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/

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

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 ...

Goals• Hopefully, see that low cost wireless is fun

and can bring you wonderful places :)

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

The basics• Introduction to wireless networking– Standards, Modes, Topologies

• Wireless Hardware– Routers & Access Points– Antennas

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!

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!

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)

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

Frequency planning

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!

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!

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

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!

Putting it all together -wired

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

Putting it all together -adding wireless elements

• Design 1+ wireless here

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

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?

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

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

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

IP design for edge access

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