Amer Networks E5Web GUI User Manual
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of the packet. DuplicateFrags determines whether such a fragment should be logged. Note that
DuplicateFragData can also cause such fragments to be logged if the data contained in them
does not match up. Possible settings are as follows:
•
NoLog - No logging is carried out under normal circumstances.
•
LogSuspect - Logs duplicated fragments if the reassembly procedure has been affected by
"suspect" fragments.
•
LogAll - Always logs duplicated fragments.
Default: LogSuspect
Fragmented ICMP
Other than ICMP ECHO (Ping), ICMP messages should not normally be fragmented as they
contain so little data that fragmentation should never be necessary. FragmentedICMP
determines the action taken when cOS Core receives fragmented ICMP messages that are not
either ICMP ECHO or ECHOREPLY.
Default: DropLog
Minimum Fragment Length
Minimum Fragment Length determines how small all fragments, with the exception of the final
fragment, of a packet can be expressed in bytes.
Although the arrival of too many fragments that are too small may cause problems for IP stacks,
it is usually not possible to set this limit too high. It is rarely the case that senders create very
small fragments. However, a sender may send 1480 byte fragments and a router or VPN tunnel
on the route to the recipient subsequently reduce the effective MTU to 1440 bytes. This would
result in the creation of a number of 1440 byte fragments and an equal number of 40 byte
fragments. Because of potential problems this can cause, the default settings in cOS Core has
been designed to allow the smallest possible fragments, 8 bytes, to pass. For internal use, where
all media sizes are known, this value can be raised to 200 bytes or more.
Default: 8
Reassembly Timeout
A reassembly attempt will be interrupted if no further fragments arrive within Reassembly
Timeout seconds of receipt of the previous fragment.
Default: 65
Max Reassembly Time Limit
A reassembly attempt will always be interrupted Reassembly Time Limit seconds after the first
received fragment arrived.
Default: 90
Reassembly Done Limit
Once a packet has been reassembled, cOS Core is able to remember reassembly for this number
of seconds in order to prevent further fragments, for example old duplicate fragments, of that
Chapter 12: Advanced Settings
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