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

Table 15-5 ICMP Options
ICMP Option Description
Allow Outgoing
Destination Unreachable
Allow Outgoing Source
Quench
Allow Outgoing
Parameter Problem
Allow Outgoing
Time Exceeded
Lesson 5 Configuring Windows Firewall
15-55
Security Alert Generally, you should enable ICMP exceptions only when you need them for
troubleshooting, and then disable them after you have completed troubleshooting. Make sure
that you do not allow or enable these options without a full understanding of them and of the
consequences and risks involved.
How to Enable ICMP Exceptions
The computer sends a Destination Unreachable error message to
clients who attempt to send packets through the computer to a
remote network for which there is no route.
Offers information to routers about the rate at which data is
received; tells routers to slow down if too much data is being
sent and it cannot be received fast enough to keep up.
The computer sends a Bad Header error message when the computer
discards data it has received that has a problematic header.
This message allows the sender to understand that the host
exists, but that there were unknown problems with the message
itself.
The computer sends the sender a Time Expired message when
the computer must discard messages because the messages
timed out.
Allow Redirect Data that is sent from this computer will be rerouted if the path
changes.
To enable a global ICMP exception for all connections on a computer, use these steps:
1. Click Start, and then click Control Panel.
2. In the Control Panel window, click Network And Internet Connections.
3. In the Network And Internet Connections window, click Windows Firewall.
4. In the Windows Firewall dialog box, click the Advanced tab.
5. In the ICMP section, click Settings.
6. Select the check box for the exception you want to enable.
7. Click OK to close the ICMP Settings dialog box. Click OK again to close the Windows
Firewall dialog box.