Network Devices
Hub
• Hubs operate at layer 1 of the OSI model. A
hub sees a signal come in and broadcasts that
signal out every port except the one it came in
on. Hubs are really obsolete at this point in
time, and I would personally never pay for/use
one, but I wouldn’t imagine a hub costing
more than $50.
Ethernet hub
Switch
• A switch operates at layer 2 of the OSI model
traditionally. This being the case, each port on
the switch is it’s on collision domain. The price
of a switch varies greatly based on port
density, speed, etc. Switches can go anywhere
from $40 up to Tens of thousands of dollars
like the switches I manage.
Cisco Nexus 7010
Router
• A router operates at layer 3 of the OSI model,
and forwards IP packets based on destination
IP address. A router separates broadcast
domains. Routers range in price from $50 for a
consumer router all the way up in to the
millions like the routers I manage.
Cisco CRS 3 router and RLCs
Bridge
• A bridge allows the aggregation of multiple
networks. I have not personally used a
Network Bridge, and would assume that few
do anymore, as bridging seems obsolete since
the introduction of the .1q header/VLAN
tagging which allows link aggregation/the
security of segregation of broadcast domains
at layer 2, even when utilizing the same
physical link. Bridges operate at layer 1 & 2 of
the OSI model.
Bridge
Gateway
• A gateway is a device that separates networks.
The Most common example of a gateway
would be a router. A computers default
gateway would be the first layer 3 hop (first
router) that IP packets destined for a different
IP subnet must traverse.
Gateway: Cisco CRS 3 Router
Firewall
• Modern day firewalls operate at layer 3 and 4 of
the OSI model and are considered stateful; that
is, they maintain a session state table, so that
once the TCP three way handshake occurs (syn,
syn ack, ack) bidirectional traffic flow is permitted
unless the TCP session times out. Firewalls
perform packet inspection based on Source/dest
IP and port typically. Firewalls range greatly in
price; from free (included in your router) to
Hundreds of thousands like the ones I manage.
Juniper SRX 5800
Wireless access point
• A wireless access point allows a wifi enabled
client access to a network or the internet. In an
enterprise environment, WAPs are typically
plugged in to a switch or controller. A controller is
a means of managing a large number of WAPs,
seamlessly. In an enterprise environment, a WAP
is normally not responsible for the assignment of
an IP address to the client. Rather, the router or
DHCP server in the same network segment is
typically responsible for assignment of IP address.
Cisco 1252AG