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Client Connection Problem


Gokay Aydin

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Hi guys,

 

We have a problem with one application where some customers are not able to connect to application at all. But, some customers does not have a problem at all. I took some traces during problem and i saw almost same pattern when there is problem. I added tcpdump file :

 

Client Ip Address = 10.10.10.10

Netscaler VIP = 20.20.20.20

 

Everything looks fine in the beginning of the dump , there is three-way handshake , client and server hellos and change cipher specs as usual. After that data traffic begins. But, after some point Netscaler sends packets and client does not send any response, so Netscaler starts retransmission the packets and eventually sends Reset.

 

There is something going on on packets 247,248,249 and 250. After that restransmissions start. What i'm trying to understand is that part actually. What happens there and client stops responding the packets ? Do you have any idea why this is happening.

 

We did not able to get a capture from client side so far. I will let you know when we can.

 

Best Regards,

Gokay

 

 

Retransmission_Problem_V2.pcap

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hi!

 

on the last packet , the Reset one sent by Netscaler , you can see that the value on Windows size is : 9300

this means : Cleanup of idle connections. See the article below.

https://www.citrix.com/blogs/2014/05/20/whats-that-netscaler-reset-packet/

 

You capture only says one part of the story, the front-end.

You need to do a dump that includes the back-end also. 

 

Check this and see how you can configure wireshark  ans laso use nstrace:

https://www.citrix.com/blogs/2014/05/03/netscaler-wireshark-a-perfect-combination/

 

Basically you need something like this:

start nstrace -filter "ip == 20.20.20.20 && PORT == 443" -link ENABLED -size 0 -capsslkeys ENABLED 

 

I also see that the netscaler send a lot of retransmissions ,waits(tcp delta) and the resets the connection.

this is normal if the client ip is not send any ack.

There might be some network issues between the client and the netscaler.

 

 

image.thumb.png.2debc366d1277ac98870c3c036ea15e1.png

 

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