DOCUMENT:Q181347  09-AUG-2001  [winnt]
TITLE   :Configuring RRAS Filters to Permit a One-Way Ping
PRODUCT :Microsoft Windows NT
PROD/VER:WinNT:4.0
OPER/SYS:
KEYWORDS:kbnetwork

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The information in this article applies to:

 - Microsoft Windows NT Server version 4.0 
 - Microsoft Windows NT Server, Enterprise Edition version 4.0 
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SYMPTOMS
========

With filters on your Routing and Remote Access Service (RRAS) server configured
to allow your network to ping remote hosts and to disallow the remote hosts from
pinging your RRAS server or internal network hosts, you may notice that ping
does not work in either direction.

CAUSE
=====

When setting the input ICMP filter, the ICMP type and ICMP code fields are
blank. This causes the default type and code value of 255 to be used. When 255
is used, all ICMP packets will be blocked (not received), including type 0,
which is Echo Reply. When your computer tries to ping a host, the host replies
with an Echo Reply ICMP packet, but because of the filter, the packet is
discarded.

RESOLUTION
==========

To resolve this issue set up the filters using the following steps:

1. Click Start, point to Programs, point to Administrative Tools, and then click
   Routing and RAS Admin.

2. Double-click IP Routing, click Summary, and then right-click the interface on
   which you want to configure filters.

3. Click Configure Interface, click Input Filters, and then click Add.

4. In the Protocol drop-down list, select ICMP and type 8 in the ICMP type
   field.

   NOTE: Type 8 denotes an Echo Request.

5. Click OK and click Receive all except listed below.

6. Click OK in the IP Packet Filters Configuration dialog box.

7. Click OK in the IP Configuration dialog box for the specific interface.

For more information, please see the following article in the Microsoft Knowledge
base:

   ARTICLE-ID: Q170292
   TITLE : Internet Control Message Protocol (ICMP) Basics
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Keywords          : kbnetwork 
Technology        : kbWinNTsearch kbWinNT400search kbWinNTSsearch kbWinNTSEntSearch kbWinNTSEnt400 kbWinNTS400search kbWinNTS400
Version           : WinNT:4.0
Issue type        : kbprb

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