Ch1 - 1.01 - Network Device Flashcards
Hub
The network hub is an older networking device used to connect all the systems together in a network environment. The hub is a layer-1 device of the OSI (Open Systems Interconnection) model that simply receives a signal from one system and then sends the signal to all other ports on the hub.
Switch
A network switch is similar to a network hub in that it is used to connect all systems together in a network environment, but the difference is that a switch is a layer-2 device that filters traffic by the layer-2 address. Remember from the Network+ exam that the layer-2 address is the MAC address, or hardware address, that is assigned to the network card by the manufacturer.
The switch is able to filter the traffic because it stores the MAC addresses of each system connected to the switch, and what port that system is connected to, in the MAC address table. The MAC address table is a table stored in memory on the switch and is responsible for tracking what ports each system is connected to
For the exam, remember that a switch offers great security because it filters traffic by sending the traffic only to the port that the destination system resides on. You should also be able to describe features such as port security, port mirroring, and the capability to disable unused ports.
Naming Switch’s Common Features
- Filtering
- Port Mirroring (Monitoring)
- Port Security
- Capability to Disable Ports
- Collision Domains
- VLAN
Switch - Port Mirroring (Monitoring)
Port mirroring, also known as port monitoring, is a
feature of some switches that allows the administrator to copy traffic from other ports to a single destination port (known as a monitoring port). Because the switch filters traffic by default, the administrator cannot monitor network traffic. The switch vendors had to come up
with a way to copy all the traffic to a single port so the administrator could connect their monitoring system to that port.
Switch - Port Security
Port security is a feature of a network switch that lets you configure a port for a specific MAC address. This allows you to control which systems can connect to the switch because the switch can temporarily disable the port until the correct system is plugged into the
switch.
Switch - Capability to Disable Ports
If you have ports on the switch that are not being used, it is a security best practice to disable them so that they
cannot be used.
Switch - Collision Domains
Another important feature of a switch is known as a
collision domain. A collision domain is a group of networked systems that share the same network segment and therefore can have their data collide with
one another.
Switch - VLAN
Most switches today support a feature known as virtual LANs (VLANs). The purpose of a VLAN is to create multiple networks within the one network switch. One way to do this is by placing ports on the switch into
groupings known as VLANs. When a system is connected to a port on the switch, it becomes a member of the VLAN that the port is associated with. The important point is that when a system is a member of one VLAN, it cannot communicate with systems in another VLAN. It’s as if each VLAN has its own switch with no connection to another switch.
For the exam, remember that VLANs are a way to create
communication boundaries on the network. By default, systems in one VLAN cannot communicate with systems in another VLAN.
Router
A router is a layer-3 device that is responsible for routing, or sending, data from one network to another network. The router uses a routing table that resides in its memory to determine the networks that the router knows how to send data to
Routers are great network devices because they define the boundary of the network by creating what is called a broadcast domain. A broadcast domain is a group of systems that can receive one another’s broadcast messages. A broadcast message is a message that is destined for all systems—and the router is strategically placed on the network to keep those broadcast messages within your network because broadcast traffic does not pass through the router.
Load Balancer
A load balancer is a device that is designed to split the load between components such as servers or routers. Load balancing is the concept of trying to improve performance.
Load Balancer - Settings (Load Distribution)
Round-robin
Sends the request from a client to each backend server
in order. The load balancer has a list of servers and simply goes through them in order.
Affinity
Controls whether all request from a client go to the same server in the load balancer or if each request can potentially be routed to a different server. Affinity essentially ties a client to a particular server.
Scheduling
Specifies which algorithm will be used to send the request to one of the nodes. Scheduling uses a number of configuration values to determine which server to send the request to, such as round-robin, affinity, and CPU load.
Load Balancer - Active/Passive vs. Active/Active
There are two common configurations for
load balancing.
With an active/passive configuration, one system, called a node, handles all the work (the active node), while the other node (the passive node) is on standby, ready to take over if the active node fails.
With an active/active configuration, both nodes are online and able to handle requests, essentially splitting the workload. If one node fails, the
other node handles all the workload until the failed node is recovered.
With both of these setups, the load balancer has an IP address assigned to it (known as the virtual IP), and you configure all clients to send requests to the virtual IP. The virtual IP then forwards the request to an active node in the load balancer.
Firewalls
A firewall is a network device that controls which traffic is allowed to enter or leave the network. The firewall filters traffic based on rules you place on the firewall indicating which traffic is allowed or not allowed to enter or leave the network. You typically start with a deny-all rule that states all traffic is denied unless you specify otherwise by building a rule for a specific type of traffic.
Proxy Servers
A proxy server makes the request for the Internet resource on behalf of the user, and commonly the company filters and logs which web sites users have visited.
A proxy server is a type of firewall, but it is typically associated with being able to control outbound communication by limiting which web sites an
employee can visit. Proxy servers are a little different from firewalls in the sense that the employee will typically first authenticate to the proxy server (via a username and password), and based on that username, the proxy administrator will decide whether the employee is allowed to use the Internet and which web sites they can visit. Proxy servers also perform a high level of logging so that the administrator can see which sites are visited each day.
