I have created a RAW socket and set the socket option as "IP_HDRINCL". I am setting the identification field in the outgoing UDP packet and
sending the same out. I see that this field is changed to a random number when the packet is sent out. I can see the same in the sniffer capture.
The same code when built and tested in a different Windows XP machine, works fine ie. I can see that the identification field in the IP header of the outgoing packet carries the same value that I have set.
Not sure whats going wrong. Please let me if you have any insights.
Thanks,
Renu
Raw sockets with IP_HDRINCL automatically set the values of certain field of ip packets that are going to get sent out.
In your case, the packet id will get overwritten in case is zero. (is it your case?)
This are the cases: (taken from Raw Socket man page)
+---------------------------------------------------+
|IP Header fields modified on sending by IP_HDRINCL |
+----------------------+----------------------------+
|IP Checksum |Always filled in. |
+----------------------+----------------------------+
|Source Address |Filled in when zero. |
+----------------------+----------------------------+
|Packet Id |Filled in when zero. |
+----------------------+----------------------------+
|Total Length |Always filled in. |
+----------------------+----------------------------+
Related
Apache (ec2) --- Client (ELB)
| |
|-------[1.]FIN------->|
| |
|<-----[2.]FIN+ACK-----|
| |
|---------ACK--------->|
| |
With Wireshark I'd like to extract only the packet "[1.]FIN" described above figure which is emitted by server's 80 port and which "initiates" FIN sequence.
I've tried a filter:
tcp.flags.fin && tcp.srcport==80
but the filter also extracts the extra "[2.]FIN+ACK" packets.
How can I filter out only [1.] packet considering "FIN" sequence initiator?
Background:
I'm struggling to get rid of 504 errors with AWS ELB and ec2 (apache), where "FIN - FIN/ACK - ACK" sequence is initiated by the backend apache-side. In such environment FIN sequence initiated by ELB is ideal as AWS official sais: http://docs.aws.amazon.com/elasticloadbalancing/latest/classic/config-idle-timeout.html
According to https://aws.amazon.com/jp/premiumsupport/knowledge-center/504-error-classic/, I've tried changing replace MPM (event -> worker) and disabling TCP_DEFER_ACCEPT, which slightly reduced 504 errors. However the situation is not much improved.
The point I think will be to find the cause which makes apache initiate active-close sequence, thus I'm firstly trying to extract initiating FIN packet from apache among at most 512 parallel connections between ELB and EC2 (apache).
tcp.flags.fin == 1 && tcp.flags.ack == 0
A filter such as tcp.flags.fin only checks for the presence of the parameter. To find certain values of a parameter, a comparison is needed. That is why filters like "tcp" work to find TCP packets.
The filter match for FIN does not exclude other flags being set or not set, so a comparison is needed for each flag that should be part of the filter.
I have two similar modems, when I insert the SIM in the first modem it connects automatically to the network. But if I insert the same SIM in the second modem, it doesn't connect to the network.
I launched the command: AT&V to read the profile of each modem. I compared the settings and they are all the same except for the following:
+CGDCONT: (1,"IP","cmnet","0.0.0.0",0,0)
+CGDCONT: (1,"IP","internet","0.0.0.0",0,0)
----------------------
+CIND: 0,3,1,0,0,0,1,0
+CIND: 0,0,0,0,0,0,0,0
----------------------
+CGATT: 1
+CGATT: 0
----------------------
+COPS: 1,0,""
+COPS: 0,2,""
----------------------
Q1: Could one of these settings cause the problem?
Q2: Is there a way to save/restore a modem config?
NB. The first setting of each pair is of the working modem.
Looks like the APN of the second modem is different from the first one. The APN of second modem is "internet", while the first one is "cmnet". This can cause the problem (first one is attached while the second one did not: +CGATT 1 vs 0), if the network does not support "internet" APN.
You can set same APN for the second modem as the first one to have a try. i.e.
AT+CGDCONT =1,"IP","cmnet"
But, APN difference is only one of the possible reasons. For analyzing the actual reason of attach failure, logs are needed.
I am trying to find any element refer to IncomingBitrate in webrtc dump file .
Where I can find the incoming bitrate in webrtc-internals?
Also, How I can calculate incoming bitrate from webrtc stats?
In webrtc-internals check the active connection -- it's printed in bold. Usually it is Conn-Audio-1-0. There are two fields bytesSent and bytesReceived which will allow you to calculate the bitrate. Also check the constraints + stats demo for an actual example: https://webrtc.github.io/samples/src/content/peerconnection/constraints/
In getStats, iterate the reports until you find one of kind googCandidatePair with .stat('googActiveConnection') === 'true'. That is giving you the same information as webrtc-internals. If you want per-track/stream values, reports of type ssrc have bytesSent or bytesReceived, depending on whether they are sent or received.
Then calculate the bitrate by dividing the bytes sent/received by the time difference between the getStats calls.
I have a snmp enabled device whose monitoring i want to do.
But this device gives response with Request-ID 0 for all the get request. snmp4j library
discards these received packets because it sends get request with some Request-ID value other than 0. On receiving the response it matches the sent "Request-ID" value with the received "Request-ID" value and on finding mismatch it just discards the received packet and returns "null" value to response.
If I set the Request-ID to 0 in snmp packet before sending get request then response snmp packet can be processed.
For this snmp4j library contains the "setRequestID(Integer32 (value))" function to set the desired Request-ID of any snmp packet, but this function cannot set the Request-ID value to 0. When I set the value to 0, this function replaces this value to some random Request-ID value.
If any one having solution then please give response.
Thank you.
The request-id field is used to identify the response when it arrives back to the client. So, if the device you are querying at is returning all requests with a request-id value of 0 instead of the supplied value, then the client (snmp4j) is correctly discarding the response because it is invalid. The request-id in the response packet must always match the request-id in the original request. The device has a buggy SNMP stack. If you change your code to force the requests to always have a request-id of 0 you are breaking functionality to enable compatibility with a non-standard agent and I would advise against it.
I'm building an embedded device with a couple of sensors. The device will 'stream' digital data from these sensors over Bluetooth or USB.
Most of the communication will be from the embedded device to the host. The host will infrequently be sending control messages, to control the gain etc.
Since the physical and data link layers are taken care of, I'm looking for a simple message protocol that will make it easy to develop user applications to process/display data on the host computer. Does anyone have any suggestions?
A simple text protocol may be the best for this application.
Use the communication channel as a bi-directional serial pipe.
The device can stream sensor values in ASCII (text) format, separated by commas, with each set separated by the newline character. The rate is preferably set by the host.
For example,
21204,32014 (new line character '\n' - 0x0A) at the end of each line
21203,32014
21202,32011
....
This makes it easier to test, to stream the values to a file, import in to a spreadsheet etc.
Similarly commands to the device too, is best done in text.
SET GAIN_1 2 ( sent by host )
OK ( reply by device )
SET GAIN_2 4 (sent by host )
OK ( reply by device )
SET GAIN_9 2 (sent by host )
ERROR ( reply by device if it does not understand)
SET RATE 500 ( set the sensor dump rate to every 500 ms )
OK