Nokia IP60 - Security Appliance, User Manual

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SmartDefense Categories
Chapter 13: Using SmartDefense 291
Small PMTU
Small PMTU (Packet MTU) is a bandwidth attack in which the client fools the server into sending large
amounts of data using small packets. Each packet has a large overhead that creates a "bottleneck" on the
server.
You can protect against this attack by specifying a minimum packet size for data sent over the Internet.
Table 70: Small PMTU Fields
In this field… Do this…
Action Specify what action to take when a packet is smaller than the
Minimal MTU
Size
threshold, by selecting one of the following:
Block.
Block the packet.
None.
No action. This is the default.
Track Specify whether to issue logs for packets are smaller than the
Minimal MTU
Size
threshold, by selecting one of the following:
Log.
Issue logs. This is the default.
None.
Do not issue logs.
Minimal MTU
Size
Type the minimum value allowed for the MTU field in IP packets sent by a
client.
An overly small value will not prevent an attack, while an overly large value
might degrade performance and cause legitimate requests to be dropped.
The default value is 300.