NoteHKLM\SYSTEM\CurrentControlSet\Services\Tcpip\Parameters
| Data type | Range | Default value |
|---|---|---|
| REG_DWORD | 0 | 1 | 0 |
Determines whether this computer responds to ICMP address mask requests by sending ICMP address mask replies.
Internet Control Message Protocol (ICMP) is an error reporting and diagnostic utility in IP. Routers, intermediary devices, and hosts use ICMP messages to communicate with each other.
An address mask request (ICMP Type 17) is an ICMP message that a networked computer issues to determine the subnet mask on the local network. RFC 1122 restricts the computers that can reply to address mask request to authoritative agents (hosts or gateways) that are explicitly configured to respond to address masks.
If your computer responds to address mask requests, it might enable malicious users to discover sections of your network topology.
| Value | Meaning |
|---|---|
| 0 | Disabled. This system does not reply to address mask requests. |
| 1 | Enabled. This system responds to address mask requests by sending address mask replies (ICMP Type 18). |
Note
Windows 2000 does not add this entry to the registry. You can add it by editing the registry or by using a program that edits the registry.