Networking
Components
DANIEL BELL
HUBS
A hub is a Layer 1 device connects multiple Ethernet devices in
order to make them operate as one network segment.
Hubs are not widely used anymore except in older networks, and
sometimes used in place of a network tap or port mirror for
network traffic analysis.
The cost of hubs that I have seen recently have been anywhere
from $10 to $100.
HOW HUBS WORK
When a device’s packets arrive at the hubs interface, the hub will
then flood those packets to all other devices connected to the
hub so they can be received.
The issue with hubs is that networked devices on that hub are one
large collision domain. This means that if multiple devices are
sending packets across the transmission media, the packets can
collide, causing them to not reach their destination.
SWITCHES
Switches are layer 2 devices that connect devices on a LAN.
Switches are widely used, replacing the need for hubs in most
cases. They can be used to separate network segments logically
by using VLANS, rather than separation using more hardware and
space.
Switch prices vary on type. The cheap switches can be bought as
low as $10 in some cases. Higher end switches can be over
$10000.
HOW SWITCHES WORK
Looking at the diagram to the right, if Computer A wanted to
send data to Computer B, the frames would enter port 1. The
switch would then look through its MAC address table to see what
port corresponds with the matching MAC address for Computer B.
Once that has been determined, it would send it out that port. In
this case, frames destined for B will be sent out port 2.
If a switch has no MAC address entry in its table, it will flood it out
all ports except for the one it came in on. Then it will be able to
add the entry to its table.
ROUTERS
Routers are network devices that allow packets to be sent
between networks. They operate at Layer 3 of the OSI
model. Routers also separate broadcast domains.
Depending on what you’re looking for, like switch prices,
router prices will vary. A home router could be anywhere
from $20 to almost $300. An enterprise grade router can cost
anywhere from $300 to over $11000 new.
HOW ROUTERS WORK
Routing protocols are used by routers to advertise routes in
between networks. Examples of routing protocols include OSPF,
EIGRP, and RIPv2.
Looking at the diagram on the right, in order for hosts on Network
A to send data to hosts on Network B, they must first go to a
router, in this case, router 1. Once the packets from Net A get to
the router, the router looks at its routing table to determine the
best path to Net B, and sends it out that path.
BRIDGES
Bridges are devices that operate at Layers 1 and 2 of the OSI
model. The function of a bridge is to connect one LAN to another,
creating an aggregate network.
The cost of bridges are anywhere from $30 to $130.
HOW BRIDGES WORK
Bridges somewhat create a single network, out of multiple
networks. They build learning tables to decide whether to send
messages to one LAN or another LAN.
Bridges sound similar to routers, but routers connect different
networks while keeping them separate.
GATEWAYS
A gateway on a network is a device, usually a router interface,
that serves as the access point to another network.
When a host on one network sends a message to a host on
another network or the Internet, it must pass through it’s default
gateway (router).
FIREWALLS
Firewalls are devices that protect a LAN by creating a barrier
between an untrusted network, typically the Internet, and an
internal network. They also serve other functions such as basic
routing, acting as a the gateway, sometimes acting as a DHCP
server, and depending on the firewall, they can perform IPS
services.
Of course, like all equipment, firewall prices will vary. They can be
found from $150 to over $10000 depending on features.
HOW FIREWALLS
WORK
Firewalls control what is allowed in or out of the network. They
refer to an Access Control List (ACL), which are the rules for what
is allowed to pass. When a packet reaches the firewall, it will read
the ACL from top to bottom, checking for matching “permit” or
“deny” statements.
WIRELESS APs
As the name suggests, wireless access points are what
allow users to connect to a network wirelessly.
WAPs run about $10 to $450.
HOW WIRELESS APs
WORK
A WAP utilizes a beacon to let wireless NICs know what it’s SSID is.
A user connecting to that network will choose the correct SSID
and sign in if needed. After the signal reaches the AP, the packets
will be sent through the network as normal.
At home, your WAP is typically the device that your ISP provides.
In businesses, WAPs might be placed on a ceiling for guest to be
able to utilize the wireless network.
A sample network using these
devices and concepts: