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Purpose: Since we began exploring basic functionality of switches in the last e
xercise, we will discuss more advance topics now. This exercise covers creating
VLAN port tagging, and Spanning Tree Protocol. We will briefly discuss some pros
and cons with using switches. We will introduce terminal configuration via Putt
y as well.
Background: Switches are plug and play devices, which make them very easy to set
up with minimum configuration. They also have very high filtering and forwarding
rates since they only process requests up to Layer 2, compared to a router that
processes datagrams at Layer 3. This is why they tend to be significantly faste
r than routers. However, to prevent the cycling of broadcast frames, the topolo
gy of a switched network is limited to a spanning tree. Additionally, a large sw
itch with an enormous number of ports requires a large ARP table, which would ge
nerate significant ARP traffic. A large ARP table would consume valuable network
bandwidth and resources.
Managed switches are powerful enough to handle special features as well that enh
ance and provide granular control of the LAN including the following:
Power over Ethernet (PoE): IEEE 802.3af, IEEE 802.3at. This technology enables
Ethernet network cables to provide both data and power to a device. It was desi
gned for use with portable and wireless electronic equipment like Access Points
(APs).
Quality of Service (QoS): QoS has the ability to characterize the network traffi
c in order to prioritize certain types. This is accomplished with a collection o
f networking technologies that work together to calculate a predictable flow of
the network traffic through the switch. The different components considered incl
ude uptime (i.e., link reliability), bandwidth (i.e., the potential throughput),
latency (i.e., network delay), and error rate. Certain applications like Voice
over IP (VoIP), and video streaming, require higher guaranteed performance level
s to ensure reliable functionality. NOTE: These QoS settings can help with but not
guarantee a maximum delay or minimum bandwidth for a particular application.
Spanning Tree Protocol (STP): The continual transmission (cycling) of broadcast
frames may become a problem in Layer 2 components if cycles exist in the topolog
y. Therefore, a spanning tree is created to ensure that the topology is free of
loops for any bridged Ethernet LAN.
The managed HP switches are capable of using RSTP (IEEE 802.1D-2004) Rapid Spann
ing Tree Protocol (RSTP), which is an enhancement of the traditional STP protoco
l. Using STP/RSTP a spanning tree is created within a LAN for transmission with
out cycles. STP/RSTP ensures that only one active path exists between any two ne
twork nodes. The parameters that are used to form the spanning tree are:
Switch (bridge) based Priority: This is used to identify the priority of switch
with respect to other switches for forwarding traffic with no configured VLANs.
HP refers to this as Global configuration since it affects all ports on the device
. The switch with the lowest numerical value is considered the highest priority,
indicating that it is the root bridge in the network. Possible values: 0-65535
. Default value: 32768
Port based Priority: This is used to identify the root bridge of a specific VLAN
when a switch has multiple VLANs configured. A higher numerical value means a l
ower priority. Possible values: 0-65535. Default value: 128
Port Path Cost: The cost of using a specific port as a path to reach the root br
idge. The default cost depends on the port type (i.e., 10 Mbps = 100, 100 Mbps =
19, and Gigabit = 4).
Parameters:
Root ID: The ID assigned by the STP to the root bridge for this spanning tree.
Root Cost: The cumulative cost from the current bridge to the root bridge. If th
e device is the root bridge then the value is Root instead of a number.
Root Port: The port on the current bridge that connects to the root bridge.
Priority Hex: This device s STP priority. The value is shown in HEX but needs to
be entered in decimal form. In our case with the Big Apple Topology, the core se
rver is considered the Root Bridge. This is indicated by using the lowest bridg
e ID to identify it.

State:
Blocking: STP has blocked Layer 2 traffic on this port to prevent a loop. The de
vice will still be able to reach the root bridge but only using another port wit
h a forwarding state.
Disabled: This port is not participating in STP.
Forwarding: STP is allowing the port to send and receive frames.
Listening: STP is responding to a topology change and this port is listening for
updates from its neighbor bridges. No forwarding is allowed during this state.
Learning: The port is in learning state (after the listening state) and will cha
nge to blocking or forwarding depending on the STP re-convergence.
Network Isolation using Virtual LANs
Most modern high-end switches support the creation multiple virtual LANs across on
e physical network. Hosts within a VLAN see only the other hosts in the VLAN as
local (i.e., as if they were physically connected to the same LAN). For managed
switches in Netlab, the switch ports are used to indicate which group a VLAN wil
l communicate with. Each group resides

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