Network Bridges and Routers

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Network Bridges and Routers

• Brandon York

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What exactly is a Bridge in Networking?

• _____________________________________
• A Bridge is a device that filters data traffic at
  a network boundary. Bridges reduce the amount of
  traffic on a LAN by dividing it into two
  segments. It connects on the data-link layer,
  (layer 2) of the OSI model.

In the picture to the right, the data is coming
from the database server. The bridge filters the
data, sending the data to the correct locations.
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How does a bridge work?__________________________
_

• Bridges are similar to repeaters and network
  hubs, devices that connect at the physical layer,
  however, with bridging, traffic from one network
  is managed rather than simply rebroadcast to
  adjacent network segments.
• Bridges tend to be more complex than hubs or
  repeaters. Bridges can analyze incoming data
  packets to determine if the bridge is able to
  send the given packet to another segment of the
  network

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Bridges Continued___________________________

• Since bridging takes place at the data-link
  layer of the OSI model, a bridge processes the
  information from each frame of data it receives.
  In an Ethernet frame, this provides the MAC
  address of the frame's source and destination.
  Bridges use two methods to resolve the network
  segment that a MAC address belongs to.

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The Data-Link Layer

• The data link layer is divided into two sub
  layers
• The Media Access Control (MAC) layer and the
  Logical Link Control (LLC) layer. The MAC sub
  layer controls how a computer on the network
  gains access to the data and permission to
  transmit it. The LLC layer controls frame
  synchronization, flow control and error checking.

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The Data-Link Layer!
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Transparent Bridging

• This method uses a forwarding database to
  send frames across network segments. The
  forwarding database is initially empty and
  entries in the database are built as the bridge
  receives frames. If an address entry is not found
  in the forwarding database, the frame is
  rebroadcast to all ports of the bridge,
  forwarding the frame to all segments except the
  source address. By means of these broadcast
  frames, the destination network will respond and
  a route will be created. Along with recording the
  network segment to which a particular frame is to
  be sent, bridges may also record a bandwidth
  metric to avoid looping when multiple paths are
  available. Devices that have this transparent
  bridging functionality are also known as adaptive
  bridges. They are primarily found in Ethernet
  networks.

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Source Route Bridging

• Source route bridging is used primarily on token
  ring networks.The spanning tree protocol is not
  used, the operation of the network bridges is
  simpler, and much of the bridging functions are
  performed by the end systems, particularly the
  sources. A field in the token ring header, the
  routing information field (RIF), is used to
  support source-route bridging. Upon sending a
  packet, a host attaches a RIF to the packet
  indicating the series of bridges and network
  segments to be used for delivering the packet to
  its destination. The bridges merely follow the
  list given in the RIF - if a given bridge is next
  in the list, it forwards the packet, otherwise it
  ignores it. Loops are avoided by requiring each
  bridge to ignore packets which already contain
  its bridge number in the RIF field.

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Bridge History

• Bridges were one of the first network devices.
  Early bridges were more intelligent than network
  repeaters and faster than routers. Although
  bridges are rarely used in modern-day networks,
  it is important to understand their function as
  many modern-day network devices are based on the
  principles first pioneered by the network bridge.
  
• Bridges became popular in the late 1980s and
  reached the peak of their popularity in the late
  1990s. Since that time, bridges have been losing
  ground due to the invention of the network
  switch.

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Network Bridge Manufacturers

• Just to name a few
• Pulsar Linksys
  Cisco

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Price..

• 9 to 17,000

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Yes 17,000 dollars.
9 dollars
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What is a Router?

• Its an electronic device used to connect two or
  more computers or other electronic devices to
  each other, and usually to the Internet, by wire
  or radio signals. This allows several computers
  to communicate with each other and to the
  Internet at the same time. More technically, a
  router is a networking device whose software and
  hardware are usually assigned to the tasks of
  routing and forwarding information. Routers
  operate on 3rd layer of the OSI model. The
  network layer.

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Router Table

• What is it? Its an electronic file, database
  type object that is stored in a router or a
  networked computer. The routing table stores the
  routes to particular network destinations. This
  information contains the topology of the network
  immediately around it. The construction of
  routing tables is the primary goal of routing
  protocols and static routes.
• Routing tables are generally not used directly
  for packet forwarding in modern router
  architectures instead, they are used to generate
  the information for a smaller forwarding table
  which contains only the routes which are chosen
  by the routing algorithm as preferred routes for
  packet forwarding, often in a compressed or
  pre-compiled format that is optimized for
  hardware storage and lookup.

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The Two Planes of Routing

• Control plane in which the router learns the
  outgoing interface that is most appropriate for
  forwarding specific packets to specific
  destinations.
• Forwarding plane which is responsible for the
  actual process of sending a packet received on a
  logical interface to an outbound logical
  interface.

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Types of Routers

• Edge Router Placed at the edge of an ISP
  network, it speaks external BGP (eBGP) to a BGP
  speaker in another provider or large enterprise
  Autonomous System(AS) .
• Subscriber Edge Router Located at the edge of
  the subscriber's network, it speaks eBGP to its
  provider's AS(s). It belongs to an end user
  (enterprise) organization.

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Types Cont.

• Inter-provider Border Router Interconnecting
  ISPs, this is a BGP speaking router that
  maintains BGP sessions with other BGP speaking
  routers in other providers' ASes
• Core router A router that resides within the
  middle or backbone of the LAN network rather than
  at its periphery

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Types cont

• Access routers are located at customer sites
  such as branch offices that do not need
  hierarchical routing of their own. Typically,
  they are optimized for low cost.

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History of Routers

• The idea for a router (although they were called
  "gateways" at the time) initially came about
  through an international group of computer
  networking researchers called the International
  Network Working Group (INWG). Set up in 1972 as
  an informal group to consider the technical
  issues involved in connecting different networks.

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History Cont.

• The idea was explored in more detail, with the
  intention to produce a real prototype system, as
  part of two contemporaneous programs. One was the
  initial DARPA-initiated program, which created
  the TCP/IP architecture of today.

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History Cont

• The first true IP router was developed by
  Virginia Strazisar at BBN, as part of that
  DARPA-initiated effort, during 1975-1976. By the
  end of 1976, three PDP-11-based routers were in
  service in the experimental prototype Internet.
  The first multiprotocol routers were
  independently created by staff researchers at MIT
  and Stanford in 1981. Virtually all networking
  now uses IP at the network layer, multiprotocol
  routers are largely obsolete, although they were
  important in the early stages of the growth of
  computer networking.

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Router Manufacturers

• D-Link, NetGear, Linksys, TrendNet, Belkin,
  Cisco, Buffalo, SMC, USRobotics, TP-Link,
  Asus, 3Com, Syswan, Zonet, Edimax, HP,
  Hawking, and Encore.

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Sources