1. Data and Computer Communications
Internet Protocols

2. Network Architecture Features
Addressing
Packet size
Access mechanism
Timeouts
Error recovery
Flow control
Routing
User access control
Connection based or connectionless

3. Connectionless Internetworking
Advantages
Flexibility
Robust
No unnecessary overhead
Unreliable
Not guaranteed delivery
Not guaranteed order of delivery
Packets can take different routes
Reliability is responsibility of next layer up (e.g. TCP)

4. IP Operation IP PDU Encapsulated with LAN protocol
Go to Router X
MAC address for Router X
IP PDU
Encapsulated with LAN protocol
Encapsulated with X.25 protocol

5. Design Issues Routing Datagram lifetime Fragmentation and re-assembly
Error control
Flow control

6. Routing End systems and routers maintain routing tables Source routing
Indicate next router to which datagram should be sent
Static
May contain alternative routes
Dynamic
Flexible response to congestion and errors
Source routing
Source specifies route as sequential list of routers to be followed

7. Datagram Lifetime Datagrams could loop indefinitely
Consumes resources
Transport protocol may need upper bound on datagram life
Datagram marked with lifetime
Time To Live field in IP
Once lifetime expires, datagram discarded (not forwarded)
Hop count
Decrement time to live on passing through a each router
Time count
Need to know how long since last router

8. Fragmentation and Re-assembly
Different packet sizes
When to re-assemble
At destination
Results in packets getting smaller as data traverses internet
Intermediate re-assembly
Need large buffers at routers
Buffers may fill with fragments
All fragments must go through same router
Inhibits dynamic routing

9. IP Fragmentation (1) IP re-assembles at destination only
Uses fields in header
Data Unit Identifier (ID)
Identifies end system originated datagram
Source and destination address
Protocol layer generating data (e.g. TCP)
Identification supplied by that layer
Data length
Length of user data in octets

10. IP Fragmentation (2) Offset More flag
Position of fragment of user data in original datagram
In multiples of 64 bits (8 octets)
More flag
Indicates that this is not the last fragment

11. Fragmentation Example
Application data
IP header is the same as origin
TCP header is not duplicated –
More is the same as original

12. Internet Protocol (IP)
Part of TCP/IP
Used by the Internet
Specifies interface with higher layer
e.g. TCP
Specifies protocol format and mechanisms
IPv4
addresses are 32 bits wide
Its header is 20 bytes at minimum
Uses doted-decimal notation (e.g )
IPv6
Provides larges address domain; addresses are 128 bits wide
Multiple separate headers are supported
Handles audio and video; providing high quality paths
Supports unicast, multicast, anycast

13. Dealing with Failure Re-assembly may fail if some fragments get lost
Requires buffer
Need to detect failure – but how?
Re-assembly time out
Assigned to first fragment to arrive
If timeout expires before all fragments arrive, discard partial data
Use packet lifetime (time to live in IP)
If time to live runs out, kill partial data

14. Parameters (1) Source address Destination address Protocol
Recipient e.g. TCP
Type of Service
Specify treatment of data unit during transmission through networks
Identification
Source, destination address and user protocol
Uniquely identifies PDU
Needed for re-assembly and error reporting
Send only +
0 - 3
4 - 7
8 - 15
Version
Header length
Type of Service
Total Length 32
Identification
Flags
Fragment Offset 64
Time to Live
Protocol
Header Checksum 96
Source Address
128
Destination Address
160
Options + padding
192
  Data  

15. IP Packet Format - TTL
TTL (time-to-live) refers to the number of router hops the IP packet is allowed before it must be discarded.
Each router that receives a packet subtracts one from the count in the TTL field.
When the count reaches zero, the router detecting it discards the packet and sends an Internet Control Message Protocol (ICMP) message back to the originating host

16. IP Header The IP datagram contains data and IP address
The IP datagram is encapsulated in a frame with physical address
The header changes as the frame goes from one network domain to the next
IP Datagram
Frame
Data IP
Address

17. Encapsulated IP Packet in Ethernet Frame
Ethernet Frame Carrying IP Packet
MAC and Associated IP address

18. Encapsulated IP Packet in Ethernet Frame
Ethernet Frame Carrying IP Packet
An Ethernet frame containing IP information has in its type field
IP starting with 45 Hex indicates IPv4 with standard length of 20 bytes
IP starting with 4F Hex indicates IPv4 with standard length of 60 bytes
Remember: 24=16; 45= = One Byte
Protocol Analyzer Display:
C0 A C A
A DC FF C0 99 B8 01 C0 99
0020 B8 03 2a B4 DD …..
Example:
99 is one byte

19. IP Addressing Two address types
Physical address (the frame has the physical address)
Embedded in the hardware (NIC, e.g., )
Also called the Media Address Control (MAC) address
Logical
IP datagram contains the logical IP address
To transport IP packets both physical and IP addresses must be known
Static address resolution
Dynamic address resolution
How to map physical and IP addresses
Local tables of IP addresses
Centralized directory
Address resolution mechanism
Address resolution mechanisms
ARP (address resolution protocol) – IP48 bit Ethernet address
RARP (reverse) address resolution protocol are used to convert MAC to IP address and vice versa

20. IP Addressing – IPv4
A network address is divided into Netid and Hostid
IP Address classification
(number of hosts per network)
Class
Leading bits
Network
Address (Netid)
Host
Address (Hostid)
Class A
    0
    7 bit (125)*
    24 bit (16,777,151,750)
Class B
    10
    14 bit (16,368)
    16 bit (65,534)
Class C
    110
    21 bit (2,096,896)
    8 bit (254)
Class D (multicast)
    1110
Class E (reserved)
    1111
* Some values are reserved!

21. IP Addressing Classification
Network
Address
Host Address
Multicast Address
Network Address
Host Address
Reserved for Internet research
Network
Address
Host
Address

22. Example of IP Addressing
Q1: Determine the network address
for the following IP addresses:
(84 = 54 Hex = )
 Netid=
 Class A
 Hostid=
(144 = 90 Hex = )
 Netid=
 Class B
 Hostid=
Q2: What type of IP address classification
will a large organization with 1000
individual users in 150 dispersed buildings use?  Class B

23. IP Routing Protocols
Routing packets requires having knowledge about the network
Partial (know your own neighbors)
Full (know the entire network elements)
Retrieving network information (network discovery protocols)
RIP (routing information protocol): routing based on the least number of hops
OSPF (open shortest path first): Routing based on number of hops, link speed, congestion

24. TCP/IP Stack Protocol Bridge Router
IS used to connect two LANs using similar LAN protocols
Address filter passing on packets to the required network only
OSI layer 2 (Data Link)
Router
Connects two (possibly dissimilar) networks
Uses internet protocol present in each router and end system
OSI Layer 3 (Network)

25. Subnets and Subnet Masks
Subnets and Subnet Masks
Each LAN assigned subnet number
Site looks to rest of internet like single network
Host portion of address partitioned into subnet number and host number
Local routers route within subnetted network
Subnet mask indicates which bits are subnet number and which are host number
Allow arbitrary complexity of internetworked LANs within organization
Insulate overall internet from growth of network numbers and routing complexity

26. Routing Using Subnets

27. Masking 3-bit subnet IP Address of B: 192.228.17.57 00 1|1 10 01
IP Address of A: |
IP Address of X: |
Subnet mask:
5-bit host
Note: if we XOR IP Address of B & Subnet Mask
We will have:
XOR =
Host number is 25  ;
192  , hence, Class C network (8-bit host/subnet) !
NetId
SubNetId
Host

28. Why Change IP? Address space exhaustion
Two level addressing (network and host) wastes space
Network addresses used even if not connected to Internet
Growth of networks and the Internet
Extended use of TCP/IP
Single address per host
Requirements for new types of service

29. IP v6 Header vs. IPV4 Features: Extended address space
Note:
IPv5 used for Stream Protocol- IP-layer protocol that provides end-to-end guaranteed service across a network.
Features:
Extended address space
Improved option mechanism
Dynamic address assignment
Multicasting and anycasting
Flow routing
128 bits
128 bits

30. Internet Addressing
Over half million networks are connected to the Internet
Network numbers are managed by ICNN (Internet Corporation for Assigned Names and Numbers) -
Delegates part of address assignments to regional authorities
IP addresses are given to ISPs and companies
IP addresses are based on dotted decimal notation:
IP address refer to machine’s own network when it is being booted (This host)
broadcast on the LAN
127.x.y.z reserved for loopback testing

31. More about subnets…. Routers can be connected to multiple LANs
LANS are divided into subnets each identified by a subnet mask: (… )  32-10=22 to identify the subnet!
Mask: netID + SunnetID or /22 (subnet mask is 22 bit long)
Subnets are not visible outside the network
Example: Assume subnet mask is /22
Subnet 1:
Subnet 2:  …000010|
Subnet 3:  …000011|
Assume a packet’s destination is  which subnet does it belong to?
Mask: … |
Adrs: … |
Hence: the packet must go to Subnet 3

32. Classes and subnets… Classful routing is not very efficient
Having IP address classes creates issues
Addresses can be under utilized (Class A)
Addresses can be over utilized (Class C)
Management of addresses may be difficult
Organizations can grow!
Classless InterDomain Routing (CIDR)
Allocate remaining IP addresses in variable-sized block; no regard to class!
Use 32-bit mask!
Uses a single routing table

33. Classless Routing - Example
What happens if a packet has an address of ?
Where does it go?
O: … AND 
… ( )
How do you represent class B using CIDR?
16-bit NetID + 16-bit HostID  /16

34. Network Address Translation (NAT)
Addresses are growing! What is the solution?
Use IPV6
Use NAT
NAT:
Allows using one IP address per company
Internally new nodes can be added!
How?

35. NAT Operation 198.60.42.12 IP reserved addresses
10.x.y.z
x.y
x.y
Receiving a packet from the Internet
Sender
Add IP address
TCP will have the destination port (0-1023)
The port determines which server on the remote (destination) side to process the packet
NAT box:
Using the PORT address in TCP, change the IP address to a designated address ( )
Sending a packet into the Internet
Changes to

36. NAT Issues… Addresses are not unique: many 10.0.0.1!
NAT controls are the incoming and outgoing packets – reliability!
NAT accesses TCP and IP layers – layers should work independent of one another
NAT only allows TCP/IP or UDP/IP
NAT does not support applications which insert the IP address in the body (FTP or H.323)

37. Internet Control Protocols
IP protocol only deal with the data transfer
We need control protocol to check the network
ICMP, ARP, RARP, BOOTP, HDCP

38. Internet Control Message Protocol (ICMP)
ICMP error messages are used by routers and hosts to tell a device that sent a datagram about problems encountered in delivering it
Used to test the network
Messages are encapsulated in the IP packet
Has many message types
Code field is used for subtypes

39. ARP (address resolution protocol)
Exploits broadcast property of a LAN
Each host on LAN maintains a a table of IP subnetwork addresses
If the address can not be found ARP broadcasts a request
Shouting: Who know about this IP address?
Other hosts listen and reply
The reply includes IP address and MAC
Any interested host can learn about the new information

40. ARP Example Assume 1 is sending a message to 2 (rose@sonoma.edu)
Sonoma.edu is the host
Host 1 sends a message to Domain Name System (DNS): what is the IP address for Sonoma.edu? 
What is the MAC address for ? Use ARP broadcast!
Host 2 respond: it is E2
Host 1 maps IP and MAC; encapsulate the IP message in the Ethernet frame and send it
Cashing can enhance ARP operation

41. ARP Example Assume 1 is sending a message to 4 (rose@sonoma.edu)
Sonoma.edu is the host
Host 1 sends a message to Domain Name System (DNS): what is the IP address for Sonoma.edu?  What is the MAC address for ? ARP cannot pass through the router!
Two choices:
Reconfigure routers to response to ARP (Proxy ARP)
Send the message to the LAN router (E3)F1F34 – Each router looks are the IP address and passes it to the next node using the routing table

42. RARP and BOOTP
Reverse ARP translates the Ethernet address to IP address
A diskless machine when it is booking can ask: My MAC is ; what is my IP?
RARP broadcasts the question (destination address is all one)
Not passed through the router!
Each LAN needs a RARP server!
Bootstrap protocol uses UDP and forwards over routers
Mapping must be done manually in each router!
Uses one server but harder to implement!

43. Dynamic Host Configuration Protocol
DHCP allows many and automatic configuration
Replaces BOOTP and RARP
DHCP sends a DISCOVER Packet
What is the IP address for this MAC?
Even when an IP address is assigned, how long is it good for?
Before the IP address is removed find another IP address….called Leasing

44. Remember… This is My MAC; what is my IP address? RARP / DHCP
This is the destination host name, what it is IP address? DNS Server
This is the IP address, what is your` MAC address? ARP

45. References
Tanenbaum
Tomasi Text Book
Comer Text book