Questions tagged [tcp]

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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Under what circumstances is TCP-over-TCP performing significantly worse than TCP alone (2014)?

Many admins keep perpetuating - on ServerFault and elsewhere - how bad of an idea TCP-over-TCP is, e.g. in VPNs. That even the slightest packet loss will make one suffer from at least severe ...
Nils Toedtmann's user avatar
-1 votes
1 answer
78 views

Application protocol-based port forwarding/redirection [closed]

I need to split traffic on port 80 between HTTP and non-HTTP, and internally forward HTTP traffic to a port nginx will listen to, and non-HTTP traffic to port 22. Does anyone know of a piece of ...
rapht's user avatar
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1 vote
2 answers
23k views

Send Text String to a Socket In Windows

I have a server that has an open socket that listens for a particular text string on it in order to perform an action. Our linux machines send this data via: echo "text_string" | nc -w 2 server-...
cheesesticksricepuck's user avatar
-1 votes
1 answer
125 views

FTP upload slows down when devices are connected via hub [closed]

I have a setup with a network hub and three Ethernet devices. One of them is a PC (running windows XP), two others are hardware components that need to communicate with each other over the network. ...
user1234567's user avatar
3 votes
1 answer
876 views

Why do some outgoing IP traffic not contain UID information?

I am doing egress logging on my server using IPTABLES with the following line which is supposed to provide UID information on all traffic that is logged: -A OUTPUT -j LOG --log-prefix "IPTABLES(O): " ...
Question Overflow's user avatar
2 votes
2 answers
2k views

tcp ack delay almost 600ms, is this all right?

As far as I konw, tcp delay ack always 200ms, but now in my production environment it delay almost 600ms, my environment is below: ubuntu 11.04 48G memory 16 core, load not heavy; I catch packet in ...
good90's user avatar
  • 21
2 votes
1 answer
940 views

Why do I get connection timeouts to private services in Azure?

I seem to be seeing this with both my SQL Server, and my MongoDB replica set. I only get a handful a day, but it still concerns me. I am getting a timeout when trying to open a new connection to the ...
Tracker1's user avatar
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1 vote
0 answers
614 views

TCP Window Size Allocation, TCP Window Zero Errors and Network Latency

My mind is about to explode as everyone is always blaming the network guys for disconnections and slowness in the networks, but Solarwinds Reports that all utilization in the network devices and links ...
Rufi's user avatar
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11 votes
2 answers
44k views

What does TCP: too many orphaned sockets mean?

When I use dmesg to look at linux kernel messages, I see a flood of.... TCP: too many orphaned sockets messages. My guess is this is sockets that are hanging around in TIME_WAIT after being closed ...
andrew pate's user avatar
0 votes
0 answers
3k views

Connection Timeout Issues - Solaris 11 SPARC

We're currently running some performance tests using Solaris 11 (SPARC) on some large hardware. The tests, which consist of sending SOAP requests (50kb per request), are running well up until we get ...
user3474444's user avatar
7 votes
2 answers
13k views

TCP under OpenVPN is very slow (tsg attached)

I have a very weird problem with OpenVPN. Most VPNs work fine, except this one. Here I get very low performance from TCP connections, but the CPU load is low (so, not a CPU issue). OpenVPN is ...
Pentium100's user avatar
0 votes
0 answers
121 views

Single TCP-CLOSE_WAIT connection brings down application till restart

Recently found a behaviour where my application had a connection in TCP Close_wait state till the app was restarted (after about 5 hours). But during this period the SUnreclaim space was also ...
broun's user avatar
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0 votes
1 answer
113 views

cannot send emails to other Web servers

I'm trying to limit my server's open ports in CSF. The IPv4 port settings include: # Allow incoming TCP ports TCP_IN = "22,25,53,80,110,143,443,587,3654,53343” # Allow outgoing TCP ports TCP_OUT = "...
developer's user avatar
  • 555
6 votes
1 answer
15k views

What do I need to consider when setting TCP idle timeouts?

What's purpose of having a [low] TCP idle timeouts? E.g., why have a 60 second timeout on a firewall or load-balancer? Is it a memory management or /performance optimization thing? Is there a security ...
svidgen's user avatar
  • 191
4 votes
1 answer
14k views

Linux iptables - reject tcp SYN with RST

I am doing an implementation on a linux machine to reject incoming telnet requests from wan side telnet port 8023. The functionality is achieved by using the below iptables rules. The first rule in ...
UserM's user avatar
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1 vote
0 answers
184 views

periodic connection timeouts to nginx server

We have the following setup: One nginx server as a loadbalancer in front of four worker application servers. The nginx server get about 100 requests per second, sometimes more that that, active ...
Malax's user avatar
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2 votes
1 answer
3k views

iptables and TPROXY support

I'm running iptables v1.4.21 on Ubuntu 14.04 and is trying to setup iptables to use TPROXY. How can I check whether my current build of iptables supports TPROXY? I can check TPROXY support for ...
Athena Wisdom's user avatar
2 votes
1 answer
639 views

remote login failed on windows XP, but remote telnet successful on mac

I recently set up an Oracle DB, started the listener on port 1561, and enabled TCP access. I then opened that port to all incoming connections. When I get on my Mac - I can use telnet remoteserver ...
jwillis0720's user avatar
2 votes
1 answer
258 views

TCP rsyslogd events showing up as 2000 character continuations

I'm taking syslog events from a proprietary app. This could be the app's fault or it could be rsyslogd. Events are written like: Aug 15 16:00:00 10.11.12.13 Event1 from this wonderful product using ...
mgjk's user avatar
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1 vote
2 answers
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When a socket switch to TIME_WAIT state, why I can't see its inode number?

I'm developing a program in python that parses /proc/net/tcp informations, but unfortunately, while I was doing this, I saw a strange thing. Practically, when a socket change in TIME_WAIT state, ...
LordFire's user avatar
-1 votes
1 answer
263 views

CentOS 5.10 TCP Sequence Number

We have done a security check on a server and its come back with Linux Kernel TCP Sequence Number Generation Security Weakness. We are looking to correct this being flagged up on the check We are ...
toza's user avatar
  • 13
2 votes
2 answers
1k views

Using (r)syslog's dynamic file generation

I am in the middle of configuring a (r)syslog server as a remote server that receives logs from various clients. I wonder whether there is a nicer way to dynamically generate multiple file names as ...
Andrew Tobey's user avatar
-1 votes
1 answer
420 views

HAProxy - proxy to webserver via tcp

I have a simple web application, All requests to that application are HTTP based (RESTfull API and standard ajax) I have an haproxy before my tomcat cluster. So now i have clients that http request ...
Urbanleg's user avatar
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3 votes
0 answers
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TCP Connection Issue Between Linux Machine and VMWare Windows Server

I have a TCP connection issue as follows. The setup: VMWare Virtual Machine: Windows Server 2008 R2 DataCenter SP1, IP: 192.168.2.111, DG: 192.168.2.254 Host Machine: Windows 7 Professional SP1, IP: ...
user3416108's user avatar
5 votes
5 answers
12k views

Troubleshooting High TCP Retransmit Rate

I've been attempting to troubleshoot a network issue that presents with very high rate of TCP retransmits. 36 samples (taken with Wireshark 1.10.8 running on 32-bit Windows 7) totaling a little over ...
Erick Brown's user avatar
11 votes
3 answers
6k views

How does anycast work with tcp?

TCP, being stateful, should require subsequent packets to reach the same server. (Stateless) HTTP runs on top of TCP, and CDN's can use anycast. So how does TCP work with anycast? What if the syn ...
Filip Haglund's user avatar
0 votes
0 answers
273 views

FortiBalancer and IE TCP issues

We are using a Fortibalancer for our web servers (Win2012 with IIS) and we have run into a strange issue. IE users will experience timeouts (~77s) in getting a response from our servers. Packet traces ...
schroeder's user avatar
  • 274
21 votes
2 answers
134k views

What is [PSH, ACK] doing during my connection to a global catalog server?

A linux server of mine is trying to establish a LDAPS connection to a global catalog server and the connection is getting dropped (presumably by the GC side). For the purpose of discussion, let's ...
Mike B's user avatar
  • 12k
6 votes
2 answers
8k views

Haproxy using 10GB Memory and 100% CPU with 50k connections

On a Ubuntu 14.04 x64 server, Haproxy uses 3.3 GB of memory and 6.8 GB of swap, while handling 52k connections. The CPU usage also keeps spiking to 100% before most of the traffic was redirected to ...
Nyxynyx's user avatar
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1 vote
1 answer
617 views

How to Add/Remove New Server behind Haproxy with Minimal Disruption

Haproxy is currently balancing the load between 2 servers, A an B. Clients are connecting to these servers via persistent TCP connections. Question: We want to upgrade from server A to a more ...
Nyxynyx's user avatar
  • 1,479
2 votes
1 answer
122 views

Why some tcp_[rw]?mem$ voodoo show all equal values?

Looking at TCP optimization guides across the Internet, a common theme is setting the tcp_mem, tcp_rmem, or tcp_wmem three-integer vector to have equal values in the sysctl.conf file. Borrowing from ...
Robert's user avatar
  • 105
1 vote
0 answers
336 views

trying to reach a port forwarded server from the subnet using the public IP not working

I set up a server which is connected to my router. The router forwards a port of my server. So when I scan that port using http://www.t1shopper.com/tools/port-scan/ I got: 188.143.126.14 is ...
laplasz's user avatar
  • 135
0 votes
1 answer
365 views

Prevent TCP Connections from Timing out on Restarting Service

On Ubuntu 14.04, an app communicates with clients at intervals of about 1 per sec to 1 per min. However the service have to be restarted regularly and this causes all the connections to drop/timeout. ...
Nyxynyx's user avatar
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3 votes
2 answers
5k views

FTP client/server failing on switching to PASV mode

Update The ISP said that they recently added the area where this computer is located to their IPv6 network. Coincidentally, ever since the day they added that area to their IPv6 network, no FTP ...
Steffen Winkler's user avatar
0 votes
2 answers
145 views

Strange data in HTTP request

I have a HTTP server that serve many short time connections from many clients, the server logged that there are some invalid HTTP requests, so I decide to capture the network traffic. This is what I ...
secmask's user avatar
  • 101
1 vote
0 answers
146 views

Multipath tcp application level performance measurement

I am working on a project related to Multipath tcp and I want to measure the goodput and the RTT at the application level. I don't want to use a traditional tool(netperf, iperf, ...) and I want to ...
evelina's user avatar
  • 11
52 votes
10 answers
39k views

Windows TCP Window Scaling Hitting plateau too early

Scenario: We have a number of Windows clients regularly uploading large files (FTP/SVN/HTTP PUT/SCP) to Linux servers that are ~100-160ms away. We have 1Gbit/s synchronous bandwidth at the office and ...
SmallClanger's user avatar
  • 9,187
1 vote
2 answers
2k views

Incoming TCP SYNs possibilities

This might be a general TCP question. Can I receive TCP SYN packet on an ESTABLISHED connection OR a connection in TIME-WAIT state? Is this possible?
hari's user avatar
  • 270
18 votes
6 answers
37k views

dump tcp connections without tcpdump

On a centos box, I like to dump tcp connections - I would like to see if a server tries to send requests to a certain IP. Usually tcpdump would do the trick - but tcpdump is not installed, and ...
Isaac's user avatar
  • 1,215
0 votes
1 answer
835 views

TCP RST from telnet/ssh daemons when connecting from openvpn

I have LAN_1 and LAN_2 interconnected with an openvpn tunnel terminated ona pair of SOHO routers running busybox. One of the vpn purpose is to allow clients on both LAN_1 and LAN_2, to administer the ...
rokafeller's user avatar
17 votes
5 answers
9k views

How does Intel AMT (Active Management Technology) not interfere with the TCP/IP host stack?

The Intel dev kit I've been using includes a remote management feature (also see the Ubuntu man page here) which allows remote reboots in case the operating system hangs. It has the capability of ...
mpontillo's user avatar
  • 924
2 votes
1 answer
3k views

Cisco ASA 5510 Out-of-Order Packets to Google

We're seeing a large number of packets being dropped due to being Out-of-Order. The numbers are large enough that it may be having an impact on network performance. We've isolated it down to a few ...
VSack's user avatar
  • 215
3 votes
1 answer
4k views

How to configure SSH client timeout after network failure?

Let's say I connect from a client to a server via SSH, and in the middle of the session I pull the server's network cable. On the client, the ssh connection stays alive for around 15 minutes before ...
gpothier's user avatar
  • 133
3 votes
2 answers
2k views

When a server IP changes, do exising TCP (e.g. http/mysql) connections remain running

We have some PHP-FPM servers and when they need a database connection, they connect to an HAProxy server which selects them a database server to use and the connection opens. When we then want to ...
Luke Cousins's user avatar
11 votes
1 answer
35k views

How to send 0x80 byte to a tcp port using netcat or similar tool?

I'm trying to make a Memcached server respond as if I were using a binary protocol. If possible just command line answers pls, no code snippet in any programming language.
user avatar
3 votes
1 answer
2k views

Is net.ipv4.vs.timeout_timewait used also for IPv6?

Does this setting for TCP net.ipv4.vs.timeout_timewait apply only to TCP connections established over IPv4 or does it also apply to TCP connections established over IPv6? I have found this for ...
user avatar
-1 votes
1 answer
762 views

TCP Server Memory management: #Connections Vs. #Requests

Given that, there is no theoretical limit to number of concurrent TCP connections a Windows 2008 server can handle. Only thing will happen is, with each connection there will be memory consumption in ...
Atul's user avatar
  • 396
2 votes
2 answers
5k views

How to measure TCP connection time in Linux

I want to measure the overhead in creating a TCP connection. I know of many tools like hping and netperf, but they seem oriented at measuring latency. I want to know how long the 3-way handshake ...
Paul Draper's user avatar
1 vote
0 answers
538 views

Improving TCP performance over a gigabit network lots of connections and high traffic for storage and streaming services

I have two servers, Both servers hardware Specification are Processor : Dual Processor RAM : over 128 G.B Hard disk : SSD Hard disk Outging Traffic bandwidth : 3 Gbps network cards speed : 10 Gbps ...
Linux Guy's user avatar
4 votes
2 answers
38k views

Wireshark TCP Window Size Value

I am debugging an application with Wireshark and watching the TCP Window Size value shrink on one side of the communication. If the packet's TCP section shows a "Window size value: 1", does that mean ...
T Vernon's user avatar

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