IP
Internet Protocol
Based on notes from D. Hollinger

Recall the OSI Model:
7    Application
6    Presentation
5    Session
4    Transport
3    Network
2    Data-Link
1    Physical

Slide 3

IP & OSI
In OSI reference model terminology -the IP protocol covers the network layer.
IP can be used on many data-link layers (can support many network hardware implementations).

But First ...

Ethernet - A Real Data-Link Layer
It will be useful to discuss a real data-link layer.
Ethernet (really IEEE 802.3) is widely used.
Supported by a variety of physical layer implementations.

Ethernet
Multi-access (shared medium).
Every Ethernet interface has a unique 48 bit address (a.k.a. hardware address).
Example:   C0:B3:44:17:21:17
The broadcast address is all 1’s.
Addresses are assigned to vendors by a central authority.

CSMA/CD
 Carrier Sense Multiple Access
with
Collision Detection
Carrier Sense: can tell when another host is transmitting
Multiple Access: many hosts on 1 wire
Collision Detection: can tell when another host transmits at the same time.

An Ethernet Frame
The preamble is a sequence of alternating 1s and 0s used for synchronization.
CRC is Cyclic Redundancy Check

Ethernet Addressing
Each interface looks at every frame and inspects the destination address. If the address does not match the hardware address of the interface or the broadcast address, the frame is discarded.
Some interfaces can also be programmed to recognize multicast addresses.

Back to IP

Internet Protocol
The IP in UDP/IP and TCP/IP
IP is the network layer
packet delivery service (host-to-host).
translation between different data-link protocols.

IP Datagrams
IP provides connectionless, unreliable delivery of IP datagrams.
Connectionless: each datagram is independent of all others.
Unreliable: there is no guarantee that datagrams are delivered correctly or at all.

IP Addresses
IP addresses are not the same as the underlying data-link (MAC) addresses.
            Why ?

IP Addresses
IP is a network layer - it must be capable of providing communication between hosts on different kinds of networks (different data-link implementations).
The address must include information about what network the receiving host is on. This makes routing feasible.

IP Addresses
IP addresses are logical addresses (not physical)
32 bits.
Includes a network ID and a host ID.
Every host must have a unique IP address.
IP addresses are assigned by a central authority (Internet Corporation for Assigned Names and Numbers -- ICANN)

The four formats of IP Addresses

"Class A"
Class A
128 possible network IDs
over 4 million host IDs per network ID

Network and Host IDs
A Network ID is assigned to an organization by a global authority.
Host IDs are assigned locally by a system administrator.
Both the Network ID and the Host ID are used for routing.

IP Addresses
IP Addresses are usually shown in dotted decimal notation:
1.2.3.4        00000001 00000010 00000011 00000100
cs.rpi.edu is  128.213.1.1
10000000 11010101 00000001 00000001

Host and Network Addresses
A single network interface is assigned a single IP address called the host address.
A host may have multiple interfaces, and therefore multiple host addresses.
Hosts that share a network all have the same IP network address (the network ID).

IP Broadcast and Network Addresses
An IP broadcast addresses has a host ID of all 1s.
IP broadcasting is not necessarily a true broadcast, it relies on the underlying hardware technology.
An IP address that has a  host ID of all 0s is called a network address and refers to an entire network.

Subnet Addresses
An organization can subdivide it’s host address space into groups called subnets.
The subnet ID is generally used to group hosts based on the physical network topology.

Subnetting

Subnetting
Subnets can simplify routing.
IP subnet broadcasts have a hostID of all 1s.
It is possible to have a single wire network with multiple subnets.

Mapping IP Addresses  to Hardware Addresses
IP Addresses are not recognized by hardware.
If we know the IP address of a host, how do we find out the hardware address ?
The process of finding the hardware address of a host given the IP address is called
Address  Resolution

Reverse Address Resolution
The process of finding out the IP address of a host given a hardware address is called
Reverse Address Resolution
Reverse address resolution is needed by diskless workstations when booting.

ARP
The Address Resolution Protocol is used by a sending host when it  knows the IP address  of the destination but needs the Ethernet address.
ARP is a broadcast protocol - every host on the network receives the request.
Each host checks the request against it’s IP address - the right one responds.

ARP (cont.)
ARP does not need to be done every time an IP datagram is sent - hosts remember the hardware addresses of each other.
Part of the ARP protocol specifies that the receiving host should also remember the IP and hardware addresses of the sending host.

ARP conversation

RARP conversation

Services provided by IP
Connectionless Delivery (each datagram is treated individually).
Unreliable (delivery is not guaranteed).
Fragmentation / Reassembly (based on hardware MTU).
Routing.
Error detection.

IP Datagram

IP Datagram Fragmentation
Each fragment (packet) has the same structure as the IP datagram.
IP specifies that datagram reassembly is done only at the destination (not on a hop-by-hop basis).
If any of the fragments are lost - the entire datagram is discarded (and an ICMP message is sent to the sender).

IP Flow Control & Error Detection
If packets arrive too fast - the receiver discards excessive packets and sends an ICMP message to the sender (SOURCE QUENCH).
If an error is found (header checksum problem) the packet is discarded and an ICMP message is sent to the sender.

ICMP
Internet Control Message Protocol
ICMP is a protocol used for exchanging control messages.
ICMP uses IP to deliver messages.
ICMP messages are usually generated and processed by the IP software, not the user process.

ICMP Message Types
Echo Request
Echo Response
Destination Unreachable
Redirect
Time Exceeded
Redirect (route change)
there are more ...

IP/BYE-BYE
IP/BYE-BYE is a lecture protocol used to signal the class that we have just finished our discussion of IP - the network layer of UDP/IP and TCP/IP.
The appropriate response to an IP/BYE-BYE request is immediate applause, although simply opening your eyes is enough (known as a WAKEUP response).

UDP User Datagram Protocol
UDP is a transport-layer protocol
communication between processes
UDP uses IP to deliver datagrams to the right host.

Ports
UDP/IP uses an abstract destination point called a protocol port.
Ports are identified by a positive integer.
Operating systems provide some mechanism that processes use to specify a port.

Ports

UDP
Datagram Delivery
Connectionless
Unreliable
Minimal

TCP
Transmission Control Protocol
TCP is an alternative transport layer protocol supported by TCP/IP.
TCP provides:
Connection-oriented
Reliable
Full-duplex
Byte-Stream

TCP vs. UDP
Q: Which protocol is better ?
A: It depends on the application.
TCP provides a connection-oriented, reliable byte stream service (lots of overhead).
UDP offers minimal datagram delivery service (as little overhead as possible).

Hmmmmm. TCP or UDP ?
Internet commerce ?
Video server?
File transfer?
Email ?
Chat groups?
Robotic surgery controlled remotely over a network?