Transcript Network Devices - courses.psu.edu

IST 228\Ch3\IP Addressing
TCP/IP and DoD Model (TCP/IP Model)
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IST 228\Ch3\IP Addressing
Process/Application Layer
• Defines protocols node-to-node application
communication such as
– DCHP, LPD, SNMP, DNS, NFS, Telnet, FTP,
SMTP, TFTP
• Controls user-interface specifications
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IST 228\Ch3\IP Addressing
Process/Application Layer Protocols
• Telnet- terminal emulation
• File Transfer Protocol (FTP)
• Network File System: allows to different types of
file systems operate.
• Simple Mail Transfer Protocol (SMTP)
• Line Printer Daemon (LDP): facilitates printer
sharing
• HTTP
• Simple Network Management Protocol (SNMP)
• X Windows
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IST 228\Ch3\IP Addressing
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Domain Name Service (DNS)
• Resolves host names into IP addresses.
– Discussion: Why do we need this?
– Use nslookup, dig, and host to find the IP addresses for
psu.edu and mit.edu
• The DNS system is divided into nonoverlapping zones.
• Each zones have one or more DNS servers.
edu name
server
psu.edu
bk.psu.edu
yale.edu
cs.yale.edu
ist.bk.psu.edu is looking for the IP address for linda.cs.yale.edu
IST 228\Ch3\IP Addressing
Dynamic Host Configuration Protocol
(DHCP)
• Gives IP addresses to hosts, and more
– IP address
– Subnet mask
– Domain name
– Default gateway (routers)
– DNS
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IST 228\Ch3\IP Addressing
The Host-to-Host Layer
• Functions
– Reliable end-to-end communication
– Ensuring error free delivery of data
– Prepares the data for delivery
• Protocols
– Transmission Control Protocol (TCP)
– User Datagram Protocol (UDP)
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IST 228\Ch3\IP Addressing
Ports
• TCP and UDP use port numbers to communicate with the
upper layers.
• Ports help to keep track of different conversations over
the network simultaneously
– The Well Known Ports are those from 0 through 1023.
– The Registered Ports are those from 1024 through 49151
– The Dynamic and/or Private Ports are those from 49152 through
65535
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Visit http://www.iana.org/assignments/port-numbers for well-known port numbers
You can see LINUX ports /etc/services (type cat /etc/services |more)
Use nmap to scan open ports of a machine.
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IST 228\Ch3\IP Addressing
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• Be familiar with these ports
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TCP port 20 – FTP data transfer
TCP port 21 – FTP control port
TCP port 23 – Telnet
TCP port 25 – SMTP
TCP & UDP port 53 – DNS
TCP (port 80) – HTTP Web services
TCP & UDP port 123 – Network Time Protocol (NTP)
TCP port 110 – Post Office Protocol version 3 (POP3)
TCP port 119 – Network News Transport Protocol (NNTP)
UDP port 69 – TFTP
UDP port 161 – SNMP
• How does it work?
Telnet Z.
A
I got a packet. Destination
port is 1030. Currently, my
Telnet application is using this
port, send it to the Telnet
application.
SP
Destination port
=23. I better send
the packet to my
Telnet application.
B
DP
1030 23
...........
SP
DP
23 1030
...........
IST 228\Ch3\IP Addressing
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TCP
Function
Definition
Ordered data
transfer and
segmentation
Continuous stream of bytes from
upper-layer process that is
segmented, numbered, and
sequenced for transmission
Establish and
terminate a
connection
Process used to initialize port
numbers and sequence and
acknowledgement fields
Flow control using
windowing
Process that uses window sizes to
protect buffer space and routing
devices
Error recovery
(reliability)
Process of numbering and
acknowledging data with
sequence and acknowledgment
header fields
Multiplexing
Multiplexing Function that allows
receiving hosts to decide the
correct application for which the
data is destined, based on the
port number
Three-way hand shake
IST 228\Ch3\IP Addressing
TCP Segment Format
• TCP creates a lot of
overhead.
• Discussion: Why do
we need that much
overhead?
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IST 228\Ch3\IP Addressing
User Datagram Protocol
• Used transporting information that does not
require reliable delivery
• Does not sequence the segments
• Sends the segments off and forgets about them
• Does not create a virtual circuit
• Connectionless protocol
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IST 228\Ch3\IP Addressing
The Internet Layer Protocols
• Functions
– Routing
– Provide single network interface to upper
layers
• Protocols
– Internet Protocol (IP)
– Internet Control Message Protocol (ICMP)
– Address Resolution Protocol (ARP)
– Reverse Address Resolution Protocol (RARP)
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IST 228\Ch3\IP Addressing
Internet Protocol
• IP sees the picture
• Functions:
– Receives segment from Host-to-Host Layer,
fragment them into packets, using routing
tables, routes them over the network, and
then reassembles them into segments on the
receiving end.
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IST 228\Ch3\IP Addressing
IP Header
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Internet Control Message Protocol
(ICMP)
• Provides message control and errorreporting services between two TCP/IP
host and between a host server and
gateway to the Internet
• Routes periodically sends following
messages
– Destination unreachable
– Buffer full
– Hops
– Pings
– Traceroute
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Address Resolution Protocol (ARP)
• finds the hardware address
of a host from a known IP
address
• How does it work?
– First look at the ARP cache
(ARP table).
– If IP to MAC mapping is not
in the cache, broadcast a
ARP request to hosts on the
local segment
– If the device in the local
network, it returns a ARP
reply.
– ..
• Discussions:
– How does the source know the IP of the
destination?
– What would happen if no ARP reply is
received?
– What happens when an ARP reply is
received?
– Why is it not a good idea to use static
ARP cache in the local network?
IST 228\Ch3\IP Addressing
Reverse Address Resolution Protocol
(RARP)
• Discovers the identity
of the IP address for
diskless machines.
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IST 228\Ch3\IP Addressing
Routers on the network
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Putting Things Together IP Routing
1. ICMP creates an echo pay load
2. ICMP hands the pay load to IP, which creates a packet. What is the
information loaded in the IP header?
3. IP works with ARP to determine the destination is on the local
network or not
4. No the destination is not on the local network, the packet needs to
be sent to the default gateway. Look for the address of the local
gateway.
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IST 228\Ch3\IP Addressing
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The default gateway address is 172.16.10.1 (the IP address of
interface E0). MAC address must be known for this interface.
Why?
Check the ARP cache for the MAC address corresponding
172.16.10.1.
MAC address is known now. Hand packet down to Data Link Layer.
A frame is generated.
The frame is handed down to the Physical Layer to be put on the
medium.
Every device on the collision domain receives the bits. They run
CRC and check FCS field. The interface E0 matches the FCS field.
Look what type of Network layer protocol is used.
The packet is pulled out from the frame, and the frame is
discarded.
IP receives the packet and checks the destination IP address.
The routing table must have an entity for 172.16.20.0, or the
packet is discarded.
The router finds an entity for 172.16.20.0
The router forwards the packet to the E1 buffer
The E1 buffer must know the hardware address of the destination
host. Why?
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IST 228\Ch3\IP Addressing
16. The router sends an ARP request for 172.16.20.2.
17. Host B responds with its MAC address.
18. The Data Link Layer (in router) creates a frame. The
frame is handed down to the Physical Layer to be sent
out on the physical medium.
19. Host B receives the frame and runs a CRC. It is a
match.
20. At the network layer, IP receives the packet. The
protocol field is checked to find the owner of the
payload.
21. It is for ICMP. The payload is handed to ICMP.
22. Happy Ending.
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