IP
Internet Protocol
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Based on notes from D. Hollinger |
Recall the OSI Model:
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7
Application |
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6 Presentation |
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5 Session |
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4 Transport |
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3 Network |
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2 Data-Link |
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1 Physical |
Slide 3
IP & OSI
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In OSI reference model terminology -the
IP protocol covers the network layer. |
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IP can be used on many data-link layers
(can support many network hardware implementations). |
But First ...
Ethernet - A Real
Data-Link Layer
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It will be useful to discuss a real
data-link layer. |
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Ethernet (really IEEE 802.3) is widely
used. |
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Supported by a variety of physical
layer implementations. |
Ethernet
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Multi-access (shared medium). |
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Every Ethernet interface has a unique
48 bit address (a.k.a. hardware address). |
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Example: C0:B3:44:17:21:17 |
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The broadcast address is all 1’s. |
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Addresses are assigned to vendors by a
central authority. |
CSMA/CD
Carrier
Sense Multiple Access
with
Collision Detection
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Carrier Sense: can tell when another
host is transmitting |
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Multiple Access: many hosts on 1 wire |
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Collision Detection: can tell when
another host transmits at the same time. |
An Ethernet Frame
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The preamble is a sequence of
alternating 1s and 0s used for synchronization. |
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CRC is Cyclic Redundancy Check |
Ethernet Addressing
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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. |
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Some interfaces can also be programmed
to recognize multicast addresses. |
Back to IP
Internet Protocol
The
IP in UDP/IP and TCP/IP
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IP is the network layer |
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packet delivery service (host-to-host). |
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translation between different data-link
protocols. |
IP Datagrams
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IP provides connectionless, unreliable
delivery of IP datagrams. |
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Connectionless: each datagram is
independent of all others. |
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Unreliable: there is no guarantee that
datagrams are delivered correctly or at all. |
IP Addresses
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IP addresses are not the same as the
underlying data-link (MAC) addresses. |
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Why ? |
IP Addresses
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IP is a network layer - it must be
capable of providing communication between hosts on different kinds of
networks (different data-link implementations). |
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The address must include information
about what network the receiving host is on. This makes routing feasible. |
IP Addresses
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IP addresses are logical addresses (not
physical) |
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32 bits. |
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Includes a network ID and a host ID. |
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Every host must have a unique IP
address. |
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IP addresses are assigned by a central
authority (Internet Corporation for Assigned Names and Numbers -- ICANN) |
The four formats of IP
Addresses
"Class A"
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Class A |
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128 possible network IDs |
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over 4 million host IDs per network ID |
Network and Host IDs
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A Network ID is assigned to an
organization by a global authority. |
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Host IDs are assigned locally by a
system administrator. |
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Both the Network ID and the Host ID are
used for routing. |
IP Addresses
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IP Addresses are usually shown in dotted
decimal notation: |
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1.2.3.4 00000001 00000010 00000011 00000100 |
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cs.rpi.edu is 128.213.1.1 |
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10000000 11010101 00000001 00000001 |
Host and Network
Addresses
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A single network interface is assigned
a single IP address called the host address. |
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A host may have multiple interfaces,
and therefore multiple host addresses. |
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Hosts that share a network all have the
same IP network address (the network ID). |
IP Broadcast and Network
Addresses
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An IP broadcast addresses has a host ID
of all 1s. |
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IP broadcasting is not necessarily a
true broadcast, it relies on the underlying hardware technology. |
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An IP address that has a host ID of all 0s is called a network
address and refers to an entire network. |
Subnet Addresses
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An organization can subdivide it’s host
address space into groups called subnets. |
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The subnet ID is generally used to
group hosts based on the physical network topology. |
Subnetting
Subnetting
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Subnets can simplify routing. |
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IP subnet broadcasts have a hostID of
all 1s. |
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It is possible to have a single wire
network with multiple subnets. |
Mapping IP Addresses to Hardware Addresses
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IP Addresses are not recognized by
hardware. |
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If we know the IP address of a host,
how do we find out the hardware address ? |
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The process of finding the hardware
address of a host given the IP address is called |
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Address Resolution |
Reverse Address
Resolution
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The process of finding out the IP
address of a host given a hardware address is called |
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Reverse Address Resolution |
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Reverse address resolution is needed by
diskless workstations when booting. |
ARP
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The Address Resolution Protocol is used
by a sending host when it knows the
IP address of the destination but
needs the Ethernet address. |
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ARP is a broadcast protocol - every
host on the network receives the request. |
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Each host checks the request against
it’s IP address - the right one responds. |
ARP (cont.)
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ARP does not need to be done every time
an IP datagram is sent - hosts remember the hardware addresses of each other. |
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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
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Connectionless Delivery (each datagram
is treated individually). |
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Unreliable (delivery is not
guaranteed). |
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Fragmentation / Reassembly (based on
hardware MTU). |
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Routing. |
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Error detection. |
IP Datagram
IP Datagram Fragmentation
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Each fragment (packet) has the same
structure as the IP datagram. |
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IP specifies that datagram reassembly
is done only at the destination (not on a hop-by-hop basis). |
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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
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If packets arrive too fast - the
receiver discards excessive packets and sends an ICMP message to the sender
(SOURCE QUENCH). |
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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
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ICMP is a protocol used for exchanging
control messages. |
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ICMP uses IP to deliver messages. |
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ICMP messages are usually generated and
processed by the IP software, not the user process. |
ICMP Message Types
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Echo Request |
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Echo Response |
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Destination Unreachable |
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Redirect |
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Time Exceeded |
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Redirect (route change) |
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there are more ... |
IP/BYE-BYE
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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. |
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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
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UDP is a transport-layer protocol |
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communication between processes |
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UDP uses IP to deliver datagrams to the
right host. |
Ports
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UDP/IP uses an abstract destination
point called a protocol port. |
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Ports are identified by a positive
integer. |
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Operating systems provide some
mechanism that processes use to specify a port. |
Ports
UDP
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Datagram Delivery |
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Connectionless |
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Unreliable |
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Minimal |
TCP
Transmission
Control Protocol
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TCP is an alternative transport layer
protocol supported by TCP/IP. |
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TCP provides: |
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Connection-oriented |
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Reliable |
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Full-duplex |
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Byte-Stream |
TCP vs. UDP
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Q: Which protocol is better ? |
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A: It depends on the application. |
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TCP provides a connection-oriented,
reliable byte stream service (lots of overhead). |
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UDP offers minimal datagram delivery
service (as little overhead as possible). |
Hmmmmm. TCP or UDP ?
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Internet commerce ? |
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Video server? |
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File transfer? |
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Email ? |
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Chat groups? |
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Robotic surgery controlled remotely
over a network? |