Local Internets

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Local Internets
Cabletron SmartSwitch 2100
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Local Internets

• Internet
• System of subnets such that any station on any
  subnet can communicate with any station on any
  other subnet by placing the receivers address in
  a message
• Subnets are individual networks in an internet

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Local Internets
LAN
LAN
LAN
LAN

• Local Internets
• Links multiple LANs at a single site
• Entirely on customer premises
• Planned and managed by the owner
• Company has no limits
• Company has all the headaches
• High-speed transmission (roughly LAN speeds)

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Why a Local Internet?

• Overcome distance limitations
• 100Base-T networks span only 500 meters
• Overcome congestion and latency
• Individual shared media networks running around
  100 Mbps become saturated at 200-300 stations.
• Connect dissimilar LANs
• Link Ethernet and Token-Ring Network LANs

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Local Internetting to Increase Distance Spans
Internetting Device
100Base-T LAN in Headquarters Building (500 m
maximum distance)
HQ LAN
Transmission Link (no max distance)
Internetting Device
100Base-T LAN in Factory Building (500 m maximum
distance)
Factory LAN
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A Congested Shared Media LAN
Before Single LAN
Department 1 150 Stations
Department 2 150 Stations
A
B
C
D
Stations
Stations
All stations in Department 2 hear the message
B transmits to A
Each station hears the traffic of 300
stations Heavily congested.
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Internetting keep most traffic within LANs
After Resegmentation
Department 1 150 Stations
Department 2 150 Stations
Internetting Device
A
B
C
D
Stations
Stations
Internetting Device Blocks the Transmission of
this message to Department 2
B transmits to A
Traffic of 150 stations Not Congested
Traffic of 150 stations Not Congested
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Internetting Devices Bridges

• Simple, automatic, inexpensive, fast
• Usually only two ports
• A fast, cost-effective choice for small internets
• See CISCO whitepaper for more details

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Multiple Bridges
LAN 2
X
LAN 3
LAN 1
LAN 4
No Loops Allowed Problematic for large bridged
internets
LAN 5
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Multiple Bridges
Route Between LANs 1, 5
LAN 2
LAN 3
X
LAN 1
No loops means only one path between LANs No
alternative routing if failures, congestion No
way to optimize routing for security, etc.
LAN 5
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802.1 Spanning Tree Standard
Route Between LANs 1, 5
LAN 2
LAN 3
Backup Link
LAN 1
Allows backup links Disabled during normal
operation If a failure occurs, automatically
initiated
LAN 5
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Bridging LANs with Different Physical and MAC
Layers
Bridge
802.5 Token-Ring Network
802.3 10Base-T Ethernet LAN
Hub
10Base-T Connection
802.5 Connection
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Bridging LANs with Different Physical and MAC
Layers
802.2 LLC Standard
LLC Layer (Same)
802.2 LLC Standard
802.1 Bridging Standard
802.1 Bridging Standard
Bridging Layer (Same)
802.5 MAC Layer (Token-Passing)
802.3 MAC Layer (CSMA/CD)
MAC Layer (Different)
802.5 Connection to Access Unit
Physical Layer (Different)
10Base-T Connection to Hub
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Problems of Bridges

• Do Not Stop Broadcast Messages
• Servers broadcast their existence about twice a
  minute
• In contrast to normal messages, which are
  designed to go to single stations, broadcast
  messages go to all stations.
• Goes to all stations on the network bridges pass
  these messages on
• Problematic in large bridged intranets

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Problems of Bridges

• Do Not Stop Any Client from Logging into Any
  Server
• Poor security. Only password protection on
  servers
• Bad if servers hold grades in a university
• Bad for departmental servers holding key
  personnel or financial data in a firm

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Switches Solve Bridge Problems

• Begin as Multiport Bridges
• Add broadcast reduction, security

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Simple Switched Internet
Connection 1
LAN A
Connection 1
LAN C
No Waiting!
LAN B
Connection 2
Switches can carry messages between several pairs
of LANs simultaneously.
Connection 2
LAN D
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Switched Internet with Multiple Switches
Switch A
Switch B
Switch C
Switch D
LAN 1
LAN 2
Switches are arranged in a hierarchy Only one
route between any two LANs No routing around
failure, congestion No optimization of routes
Route 1-B-A-C-2
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Switch Hierarchy

• Switches can be arranged hierarchically
• Levels of Switches
• Desktop switches (only a few MAC addresses can be
  supported)
• Workgroup switches (MAC addresses for members of
  a department)
• Enterprise switches (large number of MAC
  addresses)

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Virtual LANs Reduce Broadcasting

• Stations are Divided into Groups
• Called Virtual LANs (VLANs)
• Server, other broadcasts limited to VLANs
• Not to all stations on all ports

LAN A
LAN B
LAN C
LAN D
Server only broadcasts to its VLAN stations on
LAN A, LAN C
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VLANs Add Security

• Only stations on the same VLAN as a server can
  reach it to log in

On VLAN 36
On VLAN 7
X
LAN A
LAN B
LAN C
LAN D
Client can only reach server if they are on the
same VLAN
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Routers

• Most sophisticated internetting devices
• Provide services for linking thousands of subnets
• Used in the worldwide Internet, also within firms
• Efficient for long-distance transmission
• Provide wide range of management services to give
  relatively automatic operation
• By far the most expensive internetting devices

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Route

• End-to-End Connection

1
LAN A
LAN B
3
2
4
LAN D
LAN A - 1 - 3 - 5 - LAN D
5
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Alternative Routes

• Multiple Ways to Get from LAN A to LAN D

1
LAN A
LAN B
3
2
4
A-1-3-5-D A-1-3-4-D A-2-5-D Etc.
LAN D
5
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Advantages of Alternative Routing

• Routing Around Failures
• Failed switches, trunk lines connecting switches
• Routing Around Congestion
• More common than outright failures
• Route Optimization
• Least cost route
• Most reliable route
• Most secure route, etc.

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Mixing Switches and Routers
Site A
LAN
LAN
Site B
Switch
LAN
Router
Switch
Router
LAN
Site C
Router
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Distributed Backbone Network
LAN 1
LAN 2
FDDI Backbone Ring
Router
Router
Router
LAN 3
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Backbone Network

• Network that Links Subnets
• Subnets take the place of stations
• Distributed Backbone
• Backbone runs past all stations
• If a single router (or other internetting device)
  fails, only that station is disconnected
• FDDI is popular because of its possible 200 km
  circumference, 100 Mbps speeds, but Gigabit
  Ethernet gaining.

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Local Internet Using Collapsed Backbone
LAN A
LAN B
LAN C
Routers at LANs
Routers at LANs
Central Switch or Router
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Collapsed Backbone

• Single point of maintenance
• Easy to maintain the network
• Single point of failure
• If the central device fails, serious problems
• Types of central devices
• Switches
• Routers

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Backbone Network Architectures

• Identifies the way backbone interconnects LANs
• Defines how it manages packets moving through BB
• Fundamental architectures
• Bridged Backbones
• Routed Backbones
• Collapsed Backbones
• Rack-based
• Chassis-based
• Virtual LANs
• Single-switch VLAN
• Multiswitch VLAN

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Backbone Architecture Layers

• Access Layer (not part of BB)
• Closest to the users
• Backbone Design Layers
• Distribution Layer
• Connects the LANs together (often in one building
• Core Layer (for large campus/enterprise networks)
• Connects different BNs together (building to
  building)

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Bridged Backbone
bus topology
Entire network is just one subnet
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Bridged Backbones

• Move packets between networks based on their data
  link layer addresses
• Cheaper (since bridges are cheaper than routers)
  and easier to install (configure)
• Just one subnet to worry
• Change in one part may effect the whole network
• Performs well for small networks
• For large networks broadcast messages (e.g.,
  address request, printer shutting down) can lower
  performance
• Formerly common in the distribution layer
• Declining due to performance problems

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Routed Backbone
Example of a routed BB at the Distribution layer
Usually a bus topology
Each LAN is a separate subnet
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Routed Backbones

• Move packets using network layer addresses
• Commonly used at the core layer
• Connecting LANs in different buildings in the
  campus
• Can be used at the distribution layer as well
• LANs can use different data link layer protocols
• Main advantage LAN segmentation
• Each message stays in one LAN unless addressed
  outside the LAN
• Easier to manage
• Main disadvantages
• Tend to impose time delays compared to bridging
• Require more management than bridges switches

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Collapsed Backbone
Most common type BB mainly used in distribution
layer
A connection to the switch is a separate
point-to-point circuit
Star topology
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Collapsed Backbones

• Replaces the many routers or bridges of the
  previous designs
• Backbone has more cables, but fewer devices
• No backbone cable used switch is the backbone.
• Advantages
• Improved performance (200-600 higher)
• Simultaneous access switched operations
• A simpler more easily managed network less
  devices
• Two minor disadvantages
• Use more and longer cables
• Reliability
• If the central switch fails, the network goes
  down.

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Rack-Based Collapsed Backbones

• Places all network equipment (hubs and switch) in
  one room (rack room)
• Easy maintenance and upgrade
• Requires more cables (but cables are cheap)
• Main Distribution Facility (MDF) or Central
  Distribution Facility
• Another name for the rack room
• Place where many cables come together
• Patch cables used to connect devices on the rack
• Easier to move computers among LANs
• Useful when a busy hub requires offloading

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Chassis-Based Collapsed Backbones

• Use a chassis switch instead of a rack
• A collection of modules
• Number of hubs with different speeds
• L2 switches
• Example of a chassis switch with 710 Mbps
  capacity
• 5 10Base-T hubs, 2 10Base-T switches (8 ports
  each)
• 1 100Base-T switch (4 ports), 100Base-T router
• ? ( 5 x 10) (2 x 10 x 8) (4 x 100) 100
  710 Mbps
• Flexible
• Enables users to plug modules directly into the
  switch
• Simple to add new modules

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Virtual LANs (VLANs)

• A type of LAN-BN architecture
• Made possible by high-speed intelligent switches
• Computers assigned to LAN segments by software
• Often faster and provide more flexible network
  management
• Much easier to assign computers to different
  segments
• More complex and so far usually used for larger
  networks
• Basic VLAN designs
• Single switch VLANs
• Multi-switch VLANs

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Single Switch VLAN Collapsed Backbone
acting as a large physical switch
Computers assigned to different LANs by software
Switch
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Types of Single Switch VLANs

• Port-based VLANs (Layer 1 VLANs)
• Use physical layer port numbers on the front of
  the VLAN switch to assign computers to VLAN
  segments
• Use a special software to tell the switch about
  the computer - port number mapping
• MAC-based VLANs (Layer 2 VLANs)
• Use MAC addresses to form VLANs
• Use a special software to tell the switch about
  the computer - MAC address mapping
• Simpler to manage
• Even if a computer is moved and connected to
  another port, its MAC address determines which
  LAN it is on

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Types of Single Switch VLANs

• IP-based VLANs (Layer 3 VLANs, protocol based
  VLANs)
• Use IP addresses of the computers to form VLANs
• Similar to MAC based approach (use of IP instead
  of MAC address)
• Application-based VLANs (Layer 4 VLANs,
  policy-based VLANs)
• Use a combination of
• the type of application (Indicated by the port
  number in TCP packet) and
• The IP address to form VLANs
• Complex process to make assignments
• Allow precise allocation of network capacity

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Multi-switch VLAN-Collapsed Backbone
Switch
Switch
Switch
Switch
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Multi-switch VLAN Operations

• Inter-switch protocols
• Must be able to identify the VLAN to which the
  packet belongs
• Use IEEE 802.1q
• When a packet needs to go from one switch to
  another
• 16-byte VLAN tag inserted into the 802.3 packet
  by the sending switch
• When the IEEE 802.1q packet reaches its
  destination switch
• Its header (VLAN tag) stripped off and Ethernet
  packet inside is sent to its destination computer

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VLAN Operating Characteristics

• Advantages of VLANs
• Faster performance
• Precise management of traffic flow
• Ability to allocate resources to different type
  of applications
• Traffic prioritization (via 802.1q VLAN tag)
• Include in the tag a priority code based on
  802.1p
• Can have QoS capability at MAC level
• Similar to RSVP and QoS capabilities at network
  and transport layers
• Drawbacks
• Cost
• Management complexity