laning the hp
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hp education services
education.hp.com
1
LAN Concepts
Version C.01
H3065S Module 1 Slides
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What Is a Network?
A Network is a series of devices interconnected by communication pathways. Local Area Networks (LANs) span relatively small geographic areas.Wide Area Networks (WANs) span relatively large geographic areas.
Chicago Office LAN Tokyo Office LAN
Boston Office LAN
WAN
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The OSI Model in a Nutshell7 Application How is data created and used?
6 Presentation How is the data represented to the application?
Is the data in EBCDIC or ASCII format?
5 Session How does an application initiate a connection?
How does an application actually transmit/receive data?
How does an application know data has been received?
4 Transport Should the receiver acknowledge receipt of a packet?
How should the acknowledgement be handled?
Which process should receive the data?
3 Network How is data routed between networks?
2 Data link How do I know when its my turn to transmit?
How do I know which data is for me?
How are collisions handled?
1 Physical What kinds of cabling are supported?
What kinds of connectors are supported?
Whats the longest supported cable segment?
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Media Access Control (MAC) Addresses
Every LAN card has a unique 48-bit MAC address. Every frame of data contains a source and destination MAC.
Hosts accept frames destined for their MAC address.
Hosts ignore frames destined for other MAC addresses.
0x0060B07ef226
These six hex
digits identify
the card
manufacturer
Following
number is
in hex ...
These six hex
digits uniquely
identify this
card
Which frames
are for me?
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Internet Protocol (IP) Addresses
128.1.1.1
Which network
is the host on?
What is the
host's address
on that
network?
Every host on an IP network has a unique, 32-bit IP address. IP addresses make it possible to logically group nodes into IP networks. Network bits within the IP determine which network the host is on.Host bits within the IP distinguish each host from all other hosts on the network. Hosts with identical network bits are said to be on the same IP network.
128.1 Network
128.1.1.1 128.1.1.2
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IP Network Classes
/8 Network
/16 Network
/24 Network
The IP address network/host bit boundary varies from network to network.
Networks with more host bits may have more hosts.
Networks with fewer host bits may have fewer hosts.
8 Network Bits 8 Network Bits 8 Network Bits
8 Network Bits 8 Network Bits
8 Network Bits 8 Host Bits 8 Host Bits 8 Host Bits
8 Host Bits 8 Host Bits
8 Host Bits
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The IP Netmask
Netmask 1's identify network bits Netmask 0's identify host bits
111111111 11111111 00000000 00000000Netmask:
255.255.0.0 or0x ff ff 00 00
100000000 00000001 00000001 00000001IP Address:
128.1.1.1/16
Q: How many bits in my IP are network bits?
A: The netmask has the answer!
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The IP Network Address
Every host must know which network it is connected to.
Formulate the network address by setting all IP host bits to "0".
128.1.1.1/16128.1.1.2/16
128.1.1.3/16
192.1.1.1/24
192.1.1.2/24
192.1.1.3/24
100000000 00000001 00000000 00000000
Network Address: 128.1.0.0/16
110000000 00000001 00000001 00000000
Network Address: 192.1.1.0/24
Q: Which network am I on?
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The IP Broadcast Address
# ping 128.1.255.255
128.1.1.1 128.1.1.2 128.1.1.3
Packets sent
to the network
broadcast addressare received by ALL
hosts on the
network.
Formulate the
broadcast addressby setting all
host bits to "1".
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The IP Loopback Address
128.1.1.2128.1.1.1 128.1.1.3
# ping 127.0.0.1
The loopback address, 127.0.0.1, is a special addressthat always references your local host.
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Obtaining an IP Address
Private Intranet
Firewall
Obtaining an IP address on
a Private Intranet allows
limited access to the Internet
via a network Firewall.
Obtaining an IP address on
the Public Internet allows
direct connectivity to millions
of hosts worldwide.
Public Internet
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IP Address Examples
IP Address
192.66.123.4/24
148.10.12.14/16
9.12.36.1/8
163.128.19.9/16
123.45.65.23/8
199.66.55.4/24
Netmask BroadcastNetwork
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Host Names
I can reference nodes
by host name and let
HP-UX automatically
determine the IP
addresses for me!
# telnet oakland
128.1.1.1 sanfran
128.1.1.2 oakland
128.1.1.3 la
128.1.1.4 sandiego
/etc/hosts
Telnet request
To: 128.1.1.2
128.1.1.2 (oakland)
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128.1.1.1 080009-000001
128.1.1.2 080009-000002
128.1.1.3 080009-000003
Converting IP Addresses to
MAC AddressesSource MAC: 080009-000001
Destination MAC: 080009-000002
Outbound Frame
128.1.1.2
(oakland)
080009-000002
1. Resolve hostname oakland to an IP address.
2. Lookup the MAC address in the ARP cache corresponding to oakland's IP address.
3. Send the packet to oakland's MAC address.
Example: System sanfran pings system oakland
128.1.1.1 sanfran
128.1.1.2 oakland
128.1.1.3 la
/etc/hosts ARP cache (memory resident)
128.1.1.1
(sanfran)
080009-000001
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Populating the ARP Cache
128.1.1.1 080009-000001
128.1.1.2 080009-000002
128.1.1.3 080009-000003
128.1.1.4 incomplete!
ARP cache
$ ping sandiego
128.1.1.4
(sandiego)
128.1.1.3
(la)
128.1.1.2
(oakland)
128.1.1.1
(sanfran)
BroadcastPacket
2
3
4
5
6
128.1.1.4 080009-23EF45
1. sanfran pings sandiego. sanfran resolves sandiego's IP address via /etc/hosts.2. Search for sandiego's IP in the arp cache the IP address is not found in ARP cache.
3. Send ARP broadcast on the local network to find the MAC address for 128.1.1.4.
4. System with the specified IP address responds with a packet containing its MAC.
5. The MAC address and corresponding IP address are added to sanfran's ARP cache.
6. The frame specifically addressed to sandiego's MAC address is sent.
Example: sanfran pings sandiego
1
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Putting It All Together
Is the
destination a hostname
or an IP address?
Is the
destination on the
local network?
Look for the destination
IP address in routing table.
Resolve hostname
to corresponding
IP address.
Destination machine responds
with its MAC address.
Record the found MAC address
in the ARP cache for later reference.
Send the packet out on the wire
with the source and destination
MAC and IP addresses.
IP address
hostname
Is the
destination IP address
found in ARP cache?
Yes, on localnetwork
No
Send packet to router
to be forwarded to
destination host.
No Yes
Send a broadcast requesting
the MAC for the destination IP.Use the MAC address found
in ARP cache as the
destination MAC.
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Managing Packet Flow with TCP
oakland
128.1.1.2
sanfran
128.1.1.1
1
34
5
2
6
1 122 3 3 2
1
2
3
Acknowledgements
1
2
3
Open
Data Packets
Close
Segment
Data
Send
PacketRetransmit
Reassemble
1. Open connection to remote node.
2. Segment data into datagram packets.
3. Send datagrams to destination node.
4. If there is no acknowledgement, retransmit!
5. Close connection after all datagrams are received.
6. Receiver node reassembles datagrams into proper order.
Sending a packet with TCP:
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Managing Packet Flow with UDP
Sending a packet with UDP:
128.1.1.2
(oakland)
128.1.1.1
(sanfran)
2
1 3
12
2
1. Packets cannot be segmented or streamed; a packet is always sent as a single message.
2. No connection is opened with the node; the packet is simply sent to the node.3. No acknowledgement is sent back to the original sender.
1 1
Since the original sender never knows if packet is received, sender never retransmits.
The receiver doesnt know if it received all of the intended packets.
With UDP, the applicationis responsible for ensuring data transmission is complete.
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Sending Data to Applications via Ports
Problem: Who gets the data?
128.1.1.4
(sandiego)
128.1.1.3
(la)
128.1.1.2
(oakland)
128.1.1.1 (sanfran)
Thousands of packets arrive every minute on the LAN interface card.
How does the network subsystem know to which application to deliver the network packets?
telnetd
$ telnet sanfran $ rlogin sanfran$ ftp sanfran
ftpd rlogind
Network Subsystem
Solution: Assign each application a unique port number.
When each packet is sent, aport numberwill be included in the packet.
The port numbers identify which network application is to receive the packet.
To: port 23 To: port 21 To: port 513
port 23 port 21 port 513
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Managing Ports with Sockets
128.1.1.3
(la)
128.1.1.2
(oakland)
128.1.1.1 (sanfran)
telnetd
$ telnet sanfran
$ telnet sanfran
$ telnet sanfran
$ ftp sanfran
Network Subsystem
telnetd
ftpd
telnetd
Problem: Which network application gets the data when multiple instances are present?
Multiple clients can be executing the same network application.
Multiple instances of the network application can be running on the same client.
Solution: Create a unique socket for each process which runs a network application.
A socketis a port number combined with a nodes IP address.A socket connection is the coupling of a client socket address with a server socket address.
To: port 23 To: port 23 To: port 23
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More on Socket Connections
128.1.1.2 (oakland)
128.1.1.1 (sanfran)$ telnet sanfran
Network Subsystem
telnetd telnetd
128.1.1.1 . 23
128.1.1.1 . 23
128.1.1.2 . 50001
Socket
Socket
To: port 23 To: port 23
$ telnet sanfran128.1.1.2 . 50002
128.1.1.1.23 128.1.1.1.23
128.1.1.2.50001
telnet telnet
128.1.1.2.50002
Communications between two processes
over the network are uniquely defined by
their socket connection.
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Revisiting the OSI Model7 Application Creates/receives the data.
6 Presentation Determines the format in which to represent the data.
Possible choices are EBCDIC or ASCII format.
5 Session Establishes a unique communication path between client/server.
Sockets are used to communicate between two systems.A socket is an IP address plus a port number.
4 Transport TCP requires that a socket connection be established; UDP does not.TCP requires packets be acknowledged; UDP does not.
TCP is streams-based; UDP is message-based.
3 Network IP addressesdefine a systems network and host number.2 Data link MAC addresses uniquely identify a LAN card.
Ultimately, packets are sent from one MAC address to another.
ARP caches map IP addresses to MAC addresses.
1 Physical The type of media used to connect the machines together.
The type of cabling used for the network.
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