Hi All, I came across an interesting article at this link http://www.feedspot.com/?dadi=1#feed/f_93941/article/3110429817?dd=43114917050607 and was wondering whether this could be applicable to DHIS2 as well, particularly when connecting via mobile devices? Below just an extract of the main point. Regards
Client connected to itself...Isn't it Strange (effect of TCP Simultaneous Connect) Yes I observed this strange behavior during one of my work, which I would like to share. The symptom of the issue was that client was getting some unexpected junk response, which server never sent. *Background* While working on a system, where client application has logic to keep reconnecting to server till connection becomes successful. At one point of time it was observed that the client connection has been established successfully even though server has not yet come up. Later when Server was brought up, it failed to start saying "Address already in use". Which gave us hint that client must have connected to any other application running on same address as the server. Then we saw the result of netstat command at this point of time and below were the result: * netstat -nA inet | fgrep :32246* * tcp 0 0 127.0.0.1:32246 <http://127.0.0.1:32246> 127.0.0.1:32246 <http://127.0.0.1:32246> ESTABLISHED* Which shows client has connected to itself (source and destination IP:Port is same). Also there is no additional application listening on 32246 port. Address 127.0.0.1:32246 was the address on which client was trying to connect. *Cause Analysis* In our case we were trying to reconnect to server repetitively and every time it keeps failing as server was still down. As per TCP, every time client tries to re-connect it is assigned one new source port in increasing order from the range of ephemeral ports(Its range is defined in file /proc/sys/net/ipv4/ip_local_port_range). So at one point of time, it may use the same source port as used for destination (if destination port is also in the range of ephemeral ports). *Ant Snyman* *Cell: 0824910449* *Landline: 028 2713242* Health Information Systems Program - SA -- *This message and any attachments are subject to a disclaimer published at http://www.hisp.org/policies.html#comms_disclaimer <http://www.hisp.org/policies.html#comms_disclaimer>. Please read the disclaimer before opening any attachment or taking any other action in terms of this electronic transmission. If you cannot access the disclaimer, kindly send an email to [email protected] <[email protected]> and a copy will be provided to you. By replying to this e-mail or opening any attachment you agree to be bound by the provisions of the disclaimer.*
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