1. Protocol Headers Pre DA SA 0800h … version H L 6 TCP Header Data FCS
Ether Type
0800h …
version
H L
Protocol 6
TCP Header
Data
FCS
Data Link Header
IP Header
Trailer
1: Internet Control Message Protocol (ICMP)
2: Internet Group Management Protocol (IGMP)
6: Transmission Control Protocol (TCP)
17: User Datagram Protocol (UDP)
89: Open Shortest Path First (OSPF)
0x0800 Internet Protocol, Version 4 (IPv4)
0x0806 Address Resolution Protocol (ARP)
0x8100 IEEE 802.1Q-tagged frame
0x86DD Internet Protocol, Version 6 (IPv6)
0x8847 MPLS unicast
0x8848 MPLS multicast

2. Simple internetwork (example)

3. Service model Host-to-host service
Philosophy: Define a model that is so undemanding that almost any network technology is able to provide the required service. (IP)

4. IPv4 Header

5. IPv4 Header

6. IPv4 Header

7. IPv4 Header

8. Protocol Headers Pre DA SA 0800h … version H L 6 TCP Header Data FCS
Ether Type
0800h …
version
H L
Protocol 6
TCP Header
Data
FCS
Data Link Header
IP Header
Trailer
1: Internet Control Message Protocol (ICMP)
2: Internet Group Management Protocol (IGMP)
6: Transmission Control Protocol (TCP)
17: User Datagram Protocol (UDP)
89: Open Shortest Path First (OSPF)
0x0800 Internet Protocol, Version 4 (IPv4)
0x0806 Address Resolution Protocol (ARP)
0x8100 IEEE 802.1Q-tagged frame
0x86DD Internet Protocol, Version 6 (IPv6)
0x8847 MPLS unicast
0x8848 MPLS multicast

9. TCP/IP Protocols

10. IP Addressing
An IP address is a numeric identifier assigned to each machine on an IP network
It designates the specific location of a device on the network
An IP address is a software address, not a hardware address
Hardware address is hard-coded on a Network Interface Card (NIC) and used for finding hosts on a local network

11. IP Addressing Scheme An IP address consists of 32 bits of information
These bits are divided into four sections, referred to as octets or bytes
Three methods of depiction
Dotted-decimal, as in
Binary, as in
Hexadecimal, as in AC.10.1E.38

12. ……

13. Network Addressing
The network address (which can also be called the network number) uniquely identifies each network
Every machine on the same network shares that network address as part of its IP address
In the IP address , for example, is the network address
The node address uniquely identifies, each machine on a network
This part of the address must be unique because it identifies a particular machine, also referred as a host address
In the sample IP address , the is the node address

14. Network Addressing
The designers of the Internet decided to create classes of networks based on network size
For the small number of networks possessing a very large number of nodes, they created the rank Class A network
At the other extreme is the Class C network, which is reserved for the numerous networks with a small number of nodes
The class distinction for networks between very large and very small is predictably called the Class B network

15. Network Address Range: Class A
First bit of the first byte in a Class A network address must always be off, or 0
This means a Class A address must be between 0 and 127
Consider the following network address:
0xxxxxxx
If we turn the other 7 bits all off and then turn them all on, we’ll find the Class A range of network addresses:
= 0
= 127

16. Network Address Range: Class B
First bit of the first byte must always be turned on, but the second bit must always be turned off
If you turn the other 6 bits all off and then all on, you will find the range for a Class B network:
= 128
= 191
As you can see, a Class B network is defined when the first byte is configured from 128 to 191

17. Network Address Range: Class C
For Class C networks, first 2 bits of the first octet are always turned on, but the third bit can never be on
Following the same process as the previous classes, convert from binary to decimal to find the range
Range for a Class C network:
= 192
= 223

18. Network Address Ranges: Classes D and E
The addresses between 224 and 255 are reserved for Class D and E networks
Class D (224–239) is used for multicast addresses
Class E (240–255) for scientific purposes

19. …… A B C D E
Loop back

20. IP Addressing

21. Reserved IP Addresses Network address of all 0s
Network Reserved for loopback tests. Designates the local node and allows that node to send a test packet to itself without generating network traffic.
Node address of all 0s Interpreted to mean “network address” or any host on specified network.
Node address of all 1s Interpreted to mean “all nodes” on the specified network; for example, means “all nodes” on network (Class B address).
Entire IP address set to all 1s (same as ) Broadcast to all nodes on the current network; sometimes called an “all 1s broadcast” or limited broadcast.

22. Private IP Addresses
These addresses can be used on a private network, but they’re not routable through the Internet
A measure of well-needed security
Also conveniently saves valuable IP address space
Network Address Translation (NAT), which basically takes a private IP address and converts it for use on the Internet

23. Private IP Addresses Class A 10.0.0.0 through 10.255.255.255 Class B
Class C
through

24. The Problem Application layer usually deals with URL’s
How a name gets resolved to its corresponding IP ???
IP layer deals with IP addresses
IP addresses (in IP Packet) are part of the data of an Ethernet frame
Ethernet only recognizes physical addresses

25. The Problem
Two machines on a given network can communicate only if they know each others physical addresses
How a host or a router maps an IP address to a correct physical address when it needs to send a packet across a physical network ???
This mapping is required at each step along a path from the original source to its ultimate destination
The problem of mapping high level IP addresses to the physical addresses is know as the address resolution problem

26. Address Resolution Protocol (ARP)
ARP is the Address Resolution Protocol (RFC 826)
It dynamically maps the IP address to physical address
ARP allows a host to find the physical address of a target host on the same physical network given only the targets IP address
For networks like ethernet that have broadcast capability
It does not need a centralized database
Where does the ARP lies in the TCP/IP protocol stack??

27. ARP
6 Octets
2 Octets
Octets
4 Octets
D.Address
S.Address
Frame
Type
Frame Data
CRC
Network software in the receiver further examines the ARP message to distinguish between ARP requests and replies
0806
ARP req/reply (28 Octet)
Pad (18)

28. Working of ARP
IP layer datagram is sent to a host or a router on a locally attached network
The sender knows the IP address of destination
ARP sends an ethernet frame called an ARP request to every host on the network (broadcast)
The ARP request message means, “if you are the owner of this IP address, please respond to me with your hardware address”

29. 0:0:0C:75 Sender HA (octet 0-3)
Working of ARP 8 16 24 32
Hardware Type
Protocol Type (080616)
HLEN
PLEN
(Operation) 1
0:0:0C:75 Sender HA (octet 0-3)
25:12 (Sender HA,octet 4-5)
Sender IP (octet 0-1)
1.94 (Sender IP,octet 2-3)
Target HA (octet 0-1)
Target HA (octet 2-5)
Target IP (octet 0-3)

30. Working of ARP Hardware Type Protocol Type (080616) HLEN PLEN8 16 24 32
Hardware Type
Protocol Type (080616)
HLEN
PLEN
(Operation) 2
0:0:0C:75 Sender HA (octet 0-3)
80:37 (Sender HA,octet 4-5)
Sender IP (octet 0-1)
1.10 (Sender IP,octet 2-3)
0:0 Target HA (octet 0-1)
0C:75:25:12 Target HA (octet 2-5)
Target IP (octet 0-3)

31. ARP Cache The ARP requests are broadcasted
Broadcasting is far more expensive if every time a machine needs to transmit a packet to another
Computers maintains a cache of recently acquired IP-to-Physical address mapping
Thus before sending an ARP request, a machine always looks its ARP cache to find the desired mapping
ARP requests only broadcasted if no mapping found in the cache

32. RARP RARP is Reverse Address Resolution Protocol
Used to map hardware addresses to IP addresses (normally at booting time)
In case of diskless booting, the systems reads its hardware address from the interface card and send as RARP request asking for someone to reply with the diskless system’s IP address (in an RARP reply)
It says: “My 48-bit MAC address is x.x.x.x.x.x, does anyone out there knows my IP ?”

33. RARP
The RARP server sees the request, looks up and map the ethernet address and sends back corresponding IP address
As with ARP, the RARP requests is broadcasted and RARP reply is unicasted
The frame structure of ARP and RARP is same

34. RARP Frame Hardware Type Protocol Type (083516) HLEN PLEN8 16 24 32
Hardware Type
Protocol Type (083516)
HLEN
PLEN
Operation (3 or 4)
Sender HA (octet 0-3)
Sender HA (octet 4-5)
Sender IP (octet 0-1)
Sender IP (octet 2-3)
Target HA (octet 0-1)
Target HA (octet 2-5)
Target IP (octet 0-3)