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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TCP connection RST after FIN, ACK

I have a situation that would like to clarify with the experts here. I am no network expert so maybe it's normal, but i rather ask. We are trying to diagnose a problem between two servers, both are ...
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8 views

Identify local IP address in tcp dump [on hold]

I have a tcp dump file with 4100 connection details. How can i filter the data to identify the local IP address and the number of host?
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3answers
39 views

Do clients typically implement failover/load-balancing on multiple A records?

Typically, load balancers like Amazon's Elastic Load Balancers use a DNS record set with multiple A records to provide multiple load balancer instances which can handle traffic to requesting ...
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5answers
2k views

Netcat fails to start in listening mode

I'm using CentOS 6.7 (Final) system, and when I try to run nc in listening mode it prints the following: # nc -l 1234 nc: Protocol not available The port is not bound. I tried other port numbers ...
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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 ...
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29 views

multiplexing a TCP connection through a dumb shell connection?

I am connecting to a VPN whose gateway is sufficiently misconfigured that basically the only useful thing I can do with it is to ssh to a specific Linux host set up for my usage inside the VPN, and ...
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13 views

stunnel keeps stopping with WSAECONNREFUSED given

Right so bit of background to start with I've got 2 stunnel installs on 2 different servers and basically using ensemble and stunnel to bounce a message around with ssl cert. Here is the flow. Where ...
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26 views

TCP Balancer active/standby active/passive

I have two Servers, Server A,ServerB. running as TCP socket server. I want to a active/standby or /active/passive failover. that means: 1:Server A and Server B Running, route ALL connection to ...
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1answer
25 views

TcpTimedWaitDelay is missing in Windows Server 2012

Suddenly my server log shows: An operation on a socket could not be performed because the system lacked sufficient buffer space or because a queue was full And I googled and found these links as ...
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2answers
11k views

tcp syn checking

I have a WatchGuard Firebox that I've recently configured. All of the policies look fine and all appropriate services seem to be working correctly. However, one or two (seemingly) random nodes keep ...
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2answers
344 views

TCP timeout for established connections in Windows

I have the following situation: Application (Firebird DB client) on a client computer opens a TCP connection to server on port 3050 Application crash on client, application terminated netstat on the ...
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2answers
506 views

(Why) does FreeBSD 'net.inet.tcp.always_keepalive' violate RFC1122?

While working on a server application that runs on FreeBSD and uses TCP, I noticed that TCP keepalive probes get sent even though my application explicitly disables SO_KEEPALIVE on TCP sockets. ...
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1answer
23 views

utility of using ALL in --tcp-flags in iptables rule

I m wondering what is the difference between the following 2 --tcp-flags rules: 1) -p tcp --tcp-flags SYN,FIN,RST SYN,FIN,RST 2) -p tcp --tcp-flags ALL SYN,FIN,RST
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2answers
2k views

How to achieve multiple NFS/TCP connections to the same server?

I'm trying to maximize the NFS/TCP bandwidth between a Linux client and a single NFS server over a 10Gbps link. Although each NFS mount has its own device (major/minor), everything comes down to a ...
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0answers
24 views

Nginx log to syslog on TCP port

I need to redirect Nginx access and error logs to a remote syslog server. From http://nginx.org/en/docs/syslog.html I saw that I can do: error_log syslog:server=192.168.1.1; However I need to ...
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1answer
1k views

How to increase nginx connections

I am facing the problem of nginx max connection issues. I am not able to increase max active connections(520) made by nginx. Some time it is using whole writing (516) operation connections. and due to ...
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2answers
1k views

Where are my TIME_WAITs on Mac OS X?

No TIME_WAITs on Mac OS X Normally, when a TCP connection is closed, the socket on the side where close() is called first is left in the TIME_WAIT state. When one of the peers is a Mac OS X (Lion) ...
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1answer
25 views

PCI Scan failing at TCP Source Port Pass Firewall testing

I'm trying to get PCI scan PASS for my website, Scan failing at this step. The host responded 4 times to 4 TCP SYN probes sent to destination port 20 using source port 80. However, it did not ...
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0answers
7 views

Windows/IIS7.5 half-closing connections resulting in sockets in TIME_WAIT

I'm seeing scenarios where the client side initiates the TCP close but the webserver (IIS 7.5) simply responds with an ACK and the connection ends up in TIME_WAIT. Why would it do that? Typical HTTP ...
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4answers
4k views

Need help troubleshooting intermittant TCP timeout in HAProxy

I have an application where the client connects to a server via a simple TCP based protocol over TLS/SSL. In development, this has worked great for many months while we were building our application ...
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0answers
23 views

lower tcp throughput than expected

I've conducted some tests which measured tcp throughput via wireless and wired connection. (a) was wired link between my desktop and my home router. (b) was wireless link between my desktop and my ...
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1answer
29 views

Manually sent ICMP redirect packets [closed]

I'm trying to sent a ICMP redirect to my router to add a new route, as I can not configure it from the portal, and have no access to it though telnet/ssh. The scenario is the next. LAN network ...
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9 views

What filter in Wireshark, can return the ACKs packets employed to complete TCP three-way handshakes instigated by a particular party?

What filter in Wireshark, can return the ACKs packets employed to complete TCP three-way handshakes instigated by a particular party? For instance if machine A requests for a TCP connection to be ...
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1answer
31 views

Is it normal to have HTTP 499 errors in 1 out of 4000 requests?

I made a website, behind CloudFlare, and sometimes I get an early terminated (nginx 499) request, which is really hard to work around in the codebase. This happens in about 1 out of 4000 requests. ...
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1answer
1k 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 ...
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1k views

Improving TCP performance over a network with small packet loss

I’m trying to improve my TCP throughput over a “high delay network”, with some packet drops, between Linux machines. I set tcp_mem, tcp_wmem and tcp_rmem to “8192 20530752 20530752”. I set rmem_max, ...
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12 views

TCP tuning for DPM on Windows 2012

I've got a pair of servers on opposite ends of a fast (1-10Gb depending on the server) but higher latency (40-60ms) link. Various network tuning options have been set resulting in iperf3 yielding ...
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0answers
229 views

Weird CLOSE_WAIT statuses at standard PHP application

I am asking for help regarding tcp problems on a webserver serving a web application built in PHP. The client is a standard html/js page viewed in the web browser. This client sends Ajax requests ...
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14 views

How to debug lost connections

I'm having a problem between a computer running Filemaker Server and their clients: clients loose the connection often (3-4 times per day), even when the user is using it (so no disconnect on idle). ...
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2answers
1k views

How to configure iptables so an unwanted port is not reported as filtered

I'd like to stop others from seeing my ports as filtered in the nmap standard scan (unprivileged). Let's say that I have the following ports open: 22, 3306, 995 and a firewall configured like this: ...
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1answer
42 views

Cannot ping through one of the network interfaces

Setup ubuntu linux VM ( virtual-box) is configured with two interfaces, eth0 and eth1. eth0 is on a bridged network and directly connected to external network. eth1 is on "nat network", which is ...
26
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3answers
23k views

What's the difference between Unix socket and TCP/IP socket?

It's from this answer: http://stackoverflow.com/questions/2482411/is-this-pdo-bug-fixed-now/2482424#2482424
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1answer
55 views

Nginx TCP stream routing based on source IP

I have configured nginx as a reverse proxy for a TCP (non-http) stream. I'd like to apply different routing for a particular source IP address - can this be done, and how? I'm aware of recomendations ...
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2answers
2k views

How to reset a tcp connection immediately on both ends on a certain condition using linux netfilter/iptables?

Dear Serverfault community, I have the following problem: I need to reset (disconnect) tcp connections on both network sides immediately if a certain string is encountered in the packet data. I don't ...
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2answers
24 views

How should a long-lived connection behave when there is a DNS change?

Scenario: Connector.com connects to server.net, which resolves to 20.30.40.50 Connector.com and 20.30.40.50 keep the connection open DNS is updated so that server.net now resolves to 7.8.9.10 ...
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3answers
26k views

Troubleshoot large number of TCP retransmits / dup ack / segment lost

I have a problem with RDC slowing to a crawl or disconnecting entirely. Client is XP SP3 w/ RDC 6, server is Win 2k8 R2. Both have been scanned thoroughly and found to be virus free. I downloaded ...
2
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1answer
573 views

network setup does not work: icmp works, tcp not

I experiencing a small problem with my network setup: In this network, I can ping from 192.168.3.0 to 192.168.2.0 and reverse, but it does not work with TCP connections. The handshake fails (no ...
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1answer
72 views

Nginx TLS Performance Optimization

I switched a busy site to TLS-everywhere and HTTP/2 last week. Performance hasn't improved as much as hoped. In fact, depending on how you measure it, you can argue it has degraded. There is plenty ...
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2answers
3k views

TCP Window Size going to 0 / Wget stops downloading?

I have a somewhat complex setup that doesn't work, and I'm struggeling quite a bit to track down the root cause. First of all the big picture: Node backend is a medium size windows azure worker role ...
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1answer
45 views

Ephemeral port reuse for TCP connections to different IP addresses

I know that a web server running a website on TCP port 80 can receive TCP connections from many different IP addresses sourced from many different ephemeral ports. Can a client initiate multiple ...
2
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2answers
126 views

Minimal size of TCP communication

I am sending small amounts of data (up to 100 bytes) every 10 minutes from devices to TCP server. In my case overhead seems to be huge (we pay for each byte). I found that I have at least 7-10 packets ...
0
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1answer
67 views

Sonicwall: cannot send email (outlook) and drops connection (google drive)

I will start by saying Im a web developer and my networking knowledge is very limited, please be patient =) . We dont have network/sysad in our company. We are having problem with our connection. We ...
2
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1answer
43 views

Can I trust a TCP segment with a payload of 255 bytes will be delivered in a single Ethernet frame?

I'm writing some server software that upgrades the firmware on an electronic device. It's a tricky task, because currently these devices don't have enough memory to hold a full firmware before ...
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1answer
37 views

Long lived TCP connection to DNS servers

Typically the TCP connections to DNS servers are expected to be short lived, ie: the client connects, sends the query and disconnects on getting the response. If a client wants to keep a long lived ...
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0answers
650 views

tcp connection reset [RST, ACK]

getting this errors looks like server is restating the connection because of some packet loss any possible suggestion's to figure out this 37713 591.925575000 ...
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1answer
28 views

How to open entire subnet with iptables [closed]

I want to enable the entire subnet 192.168.1.0/24 which is connected to eth0 in input. I'm very unfamiliar with iptables. If I add the rule: # iptables -A INPUT -s 192.168.1.0/24 -p tcp -m tcp ...
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1answer
37 views

What is a TCP Relay and when is it used? [closed]

Tcprelay is a TCP connection forwarder with load balancing capabilities. If compiled with TLS support, it may be used as SSL encryption wrapper. What are some practical applications of TCP relay?
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30 views

What happens when connecting to port in TIME_WAIT state?

I'm trying to understand the effect of TIME_WAIT on subsequent TCP connections. I understand how TIME_WAIT behaves when net.ipv4.tcp_tw_reuse = 1, as explained by this answer. But what happens when ...
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1answer
25 views

Is it possible for SYN/ACK to not be immediately proceeded by a SYN in a network trace

I'm writing a simple program to calculate initial RTTs from a network capture I took using Wireshark. To do this I wan't to calculate the difference in time between the SYN and the SYN/ACK. I don't ...
2
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0answers
29 views

TCP Handshake fails when ICMP Redirects are enabled

So it seems that due to ICMP redirects it's not possible to connect to a server behind a VPN connection. It immediately responds with a TCP RST (with manifests itself in SSH as ...