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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3
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2answers
6k views

Traceroute, ICMP, UDP and TCP

When does traceroute use TCP? Or does it just use UDP, also why does Traceroute use UDP on MacX and ICMP on windows? I thought ICMP just contains a message saying what caused the error of a packet and ...
0
votes
0answers
52 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 ...
0
votes
0answers
19 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 ...
0
votes
0answers
46 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 ...
1
vote
1answer
61 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 ...
3
votes
2answers
12k 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 ...
1
vote
2answers
688 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 ...
5
votes
2answers
541 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. ...
1
vote
1answer
24 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
6
votes
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 ...
1
vote
0answers
105 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 ...
0
votes
1answer
38 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 ...
0
votes
0answers
10 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 ...
4
votes
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 ...
0
votes
0answers
26 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 ...
-1
votes
1answer
35 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 192....
0
votes
0answers
11 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 ...
0
votes
1answer
44 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. ...
1
vote
1answer
2k 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 ...
1
vote
0answers
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, ...
1
vote
0answers
18 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 ...
0
votes
0answers
404 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 ...
0
votes
0answers
17 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). ...
8
votes
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: -...
1
vote
1answer
72 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 ...
28
votes
3answers
25k 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
1
vote
1answer
109 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 ...
0
votes
2answers
25 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 ...
1
vote
3answers
27k 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
votes
1answer
602 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 ...
0
votes
1answer
88 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 ...
2
votes
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 ...
1
vote
1answer
60 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
votes
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
votes
1answer
97 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
votes
1answer
44 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 ...
1
vote
1answer
42 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 ...
1
vote
0answers
706 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 Sourceip==>>...
-4
votes
1answer
29 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 --...
-1
votes
1answer
44 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?
0
votes
0answers
46 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 ...
-1
votes
1answer
26 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
votes
0answers
36 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 ...
6
votes
4answers
660 views

ran out of tcp udp ports [closed]

How to resolve a Windows or Linux system that runs out of the tcp/udp ports on a single server? I have over around 65000 tcp/udp ports being used on a single server as a result of SQL connections, ...
0
votes
0answers
25 views

tcp receive buffer size min value seems not work

I tried to increase tcp min receive buffer size to 87380, so in my test it would OOM quickly with a little connections. net.ipv4.tcp_rmem = 87380 87380 6291456 net.ipv4.tcp_wmem = 87380 87380 ...
15
votes
8answers
32k views

Apache Tomcat chokes after 300 connections

We have an apache webserver in front of Tomcat hosted on EC2, instance type is extra large with 34GB memory. Our application deals with lot of external webservices and we have a very lousy external ...
5
votes
3answers
376 views

How to fine tune TCP performance on Linux with a 10Gb fiber connection

We have 2 Red Hat servers that are dedicated for customer speedtest. They both use 10Gb fiber connections and sit on 10Gb links. All network gear in between these servers fully support 10Gb/s. Using ...
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 ...
1
vote
0answers
20 views

Measure goodput before sending a response

My idea is to make it possible for web applications working on slower connections to fallback on alternative smaller asset versions(like images, videos, etc.). HTTP Live Streaming has similar behavior ...
33
votes
5answers
54k views

How passively monitor for tcp packet loss? (Linux)

How can I passively monitor the packet loss on TCP connections to/from my machine? Basically, I'd like a tool that sits in the background and watches TCP ack/nak/re-transmits to generate a report on ...