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.

learn more… | top users | synonyms

1
vote
1answer
95 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 ...
3
votes
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 ...
0
votes
0answers
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 ...
1
vote
1answer
237 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 ...
1
vote
0answers
28 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 ...
0
votes
1answer
156 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 ...
0
votes
0answers
80 views

Can I use MS Host Integration Server to connect to an IBM without using SNA

I'm sorry, this will represent a lot of information, but I'd like to avoid some of the back and forth I'm having with various forums trying to resolve this issue. So please, bear with me. I've taken ...
1
vote
2answers
629 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:/...
0
votes
1answer
840 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 ...
0
votes
0answers
188 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 ...
0
votes
1answer
102 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
votes
2answers
323 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
votes
2answers
776 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 ...
0
votes
0answers
98 views

what is the significance of URGENT POINTER in TCP Header?

Urgent Pointer: Used in conjunction with the URG control bit for priority data transfer. This field contains the sequence number of the last byte of urgent data. It is possible to identify the urgent ...
0
votes
0answers
44 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 ...
0
votes
1answer
545 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 ...
1
vote
1answer
88 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 ...
0
votes
0answers
96 views

Why would Windows 7 not complete this TCP handshake?

One of our customers is running Windows 7, and cannot reach some of our servers because it seems Windows 7 cannot complete a TCP handshake. Here's a packet trace to one our servers -- note that a SYN ...
1
vote
0answers
81 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 ...
1
vote
0answers
272 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 ...
0
votes
1answer
164 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 ...
0
votes
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 ...
5
votes
3answers
696 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 ...
-1
votes
1answer
63 views

ufw status (what does the v6 stand for?)

My ufw status output looks like this: To Action From -- ------ ---- 22 ALLOW Anywhere 80/tcp ...
1
vote
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
votes
0answers
56 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 ...
1
vote
0answers
99 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 (? ...
-1
votes
1answer
65 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 ...
0
votes
0answers
140 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
votes
1answer
123 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 ...
1
vote
0answers
104 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 ...
0
votes
0answers
110 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 ...
0
votes
1answer
363 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
votes
1answer
437 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. ------- ...
-1
votes
1answer
71 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
votes
4answers
558 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
votes
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
votes
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
votes
1answer
67 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 ...
1
vote
1answer
151 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 ...
0
votes
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/...
1
vote
0answers
557 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 { ...
1
vote
0answers
161 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 ...
0
votes
1answer
191 views

ssh tunneling lmgrd port what I've missed?

I've got 2 machines: one local , one flexserver I'd like to do a ssh connection for forwarding the TCP port of the flexserver. On the flexserver, lmutil lmstat -c 5280@localhost is working fine So I ...
0
votes
1answer
151 views

How to ping a host with different MTU size to simulate icmpv6 packet too big scenario?

As the Title states,I want to check whether my host will actually send a ICMPv6 packet too big if i send a packet with beyond the defined MTU size.I don't have a cisco router(extended ping) to try out ...
0
votes
0answers
575 views

massive amount of CLOSE_WAIT due nginx (lsof)

My VPS keeps hanging up every 5 days. I can see that the nginx worker processes are eating up my memory over time. I think this is due the massive amount of CLOSE_WAIT's open. When I type LSOF, I get ...
7
votes
4answers
1k views

Why is my web server dropping connections with a TCP reset at high load?

I have a small VPS setup with nginx. I want to squeeze as much performance as possible out of it, so I've been experimenting with optimization and load testing. I'm using Blitz.io to do load testing ...
1
vote
1answer
1k views

Squid3 CONNECT imap.gmail.com:993 TCP_DENIED:NONE

I have the following configuration under squid.conf. However, when my Blackberry email client attempts to fetch new emails, etc. Squid access log show the following error: imap.gmail.com "CONNECT ...
1
vote
1answer
118 views

Does TCP's MSS hide a mismatched intra-LAN MTU?

I'm trying to understand how mismatched MTUs behave in a network. Suppose two hosts are able to talk to each other through an Ethernet-based network. The network and host A are configured for jumbo ...