AS into areas.
Special routers called autonomous system boundary routers are responsible for dissipating information about other ASs into the current system

85. OSPF

86. Areas in an Autonomous System
Area is a collection of networks, hosts, and routers all contained within an autonomous system.
Routers inside an area flood the area with routing information.
Area border routers
Summarize the information about the area and send it to other routers
Backbone area [Primary area]
All the areas inside an autonomous system must be connected to the backbone
Routers in this area are called as backbone routers. This area identification number is 0.
If, due to some problem, the connectivity between a backbone and an area is broken, a virtual link between routers must be created by the administration to allow continuity of the functions of the backbone as the primary area

87. OSPF
Each router should have the exact topology of the internet at every moment (LSP).
From this topology, a router can calculate the shortest path between itself and each network using Dijkstra algorithm

88. Point-to-point Link
Connects 2 routers without any other router or host in between
Directly connected routers using serial line.
Only one neighbor.
No need to assign a network address to this type of link
The metrics are the same at the two ends

89. Transient link A network with several routers attached to it.
Each router has many neighbors.
Lot of advertisements about their neighbors.
One of the routers in the network has two duties
true router and designated router (network)
Each router has only one neighbor, the designated router (network). On the other hand, the designated router (network) has five neighbors.
Designated router represents a network. There exists a metric between each node to the designated router but there is no metric from the designated router to any other node.

90. Stub Link A network that is connected to only one router
The data packets enter the network through this single router and leave the network through this same
Virtual Link
When the link between two routers is broken, the administration may create a virtual link between them, using a longer path that probably goes through several routers.

91. Example of an internet & Graphical representation

92. Dijkstra Algorithm
Calculates the shortest path between two points on a network, using a graph made up of nodes and edges.
Algorithm divides the nodes into two sets
tentative and permanent
It chooses nodes, makes them tentative, examines them, and if they pass the criteria, makes them permanent

93. Dijkstra Algorithm
Start with the local node (router): the root of the tree.
Examine each neighbor node of the node that was the last permanent node
Assign a cost of 0 to this node and make it the first permanent node
Assign a cumulative cost to each node and make it tentative
Among the list of tentative nodes
Find the node with the smallest cumulative cost and make it permanent
If a node can be reached from more than one direction. Select the direction with the shortest cumulative
Repeat steps 3 to 5 until every node becomes permanent

94. Example 1 Shortest-path calculation using Dijkstra

95. Example 1 Shortest-path calculation using Dijkstra

96. Example 1 Shortest-path calculation using Dijkstra

97. Example 1 Shortest-path calculation using Dijkstra
Routing Table for Router A

98. Example 2 Shortest-path calculation using Dijkstra

99. Example 2 Shortest-path calculation using Dijkstra

100. Example 2 Shortest-path calculation using Dijkstra

101. OSPF Reaction to Failure
If a link fails,
Router sets link distance to infinity & floods the network with an update packet
All routers immediately update their link database &recalculate their shortest paths
Recovery very quick
NOTE
OSPF differs from RIP in that each router knows the exact topology of the network
OSPF reduces routing bandwidth usage
OSPF is faster than RIP

102. DHCP Dynamic Host Configuration Protocol
Designed to provide information dynamically
It is a client-server program
Used to assign addresses to hosts dynamically

103. Data are transmitted in discrete units (packets)
A physical link is dedicated between source
and destination
Data is sent out as stream of bits
No packetization
Data are transmitted in discrete units (packets)

104. Each packet is treated independently of all others
Datagram approach
Each packet is treated independently of all others
Packet here is called datagram
Datagrams might arrive at destination out of order

105. Virtual Circuit
Relationship between all packets belonging to a message is preserved
A single route is chosen between sender and receiver at the beginning of the session
Data are sent one after another
WAN uses this approach which needs
Call setup to establish VC between sender and receiver
Call teardown to delete the VC