Configuring RRAS Filters to Permit a One-Way Ping

• Microsoft Windows NT Server version 4.0
• Microsoft Windows NT Server, Enterprise Edition version 4.0

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.

ARTICLE-ID: Q170292
TITLE : Internet Control Message Protocol (ICMP) Basics

Keywords : kbnetwork nthowto ntnetserv ntrouter NTSrv
Version : WinNT:4.0
Platform : winnt
Issue type : kbprb