TCP stands for Transmission Control Protocol and is one of the core protocols of the Internet Protocol Suite. TCP complements the Internet Protocol (IP), and therefore the entire suite is commonly referred to as TCP/IP.

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Send proper UUID over tcp

I have a small ingest TCP server that should accept a device UUID as a first message, which is only 16 bytes. I'd like to test this manually from terminal, but sending a string won't work, since it ...
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1answer
83 views

Is “keeping alive connections” the smartest approach to access devices behind a router? [closed]

The problem I'm developing an IOT device that will connect to a common Wifi router. As you know in order to make this device publicly accessible from WAN you'll have to do some ports forwarding or ...
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0answers
145 views

tcp previous segment not captured when NAT

I have a client request web service on a server behide NAT. My client IP is 10.54.10.193 NAT address: 10.54.28.183 Server address: 62.209.39.203 When client request web service on server we have TCP ...
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2answers
249 views

Keeping TCP connections alive to track which clients are online

I am developing an application where a server needs to stay in touch with lots of simple IoT devices. Nearly no information exchange is needed between the server and each device, but devices need to ...
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0answers
162 views

Inconsistency in TCP and HTTP connection management

I observe following scenario in WireShark: The problem I see here is that after receiving [FIN, ACK] from server (4090) and acknowledging it (4092), http client attempts to send another HTTP ...
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1answer
97 views

Packets being routed to the wrong IP

Looked around, can't find a similar issue anywhere... I have been having some very strange and hard to explain problems on my network lately, and in my efforts to find the cause, I came across an ...
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0answers
87 views

What exactly constitutes a bad TCP segment?

What constitutes a bad segment as in bad segments received in the netstat output below? I would think a TCP header's checksum could do it, but are there other things? If a segment arrives after its ...
2
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1answer
171 views

(Completely) randomize IP addresses in PCAP file

I have several PCAP files which contain network traffic. To perform some experiments for a network experiment, I need real data with completely randomized IP addresses. I am well aware about the ...
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1answer
98 views

Configure Squid Proxy Server to use TCP for DNS lookups? [closed]

Is there a way to configure squid 3.5.1 to use TCP for DNS lookups? I've setup up the proxy server to use TCP for lookups by adding "options tcp" to my /etc/resolv.conf, but squid seems to be doing ...
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1answer
431 views

Nginx Configuration:504 Gateway Time-out error

We are using Nginx as a Load balancer. Nginx having IP address of :10.110.0.200 and address of host machines are 10.110.3.20|10.110.3.21 this is the configuration file: upstream test1 { server 10....
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1answer
98 views

Is it possible to run 2 concurrent tcpdump with different options?

I need to run 2 concurrent tcpdump commands with different arguments/options. Why ? Because we wrote some long long scripts compatible with following options : tcpdump -ixenbr0 -s 400 -n -A 'port sip ...
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0answers
79 views

Does Fast Retransmit and Retransmission Timer work at the same time?

When Fast Retransmit is implemented, if I received packet 1, then I will send an ACK that says I need packet 2, and then if I received packet 3, I will send a duplicate ACK that says that I need ...
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27 views

Why is server refusing new connections?

One of our proprietary closed source server applications sometimes stops accepting new connection from remote nodes on its server port. Remote nodes that are already connected work fine. Any new ...
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1answer
254 views

Millions of TCP FIN-ACK retransmissions blocking traffic on my desktop machine

In a few minutes I have received about 7 millions(!) FIN-ACK packets from IP address that belongs to Google 74.125.133.188 what totally blocked network traffic on my desktop(!) machine. Other ...
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0answers
29 views

What technology do data center use to guarantee low RTT?

I was reading about data-center-tcp DCTCP and the paper was talking about the low retransmission timer (RTT) of about 250µs, but didn't state how that is being done. Somewhere else I read that DCTCP ...
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1answer
163 views

Does ColdFusion use TCP Ports?

I am trying to access a link on our network. Whenever I try, the page times out. I have discovered that this link is a Adobe ColdFusion web page. Does ColdFusion use a TCP port other than port 80? I ...
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2answers
701 views

better alternative for tcp_syncookies in linux

In an effort to prevent DDOS attacks I followed suggestions to leave /proc/sys/net/ipv4/tcp_syncookies value set to 1 in my linux box to enable TCP syncookies. However, when I look at this URL: http:/...
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1answer
907 views

Slow Upload to IIS Server

I have a Windows 2012 R2 Server running on an Amazon EC2 instance with IIS 8.5. It hosts a web application, and a custom WebDAV server that interacts with the same database as the web application. I ...
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0answers
190 views

How to fix the amount of bandwidth of iperf in tcp mode?

I'm working on some experiments about my master's degree project. I'm studying some load-balancers (I'm not supposed to cite them here) and the aim is to get for each bandwidth the cpu % usage of a ...
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1answer
107 views

How to prevent TCP network flood triggered by KVM VPS clients?

How to to protect nodes/ detect and block KVM VPS clients that TCP flood the network ? I use SolusVM VPS management system. Recently one abuser toke several VPSs and flood it the datacenter network. ...
2
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2answers
335 views

lsof doesn't show the established TCP connection

On my system, if I run the netstat for a port, it returns: $ netstat -nat | grep "60964" tcp 0 0 192.0.0.1:60964 0.0.0.0:* LISTEN tcp 59 0 192.0.0....
4
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2answers
869 views

TCP sequence number randomization

In a recent interview, my friend was asked about firewalls’ TCP sequence number randomization feature. The interviewer mentioned that we know that a firewall randomizes the TCP sequence number, but an ...
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0answers
49 views

TCP traffic redirection

I am using an open source program called revinetd: revinetd.sourceforge.net On server side, revinet listens for incoming connections on a defined port to act as a relay server. Now, The server ...
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1answer
622 views

Openvpn: no response from server in tcp handshake

I am attempting to connect to an openVPN server that I created on pfSense 2.2.3 by using tunnelblick on my Macbook. Whenever I attempt to connect using either OpenVPN version 2.3.6 or 2.3.7 (all that ...
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1answer
89 views

Tcp connection breaking, too fast for serial?

I've been having real difficulties getting a tcp connection to work with my web server. I think the issue might have something to do with the speed or ordering of the packets as the connection seems ...
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0answers
86 views

Spurious retransmission, Dup ACK and HTTP 408

I have a server which serves as sms gateway (using kannel) and have multiple client connecting to it, but recently this one client with their particular IP said that they can't send to my server and ...
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0answers
282 views

Citrix NetScaler sending FIN, ACK for SSL VPN Clients

I realise that it's unlikely anyone here has a definite "Check this box to resolve this" answer, but I'm struggling with this issue and I'm hoping that someone with more knowledge than me can give me ...
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1answer
174 views

TCP Keepalive: Why does an idled ESTABLISHED connection end after 60 seconds, instead of tcp_keepalive_time?

I am investigating ways to mitigate a server against DoS-type attacks. In one scenario, I've opened several hundred TCP connections to my webserver. I do not send any data after the initial TCP ...
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0answers
12 views

Route only on output chain?

I have two machines A and B. I want to send iperf traffic from A to B, but first have it route through a userspace program on A. I did this with a tunneling device: therefore, I used the command ip ...
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3answers
706 views

TCP sequence number

I would like to know if two segments of same sequence number arrive at the destination, which segment will get accepted ? For eg: A clients sends a packet to a server and wait for an ...
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1answer
67 views

ufw status (what does the v6 stand for?)

My ufw status output looks like this: To Action From -- ------ ---- 22 ALLOW Anywhere 80/tcp ...
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0answers
94 views

Debian limit number of TCP sockets for a process (especially tor) on OpenVZ

I have a debian 7.8 server, running on OpenVZ. On this server I'm running a tor relay and some other network services (like apache and mysql). However the tor service seems to eat up all my available ...
2
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0answers
57 views

Network sensor for a TCP connection for collecting statistics each second [closed]

I need a Network Sensor capable to gather basic end-to-end statistics (packet loss, jitter and network delay/RTT) of several TCP connections directed to the very same destination (ip-addr:port) on ...
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0answers
105 views

Should I disable the Nagle Algorithm for Outlook / Exchange RPC/HTTP communication?

I'm investigating reasons why several Outlook clients in non-cached mode are having delays communicating... resulting in Outlook hanging. My suspicion is that a Netscaler, or intermediate device (? ...
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1answer
66 views

Can TCP be used like UDP by simply not sending ACK?

Assuming both client & server cooperated, could you emulate the functionality of UDP by not sending ACK packets, and not sending retransmissions? Or would most routers somehow bork the process if ...
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0answers
145 views

SSH stalled after a while

I am executing some commands over SSH from a linux client (centos 7) toward a server (wind river linux) and for a reason it always stopped ( not completed ). If i executed a command that take short ...
0
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1answer
131 views

REDSOCKS goes 'out of file descriptors' when trying to redirect all outgoing (TCP) traffic from my Linux machine

I'm trying to redirect all outgoing TCP traffic from my linux box to the remote SOCKS5 proxy server. Currently I'm using the following rule in the OUTPUT chain: sudo iptables -t nat -A OUTPUT -p tcp ...
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0answers
106 views

Web sites freeze after clicking link - unexplainable ACK packet

We have a sporadic problem accessing some internal links on websites. (Windows Firefox, Internet Explorer, Chrome) Behaviour On first clicking a link, the browser will load infinitely. The second ...
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0answers
113 views

How to properly configure security group at AWS?

I'm trying to reach my server's FTP-port by its Elastic IP. I've configured the security group as follows: Inbound Type Protocol Port Range Destination All traffic All All ...
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1answer
398 views

Private communications between AWS EC2 instances

I have three EC2 instances with elastic IPs. Each one contains a server. Each server needs that TCP ports 8181, 2181, 2888 and 3888 are opened on each machine. Each server should have the possibility ...
10
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1answer
444 views

SynProxy can not return syn ack packets with asymmetric dual bridge topology

I have a asymmetric dual bridge topology as shown below when i connect from 172.16.11.5 and 172.16.10.6 with ssh but i can not connect because of SynProxy. ------- ...
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1answer
73 views

TCP - MSS option and different payload

This is a tcpdump from servers side. In line 1 i see MSS=1400. Why server sent in line 6 a packet of 4230 bytes when client want max 1400?
11
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4answers
592 views

How does server-side `TIME_WAIT` really work?

I know there are quite a few SE questions on this, and I believe I read as many of them as it matters before coming to this point. By "server-side TIME_WAIT" I mean the state of a server-side socket ...
14
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7answers
3k views

Why is it good practice to compare checksums when downloading a file?

Websites which supply ISO files for download will often give the md5 checksums of those files, which we can use to confirm that the file has downloaded correctly, and has not been corrupted. Why is ...
8
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2answers
6k views

Extreme UDP packet loss at 300Mbit (14%), but TCP > 800Mbit w/o retransmits

I have a linux box I use as the iperf3 client, testing 2 identically equipped Windows 2012 R2 server boxes with Broadcom BCM5721, 1Gb adapters (2 ports, but only 1 used for the test). All machines are ...
2
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1answer
68 views

Outgoing packet has NATed src address

Configuration/Topology: There are 3 machines hadoop2 | hadoop | driver eth0 10.10.15.3 | eth0 10.10.15.2 | tap0 192.168.0.199 ...
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1answer
152 views

No response to TCP SYN packet when padding is not 0's or F's

I have this client which initiates a 3 way handshake with a SYN packet but there is no SYN ACK response. We figured out that it was because the client did not pad the end of the TCP headers with 0's ...
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1answer
38 views

Upgrading Web Application's Systems' Kernels for IW10 & other related improvements - upgrade all machines? LB first? Most important?

Stackers - We're making the push to upgrade the systems for our web app to take advantage of the various TCP improvements becoming more readily available (e.g. http://googlecode.blogspot.com/2012/01/...
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0answers
611 views

Nginx TCP Fast Open Issue

I have configured Nginx and Apache on one of my servers. The nginx server listens on port 80 and Apache on port 81. Nginx works as a reverse proxy. In nginx I configured TCP Fast Open: server { ...
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166 views

What happens if a machine gets a SYN/ACK packet without sending initial SYN packet?

I'm thinking of a situation where an attacker manipulates a SYN packet that was sent from A's source IP address to B. The server will receive the packet and think it's a legitimate packet, and send a ...