Download Networks I - Delmar

Networks I
Chapter 15
Chapter Objectives
•
•
•
•
Understand basic network terminology.
Understand the basics of the TCP/IP protocol suite.
Understand the basics of IP addresses.
Understand basic IP routing.
– Understand the basics of ARP, and DNS.
– Understand the basics of layer 2 and layer 3 “routing”.
• Understand common network hardware.
Network Protocols
• Internetworking - the process of connecting two
computer networks together.
– The interconnected networks may or may not use the
same network technology.
– The interconnected networks may or may not be in the
same location.
– The interconnected networks may or may not encompass
the same hardware.
– The interconnected networks may or may not employ the
same software.
– The Internet is one example of internetworking.
Network Protocols
WARNING:
Networking seems to encompass every two,
three, four, five, and six character
combination of letters into an acronym.
Network Protocols (ISO)
– The International Standards Organization adopted a
networking model called the Open System Interconnect.
– This network model breaks the task of networking down into
seven layers (then arranged them like a top-ten list):
•
•
•
•
•
•
•
7) Application layer - Provide end-user services
6) Presentation Layer - Deal with problems & compression
5) Session Layer - Authentication and Authorization
4) Transport Layer - Guarantee end-to-end (correct) delivery
3) Network Layer - Routing and Accounting
2) Data Link Layer - Transmit/receive packets & addressing
1) Physical Layer - The cable or media itself
Network Protocols (ISO)
• The ISO/OSI model was the result of design by committee.
• The layers had little base in reality: They did not match realworld protocol stacks.
• The ISO/OSI model suffered a horrible “death” (nobody
could make it work).
• Network theory courses still hold the ISO model up as the
“right way to do things.”
Network Protocols (TCP/IP)
• Internet Protocol (TCP/IP model)
– The TCP Protocol is designed around a simplified four layer
approach:
• Link Layer - Network hardware and device drivers
• Network Layer - Basic Communications, addressing, routing
– The network layer protocol is the Internet Protocol (IP).
• Transport Layer - Communication among programs on a net.
– There are two data Transport protocols In TCP/IP:
» User Datagram Protocol (UDP)
» Transmission Control Protocol (TCP)
• Application Layer - End user application programs
– Utilities like ftp, ssh, rlogin, rsh, DNS, NFS, CIFS, …
Network Protocols (TCP/IP)
Network Protocols (TCP/IP)
• In order for all of the computers on the Internet to communicate,
we have to:
– Ensure that the computers speak the same language.
• The language used on the Internet is TCP/IP.
– IP is the Internet Protocol
» IP provides a communication channel, including
addressing, and routing.
– TCP is the Transmission Control Protocol.
– UDP is the User Datagram Protocol..
» TCP and UDP provide data delivery over the IP
channel.
– Ensure that each network device has a unique address.
– Ensure that the computers have access to some form of
bridging hardware in order to connect dissimilar network
technologies.
Network Protocols (TCP/IP)
• Internet Protocol (Packets)
– As a packet travels through the levels of the TCP/IP
protocol, each layer adds it’s own header information
to the datagram.
• This process of each layer encoding it’s own
management information into the existing datagram
is called nesting, or encapsulation.
– Various headers contain the source and destination
address, checksum, protocol specific information, and
other handling instructions.
– At the receiving end the headers are stripped off by the
appropriate level, the header contents are examined
for special handling information, and the datagram is
delivered to the appropriate application.
Network Protocols (TCP/IP)
• Internet Protocol Version 4 (IPv4)
– An IP address consists of four byte values separated by
periods. For Example: 123.45.67.89
– This notation is also known as the dotted quad format.
– Each of the values must be in the range of 0 - 255 (8 bits).
– An IPv4 address is therefore 32 bits (4 bytes * 8 bits/byte).
• There are five classes of IP Addresses in IPv4:
– Class A, B, and C addresses are used for single host addressing.
– Class D addresses are used for multicast connections.
– Class E addresses are experimental.
Network Protocols (TCP/IP)
• Internet Protocol (IPv4)
• Class A Networks - The first byte is in the range of 1 - 127.
– The first four bits of the address are Binary 0 X X X
– There are 127 Class A networks.
– The first byte of a class A address is the network
number.
– The remaining three bytes are the host address on that
network.
110
.32.4.18
network host address
– Each Class A network can address up to 16 million
hosts.
– All Class A networks are currently assigned and in use. (lie)!
Network Protocols (TCP/IP)
• Internet Protocol (IPv4)
• Class B Networks - The first byte in the range of 128 - 191.
– The first four bits of the address are BINARY 1 0 X X
– There are 16,384 Class B networks.
– The first two bytes of a class B address are the network
number.
– The remaining two bytes are the host address on that
network.
129.74.
25.98
network host address
– Each Class B network can address up to 65,000 hosts.
– Notre Dame holds a Class B license (129.74.X.Y)
– All Class B networks are currently assigned and in use. (lie)!
Network Protocols (TCP/IP)
• Internet Protocol (IPv4)
• Class C Networks - The first byte in the range of 192 - 223.
– The first four bits of the address are 1 1 0 X
– There are 2,097,152 Class C networks.
– The first three bytes of a class C address is the network
number.
– The remaining byte is the host address on that network.
210.43.2
.8
network
host address
– Each Class C network can address up to 254 hosts.
– Most of the Class C networks are assigned and in use.
Network Protocols (TCP/IP)
• Internet Protocol (IPv4)
• Class D Networks - The first byte in the range of 224 - 239.
– The first four bits of the address are 1 1 1 0
– These addresses are used for “one to many”
communications (multicasting).
• Class E Networks - The first byte in the range of 240 - 254.
– The first four bits of the address are 1 1 1 1
– These addresses are reserved for experimental use by
the IANA/IETF.
Network Protocols (TCP/IP)
• The numbers 0, and 255 have special meaning in some
fields of IP addresses.
– A Zero host address refers to “this network”
• For example 129.74.0.0 refers to the Class B network
129.74.
– A host address of all ones is called the broadcast address.
• For example 129.74.255.255 refers to all hosts on
the 129.74 Class B network.
• The address 127.0.0.1 is the loopback address.
– This address is used for inter-process communications, and
for network testing.
– All of the 127 network is reserved (127.0.0.0 127.255.255.255).
Network Protocols (TCP/IP)
• Subnets and Supernets
– Subnets provide a way of chopping up large networks into
smaller entities:
– Networks might be split up to segment traffic.
– Networks might be split up to facilitate better use of an
assigned IP address space.
• A class A could be made to look like several class B/C networks.
• A class B could be made to look like several Class C networks.
• Even a Class C network can be sub-networked.
– To subnet a network, we apply a netmask.
• Standard netmask for Class A is 255.0.0.0
• Standard netmask for Class B is 255.255.0.0
• Standard netmask for Class C is 255.255.255.0
– By logically ANDING the address and the netmask, we can
determine the NETWORK portion of the address.
Network Protocols (TCP/IP)
• Subnets
• Network routers look at the destination IP address, and the netmask for
the address to make delivery (routing) decisions.
– Once the router determines the class of the destination address, it
consults a table to find the appropriate netmask.
• Class A netmask is 255.0.0.0
• Class B netmask is 255.255.0.0
• Class C netmask is 255.255.255.0
• For example, a packet bound from a random host on the Internet, to my
office host would generate the following operation:
– 129.74.25.98 = 10000001 . 01001010 . 00011001 . 01100010
– 255.255.0.0 = 11111111 . 11111111 . 00000000 . 00000000
10000001 . 01001010 . 00000000 . 00000000
== 129.74.0.0 or 129.74/16
Network Protocols (TCP/IP)
• The lab 129.74.46 network is subnetted into several
smaller networks.
– By “stealing” bits from the host number, we can make the network
number larger. This allows us to make a class B or C network look
like many smaller (classless) networks.
• These networks are denoted by the formula N.S.H
(network.subnet.host)
– By using a 27 bit netmask we can divide a network up into several
“32” host networks. 11111111 . 11111111 . 11111111 . 11100000
• 27 bits of network address, 5 bits of host address.
– 129.74.46.0 through 129.74.46.31 is one such network.
– 129.74.46.32 through 129.74.46.63 is one such network.
– 129.74.46.64 through 129.74.46.95 is one such network.
• 129.74.46.32/27 denotes a host on a classless network which
employs a 27 bit netmask.
• This is referred to as Classless InterDomain Routing (CIDR)
Network Protocols (TCP/IP)
• Subnets and Supernets
– Supernets allow us to aggregate several smaller
networks into one larger routing entity:
• This is the opposite of subnetting.
– Supernetting is employed to minimize routing table
entries.
» If an ISP has a customer who needs addresses for 400
hosts, a single class C address will not suffice.
» By combining two class C networks, the ISP can make a
single routing entity:
» 203.14.7.0 = 11001011 00001110 00000111 00000000
» 203.14.6.0 = 11001011 00001110 00000110 00000000
» The first 23 bits are the same for both addresses so the ISP
can advertise a single external route:
» 203.14.6/23
» This only works if the ISP also owns 203.14.4.0 and
203.14.5.0.
Network Protocols (TCP/IP)
• Classless Inter Domain Routing (CIDR)
– CIDR is the result of incorporating subnetting and
supernetting into the classful IP address structure.
• We are no longer limited to class A, B, and C addresses.
• By passing the netmask along with the address we can
make arbitrarily large/small networks, as we see fit, to
simplify routing and network design.
– CIDR allows simplified routing tables.
– CIDR is the basis of IPv6.
– You may also hear the term Variable Length Subnet
Mask (VLSM).
• This is the practice of using various length subnet masks
within a single network domain.
Network Protocols (TCP/IP)
• Internet Protocol (IPv4 trivia)
– We are running out of addresses under the current (IPv4)
addressing scheme.
– If every class A, Class B, and Class C network address was in
use using classful addresses, there would be ((127 * 16,000,000)
+ (16384 * 65,000) + (2,097,152 * 254)) (or 3,629,636,608) hosts
on the Internet. (3.6 gigahosts)
• The remainder of the addresses are the “zero”, and “broadcast
hosts (overhead).
• If subnetworking is in use, even more of the address space is lost
to “overhead”.
– Real Soon Now a new version of IP will be released. This version
is known as IPV6 (Internet Protocol version 6).
Network Protocols (TCP/IP)
•
IPv6
– Addresses go from 32 bit to 128 bit.
– Addresses will be colon separated hexadecimal quads:
• 0xFEDC:BA98:7654:3210:0123:4567:89AB:CDEF
• 0x0000:0000:0000:0000:0000:FFFF:222.33.44.55
– Shorthand
::FFFF:222.33.44.55
– IPv6 will not contain address classes – but prefix ranges
will have meaning (geographic regions).
– IPv6 will use multicasts instead of broadcasting.
– IPv6 will use CIDR routing
– IPv6 will facilitate data encryption
– IPv6 contains provisions for new services (bandwidth
reservation, guaranteed signal quality, more multicasting)
– IPv6 will provide 340 undecillion addresses
• 340 with 24 zero’s after it
Network Protocols (TCP/IP)
• Internet Protocol (packet delivery)
– The Internet protocol actually uses multiple layers of
addressing to deliver packets.
• Protocol addressed packet delivery is referred to as ISO Layer 3
(Network layer) routing.
• In addition to the IP address, each network adapter card is
assigned a unique hardware address (Media Access Controller or
MAC address).
• Ethernet MAC addresses are 6 bytes long.
• MAC addresses of other network technologies vary from 2 bytes
to 20 bytes in length.
– The mapping between the MAC address and the IP
address is handled at the Link Layer of the TCP/IP
stack by the Address Resolution Protocol (ARP).
Network Protocols (TCP/IP)
• Address Resolution Protocol
– By design, the network interface (the board in the host) wants
to communicate with another network interface board.
• Network interface boards work with multiple protocols.
• This means that they must have a way of addressing other NICs
that is independent of the software protocol address.
• All packets on the media are addressed to another MAC address.
– If the packet is bound for a host not known to the local host
what happens?
• One way to resolve such a MAC address is for the host to send
out a broadcast packet saying “Hi, I’m at MAC address
x:y:z:a:b:c, how do I get to MAC address f:g:h:i:j:k?”.
– If the host with address f:g:h:i:j:k is on the same network, it
will reply and the address is resolved.
Network Protocols (TCP/IP)
• Otherwise an intermediate can be programmed to reply “send the
packet to me, and I will forward it for you.”
– In this case the packet is sent from the host’s MAC address
to the MAC address of the intermediate!
• source addr = host MAC,
• destination addr = intermediate MAC
– The intermediate then forwards the packet on the way to the
final destination.
• source addr = intermediate MAC,
• destination addr = next hop MAC
– The host software maintains a table (the ARP cache) of these
MAC addresses.
• This is ISO layer 2 (Data Link Layer) routing (switching)
Network Protocols (TCP/IP)
Net to
Device
-----hme0
hme0
hme0
hme0
hme0
hme0
hme0
hme0
hme0
hme0
hme0
hme0
Media Table
IP Address
Mask
-------------------- --------------morticia.cse.nd.edu 255.255.255.255
wizard.cse.nd.edu
255.255.255.255
penny.helios.nd.edu 255.255.255.255
banzai.helios.nd.edu 255.255.255.255
bind.nd.edu
255.255.255.255
buckaroo.helios.nd 255.255.255.255
john.helios.nd.edu 255.255.255.255
authors.helios.nd.ed 255.255.255.255
lizardo.helios.nd.ed 255.255.255.255
hub25-1a.hub.nd.edu 255.255.255.255
grumpy.cse.nd.edu
255.255.255.255
BASE-ADDRESS.MCAST.NET 240.0.0.0
Flags Phys Addr
----- --------------00:05:02:20:dd:ba
08:00:20:10:0c:6a
00:60:2f:88:da:63
00:60:2f:88:da:63
00:60:2f:88:da:63
00:60:2f:88:da:63
00:60:2f:88:da:63
00:60:2f:88:da:63
00:60:2f:88:da:63
08:00:44:0c:17:7d
SP
08:00:20:7e:80:69
SM
01:00:5e:00:00:00
Network Protocols (TCP/IP)
• Internet Protocol (packet addressing)
– IP addresses identify machines.
• This allows us to get a datagram from one host to another.
– How do we deliver data to programs and services on these
hosts?
• The TCP and UDP protocols extend the IP addressing concept
through the use of “ports”.
– A port is a two byte number that identifies a particular
service.
– These port numbers are mapped to services through
the /etc/services file.
– Ports with numbers less than 1024 are called
privileged ports.
» These ports are (supposed to be) only accessible by
root, in an attempt to prevent impostors.
Network Protocols (TCP/IP)
• Internet Protocol (packet addressing)
– Because humans have a difficult time dealing with all
of these numbers (MAC address / IP address / Port
number), the computers/services are also allowed
symbolic names.
– Computers do not understand these names…the
computer wants to work with numbers.
• The names are mapped to numbers by a variety of
means.
– The most commons means of mapping system names to IP
addresses are the /etc/hosts file, Network Information Services
(NIS), and the Domain Name Service (DNS).
– I will talk more about how these name services work in a few
days.
Other Protocols
• NetBEUI
– Net Bios Extended User Interface
•
•
•
•
•
•
•
•
•
An extension of NetBIOS.
Not a routable protocol, as it has no network layer.
Can have bridged networks, but not routers.
Relies on broadcasts for many functions.
Connection Oriented - Connectionless
communications
Self configuration - self tuning
Error protection
Small memory overhead
Active Directory cannot use NetBEUI.
Other Protocols
• NetBIOS over TCP/IP (NBT)
– Replaces NetBEUI, allows applications to use TCP/IP
• Winsock
– Interface between socket based applications and TCP/IP.
• Server Message Block (SMB) networking.
– Used in previous versions of Windows.
– Basis for Windows file and print sharing.
– Uses NetBEUI - not routable.
– Relies on Windows Internet Naming Services (WINS).
– Being replaced by Common Internet File Service (CIFS).
• TCP/IP based networking for Windows!
• Both SMB and WINS are unpublished protocols.
– Can change on a whim!
Other Protocols
• AppleTalk
– Originally developed by Apple as a printer sharing protocol.
– Later expanded to allow more complete network services.
– Very little administration required.
• Hardware address is used, no IP address required.
• Plug in a new machine, and it works!
– The new node sends a broadcast packet that says “Hi!, I’m
Joe. I want to use address X. Does anyone object?”
– If there is no objection, Joe is now at address X.
– If there is an objection, the node with the lowest address
sends back a message stating “Hello Joe. I’m sorry, but you
will have to use Y as your address, as X is already in use.”
– Routers are very complex.
– Works with a variety of hardware and media.
• Twisted pair, coaxial cable, Ethernet, PC’s UNIX hosts.
Other Protocols
• EtherTalk
– Actually AppleTalk over Ethernet.
– Two flavors are available:
• Phase 1 was Apple’s first Ethernet network. It was
very buggy, and tended to flood the network with
broadcast packets. Phase 1 also had it’s own packet
types which were not known by TCP/IP.
• Phase 2 changed the broadcast packets to Multicast
packets, and encapsulated their odd packets as
acceptable packets.
Other Protocols
• LocalTalk
– Is actually Apple’s AppleTalk protocol implemented on
twisted pair cabling.
• AppleTalk was originally implemented with an odd
coaxial cable.
– Network speed reaches a blazing 230 Kilobits/second!
– LocalTalk allows star topology with active or passive
hubs and multiple hosts on a leg.
– Ethernet to LocalTalk bridges are very common.
– MacIP is used to encapsulate Ethernet packets in
LocalTalk packets.
Other Protocols
• AppleTalk
– AppleTalk addressing uses a multi-layer address system
like IP.
– The MAC address is hardware based.
– The Node number is dynamically assigned by AppleTalk
Address Resolution Protocol (AARP).
– AppleTalk networks are grouped into zones.
– Each AppleTalk entity has an object name (Billy Bob’s
Office Printer), an object type (LaserWriter) as well as the
zone name.
– The zone entities are bound to network and node
numbers by the AppleTalk Name Binding Protocol
(ANBP).
Other Protocols
• IPX
– IPX is the Internet Packet Exchange Protocol.
– IPX was developed by Novell for the NetWare product.
Novell is the most common network protocol in use for
PC’s.
– Novell is in the process of converting the Novell Network
to use TCP/IP protocol.
– Current IPX implementations use standard Ethernet
packet headers.
– Older versions of IPX used non-standard Ethernet packet
headers, and would not co-exist on a network with nonIPX Ethernet packets.
Other Protocols
• IPX
– IPX was derived from The Xerox Network System
Internet Datagram Protocol (XNS IDP).
– IPX uses a UDP like packet type. Headers have an
unused checksum field, a packet length, packet type, a
hop count, and the network, node, and socket numbers
of the source and destination machines.
– IPX packets are thrown away after 15 hops!
– IPX is not a standardized protocol! It is a proprietary
protocol and is subject to frequent unannounced
changes.
– Novell Loadable Modules (NLM’s) are available to add
functionality to Novell IPX based networks.
Other Protocols
• IPX
• The IPX protocol has many “helper” protocols:
– Routing Information Protocol (RIP)
– Sequenced Packet Exchanger : reliable delivery (SPX)
– ECHO (a packet echo facility)
– ERRORS (an error reporting facility)
– Packet Exchange Protocol (PEP)
» VERY inefficient, as it requires an ACK for each packet
before the next packet is sent!
» On top of PEP are the Network Core Products which
provide authentication, file service, RPC, print spooling,
accounting).
– Service Advertisement Protocol (SAP) (address broker)
Other Protocols
• DECnet
– DECnet is an implementation of the Digital Network
Architecture (DNA)
– DECnet first appeared in 1974. The first version to
support Ethernet was DECnet phase IV released in 1984.
– DECnet Phase V was released in 1991 and is referred to
as DECnet/OSI. It supports TCP/IP, OSI, and Digital’s
Network Services Protocol (NSP).
Other Protocols
• DECnet
– DECnet Addressing is somewhat different from the other
protocols:
– DECnet addresses are independent of the transport
media.
– A DECnet address is a one byte “area” and a two-byte
node number.
• An area is a logical grouping.
– One area may equate to one or more networks.
– One network may contain one or more areas.
• The machine’s address is derived from the area and
node number, not the hardware MAC address.
• All interfaces on the system use the same address!
Other Protocols
– DECnet
• Until DECnet Phase V all routing tables were static.
• Static routing limited DECnet to small network
configurations.
– DECnet Phase V implemented dynamic routing via
DECdns which is actually a distributed routing protocol.
• The routing is performed by DECnet routers.
• A level one router routes information within one area.
• A level two router routes information between two
areas.
Protocol Translators
• As you may have guessed by now, there are ways to make systems
running these “other” protocols talk to a TCP/IP network.
– Some of these protocols include TCP/IP modules.
– Other protocols use a trick called “tunneling” to allow them to “talk
on” TCP/IP networks. Tunneling is a form of packet encapsulation.
• In order for tunneling to work, the source and destination
machines have to be on the same type of network.
– There may be one (or many) other types of networks
between these two hosts and their networks.
– Another method of interconnecting dissimilar networks requires
special hardware/software which acts as a translator (bridges).
Network Hardware
• Working With Current Network Hardware
– So far all we’ve talked about is the software side of
networking.
• We saw that there are many different protocols in use on current
communications networks.
– There is also a hardware component to networking.
• Unfortunately, there are almost as many hardware standards as
there are protocols.
• We will talk about four types of network hardware:
– Ethernet
– Token Ring
– FDDI (token ring in disguise)
– ATM
Network Hardware
• Working With Current Network Hardware
• Network hardware has to take proximity into account.
– Local Area Networks (LANs) consist of machines in close
proximity to each other. Example: Notre Dame campus, or
networking within a small company building.
» LANs typically employ high speed technologies ( 1Mb 10 Gb / second throughput).
– Metropolitan Area Networks (MANs) - consist of machines
within a metropolitan area. Notre Dame could also be
considered a Metropolitan Area Network.
» MANs typically operate at lower speeds (56 Kb - 622 Mb
/ second throughput).
Network Hardware
• Working With Current Network Hardware
– Wide Area Networks (WANs) consist of
machines separated by large distances.
Example the Internet.
» WANs typically operate at rates of 56 Kb to 622
Mb / second throughput.
• The type of hardware selected for a network
must be capable of working within the
boundaries of the particular network.
Network Hardware
• Working With Current Network Hardware
– Ethernet - developed by Xerox in the 1970’s.
• Still has bugs!
• Ethernet is the most common network technology.
• Ethernet employs Carrier Sense Multiple Access with Collision
Detect to determine who gets to talk at any given time.
• Ethernet does not include built-in error detection/correction. That
is left to the software!
• Most of the protocols we discussed run on Ethernet hardware.
• Ethernet is a LAN technology that the users wanted (desperately)
to become a WAN technology.
Network Hardware
• Working With Current Network Hardware
• There are many flavors of Ethernet available:
– 802.5 - Thicknet - 10Base-5 - Screaming Yellow 50
Ohm Coaxial cable.
» Attachment Unit Interface (AUI) connectors
(DB15).
» This is the oldest form of Ethernet.
» Length Limit 500 Meters / segment.
» Up to three segments connected via repeaters.
» 10 Mb/s shared bandwidth
Network Hardware
• Working With Current Network Hardware
– 802.2 - Thinnet - 10Base-2 - cheapernet,
»Cheap coaxial cable
»cheap BNC style connectors.
»length limit: 200 Meters/segment.
»Up to two segments connected via
repeater.
»Multiport repeaters allowed.
»10 Mb/s shared bandwidth
Network Hardware
• Working With Current Network Hardware
• 10Broad36 - Broadband Ethernet.
– Not used very often
– EXPENSIVE
– Multiplex Ethernet packets onto a broadband
carrier system.
– 36 Kilometer length limit
– Cable modems use similar technology.
Network Hardware
• Working With Current Network Hardware
• 10BaseF - Fiber based Ethernet.
– Two fibers required (one for transmit, one for
receive)
– Optical to copper repeaters handle the collision
detection.
– Typical segments 2.2 Km maximum.
– Multiple segments may be connected via
repeaters
– Two repeaters/route maximum
– 10 Mb/s shared bandwidth
Network Hardware
• Working With Current Network Hardware
• 10 BaseT - Twisted pair Ethernet
– Category 4 or Category 5 twisted pair wiring, or fiber.
– Star topology - all hosts connect to
hubs/routers/switches.
– Length limit: 100 meters per connection, 500 meters
between the two most distant hosts (if shared
bandwidth).
– Cheap RJ45 connectors (telco style)
– 10 Mb/s shared or switched bandwidth
» Switched connections allow full 10Mb/s to the host
instead of shared bandwidth.
» Connections can be “full duplex”
Network Hardware
• Working With Current Network Hardware
• 100BaseT - Twisted pair Ethernet
– Category 4 or category 5 twisted pair wiring, or fiber.
– Star topology - all hosts connect to
hubs/routers/switches.
– Length limit: 100 meters per connection
– Cheap RJ45 connectors (telco style)
– 100 Mb/s switched bandwidth
» Switched connections allow full 100Mb/s to the host
instead of shared bandwidth. Half, or Full Duplex
connections.
Network Hardware
• Working With Current Network Hardware
– Token Ring Networks
• Token Rings utilize a special data structure called a
token to determine who gets to talk.
• Token Rings are typically built on a copper based
media.
• Token Rings are very common on PC systems, but not
found very often on UNIX systems (with the exception
of FDDI/CDDI).
• Token Ring systems have two modes of operation:
receive and transmit.
• Typical Token Rings run at 1, 4, 10, or 16 Mbit/second.
Network Hardware
• Working With Current Network Hardware
– Fiber Distributed Data Interconnect (FDDI)
• FDDI is a token ring in disguise.
• FDDI uses fiber optical cabling instead of copper. Copper
Distributed Data Interconnect (CDDI) is FDDI over copper.
• FDDI is capable of 100 Mbit/second data rates.
• Single Attachment Stations (SAS) require a pair of fibers and
have little fault tolerance.
– SAS FDDI networks are star-topology networks.
• Dual Attachment Stations (DAS) provide for fault tolerance and
require two pairs of fibers.
– DAS FDDI networks are ring topology networks.
Network Hardware
• Working With Current Network Hardware
– Automatic Teller Machines (ATM)
• ATM networks have been in use for many
years by the banking industry.
• Users put a card in a slot and can magically
get money out of the ATM machine.
– OOPS. Sorry. Wrong ATM!
Network Hardware
• ATM is part of a larger network:
– SONET (Synchronous Optical Network) is used for
(extremely) high speed connections between
telephone switches.
• Current Telco operations can handle 100
Gigabit/second over SONET.
• Test frames currently running at 350+
Gb/second!
– Computer network hardware is available which
allows you to use SONET connections between
systems.
– SONET is VERY expensive!
Network Hardware
• Working With Current Network Hardware
– Asynchronous Transfer Mode (ATM)
• The basic foundations for ATM were developed by people who
know about wide area networks and packet switching: Long
Distance Telephone carriers.
• ATM is the underlying technology behind the Broadband
Integrated Services Digital Network (B-ISDN).
– B-ISDN is part of the “send a fax from the beach, tuck your
kids into bed from around the world” technology.
• ATM is currently running with 622Mbit/second links.
– High-end Internet links are running at 155 Mbit/second.
– NOTE: Most hosts cannot drive such links at speeds over
350 Mbit/second.
Network Hardware
• Working With Current Network Hardware
• ATM comes in a variety of speeds. For example:
– 25 Mbit/second IBM standard
– 45 Mbit/second Digital Service-3 (DS3) (T-3)
– 51 Mbit/second SONET(OC-1)
– 100 Mbit/second Taxi interface
– 155 Mbit/second Optical Carrier-3 (OC-3)
– 622 Mbit/second Optical Carrier-12 (OC-12)
– 1.2 Gbit/second Optical Carrier-24 (OC-24)
– 2.4 Gbit/second Optical Carrier-48 (OC-48)
• Speeds are based on Telco transmission rates.
Network Hardware
• Working With Current Network Hardware
– ATM encompasses the Integrated Services Digital Network (ISDN),
• ISDN is used for (relatively) high speed connections to homes and
businesses. A typical ISDN connection is actually a multiplechannel connection over telephone wire.
– ISDN uses two B channels, and a D channel.
– The B channels are 64 Kb/second data channels.
– The D channel is a 9.6 Kb/second signaling channel.
– Current technology allows you to “bond” the two B
channels together and use 4x data compression to get
throughput up to 512 Kb/second.
Network Hardware
• Working With Current Network Hardware
– xDSL technology (new) is similar to ISDN.
• ADSL (Asymmetric Digital Subscriber Loop) has one
channel running at high speed, and one running at low
speed (for example 512Kb/sec one direction, and 128
Kb/sec the other direction).
• ADSL has been tested at rates up to 1.544 Mbit/second
(same speed as a T1 link).
• ADSL runs over standard telco wiring (ISDN and DSL
require some tweaks to run over telco infrastructure).
Network Hardware
• Working With Current Network Hardware
– Because ATM is a telephone protocol, it has some odd
“features” when used for data networking.
• ATM is a connection oriented service. No packets can
be sent until a channel is opened.
– Ethernet/FDDI/Token Rings are all “connectionless”.
– IP is also connectionless.
• ATM sends/receives fixed length data cells, as opposed
to the other technologies we discussed which
send/receive variable length packets.
– Ethernet exchanges 64 - 1500 byte packets
– FDDI exchanges 64 - 4500 byte packets
– ATM exchanges 53 byte “cells”
» Each cell has a 5 byte header and 48 data bytes.
Network Hardware
• Working With Current Network Hardware
– ATM
• Fun with International Standards:
– The European telephone industry wanted ATM to use
16 byte cells for voice traffic, but would compromise up
to 32 bytes.
– The United States telephone industry wanted 128 byte
cells for data, but would compromise down to 64 bytes.
– The CCITT split the difference, and ATM cells were
defined to be 48 bytes.
» Because headers were already defined as no more that
10% of the cell, headers became 5 bytes.
Network Hardware
– ATM
• Result:
– The ATM cell size is a poor choice for voice
(packets are too big; bandwidth is wasted)
– The ATM cell size is a poor choice for data
(packets are too small; bandwidth is wasted with
excessive overhead).
– Welcome to the fascinating world of International
Standards!
Summary
• Configuration, management, and troubleshooting network
connections is a major portion of any system administrator’s
job. The system administrator needs to:
• Understand basic network terminology.
• Understand the basics of the TCP/IP protocol suite.
• Understand the basics of IP addresses.
• Understand basic IP routing.
– Understand the basics of ARP, and DNS.
– Understand the basics of layer 2 and layer 3 “routing”.
• Understand common network hardware.