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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1answer
45 views

TCP connection; ACK not received

I am having trouble sending mail from Linux to Exchange server. When I telnet from Linux to Windows on port 25, I am not receiving any message from Exchange. The connection is automatically terminated ...
0
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0answers
9 views

Kamailio CPU usage very high and not accepting new registrations

I am facing a very strange issue with Kamailio, our Azure VM is D2 configuration with 2 cores and 7 GB of RAM, Ubuntu 14.04 LTS, through-out the day we see high CPU usage from Kamailio, and ...
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0answers
5 views

Troubleshooting for TCP exchange between an embedded Linux dist (OpenWRT) and a Fedora dist on a computer

I am facing an issue I did not succeed to solve. I have a device (Arduino Yun) using the OpenWRT distribution, on which I run a nodeJS machine to execute some function, and especially to send tcp ...
1
vote
1answer
3k views

option http-server-close on HAProxy haproxy-1.5-dev19 will result in Connection: close header sent in response

I basically have the following issue: whenever I add option http-server-close to the haproxy config (either in frontend or backend section), haproxy will send a Connection: close header in the ...
4
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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 ...
0
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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 ...
0
votes
1answer
19 views

rsyslog server listen only on tcp 514

I'm trying to set rsyslog client- server to listen to tcp messages with port other then 514, however it doesn't work. Only when using 514 it receives messages. I'm using EC2 vms. input(type="imtcp" ...
11
votes
1answer
577 views

Under HTTP2, how often are new TCP connections initiated?

I understand that HTTP2 aims to keep everything under a single TCP connection, and I was wondering how often TCP connections would be torn down. For example, if I visit youtube, do some browsing, ...
1
vote
2answers
279 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: ...
0
votes
1answer
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, ...
4
votes
4answers
1k 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 ...
0
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0answers
8 views

ss vs iftop. send XMbps doesn't match

I'm troubleshooting a cross data center network issue, and I found this mismatched. In most case, the data is send from A to B, the port on B is 38790. @Host A [root@**** zhifan]# watch "ss -ati ...
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0answers
9 views

TCP ACK delay by app / windows on VirtualBox Windows VM

I have a .NET windows service that uses an open source library (Asterisk.net - C#) to listen to TCP connections on a specific port. This service is deployed on a number of VM instances of Windows 7 ...
6
votes
1answer
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) ...
3
votes
1answer
1k views

How to force use of tcp instead of udp for rpcbind?

I'm trying to use tcp/111 for rpcbind under Debian Wheezy instead of udp/111. The portmap in Squeeze uses tcp/111 without any special configuration, but Wheezy fails. Even numerous sites (as well as ...
0
votes
1answer
43 views

Server send TCP ACK with wrong number after receiving SYN

I have a client establish new TCP connection then sends request to a server per second. Both client and server are on the same linux box (via loopback interface). The client periodically reports ...
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 ...
2
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2answers
248 views

Automatic TCP connection slowering (shaping)

I'd like to automatically shape bandwidth-hungry TCP connections corresponding to the already transmitted data. A summary would be : "The first Mbit is transferred at full bandwidth, then it ...
0
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0answers
16 views

Why my firewall rules aren't working in my NanoStation m2?

I have two NanoStation m2 as AP and Repeater for a wireless network (make them device1 and device2), both working in BRIDGE mode. Both devices are connected as WDS pairs to each other because they ...
0
votes
1answer
19 views

kill tcp port binding by deleting proc/[0-9]/net/… in linux

I have a script to call syscall Kill the process that holds a certain TCP port in Linux (ubuntu). But even if I do that, sometimes the port still remains in /proc/[0-9]/net directory binding the port. ...
-1
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0answers
25 views

How to enable port forwarding to get some TCP services

As image showing the scenario, I need a suggestion to get (http/https/pop3/smtp) access for the network(192.168.0.9) through the internet/Email server(192.168.0.123) placed on the other side of my ...
4
votes
2answers
1k 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 ...
42
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8answers
15k 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 ...
1
vote
1answer
54 views

RST ACK with Reset cause

We have a device that connects over Wired LAN (Ethernet) to our cloud servers. At certain customer locations, when the device tries to send data, we are getting RST ACK from the customer server to ...
2
votes
1answer
1k views

Does hole punching require a UDP rendezvous server Or could it be a TCP one?

I'm trying to get my head wrap around this issue... I would like to connect two users... Those users are already connected to a TCP server, which is aware of both public ip and connection TCP port. ...
11
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4answers
412 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 ...
-1
votes
1answer
71 views

What are the ports needed for L2TP VPN on Mac OS X Server 5.0.15?

I'm configuring a Mac as a server with a VPN service. So, I opened the ports listed as used by VPN in Apple documentation: UDP 500 -> 500 (+ESP and AH) UDP 4500 -> 4500 Any UDP -> 1701 (I got to ...
3
votes
2answers
608 views

TCP Messages Merged?

I have an application that sends 100 of 186-byte (excluding headers) TCP messages back to back without gap from host A to host B. I ran tcpdump to capture the packets on host A (where the sender is), ...
0
votes
1answer
42 views

Linux: How to configure TCP wrappers in /etc/hosts.allow for manually started processes?

An internal server in the company I work for has been compromised and I would like to harden CentOS machines in the organization in order to avoid any future incidents so I've been reading about ...
0
votes
0answers
31 views

Determine which equipment is causing packet loss

I'm connecting from my office to two servers (server 'A' and server 'B') hosted by two different providers. Since a few days, my connection speed to server 'A' has dramaticaly slowed down. Even when ...
0
votes
0answers
24 views

nginx monitoring failed to load status page under load

Nginx monitoring script so-called ztc failing to load nginx test page (mostly under highest load to nginx about 2000 rps, which used as proxy), causing errors like "nginx is down" on zabbix, and, in a ...
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2answers
877 views

How to learn the current tcp flavor in Fedora/Ubuntu?

How do I know which tcp flavor is used in Fedora/Ubuntu?
0
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0answers
12 views

socat Resource temporarily unavailable

I am using socat as a bridge between some devices and running socat (a couple hundreds of instances) like this: socat -d -d -d -x -d -lf "/var/log/some_log_file" ...
3
votes
1answer
306 views

ICMP Redirect Theory VS. Application

I'm trying to watch ICMP redirects in a lab using Cisco Packet Tracer (version 5.3.2) and I'm not seeing them, which leads me to believe that either my lab configuration isn't correct or my ...
1
vote
2answers
250 views

is it normal for NGINX to accumulate connections in writing state?

This is a graph showing connection count from nginx's stab_status, the drops in graph are server restarts done manually. I find this behaviour strange, looks like some leakage. I think there are ...
0
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0answers
22 views

How does TCP PSH and HTTPS works?

Right now I monitor traffic on my VPN server. I'm using tcpdump for it and it works pretty good. sudo tcpdump -n host SENDER_IP In this example you can see one HTTPS request from SENDER_IP to ...
0
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0answers
108 views

Why would Windows Server 2012 not respond on ports above 6000?

This is a new question but similar to this previous one. I've inherited the management of a Windows 2012 Server (not R2) and I'm unable to get a response from any ports above 6000. I have services ...
2
votes
2answers
652 views

Server 2012: SYN, no ACKs, on TCP ports higher than 6000

Seems ridiculous to read it back out loud, but I'm at a loss here. Server 2012 Standard. Runs a daemon for an accounting package on TCP 12502; at some point, the server stopped accepting connections ...
1
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0answers
36 views

Server socket sitting in FIN_WAIT_1 whilst network doesn't see its traffic

We've been trying to get a grip on a really weird problem where we can wget a page from Apache 2.2.19 on solaris 10 and some permutations of requests reliably take various fixed lengths of time to ...
3
votes
0answers
31 views

TCP buffer sizes and ethernet bonding

(This question was originally posted on stack overflow; Andy told me that I could get faster help here, so it is re-posted here now.) I am experimenting with TCP buffer size tuning on Linux, but ...
8
votes
2answers
3k views

More than 65536 TCP connections on Linux

I'm stuck trying to setup more than 65536 outgoing TCP connections from a Linux (RedHat5) box. I have already configured both outgoing and accepting boxes to allow enough file descriptors. I don't ...
2
votes
0answers
74 views

How to change tcp's window size?

I've tried changing the tcp's window size by modifying net.ipv4.tcp_wmem and net.ipv4.tcp_rmem values, however the changes which I make have no effect on actual window size which I can check using a ...
1
vote
1answer
31 views

Why does data sit in Send-Q? TCP sessions freezing

Issue I run an IRC server for 20-50 users. We sometimes have issues with messages not arriving in a timely fashion or at all. After some packet captures we determined that messages sit in the ...
0
votes
1answer
25 views

Reduce TCP send buffer

I have a windows 2008 R2 server, an app is constantly polling another server (using a Flash Socket) while waiting for a certain event to occur on that server. We are talking about milliseconds. When ...
0
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0answers
28 views

Too Many TIME_WAIT Connections [duplicate]

We have issue that our application sometime can not connect to DB server which is a separate server. The application server and DB server communicate locally. So I search and found out that we have ...
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votes
2answers
47 views

Does UDP includes of source address?

Both UDP and TCP does not include source address, but how does it say UDP IP spoofing is easier than TCP? For example, the following webpage also says about UDP vulnerability. "Unlike TCP, UDP does ...
0
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0answers
48 views

TCP RST/ACK packets not being sent back to NAT client with Forefront TMG

With Forefront TMG, we have an issue where all TCP connections to allowed ports work just fine when the connection is accepted with SYN/ACK, but when they are rejected with RST/ACK, the response does ...
4
votes
1answer
448 views

Why are connections in FIN_WAIT2 state not closed by the Linux kernel?

I have an issue in a long-lived process called kube-proxy being part of Kubernetes. The problem is that from time to time a connection is left in FIN_WAIT2 state. $ sudo netstat -tpn | grep ...
0
votes
1answer
55 views

TCP connection not established: Can't Connect to MySQL Server on Remote Connection (10060)

I'm running MySQL 5.6 on a WinServer 2012 system. It works great. The server is on our office intranet, not accessible to the outside world. I normally administer MySQL remotely from my office on my ...
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0answers
12 views

Iperf Tcp Client and Server

I'd really like to know why the bandwith in the client is higher than the server, i can´t find the answer explaining why this happens. Thank you, Tiago Melancia Values of the bandwidth: Client ...