designing scalable wireless networks in the campus lan
TRANSCRIPT
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Designing scalable wireless networks in the
campus LAN
Sebastian Büttrich, wire.less.dk/NSRC
edit: March 2010, KENET
http://creativecommons.org/licenses/by-nc-sa/3.0/
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Agenda• Introduction to wireless networking– Standards, Modes, Topologies
• Wireless Hardware– Routers & Access Points– Antennas
• Integration with a Campus LAN
• Wireless security
• Captive portals
• Wireless roaming
• LAB: hands-on wireless
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Goals• Understanding the basics
• Understanding that in wireless
cost and quality are not always correlated
• See how skills and brains matter
• See that we need the same brains, whether we go
low budget or BIG BUDGET
• Develop a good feeling for layer thinking
• Work towards a set of “best practices” for campus
wireless
• And ...
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Goals• Hopefully, see that low cost wireless is fun
and can bring you wonderful places :)
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Learning more• http://wirelessu.org
• http://nsrc.org
• http://wireless.ictp.it/
• Wireless Training Kit (ICTP/ITU) out soon!
• The green book: http://wndw.net
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The basics• Introduction to wireless networking– Standards, Modes, Topologies
• Wireless Hardware– Routers & Access Points– Antennas
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Integration with a campus LAN
• All the rules and best practices for general
network architecture apply
– They matter even more in wireless, as your logical
network architecture no longer is reflected in your
physical architecture
• A user on the library network might in fact be 10
miles away!
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Rules and best practices
• Build a structured network, not a flat one! Build stars
and trees, not chains or clouds
(except where you like a cloud :)
• Subnet! Subnet! Subnet!
• Reflect organisation and policies in your IP design
• Separate core and edge networks
• Planning of maximum size of subnets becomes
even more important – as the capacity of wireless cells
is limited!
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Specifically wireless
• In contrast to a wired network, you now have to
consider additional planning – as your medium is now
boundless.
– Network separation on Layer 1 / 2 • by means of Frequency (Standards, Channels)
and Polarization planning
– Reach and Power planning, Antennas
– Naming (SSIDs)
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Frequency planning
• If two people give you torch signals with a red torch,
you cant tell one from the other
• If one uses red, the other green – you can 'read' both
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Frequency planning
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Important wireless planning activities
• A Link Budget is the calculation of power – starting
with output power and including all gains and losses
(mostly for P2P, long distance links) –
no (long) link without a Link Budget!
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Important wireless planning activities
• A Site Survey is the on-site recording of all relevant
conditions – from technical (e.g. finding existing
wireless networks) to human (social factors) to
environmental – no wireless deployment without
Site Survey!
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Wireless on Layer 2
• The physical layer - Modes:
– Master / Station (managed mode) – typically used
for Point-to-Multipoint (P2MP):
hotspots, “access points”
– Ad-hoc:
typically used for P2P or MP2MP
• Modes do not have to match topologies!
– You might find a P2P link consisting of Master and
Client
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Wireless on Layer 3
• The behaviour of wireless units with regards to TCP/IP
may be:
– Pure bridging
– Routing• DHCP, NAT, Masquerade, etc
• DHCP may be integrated with network-wide DHCP (bridge through), but separate DHCP for wireless subnets is sometimes advisable
• Again, typical behaviour on Layer 2 is not necessarily
reflected on Layer 3! Dont get confused!
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Putting it all together -wired
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Putting it all together -adding wireless elements
Typical roles for wireless:
• Wireless links may replace fiber/wired links in the core
network where distance or budget or security aspects
suggest this
• Wireless “hotspot” access on the edges: offices, cafes,
libraries, workspaces, ...
• Wireless mesh clouds on the edges, e.g. for
compounds, housing, villages
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Putting it all together -adding wireless elements
• Design 1+ wireless here
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Putting it all together -IP design
• IP design must reflect organisation and logic in order to
be manageable – especially for wireless networks
• E.g. IP subnets like this:– 10.1.0.0 Infrastructure– 10.10.0.0 University internal networks, Admin– 10.20.0.0 Students– 10.30.0.0 Open networks for guests etc
• Other IP design principles:– by location– by department– by physical carrier, e.g. wired/wireless
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Putting it all together -IP design
• The important thing is that
– you are able to treat network segments in
meaningful ways (e.g. bandwidth management,
security, access time, usage rules, incident
response)
– When things go wrong, you are able to isolate and
address network segments
• This is even more important for wireless than for wired
networks! Why?
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IP design for edge access
• Let us focus on edge access
• There isn't one golden rule how to do it right -
but there are several best practices to discuss
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IP design for edge access
• Example 1:
aligning IP design with organisational logic
• For example, wireless access for administrative
employees
• Recommendation: place the wireless access on the
same subnet as the wired workplaces - with strict
access control, DHCP bridged through
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IP design for edge access
• Example 2:
open access in cafeteria, library, etc
• Usergroup is uncontrollable
• Recommendation: – place the wireless access on separate subnet– VLAN– with access control, back end integration (e.g.
through RADIUS)– DHCP bridged through, in order to secure roaming
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IP design for edge access
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IP design for edge access
• Example 3 – an alternative:
open access in cafeteria, library, etc
• Usergroup is uncontrollable
• Recommendation: – Keep wireless access completely open! Consider it
“open internet”– Make sure the wireless subnet is properly isolated– Ensure access control and security on level of• Service / server• Application