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Internet Control Message Protocol (ICMP)
house keeping protocol of the internet
ping command- identifies live systems
traceroute command- identifies network paths
handles other functions such as destinitation unreachable messages, redirects, time exceeded messages, and addresses mask requests and replies
bus network topology
used in original ethernet design
inexpensive and easy to wire
allows only one system to transmit at same time
breaks with a single wire failure
allows eavesdropping
ring network topology
uses a circular pattern
connects every device to two other devices
survives single cable failure
allows only one system to communicate at a time
allows eavesdropping
Star network topology
connects every device directly to a switch
requires more wire and switches
allows every device to transmit simultaneously
prevents eavesdropping
mesh network topology
connects every device to several other devices
requires too much wire in a wired network
improves reliability of wireless networks
tree network topology
uses hierarchical design
interconnects star networfks in tree and star topology
servers
provide services to clients
typically perform a single dedicated function
some types include web servers, file servers, database servers, DNS/DHCP servers
peer-to-peer model
does away with traditional client/server model, instead every device acts as both a client and a server
What technology provides the translation that assigns public IP addresses to privately addressed systems that wish to communicate on the Internet?
network address translation (NAT)
Dennis would like to capture the DNS traffic on his network using Wireshark. What port should he use in his capture filter to restrict his capture to DNS queries and responses?
UDP 53
Which port is not normally used by email systems?
25, 139, 143, 110
139 is server message block (SMB)
switches
connect devices to the network, has many ports
wireless access points (WAPs) connect to switches and create WiFi networks
operate at layer 2, where they work with MAC address only
may function at layer 3, where they begin to function like routers
a switch is a layer 2 switch unless specified
routers
connect networks to each other, making intelligent packet routing decision
-layer 3 device
can perform stateless inspection using ACLs
bridges
layer 2 device that connects networks using simple forwarding
demilitarized zone (DMZ)
contains systems that must accept direct external connections
isolates those systems due to risk of compromise
protects internal network from compromised DMZ systems
stateless firewall
evaluates each connection independently
stateful inspection
modern firewalls use this, it tracks open connections
firewall rule contents
source system address
destination system address
destination port and protocol
action (allow or deny)
implicit deny
if the firewall receives traffic not explicitly allowwed by a firewall rule, then that traffic must be blocked
Next Generation Firewalls (NGFW)
incorporate contextual information into their decision making
other firewall roles
NAT gateway
content or URL filtering
web application firewall
firewall deployment options
network hardware vs host based software firewalls
open source vs. proprietary
hardware appliance vs. virtual appliance
forward proxy
proxy server that works on behalf of clients
reverse proxy
works on behalf of servers
transparent proxy
works without the client or server’s knowledge
load balancer
distribute workload among multiple servers
also provide security functions like SSL certificate management, URL filtering, and other web application security tasks
autoscaling
automatically adds and removes servers as needed
active-active load balancer topology
two or more load balancers actively handle network traffic and continue to function with diminished capacity if one device fails
active-passive load balancer topology
one load balancer handles all traffic while a second monitors activity and assumes responsibility if the primary load balancer fails
site to site VPN
connects remote offices to each other and headquarters
remote access VPN
provides remote access to corporate networks for mobile users
IPsec
works at network layer 3
supports the layer 2 tunneling protocol (L2TP)
provides secure transport
difficult to configure
SSL/TLS VPNs
most VPNs have shifted away from IPsec method, and instead use this at the application layer over TCP port 443
HTML5 VPNs work entirely within the web browser
full tunnel VPN
all network traffic leaving the connected device is routed through the VPN tunnel, regardless of its final destination
split tunnel VPN
only traffic destined for the corporate network is sent through the VPN tunnel, other traffic is routed directly over the internet