Chapter 17
Connecting
Devices
And
Virtual
LANs
Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display.
Chapter 17: Outline
17.1 CONNECTING DEVICES
17.2 VIRTUAL LANS
17-1 CONNECTING DEVICES
Connecting devices are used to connect hosts
together to make a network or to connect
networks together to make an internet.
17.3
17-1 CONNECTING DEVICES
Connecting devices can operate in different
layers of the TCP/IP model.
17.4
17-1 CONNECTING DEVICES
three common connecting devices:
repeater-hubs,
link-layer switches, and
routers.
17.5
Figure 17.1: Three categories of connecting devices
17.6
17.17.1 Repeater-Hubs
A repeater-hub is a multiport device that operates only
in the physical layer.
Signals carrying information within a network can
travel a fixed distance before attenuation endangers
the integrity of the data.
17.7
17.17.1 Repeater-Hubs
A repeater receives a signal then regenerates and
retimes the original bit pattern.
A repeater-hub (hub for short) is a multiport repeater.
The incoming signal is regenerated, retimed and sent
through all ports excluding the entry port.
17.8
Figure 17.2: Hub
17.9
17.17.2 Link-Layer Switches
A link-layer switch operates in both the physical and
the data-link layers.
AKA,
2-layer switch
17.10
17.17.2 Link-Layer Switches
As a physical-layer device, it regenerates the signal it
receives.
As a link-layer device, the link-layer switch can check
the MAC addresses (source and destination)
contained in the frame.
Some switches operate using virtual circuit identifiers
or virtual path identifiers (or both).
17.11
17.17.2 Link-Layer Switches
Example (private Ethernet network with a 2-layer
switch)
The switch table needs entries for each connected
device MAC addresses and the corresponding port
number.
MAC address: 48 bits, 12 nibbles, 6 octets.
17.12
Figure 17.3: Link-Layer Switch
17.13
17.17.2 Link-Layer Switches
Example (private Ethernet network with a 2-layer
switch)
A 2-layer switch is much smarter than a
repeater(hub). The switch forwards the message
through the appropriate port or ports as determined by
the frame header fields.
17.14
17.17.2 Learning Switch
A learning switch can build a forwarding table by
looking at the source address and corresponding port
number.
Frames can be broadcast to the unassigned ports (like
a hub) until all the ports are assigned. This can be
accomplished with Switch Port Mapping Software
17.15
17.17.2 Switch Software
SNMP = Switch Network Mapping Protocol
Managed Switch Port Mapping Tool
NetDB = Network Tracking Database
OpUtils
Lan-sweeper
17.16
Figure 17.4: Learning switch
17.17
17.17.2 Switchs
Unmanaged switches – plug-n-play, without a
management interface.
Managed switches – will include a command line
interface.
• Smart switches
• Managed switches
17.18
Figure 17.5: Loop problem in a learning switch (Part a)
17.19
Figure 17.5: Loop problem in a learning switch (Part b)
17.20
Figure 17.5: Loop problem in a learning switch (Part c)
17.21
Figure 17.5: Loop problem in a learning switch (part d)
17.22
Figure 17.6: A system of connected LANs and its graph (Part a)
17.23
Switch link assignment


Switch to Lan = 1
Lan to Switch = 0
Figure 17.6: A system of connected LANs and its graph (Part b)
17.25
Figure 17.7: Finding the shortest path and the spanning tree for a
switch.
17.26
Figure 17.8: Forwarding and blocking ports after using spanning
tree algorithm
17.27
17.17.3 Routers
We will discuss routers in Part IV of the book when
we discuss the network layer.
17.28
17.17.3 Routers
A router is a three-layer device; it operates in the
physical, data-link, and network layers.
17.29
Figure 17.9: Routing example
17.30
17-2 VIRTUAL LANS
A virtual local area network (VLAN) is a local
area network configured by software, not by
physical wiring.
17.31
Figure 17.10: A switch connecting three LANs by wire
17.32
Figure 17.11: A switch using VLAN software
17.33
Figure 17.12: Two switches in a backbone using VLAN software
17.34
17.2.1 Membership
Characteristic used to group stations in a VLAN:
interface numbers,
● port numbers,
● MAC addresses,
● IP addresses,
● or a combination of two or more of these.
●
17.35
17.2.1 VLAN
VLANs …
Save time and money because stations
can be moved to any VLAN without rewiring.
●
●
Help manage network traffic
Separate LANS
management
●
17.36
for
better
security