now let's look at what we have learned
and applied to the case of a simple
campus
this campus we've got one subnet per
building
and the slide shows an ethernet switch
with a routing process turned on so it
has the layer 3 capability turned on
and the two ports on the left have been
configured
in different vlans the dark red port is
vlan 10
and the green port is in vlan 20.
each vlan has an ip address and this ip
address will be used as the default
gateway
for any devices that connect to
this switch if we've got multiple
subnets per building
then we would make the gigabit ports
on this switch rather than just an
access port we'd make them a trunk port
so you see the example here the red on
the left
that's interface gigabit one it's now
been defined as a trunk
and it's allowing vlans 10 11 and 12
in through that trunk port we've defined
ip addresses for vlan 10
to be 10 1 0 1 for vlan 11 to be 10
1 1 1 and for vlan 12 to be 10 1
2 1. so these are the default gateways
that
end users would use if they're on
the respective vlans gigabit 2
and this core switch that we have
would be similarly set up to connect to
another building
so this building would be using vlans
2021 and 22
and we have the same ip addresses
defined for vlan 2021
and 22.
so again based on what you have learned
so far in this video series
what has to be different at the building
aggregation switch
so let's have a look at some of the
hints and tips about all this remember
one subnet equals one vlan
we've advised in several sessions before
never to use vlan 1.
it's the default vlan on many different
vendor switches
and often has special default behavior
in fact in some cases you can't even
turn it off
so be very wary about vlan 1. it should
never be used
it may appear by default on all ports
it's
very hard quite often to use it with
tagging
so it's better to ignore it and if you
can
remove it but vlans 2 through to 4094
are usable
and should be more than enough for a
modern campus
what other hints and tips can we look at
well it's also important not to enable
the same vlan on links to different
buildings
we want to try and keep the group of
vlans within a building
v-lines within the building routing at
the core
has been a general theme throughout this
series
a layer-free switch lets you do this and
you find many design documents
talking about how to configure this but
that doesn't mean it's a good idea
you end up with vlan spaghetti you end
up with a big mess
that you cannot scale and you cannot
manage
so this implies you're going to have a
wired v line per building
and a wi-fi v line per building and
whatever other vlans you need
the vlans will stay in the building we
carry them
on a trunk to the core router and the
router
there will write between them and it's
actually very rare for a user on a wired
vlan in a building to need to be able to
send vast amount of data
to a user on another vlan in the same
building
most campus end users are consumers
consuming internet content or accessing
content that's in the network core
and when you're doing your vlan planning
make sure you choose a consistent scheme
so for example vlans 2 to 9 could be for
the knock
10 to 19 for building 1 20 to 29 for
building 2 and so forth
you're not likely to need more than 10
vlans per building
and so if you follow this scheme this is
going to allow for up to 400 buildings
with ease
is your campus really that big so this
could be a very viable scheme for you to
follow
and it means you can identify traffic
and users
based simply on the vlans that they are
assigned to
some layer 3 switches will let you
configure routed ports
making it work exactly like a router
instead of a switch
some also have routed sub-interfaces
with vlan tags
this means you could route multiple
subnets to each building without
actually having to create
separate vlans this will help you scale
in the case that you're going to run out
of vlans the other thing to remember is
you can actually use the same vlan tags
for different subnets in different
buildings
and this makes the distribution and edge
switch configurations almost identical
everywhere
so rather than the example we talked
about in the previous slide where we
said built
building one would have vlan 10 to 19
and building 2 would have 20 to 29
make every building use vlan 10 to 19.
because you're not going to be passing
the vlans from building to building
they're all routed in the core and as
long as the core router
knows how to get between the different
vlans configured that's all you need to
know
so looking on a switch where you've got
fully routed interface again the
configuration example shows you how this
might work
so the gigabit one interface on the left
the red one
shows that it's not a switch port so
this is now routed port
we now create sub-interfaces so
interface gig 1.10
we've said encapsulation.1 q10 that
means we're
tagging that interface sub-interface
as in vlan 10. so all the traffic on
that one will be vlan 10.
and gigabit 1.11 encapsulation.1 q11
that is vlan 11. so again
traffic on this interface going out to
the distribution
will be tagged according to which vlan
it is sitting in we can do the same with
gigabit 2
and so on and so forth both buildings in
this case are using vlan tags 10 and 11
but these are different isolated subnets
remember we are not
passing vlan 11 in one building to vlan
11 in another building
because this is a fully routed interface.
© Produced by Philip Smith and the Network Startup Resource Center, through the University of Oregon.
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