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Path measurement: Difference between revisions
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== Path measurement == | == Path measurement == | ||
The path measurement module allows to passively measure the packet loss and latency between two Allegro Network Multimeter installations. | The path measurement module allows to passively measure the packet loss and latency between two Allegro Network Multimeter installations. | ||
For example, a network connection (line/link) between the main office and a remote office can be analyzed by installing one Multimeter at the main office and another Multimeter at the remote office. | |||
For example, a network connection (line/link) between the main office and a remote office can be analyzed by installing one Multimeter at the main office and another Multimeter at the remote office. | |||
Only network traffic (packets) passing through both Multimeters can be analyzed. The packet loss and two-way-latency thereof is measured and shown in graphs. | Only network traffic (packets) passing through both Multimeters can be analyzed. The packet loss and two-way-latency thereof is measured and shown in graphs. | ||
The time synchronization setting (e.g. NTP/PTP or OFF) should be the same on both devices for the best results. | The time synchronization setting (e.g. NTP/PTP or OFF) should be the same on both devices for the best results. | ||
In Firmware version >= 3.3, it is also possible to use a single device to measure the traffic delay/losses between two different [[Virtual Link Group functionality|virtual link groups]]. In this mode, the primary device is used as a client too. | |||
== Overview == | == Overview == | ||
The main device captures packet meta data from the remote (or client) device which takes only a fraction of the total traffic. | The main device captures packet meta data from the remote (or client) device which takes only a fraction of the total traffic. | ||
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* Enable analysis: This will disable or enable the path measurement feature. When disabled, no additional memory is used. When enabled, memory for the packet buffer is used which cannot be used for other analyzing modules thus reducing the maximum time the device can go back in time. | * Enable analysis: This will disable or enable the path measurement feature. When disabled, no additional memory is used. When enabled, memory for the packet buffer is used which cannot be used for other analyzing modules thus reducing the maximum time the device can go back in time. | ||
Primary device settings: | |||
* Description of this main device: This field is only used for informational purposes to identify the main device. It can be freely chosen, for example to the location the device is installed. This field can also be left empty to use the default name '''main'''. | * Description of this main device: This field is only used for informational purposes to identify the main device. It can be freely chosen, for example to the location the device is installed. This field can also be left empty to use the default name '''main'''. | ||
* '''Primary device VLG filter:''' It is possible to limit the amount of data analyzed by any configured virtual link group. Often, the primary device is located at a central network point and thus sees a lot of traffic that is not actually going to the remote device. The algorithm will automatically take this into account, but using a filter will reduce the processing overhead as well as the amount of data that needs to be buffered. | |||
The following ''' | The following '''Client device''' configuration section configures the access to the remote device: | ||
* Device to use: To use a remote device for path measurement, you first need to add that device as a remote device the list of [[Multi-device settings]]. It does not matter if the device is active or not. You can select the device from the list of known multi-devices. | * '''Device to use''': To use a remote device for path measurement, you first need to add that device as a remote device the list of [[Multi-device settings]]. It does not matter if the device is active or not. You can select the device from the list of known multi-devices. You can also select the primary device as a client to analyze the traffic between two different virtual link groups. | ||
* Device description: Similar to the description of the main device, this field is for informational purpose only and has no other effect than helping identifying the remote device in the statistics. Usually the location of the remote device is entered. | * '''Device description''': Similar to the description of the main device, this field is for informational purpose only and has no other effect than helping identifying the remote device in the statistics. Usually the location of the remote device is entered. | ||
* | * '''Client device VLG filter''': The traffic used for comparison at the main device can be filtered to any virtual link group defined at the client device. There are two main purposes for this setting: | ||
*# reduce the amount of data required to be transferred to the main device. The path measurement only considers connections seen on both devices, but the client device of course cannot know if any connection it sees also is visible on the main device. If only traffic of a specific virtual linkg group (VLG) actually reaches the main device, using this filter can reduce the amount of data transferred and later dismissed. | *# reduce the amount of data required to be transferred to the main device. The path measurement only considers connections seen on both devices, but the client device of course cannot know if any connection it sees also is visible on the main device. If only traffic of a specific virtual linkg group (VLG) actually reaches the main device, using this filter can reduce the amount of data transferred and later dismissed. | ||
*# filter duplicate traffic: If, for some reason, traffic is seen multiple times, it can create wrong results as the number of occurrences differs from main to client devices. A VLG filter can fix this problem by only considering one part of the total traffic. | *# filter duplicate traffic: If, for some reason, traffic is seen multiple times, it can create wrong results as the number of occurrences differs from main to client devices. A VLG filter can fix this problem by only considering one part of the total traffic. | ||
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* '''Maximum packet delay''': This field describes the maximum amount of seconds to wait for packet information from the remote device. | * '''Maximum packet delay''': This field describes the maximum amount of seconds to wait for packet information from the remote device. | ||
: It basically means that the main devices waits for this number of seconds before deciding if a packet has been lost or not. If the data from the remote device arrives before those number of seconds, the path measurement can account the packet loss, if any and the two-way latency. This value must be at least as large as the worst-case latency between both measurement sites. | : It basically means that the main devices waits for this number of seconds before deciding if a packet has been lost or not. If the data from the remote device arrives before those number of seconds, the path measurement can account the packet loss, if any and the two-way latency. This value must be at least as large as the worst-case latency between both measurement sites. | ||
: Usually 3 seconds are more than enough but when the network in between can have a very long delay, you can increase the value. This will, however, use more main memory for the packet buffer. | : Usually 3 seconds are more than enough but when the network in between can have a very long delay, you can increase the value. This will, however, use more main memory for the packet buffer. | ||
* '''Ignore IP identification field''': This option can be enabled if the IP identification field in the IPv4 header is modified by some component in the network. Often it remains constant for a single packet so this option should be left disabled as it will also increase the chance of reporting duplicate packets. But if you notice symmetrical packet loss you can enable this option to see if this helps. | * '''Ignore IP identification field''': This option can be enabled if the IP identification field in the IPv4 header is modified by some component in the network. Often it remains constant for a single packet so this option should be left disabled as it will also increase the chance of reporting duplicate packets. But if you notice symmetrical packet loss you can enable this option to see if this helps. | ||
* '''Ignore VLAN tags for connection matching''': The path measurement only calculate loss and latency for connections seen on both devices. Usually the connection ID takes the IP pairs, port ports and possible VLAN tags into account. If a VLAN is different on both machines for the some connection, then this option must be enabled to be able to correlate the connection and calculate correct statistics. | |||
* ''' | *'''Ignore VLAN tags for connection matching''': The path measurement only calculate loss and latency for connections seen on both devices. Usually the connection ID takes the IP pairs, port ports and possible VLAN tags into account. If a VLAN is different on both machines for the some connection, then this option must be enabled to be able to correlate the connection and calculate correct statistics. | ||
* '''Account latency also per IP connection''': Enabling this option will let the path measurement also store the latency for each individual IP connection, which of course increases the memory usage. | |||
The settings must be saved but to actually take effect, a restart of the packet processing is necessary. If this step is required will tell so at the bottom of the page under '''Required actions'''. | The settings must be saved but to actually take effect, a restart of the packet processing is necessary. If this step is required will tell so at the bottom of the page under '''Required actions'''. | ||