Transcript routers

LAN Design
Broadcast and Collision Domains
Home
End
Table of Contents
Go There!
Design Goals & Components
Go There!
Network Design Methodology
Go There!
Layer 1 Design
Go There!
Layer 2 Design
Go There!
Layer 3 Design
Home
End
Design Goals & Components
Home
End
LAN Design Goals
•
•
Critical to design is insuring a fast and stable
network that will scale well as the organization
grows
Design steps are...
1. Gather & establish design goals based on user
requirements
2. Determine data traffic patterns now & in the future
3. Define Layer 1, 2, & 3 devices & the LAN/WAN
topologies
4. Document physical & logical network implementation
Home
End
Establish the Design Goals
• Although organizations are unique to the
customer, the following requirements tend to
be generic to all. The network must have...
– Functionality--speed and reliability
– Scalability--ability to grow without major changes
– Adaptability--easily implements new technologies
– Manageability--facilitates monitoring and ease of
management
Home
End
Critical Components of LAN Design
• With the emergence of high-speed
technologies and complex LAN technologies,
the following critical components need
addressing in design
– Collision Detection
– Micro segmentation
– Bandwidth v. Broadcast domains
– Function & placement of Servers
Home
End
MAC Address
• Contains 48-bit destination address field.
• Who is this frame for?
– 00-C0-F0-56-BD-97
• “D: It is for me”
Home
End
MAC Address
• How will all
other NICs
handle the
frame?
• Drop it out.
Home
End
Special MAC Address
• Who is this frame for?
– FF-FF-FF-FF-FF-FF
• “Hey everybody”
Home
End
Broadcast MAC Address
• FF-FF-FF-FF-FF-FF
• 48 bits, all 1s
• All NICs copy the
frame & send it up
the stack
Home
End
Broadcast Frames
• Necessary for network function
• Used for
– finding services: “Hey, is there a server out
there?”
– Advertising services: “Hey, I’m a printer you
can use.”
Home
End
Collision Domain
• Network region in
which collisions are
propagated.
• Repeaters and
hubs propagate
collisions.
• Bridges, switches
and routers do not.
Home
End
Reducing Collisions
Collision frequency can be kept low by
breaking the network into segments
bounded by:
– bridges
– switches
– routers
Home
End
Broadcast Domain
• Network region in which
broadcast frames are
propagated.
• Repeaters, hubs, bridges, &
switches propagate
broadcasts.
• Routers don’t (Stops
broadcasts).
Home
End
Reducing Broadcasts
• Broadcasts are necessary for network
function.
• Some devices and protocols produce lots
of broadcasts.
• Broadcast frequency can be kept
manageable by limiting the LAN size.
• LANs can then be cross-connected by
routers to make a larger internetwork.
Home
End
Shared Ethernet
• A single segment that is
shared among all
connected NICs.
• A single collision domain.
• The segment includes
repeaters and hubs.
• Sometimes called a “single
flat Ethernet”.
Home
End
Switched Ethernet
• Consists of a several segments, each of which is shared by NICs attached
to it.
• The network is segmented into several collision domains.
• Bridges, switches, and routers create the segment and collision domain
boundaries.
• Segments may contain hubs and repeaters.
Home
End
Micro segmented Switched Ethernet
•
•
•
•
Each user NIC is connected directly to a switch port.
Provides one switched segment to each connected NIC.
No sharing.
No collisions.
Home
End
Identify the collision domains and broadcast
domains?
switch
hub
hub
Home
End
Identify the collision domains and broadcast
domains?
hub
hub
Home
End
Identify the collision domains and broadcast
domains?
Home
End
Identify the collision domains and the
broadcast domains?
router
switch
• Routers connect separate networks.
• One broadcast domain per router interface.
Home
End
Intranets & Collisions
– Intranets are internal to the organization and are not
accessible by the public over the Internet.
– Intranet Servers provide access to only authorized users.
– This has caused an increase in needed bandwidth. Therefore,
when designing a network you must address...
• Server privileges
• Providing desktops with faster connectivity
– More processing power
– 10/100Mbps NICs to provide migration to switched technologies
– Collision detection and minimization has become a major
concern as users attempt to access the same server.
– As we’ve seen, switches can provide dedicated bandwidth to
minimize or eliminate collisions.
Home
End
Broadcasts & Segmentation
• Layer 2 devices
segment collision
domains
• Layer 3 devices
segment broadcast
domains
Home
End
Bandwidth v. Broadcast Domains
– A bandwidth domain is
shared by all devices on a
single switched port.
• Synonymous with collision
domain
– A broadcast domain is
shared by all devices on a
single router interface.
Home
End
Reminder
• Collisions
– spread throughout a LAN segment
– spread across hubs & repeaters
– are stopped by switches & bridges
• Broadcasts
– spread throughout an entire LAN
– spread across hubs, switches, bridges
– are stopped only by routers
Home
End
Summary
Term
LAN Segment
(Collision domain)
Entire LAN
(Broadcast domain)
Internetwork
Includes
Cable
Repeaters
Hubs
Boundary
Bridges
Switches
(Routers)
Everything
except
Routers
Edge of LAN
Routers
LANs &
Routers
Edge of
Internetwork
Example
switch
router
switch
(Group of LANs
cross-connected
by Routers)
Home
End
Network Design Methodology
Table of Contents
End Slide Show
Home
End
Gathering & Analyzing Requirements
– Gathering data
about the
organization
includes:
Home
End
Network Availability
– Network design seeks to
provide the greatest
availability for the least
cost.
– Factors that affect
availability include...
• Throughput (amount of
data)
• Response time
• Access to resources
Home
End
Physical Topologies
– Most LANs now days use
the star/extended star
physical topology which
typically uses the
Ethernet 802.3 standard.
– Why? Because it is the
most popular topology.
– The next three sections,
evaluate the extended
star by layers.
Home
End
Layer 1 Design
Table of Contents
End Slide Show
Home
End
Ethernet Cable Runs
– The physical cabling (also called the cable plant) is the
most important Layer 1 issue to consider when
designing a network.
– Design issues include...
• Type of cable to use (twisted-pair, coax, fiber)
• Where to use each type (e.g. fiber on the backbone)
• How far each run must travel before being terminated
(twisted-pair is limited to what distance?)
– In an existing LAN, a cable audit is performed to
determine where upgrading and/or replacement of
bad cables is needed.
Home
End
MDF & Other 568A Acronyms
– Whether the LAN is a star
or extended star, the MDF
is the center of the star.
• From the workstation to the
telecommunications outlet,
the patch cable should be no
more than 3m.
• From there to the patch
panel, called the HCC
(Horizontal cross connect),
no more than 90m.
• From the patch panel (the
HCC) to the switch, no more
than 6m.
Home
End
MDF & Other 568A Acronyms
– When distances to the
MDF are more than 100m,
an IDF is normally added.
– The cable run from the IDF
to the MDF is called the
VCC and is usually fiber.
– VCC is just another name
for the backbone.
– By adding more wiring
closets (more IDFs), you
create multiple catchment
areas (Click of graphic
button)
Home
Graphic
End
Placement of Servers
• Servers now perform special functions and can be
categorized as either...
– Enterprise Servers--supports all users on the network
• DNS and mail servers
• should be placed in the MDF (Main Distribution Facility)- A
room that will be established as the central point to which
all LAN cabling will be terminated.
– Workgroup Servers--supports a specific set of users
• file serving such as specialized databases
• should be place in the IDF (Intermediate distribution
facilities) closest to users
Graphic
Home
End
10BaseT and 100BaseT Ethernet
• 100 BaseT (also called Fast Ethernet) is now
the standard for connecting IDFs to the MDF.
– Although you can run Fast Ethernet over 10BaseT
cabling (twisted pair), the distance limitation
means fiber is most often used
– The 100BaseT standard running on twisted paid is
called 100BaseTX
– On fiber, it is called what?
Home
End
Layer 1 Logical Documentation
– Layer 1 logical documentation
is concerned with...
• exact location of MDF/IDF
• type & quantity of cabling
• room locations & # of cable
drops
• port numbers
• cable labels
– Notice Layer 1’s logical
documentation shows nothing
about logical addressing
– The Logical Diagram and Cut
Sheet are primary tools for
design, but are crucial to the
tech who is troubleshooting.
Home
End
Layer 2 Design
Table of Contents
End Slide Show
Home
End
Common Layer 2 Devices
– The two most common
Layer 2 devices are...
• Bridges and
• LAN Switches
– Both provide the added
benefit of what?
 Segmenting collision
domains into microsegments.
 Switches can also provide connections of unlike
bandwidth (e.g., 100Mbps to the server & 10Mbps to
workstations).
Home
End
Sizing Collision Domains
– In a switched LAN environment
using hubs, the bandwidth of
each switched port is shared by
all the devices. Therefore, they
also share the same collision
domain.
– To determine the bandwidth per
host, simply divide the port’s
bandwidth by the number of
hosts (see graphic).
– In a pure switched LAN
environment where each host
has its own port, the size of the
collision domain is 2. If running
full-duplex.
Home
End
Migrating to 100BaseT
– As long as your workstations all
have 10/100 NICs, increasing the
bandwidth is easy.
• Replace the hub with a 100Mbps
capable hub and patch the HCC
into a 100Mbps port on the switch.
• In addition, you can add another
100Mbps VCC from the IDF to the
MDF, which provide 200 Mbps to
the IDF’s switch.
• In the graphic, the red lines
represent migrating to 100Mbps.
Home
End
Layer 3 Design
Table of Contents
End Slide Show
Home
End
Routers and Design
• Routers provide both
physical and logical
segmentation.
– Physically, routers segment
what?
– Logically, routers segment
according to Layer 3
addressing dividing the LAN
into logical segments called
subnets.
Home
End
VLANs & Broadcast Domains
– VLAN capable switches
help routers contain
broadcasts.
– The graphic shows two
broadcast domains.
– Notice there are also
two subnets.
– The router provides
communication
between the two VLANs.
Home
End
Diagramming a LAN with Routers
– Notice in the graphic that
the two networks are
kept separate by the
router.
– Each switch serves a
different network
regardless of the physical
location of the devices.
Home
End
Logical & Physical Network Maps
– After determining your Layer 1, 2, and 3 design, you
can create your addressing (logical) and physical
maps. These are important because they:
• Give a snapshot of the network
• Show subnet mask info
• Help in troubleshooting
Home
End