Packet Effects

Note: This topic applies to Advanced Tests only – not to Quick Tests.

You can emulate IP routing effects such as disruption of packet order (reordering), packet duplication, and fragmentation, via parameters defined in the Packet Effects tab.

To instruct NV Test Manager to emulate packet effects, select the check box of the effect you want to emulate, and then configure the associated parameters.

Out of Order

To emulate packet reordering, NV Test Manager can generate an out-of-order event, based on the probability set in the Chance parameter (from 1% to 50%), by randomly removing a packet from the data stream. Then it starts counting the incoming packets. It returns the removed packet after the nth packet has entered NV Test Manager. The nth packet is picked randomly from the range that you indicate in the Maximum and Minimum (Packet offset from original location) parameters (from 1 to 64 packets). For example, if you indicate a range of 5 to 10, NV Test Manager will return the removed packet randomly to the data stream (after the 5th, or 6th…or 10th packet that follows the removed one). In order to have NV Test Manager return all removed packets after a predefined number of incoming packets, the same value can be used for both Minimum and Maximum offset.

Duplicate Packets

NV Test Manager emulates duplication by copying a packet that it selects randomly. The number of copies that will be created when the event occurs is specified in the Minimum and Maximum parameters (from 1 to 20 packets). For example, if you specify a range of 2-4 packets, NV Test Manager duplicates a packet 2, 3, or 4 times (randomly), when it decides to do so (according to the probability specified in Chance – from 1% to 99%). To instruct NV Test Manager to create a predefined number of copies, enter the same value in both the Minimum and Maximum parameters. For example, entering 3 in both parameters causes NV Test Manager to create 3 copies of the packet when the event occurs.

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To emulate the packet fragmentation effect you need to set a packet size, in bytes, in the Maximum Transmission Unit parameter (from 64 to 1,460 bytes). This would be the maximum size a gateway along the path route would allow (MTU). Bigger packets are likely to be fragmented or discarded when the fragmentation event occurs (according to the probability set in Chance – from 1% to 99%).

Whether or not the packets will be eventually fragmented depends on the state of the Do Not Fragment (DF) bit in the packet's IP header and on the policy you define via the options included in the Fragmentation group. If the flag is OFF, the packet is fragmented anyway. If the flag is set to ON, the policy you select applies.

A description of the DF=ON policies is as follows:

Option Effect
Ignore Do Not Fragment (DF) bit Fragment the packet.
Generate ICMP Error Messages to Source Discard the packet and inform the packet's source, using an ICMP packet.
Do Not Generate ICMP Error Messages Discard the packet without informing the packet's source.

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