MCSA/MCSE Self-Paced Training Kit (Exam 70-270): Installing ...

15-54 Chapter 15 Configuring Network and Internet Connections
8. Enter the port information for the service.
9. Click OK to close the Service Settings dialog box. Click OK to close the Advanced
Settings dialog box. Click OK again to close the Windows Firewall dialog box.
ICMP Exceptions
ICMP allows routers and host computers to swap basic error and configuration information.
The information includes whether or not the data sent reaches its final destination,
whether it can or cannot be forwarded by a specific router, and what the best
route for the data is. ICMP tools such as Pathping, Ping, and Tracert are often used to
troubleshoot network connectivity.
ICMP troubleshooting tools and their resulting messages are helpful when used by a
network administrator, but harmful when used by an attacker. For instance, a network
administrator sends a ping request in the form of an ICMP packet that contains an echo
request message to the IP address that is being tested. The reply to that echo request
message allows the administrator to verify that the computer is reachable. An attacker,
on the other hand, can send a storm of specially formed pings that can overload a
computer so that it cannot respond to legitimate traffic. Attackers can also use ping
commands to determine the IP addresses of computers on a network. By configuring
ICMP, you can control how a system responds (or does not respond) to such ping
requests. By default, Windows Firewall blocks all ICMP messages.
Table 15-5 provides details about ICMP exceptions you can enable in Windows
Firewall.
Table 15-5 ICMP Options
ICMP Option Description
Allow Incoming
Echo Request
Allow Incoming Timestamp
Request
Allow Incoming Mask
Request
Allow Incoming Router
Request
Controls whether a remote computer can ask for and receive a
response from the computer. Ping is a command that requires
you to enable this option. When enabled (as with other options),
attackers can see and contact the host computer.
Sends a reply to another computer, stating that an incoming
message was received and includes time and date data.
Provides the sender with the subnet mask for the network of
which the computer is a member. The sender already has the
IP address; giving the subnet mask is all an administrator (or
attacker) needs to obtain the remaining network information
about the computer’s network.
Provides information about the routes the computer recognizes
and passes on information it has about any routers to which it is
connected.