Internetworking

1
Internetworking

• Hussain Ali, MS
• hussain_at_ccse.kfupm.edu.sa
• Department of Computer Engineering
• King Fahd University of Petroleum and Minerals
• Dhahran, Saudi Arabia

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What is Internetworking ?

• Internetworking stands for
• connectivity and communication between two or
  more networks.
• dropping the s from Networks.

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How is Internetworking Achieved ?

• Cables and physical interfaces (physical
  connectivity)
• Protocols, management and applications needed to
  support user (Internetworking)

4
Motivation for Internetworking

• Overcome distance limitations and protocol
  differences for more effective sharing of data
  and resources
• Productive communication between people across a
  single network or multiple networks
• Email, newsgroups, mailing lists, live
  conferencing

5
Components of an Internetwork

• Campus Network
• Locally connected users in a building or group of
  buildings
• Wide Area Networks (WANs)
• Distant campuses connected together usually
  through connection providers such as the phone
  company
• Remote Connections
• Linking branch offices and mobile users to a
  corporate campus

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Campus Networks

• A campus is a building or group of buildings all
  connected into one enterprise network that
  consists of many local area networks.
• The distinct characteristic of a campus is that
  the company network owns the physical wires.

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• Campus network topology is primarily LAN
  technology connecting all the end systems
  together.
• Campus networks generally use LAN technologies
  such as Ethernet, Token Ring, FDDI, Fast
  Ethernet, and ATM.

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Wide Area Networks

• WAN communication occurs between geographically
  separate areas.
• In enterprise internetworks, WANs connect
  campuses together.
• When a local end station wants to communicate
  with a remote end station, information must be
  sent over one or more WAN links.

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• WAN services are provided through the following 3
  primary switching technologies
• Circuit Switching
• Packet Switching
• Cell Switching

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Remote Connection

• Remote connections link single mobile users and
  branch offices to a local campus.
• Typically a branch office is a small site that
  has few users and needs a low bandwidth WAN
  connection.
• These small sites or single users, seldom need to
  remain connected 24 hours a day.
• Remote connections are generally dial-up links or
  low bandwidth dedicated WAN links.

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Trends in LAN/WAN Integration

• Today, most of the computing power resides on the
  desktop, and this power is growing.
• Distributed applications are increasingly
  bandwidth hungry.
• Voice communications have increased
  significantly.
• All of this is driving towards an integration of
  LANs and WANS under one roof.

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• In the LAN, bandwidth is free and connectivity is
  limited only by hardware.
• In the WAN, bandwidth is an excessive cost.
• The existence and development of bandwidth
  sensitive traffic such as voice and real-time
  video has forced a requirement of better and more
  predictable LAN and WAN performance.

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Interaction of Different Networks
1. LAN-to-LAN 2. LAN-to-WAN 3.
WAN-to-WAN 4. LAN-to-WAN-to-LAN

Host
Host
Host
Host
Host
802.5 LAN
SNA WAN
MR
MR
802.3 LAN
802.4 LAN
802.3 LAN
MR
B
MR
X.25 WAN
Host
Host
Host
Host
B Bridge MR Multi-protocol router
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Relays

• Devices that interconnect LANs are known as
  relays and operate at one layer of OSI model
• There are four common types of relays
• Repeater at physical layer (bits)
• Bridge at data-link layer (frames)
• Router at network layer (packets)
• Gateways at transport and higher layers
  (protocols)

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Repeater (Hub)

• Overcomes restrictions caused by single segment
  usage such as number of users, cable length.
• Amplifies or regenerates weak signals .
• Extends cable length
• Can connect LANs of a similar type but which use
  different media.
• Provides simple connection between adjacent LANs
  at the expense of increased network congestion

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Use of Repeaters for a Multi-segment LAN
Station
Station
Printer
Segment A
Repeater
Segment B
File Server
Stations
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Bridge

• Interconnects two or more LANs (either similar or
  dissimilar) at the MAC level.
• Capable of deciding whether or not to forward
  frame.
• Creates an extended network and keeps local
  traffic off.
• Can make minor changes to frame header.
• Does not inspect or modify the network layer
  packets inside frames.

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Characteristics of Bridges

• Routing Tables
• Filtering
• Forwarding
• Learning Algorithm

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• Routing table
• Contains one entry per station of network to
  which bridge is connected.
• Is used to determine the network of destination
  station of a received packet.
• Filtering
• Is used by bridge to allow only those packets
  destined to the remote network.
• Packets are filtered with respect to their
  destination and multicast addresses.

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• Forwarding the process of passing a packet from
  one network to another.
• Learning the process by which the bridge learns
  how to reach stations on the internetwork.

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Operation of a LAN bridge from 802.3 to 802.4
Host A
Host B
Network
Network
Packet
Bridge
Packet
LLC
LLC
Packet
Packet
Packet
MAC
MAC
802.3
Packet
802.4
Packet
802.3
802.4
Physical
Physical
802.3
Packet
802.4
802.4
Packet
802.3
802.3 CSMA/CD
802.4 Token bus
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Transparent Bridges

• The first IEEE 802 bridge is a transparent
  bridge or spanning tree bridge.
• People wanted to have complete transparency when
  a site with multiple LANs buys bridges designed
  to the IEEE standard, just plug connectors into
  bridges. So,
• no need for hardware/software changes,
• no setting of address switches,
• no downloading of routing tables or parameters.

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• A transparent bridge accepts every frame
  transmitted on all the LANs to which it is
  attached.

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LAN 4
G
F
H
A
B
C
Bridge
D
E
Bridge
LAN 1
LAN 2
LAN 3
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• Topology can change dynamically.
• There must be only one path of bridges and LANs
  between any two segments in the bridged LAN
• Bridges must support Spanning Tree Protocol if
  network contains loops.
• Have the advantage of being easy to install
• Use only a subset of topology.
• Are chosen by the CSMA/CD and token bus.

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Source Routing Bridges

• Token ring people chose the source routing
  bridge.
• Transmitter, or source, of frame in source
  routing specifies which route the frame is to
  follow.
• Every machine in the network knows, or can find,
  the best path to every other machine discovery
  frame is used.
• Sender knows whether or not the destination is on
  its own LAN.

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Comparison of Bridges
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Router

• Provides a more intelligent service
• makes a decision as to the best way to deliver a
  packet from source to destination
• may fragment packets to meet packet size
  requirements of LANs
• are slower than bridges
• Permits translation between different address
  domains such as addresses of IEEE 802 LAN and X.25

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• Connects dissimilar networks, provided that
  end-systems use a common network layer protocol,
  such as IP.
• Unlike bridge, router receive only those packets
  addressed to it by either a user machine or
  another router.
• Select the best route.
• The question of who owns, operates, and maintains
  a router arises especially when two networks
  belong to independent organizations.

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Full Router and Two Half-Routers
Full Router
Buffer
Machine owned jointly by both networks
Net 1 to internet
Net 2 to internet
Network 1
Network 2
internet to Net 1
internet to Net 2
Two-Half Routers
Net 2 to internet
Net 1 to internet
Network 2
Network 1
internet to Net 2
internet to Net 1
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Disadvantages of Routers

• Routers
• are protocol-dependent devices that must
  understand the protocol they are forwarding.
• can require a considerable amount of initial
  configuration.
• are relatively complex devices, and generally are
  more expensive than bridges.

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Advantages of Routers

• Routers
• provide sophisticated routing, flow control, and
  traffic isolation
• are configurable, which allows network manager to
  make policy based on routing decisions
• allow active loops so that redundant paths are
  available

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Gateway

• Connects end-systems whose host protocols have
  varying degrees of difference
• Transport gateways make a connection between two
  networks at the transport layer.
• Application gateways connect two parts of an
  application in the application layer, e.g.,
  sending email between two machines using
  different mail formats

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• Connect two networks above the network layer of
  OSI model.
• Are capable of converting data frames and network
  protocols into the format needed by another
  network.
• Provide for translation services between
  different computer protocols.

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Routers versus Bridges

• Addressing
• Routers are explicitly addressed.
• Bridges are not addressed.
• Availability
• Routers can handle failures in links, stations,
  and other routers.
• Bridges use only source and destination MAC
  address, which does not guarantee delivery of
  frames.

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• Message Size
• Routers can perform fragmentation on packets and
  thus handle different packet sizes.
• Bridges cannot do fragmentation and should not
  forward a frame which is too big for the next
  LAN.
• Forwarding
• Routers forward a message to a specific
  destination.
• Bridges forward a message to an outgoing network.

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• Priority
• Routers can treat packets according to priorities
• Bridges treat all packets equally.
• Error Rate
• Network layers have error-checking algorithms
  that examines each received packet.
• The MAC layer provides a very low undetected bit
  error rate.

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• Security
• Both bridges and routers provide the ability to
  put security walls around specific stations.
• Routers generally provide greater security than
  bridges because
• they can be addressed directly and
• they use additional data for implementing
  security.

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Brouters Bridging Routers

• Combine features of bridges and routers.
• Capable of establishing a bridge between two
  networks as well as routing some messages from
  the bridge networks to other networks.
• Are sometimes called (Layer 2/3) switches and are
  a combination of bridge/router hardware and
  software.

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Network Connectivity Devices

• Entry-level Hubs
• Interconnect PCs in a single network segment
• Simple stand-alone device that provides a
  starting point cost-effective connectivity for
  many organizations.

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Network Connectivity Devices (contd.)

• Stackable Hubs
• Let you start small and grow your network at your
  own pace.
• Are connected by flexible expansion cables, and
  once stacked together, function as one hub.
• Manageable as one logical unit.

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Network Connectivity Devices (contd.)

• Chassis Hub
• Big iron box that can contain a variety of
  network modules.
• It has a power supply, a high speed backplane,
  and expansion slots for plug-in Hub modules.

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Network Connectivity Devices (contd.)

• Workgroup switches
• Low-end network devices that aggregate multiple
  shared segments
• Use switching technology
• Typically deployed at the desktop level
• Ethernet, Token-Ring, or ATM

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Network Connectivity Devices (contd.)

• Workgroup switches
• Low-end network devices that aggregate multiple
  shared segments
• Use switching technology.
• Typically deployed at the desktop level.

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Network Connectivity Devices (contd.)

• Backbone switches
• High-end network devices deployed at the core of
  the network.
• Use switching technology.
• Aggregate data from Hubs and Workgroup switches.
• Typically accept various networking options.

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Network Connectivity Devices (contd.)

• Routers
• Perform routing of packets among LANs.
• Provide most effective way of segmenting the
  network.
• Move data by finding the best path from the
  sender to the receiver.
• Suitable for organizations with many large LANs.