User Manual

ICMP protocol
Reference: Configuration options
The Internet Control Message Protocol (ICMP) is used to exchange error and information
messages on networks. The protocol is also used for status messages with ping or tracer.
With this rule, you can define the incoming and outgoing blocked message types, the
behavior in case of flooding and the reaction to fragmented ICMP packets. This rule
serves for preventing so-called ICMP flood attacks, which results in an increase of the
CPU load of the attacked machine as it responds to every packet.
Predefined rules for the ICMP protocol
Setting Rules
Low Incoming blocked types: no type.
Outgoing blocked types: no type.
Assume flooding if delay between packets is less than 50
ms.
Reject fragmented ICMP packets.
Medium Same rule as for the Low level.
High Incoming blocked types: several types
Outgoing blocked types: several types
Assume flooding if delay between packets is less than 50
ms.
Reject fragmented ICMP packets.
Incoming blocked types: no types/several types
With a mouse click on the link a list of ICMP packet types is displayed. From this list
you can specify the desired incoming ICMP message types you want to block.
Outgoing blocked types: no types/several types
With a mouse click on the link a list of ICMP packet types is displayed. From this list
you can select the desired outgoing ICMP message types you want to block.
Assume Flooding
With a mouse click on the link, a dialog box is displayed where you can enter the
maximum allowed ICMP delay. Example: 50 milliseconds.
Avira Professional Security - User Manual (Status: 30 Mar. 2012) 126