Microsoft Internet Security and Acceleration (ISA) Server secure network address translation (SecureNAT) is able to pass Internet Control Message Protocol (ICMP) packets between internal and external hosts. However, this feature is not enabled by default.
In ISA Server, ICMP proxying is enabled only if Internet Protocol (IP) routing is enabled and there is a corresponding packet filter under "IP Packet Filters" which enables ICMP packets to leave the external adapter and subsequent replies to be received. A filter for PING protocol requests exists in the default ISA Server installation package.
To enable internal computers to use the PING protocol to check the presence of hosts on the external network, you need to enable IP routing. This can be done by performing the following steps:
- Open the ISA Server Management user interface (UI).
- Open the Array or Server node of the applicable server.
- Open the Access Policy node.
- Right-click the IP Packet Filters folder and click Properties.
- On the General tab, select the option to enable IP routing.
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