Information Technology Education, IT Network

ARCnet Network
ARCnet (Attached Resource Computer Network)
(CR)
Topology is star and bus or a mixture. Cable type is RG-62 A/U coaxial (93 ohm), UTP or fiber-optic. A
network can use any combination of this media. Connectors used include BNC, RJ-45, and others. It
passes tokens passing for media access. Maximum segment length is 600 meters with RG-62 A/U, 121
meters with UTP, 3485 meters with fiber-optic, and 30 meters from a passive hub. The specification is
ANSI 878.1. It can have up to 255 nodes per network. The speed is 2.5 Mbps. ARCnet Plus has operating
speeds approaching 20Mbps.
Signals are broadcast across the entire network with computers processing only signals addressed to
them. ARCnet tokens travel based on a station identifier (SID) which each computer has. Each network
card has a DIP switch used to set the SID with an address between 1 and 255. Signals are generally sent
from the lowest numbered station to the next until they wrap around back to SID of 1. To determine nonexistent
stations, the station with the lowest ID indicates it has the token and begins querying IDs of
higher value until it gets a response. Then the next computer does the same until the original station is
queried. This procedure is done when a station is added or removed from the network or when the
network is originally started. How does the network know when a station has been added or removed?
How is the lowest numbered SID identified? Addresses assignment is based on proximity, which helps
the network operate more efficiently.
The acronym SID is used for a station identifier with regard to ARCnet, but as used in the Windows NT
and Windows 95 operating systems, it refers to the security identification number of a user or group.
AppleTalk Network
AppleTalk Network
Topology is bus. Cable type is STP. The connectors are specialized. The media access method is
CSMA/CA . Maximum segment and network length is 300 meters. The maximum number of connected
segments is 8. There are 32 maximum nodes per segment with 254 maximum number of nodes per
network. Speed is 230.4Kbps. The cabling system used with AppleTalk is called LocalTalk.
Addressing
Addressing is dynamic with each computer, when powered on, choosing its last used address or a random
address. The computer broadcasts that address to determine if the address is used. If it is used, it will
broadcast another random address until it finds an unused address.
EtherTalk and TokenTalk provide for use of AppleTalk network protocols on top of ethernet and token
ring architectures respectively.
LocalTalk
LocalTalk uses STP cable and bus topology. Using CSMA/CA for media access, computers will first
determine if any other computers are transmitting, before they transmit. A packet is transmitted prior to
transmitting that alerts other computers that a transmission will be sent. Usually LocalTalk is only used
in small environments.
FDDI
FDDI
Fiber Distributed Data Interface (FDDI)
Standard is ANSI X3T9.5 . Topology is ring with two counter rotating rings for reliability with no
hubs. Cable type is fiber-optic. Connectors are specialized. The media access method is token passing.
The maximum length is 100 kilometers. The maximum number of nodes on the network is 500. Speed is
100 Mbps. FDDI is normally used as a backbone to link other networks. A typical FDDI network can
include servers, concentrators, and links to other networks.
Devices called concentrators provide functions similar to hubs. Most concentrators use dual attachment
station network cards but single attachment concentrators may be used to attach more workstations to the
network.
FDDI token passing allows multiple frames to circulate around the ring at the same time. Priority levels
of a data frame and token can be set to allow servers to send more data frames. Time sensitive data may
also be given higher priority. The second ring in a FDDI network is a method of adjusting when there are
breaks in the cable. The primary ring is normally used, but if the nearest downstream neighbor stops
responding the data is sent on the secondary ring in attempt to reach the computer. Therefore a break in
the cable will result in the secondary ring being used. There are two network cards which are:
1. Dual attachment stations (DAS) used for servers and concentrators are attached to both rings.
2. Single Attachment stations (SAS) attached to one ring and used to attach workstations to
concentrators.
A router or switch can link an FDDI network to a local area network (LAN). Normally FDDI is used to
link LANs together since it covers long distances.
IPX/SPX
IPX/SPX
IPX/SPX is a routable protocol and can be used for small and large networks. The following protocols
are part of the IPX/SPX suite:
l SAP - Service Advertising Protocol packets are used by file and print servers to periodically
advertise the address of the server and the services available. It works at the application,
presentation, and session levels.
l NCP - NetWare Core Protocol provides for client/server interactions such as file and print
sharing. It works at the application, presentation, and session levels.
l SPX - Sequenced Packet Exchange operates at the transport layer providing connection oriented
communication on top of IPX.
l IPX - Internetwork Packet Exchange supports the transport and network layers of the OSI
network model. Provides for network addressing and routing. It provides fast, unreliable,
communication with network nodes using a connection less datagram service.
l RIP - Routing Information Protocol is the default routing protocol for IPX/SPX networks which
operates at the network layer. A distance-vector algorithm is used to calculate the best route for a
packet.
l ODI - Open Data-link Interface operates at the data link layer allowing IPX to work with any
network interface card.
NetWare frame types
Novell NetWare 2.x and 3.x use Ethernet 802.3 as their default frame type. Novell NetWare 4.x networks
use Ethernet 802.2 as their default frame type. If communication does not occur between two NetWare
computers it is a good idea to check the netware versions of the two computers to be sure their frame
types match. If the frame types do not match on an ethernet network, the computers cannot communicate.
NetBEUI
NetBEUI
In order to properly describe NetBEUI, the transport protocol sometimes used for Microsoft networking,
it is necessary to describe Microsoft networking in some detail and the various protocols used and what
network layers they support.
NetBIOS, NetBEUI, and SMB are Microsoft Protocols used to support Microsoft Networking. The
NetBIOS stack includes SMB, NetBIOS, and NetBEUI which are described in the table below. The
following are parts of the Microsoft networking stack:
Name Network Layer Description
Redirector Application
Directs requests for network resources to the appropriate
server and makes network resources seem to be local
resources.
SMB Presentation
Server Message Block provides redirector client to server
communication
NetBIOS Session
Controls the sessions between computers and maintains
connections.
NetBEUI Transport, Network
Provides data transportation. It is not a routable transport
protocol which is why NBT exists on large networks to use
routable TCP protocol on large networks. This protocol may
sometimes be called the NetBIOS frame (NBF) protocol.
NDIS and NIC driver Data Link
NDIS allows several adapter drivers to use any number of
transport protocols. The NIC driver is the driver software for
the network card.
NetBIOS Extended User Interface (NetBEUI)
This is a separate protocol from NetBIOS. It supports small to medium networks providing transport and
network layer support. It is fast and small and works well for the DOS operating system but NetBEUI is
not a routable protocol.
Name Resolution
There are three methods of mapping NetBIOS names to IP addresses on small networks that don't
perform routing:
1. IP broadcasting - A data packet with the NetBIOS computer name is broadcast when an
associated address is not in the local cache. The host who has that name returns its address.
NetBEUI
2. The lmhosts file - This is a file that maps IP addresses and NetBIOS computer names.
3. NBNS - NetBIOS Name Server. A server that maps NetBIOS names to IP addresses. This service
is provided by the nmbd daemon on Linux.
System wide methods of resolving NetBIOS names to IP addresses are:
1. b-node - Broadcast node
2. p-node - Point-to-point node queries an NBNS name server to resolve addresses.
3. m-node - First uses broadcasts, then falls back to querying an NBNS name server.
4. h-node - The system first attempts to query an NBNS name server, then falls back to broadcasts if
the nameserver fails. As a last resort, it will look for the lmhosts file locally.
NetBIOS name services use port 137 and NetBIOS session services use port 139. NetBIOS datagram
service uses port 138.
To resolve addresses from names, a computer on a Microsoft network will check its cache to see if the
address of the computer it wants to connect to is listed there. If not it sends a NetBIOS broadcast
requesting the computer with the name to respond with its hardware address. When the address is
received, NetBIOS will start a session between the computers. On larger networks that use routers, this is
a problem since routers do not forward broadcasts, nor is NetBEUI a routable protocol. Therefore
Microsoft implemented another method of resolving names with the Windows Internet Name Service
(WINS). The following steps are taken to resolve NetBIOS names to IP addresses for H-node resolution
on larger networks using TCP/IP (NBT):
1. NetBIOS name cache
2. WINS Server
3. NetBIOS broadcast
4. lmhosts file
5. hosts file
6. DNS server
For a more complete explanation of NetBIOS name resolution, WINS, and Windows networking in
general, see the manuals in the Windows operating system section such as the "Windows TCP/IP
Reference." Also a Windows Networking manual will be written for this section.
NetBIOS over TCP/IP (NBT)
Since NetBEUI is not a routable protocol, Microsoft implemented NBT for larger networks. NetBIOS
messages are normally encapsulated in NetBEUI datagrams, but when using NBT, they are encapsulated
in TCP/IP datagrams. The NBT protocol is defined by RFC 1001 and RFC 1002.
NetBEUI
NWLink
NWLink is Microsoft's implementation of IPX/SPX. NWLink will act as a transport mechanism for
NetBIOS similar to the use of TCP/IP described in the NBT section above. NWLink is normally used to
support medium networks and may be used where NetWare servers are present.
Windows Internet Name Service (WINS)
WINS is the Microsoft implementation of NetBIOS name service. Samba on Linux can be used as a
WINS server.
Computers configured to use WINS, when booted, contact the WINS name server and give the server
their NetBIOS name and IP address. The WINS server adds the information to its database and it may
send the information to other WINS servers on your network. When a computer that is configured to use
WINS needs to get an address of another computer, it will contact the WINS server for the information.
Without the use of a WINS server, NetBIOS will only be able to see computers on the unrouted sections
of the local network. Does this mean a WINS server must exist in each routed section of the network?
The answer is no. This is because WINS uses TCP/IP which is routable. Only one WINS server needs to
exist on the network.
The Windows Networking Environment
A domain in a Microsoft networking environment refers to a collection of computers using user level
security. It is not the same as the term domain used with regard to the domain name system (DNS).
Domain related terms are:
l BDC - Backup Domain Controller is a backup for a PDC
l TLD - Top Level domain
l PDC - Primary Domain Controller is an NT server providing central control of user access
permissions and accounts on a network.
AppleTalk Protocols
AppleTalk Protocols
AppleTalk is the architecture used on with Apple brand computers and is a suite of protocols for
networking Apple computers. Some of the protocols are:
l AppleShare - Works at the application layer to provide services.
l AFP - AppleTalk Filing protocol - Makes network files appear local by managing file sharing at
the presentation layer.
l ATP - AppleTalk Transaction Protocol provides a Transport Layer connection between
computers. Three transaction layers:
m transaction requires (TREQ)
m transaction response (TRESP)
m transaction release (TREL)
l DDP - Datagram Delivery Protocol is a routable protocol that provides for data packet
transportation. It operates at the network layer at the same level of the IP protocol.
The AppleTalk networking scheme puts computers into groups called zones. This is similar to
workgroups on a Windows network.
Four Session layer protocols
l ASP - AppleTalk session protocol controls the starting and ending of sessions between computers
called nodes. It works at the session level. The NBP, described below is used to get addresses
from computer names. ATP is used at the transport level.
l ADSP - AppleTalk data stream protocol manages the flow of data between two established socket
connections.
l ZIP - Zone information protocol used with RTMP to map zones. Routers use zone information
tables (ZITs) to define network addresses and zone names.
l PAP - Printer access protocol manages information between workstations and printers.
Other Protocols
l NBP - Name-binding protocol translates addresses into names.
l AEP - AppleTalk echo protocol uses echoes to tell if a computer, or node, is available.
l RTMP - Routing table maintenance protocol is used to update routers with information about
network status and address tables. The whole address table is sent across the network.
l ARUP - AppleTalk update routing is a newer version of RTMP.
System Network Architecture
System Network Architecture
System Network Architecture (SNA) by IBM is a suite of protocols mainly used with IBM mainframe
and AS/400 computers. Two SNA protocols are:
l APPC - Advanced Peer-to-Peer Communications provides peer to peer services at the transport
and session layer.
l APPN - Advanced Peer-to-Peer Networking supports the computer connections at the network
and transport layers.
Microsoft produced the SNA Server so PC networks could connect with SNA networks.
SNA Layers
SNA has its own network model which is:
l Physical
l Data link - Uses protocols such as token-ring or Synchronous Data Link Control (SDLC).
l Path Control - Performs routing, division, and re-assembly of data packets.
l Transmission - Connection software
l Data flow - Prevents data overflows by monitoring and handling traffic
l Presentation - Handles interfaces to applications
l Transaction - Provides an interface for applications to use network services
SNA Network Devices
l host systems
l terminals
l Output devices
l Communications controllers
l Cluster controllers - Allow many devices to connect through them. They connect ot a host or
communications controller.
SNA Network Categories
l Nodes
m Type 2 - PCs, terminals and printers
m Type 4 - Communications controllers
m type 5 - Host computers used to manage the network
l Data links - Connection between combinations of hosts, cluster controllers, or nodes.
System Network Architecture
Possible SNA communications architectures
l SDLS - Synchronous Data Link Control
l BSC - Binary Synchronous Communication sends bits in frames which are timed sequences of
data.
l Token-ring
l X.25
l Ethernet
l FDDI
SNA units
NAU - Network Addressable Units
l LU - Logical Units are ports that users use to access network resources
m Type 1 - An interactive batch session
m Type 2 - An IBM 3270 terminal
m Type 3 - An IBM 3270 printer
m Type 6.2 - A program to program session
m Type 7 - An IBM 5250 family session
l PU - Physical Units are a network device used to communicate with hosts.
m Type 2 - Cluster controllers
m Type 3 - Front end process
m Type 5 - Host communications software
SNA software components
l SSCP - Systems Services Control Point manages all resources in the host's domain.
l NCP - Network Control Program performs routing, session management tasks. It runs in the
communications controller.
Other Transport Protocols
Other Transport Protocols
DECnet
DECnet from Digital Equipment Corporation is a suite of protocols which may be used on large
networks that integrate mainframe and minicomputer systems. It is a routable protocol. DNA - Digital
Network Architecture.
Data Link Control (DLC)
This protocol operates at the data link layer and is designed for communications between Hewlett-
Packard network printers and IBM mainframe computers. This protocol is not routable.
Open Systems Interconnect (OSI)
A suite of protocols developed by the International Standards Organization (ISO) which corresponds
with the layers of the OSI model. These protocols provide a number of application protocols for various
functions. The OSI protocol stack may be used to connect large systems. OSI is a routable transport
protocol.
Network Routing
Network Routing
Simple Networking Routing and Routers
This section will explain routing in simple terms with some simple standard rules. There may be exceptions to
these rules, but for introductory purposes we will keep the first example simple. Please be aware, that the
examples in this section are working examples, but more complexity may be added when a larger network is
considered, and multiple data routes become available.
Each network interface card (NIC) has a specific address which is an IP address or number. When data is sent
between two computers, the data must be sent in a package that has the address of the intended receiver (IP) on it.
It is like an envelope (ethernet) with the sender's and recipient's address on it. There is somewhat of a difference,
however. When the computer intends to send a packet, it first checks its routing table to see if the intended data
must be sent through a gateway. Many computers only have a simple routing table, which is built from the
network mask and the gateway information entered, when you set your computer up to do networking. The
computer, when set up for networking, must be assigned an IP address, netmask, and default gateway. This may
be done manually or done automatically using Dynamic Host Configuration Protocol (DHCP) to assign this
information to the computer when it boots. DCHP is described in another section. If the computer determines that
the packet must be sent to a gateway, it puts it in a special packet (ethernet) for that gateway, with the actual
recipient's address wrapped inside.
In the above paragraph, data packets are equated to a letter with an envelope. For this type of thinking, the
envelope would be similar to the ethernet, SLIP, or PPP packet which encapsulates the IP packet. The IP packet
and its encapsulated data would similar to a letter. Here's generally what happens when a package is sent:
The sending computer checks the IP part of the package to see the sender's IP address, and based on
the address and instructions in its routing table will do one of the following:
1. Send the packet to the ethernet address of the intended recipient. The following will happen:
1. The ethernet card on the receiving computer will accept the packet.
2. The other network levels (IP, TCP) will open the packet and use it according to filtering and other
programming instructions.
2. Send the packet to the ethernet address of a router, depending on the instructions in the routing table.
1. The ethernet card on the router will accept the packet.
2. The IP level of the router will look at the packet's IP address and determine according to its routing
table where to send the packet next. It should send it to another router or to the actual recipient.
3. The router will encapsulate the IP packet in another ethernet packet with the ethernet address of the
next router or the intended recipient.
4. Router hops will continue until the packet is sent on a network where the intended recipient is
physically located unless the packet expires.
5. The ethernet card on the receiving computer will accept the packet.
6. The other network levels (IP, TCP) will open the packet and use it according to filtering and other
programming instructions.
Network Routing
Lets say you enter an IP address of 10.1.20.45 and a netmask of 255.255.0.0. This means you are on the network
10.1.0.0 (I show it as 10.1.x.x, the X's mean don't care conditions). The machine's IP address and netmask,
together define the network, that it's NIC is on. Therefore any machine that fits in the address range provided
under 10.1.x.x can be accessed directly from your NIC, and any that are not in this number range, such as
10.3.34.67 cannot be accessed directly and must be sent to a gateway machine since it is on another network.
Typically most machines will use their netmask to make this determination which means if the address does not
match their known network, the package will be sent to that machine's default gateway in a special package meant
for a router. It works similar to a post office. When you send a letter in your town, you put it in the local slot. It
can be delivered to someone else in your town (network), but if you are sending to another town (network), you
put the letter in the out of town slot (default gateway), then the mail personnel put it in a special container or box
and send it to a main town (gateway), which then decides where to send it based on its address. Although this
simple network and default gateway may be common, specific computers or gateways can have much more
complex rules for routing that allow exceptions to this example.
Please be aware that in order to be forwarded, data packets must be addressed to a router. They cannot just be sent
to the recipient's address out to a network. The router does not pick packets off the network and forward them. If
a packet is sent on a network and a valid recipient is not on that network, there will be no response. This will be
demonstrated in the next section where a subnetwork will be described.
To keep routing simple, most networks are structured as shown below. Generally, the higher networks are
10.x.x.x, then the next are 10.0-254.x.x, then 10.0-254.0-254.x. The number 10 is used as an example Class A
network. This numbering scheme keeps routing simple and is the least confusing but networks can be set up in
other ways. In the diagram below, only gateways and their networks are shown.