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Path measurement: Difference between revisions
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Since firmware version 3.7, the path measurement can also be done based on two capture files created from two different network locations. The separate configuration tab "Configuration PCAP Analysis" allows to select two files from attached storage devices. | Since firmware version 3.7, the path measurement can also be done based on two capture files created from two different network locations. The separate configuration tab "Configuration PCAP Analysis" allows to select two files from attached storage devices. | ||
The files are replayed based on the packet time stamps within each file, in chronological order. Matching packets are only recognized if they are within the maximum packet delay. If the difference of the timestamps is larger, a time-delta adjustment value can be entered which will be added to the timestamp of the client packets. Negative values are possible as well to be able to adjust the time in both directions. If the time difference is too large, a lot of packet loss are reported, or even a "network setup problem" note is shown in the overview tab. If the time delta between both files is not known, a test run can be enabled to calculate the approximate difference. When both files are fully processed in this test run, the result is shown in the overview tab and this value can be used for the actual analysis. | |||
The settings are similar to the live measurement. VLG filter can be applied to both files, but an option also allows to disable the use of the configured virtual link groups, or use separate groups for each file. In contrast to live mode, a VLG does not need to be used to differentiate traffic since it is clear from the selected file which one is the primary traffic and which one is the client traffic. But of course VLG can be used to filter out traffic that should not be part of the analysis. | The settings are similar to the live measurement. VLG filter can be applied to both files, but an option also allows to disable the use of the configured virtual link groups, or use separate groups for each file. In contrast to live mode, a VLG does not need to be used to differentiate traffic since it is clear from the selected file which one is the primary traffic and which one is the client traffic. But of course VLG can be used to filter out traffic that should not be part of the analysis. | ||
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#:This message box appears if flows have been identified for which not a single packet could be seen on both sides. Usually this means that there is some device in between both measurement points that modifies the packet. This can be WAN optimizer which rewrite TCP connection for improved network performance. Such setup is not supported. | #:This message box appears if flows have been identified for which not a single packet could be seen on both sides. Usually this means that there is some device in between both measurement points that modifies the packet. This can be WAN optimizer which rewrite TCP connection for improved network performance. Such setup is not supported. | ||
#: It can also mean that some other packet field is modified at some point in the network. One field that is known for modification is the IP identification field in the IPv4 header. For this case an additional option can be enabled to ignore this field. | #: It can also mean that some other packet field is modified at some point in the network. One field that is known for modification is the IP identification field in the IPv4 header. For this case an additional option can be enabled to ignore this field. | ||
#: When using the PCAP analysis mode, this error can also appear if the files are not time synchronized. In this case, a time adjustment value must be entered to synchronize both files. A test run can be used to calculate a possible value. | |||
# What does the note '''VLAN tag mismatch detected for matching packets on main device and client''' means? | # What does the note '''VLAN tag mismatch detected for matching packets on main device and client''' means? | ||
#:This message indicates that matching packets have been seen on both devices but the used VLAN tag is different. Depending on the measurement setup, this may indicate an error as for connection matching the IP addresses, ports, and VLAN tags are used unless the option to ignore the VLAN tag is enabled. Therefore, the identical packets will be accounted for two different connections often resulting in shown packet loss. | #:This message indicates that matching packets have been seen on both devices but the used VLAN tag is different. Depending on the measurement setup, this may indicate an error as for connection matching the IP addresses, ports, and VLAN tags are used unless the option to ignore the VLAN tag is enabled. Therefore, the identical packets will be accounted for two different connections often resulting in shown packet loss. | ||