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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195 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 ...
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1answer
154 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 ...
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0answers
604 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 ...
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4answers
2k 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 ...
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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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1answer
124 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 ...
4
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1answer
548 views

Common back pressure strategies for services under sustained high load

I'm wondering what are the common backpressure strategies people use for their web services? Imagine your service operates under heavy load, and at some point the load reaches 120% of your capacity. ...
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0answers
167 views

Azure intermittent outbound connection failure to EC2 [closed]

I have three Linux VMs (Ubuntu 14.04) running in a vnet, like this: Host Internal IP External IP prod1 10.0.1.1 104.45.234.56 <---\__ load balanced prod2 10....
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1answer
467 views

Forwarding ports and traffic to VPN tunnel

I've installed OpenVPN on my VPS. I have one question: how to forward traffic going to that VPS to go to VPN tunnel created with my local PC. I will use TCP connection. The whole traffic will be like ...
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3answers
688 views

How can one redirect to a new host all traffic destined for an old host?

We're moving a bunch of services, say from 1.2.3.4 to 5.6.7.8. In order to test that the new services are correctly configured, we'd like to redirect (to the new host) all traffic destined for the ...
2
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0answers
149 views

Why is SQL Server using all ephemeral ports connecting to itself and causing TIME_WAITs?

I've got an AWS server with Windows 2008 R2, SQL Server 2012, and Tomcat 7. When I run netstat -ano the screen is flooded with TIME_WAIT. I posted the output in a Gist. When I run CurrPorts, filter ...
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1answer
95 views

How to artificially open many tcp connection on a host (testing)? [closed]

I'm trying to build a test setup which test my server's performance under high load. In order to do that I want to open thousands of tcp connection. The problem is that I only have two hosts, one is ...
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1answer
611 views

IIS listening 127.0.0.1 instead 0.0.0.0

I configure binding on my IIS 7 server like: ip address: All Unassigned port: 8080 but in netstat -aon command see only 127.0.0.1:8080 instead 0.0.0.0:8080(which I would like) (0.0.0.0:8080 is ...
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0answers
167 views

After sending Duplicate ack by the server, it stop responding [closed]

My TCP client communicates with multiple 3rd TCP servers. However one particular server produces duplicate ack and stop responding in the specific time only. That particular server is OK other time. I ...
6
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2answers
267 views

TCP acks are paused, then resumed, then paused again. Why?

I would like some help finding the reason for the reduced data transfer rate in my application. I have 12 embedded systems and a Linux server. The embedded systems send data to the server over TCP on ...
1
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2answers
387 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 ...
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1answer
58 views

TCP ACK Window shrinking

(Note: I am not a networking engineer) We are sending files to an outside vendor and getting random timeouts on different services. It seems that we are getting timeouts most often on larger files. We ...
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1answer
611 views

what could cause a not so busy redis server to close connection?

We have 17k tcp connection in CLOSING state on redis server. My understanding is that only client would initiate closing a connection, not from a redis server. So I should see 0 connection in CLOSING ...
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0answers
76 views

TCP connections drop off after initial build up

A bizarre problem on a production setup. Scenario 1) A server listens on a particular port. 2) There are potentially thousands of TCP connection requests. 3) About 200-300 TCP connections reach ...
2
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1answer
2k views

Windows Server 2012, application needs administrative access to open port

How can I grant an application access to listen on one particular port, without running it as Administrator or disabling UAC? Per policy, had to transition from an old server (Windows Server 2003) to ...
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0answers
25 views

How do I cap each individual tcp stream, to a fixed maximum rate?

I've read but not in depth all the various traffic shaping docs and seen the long question on HSFC scheduling Does anyone really understand how HFSC scheduling in Linux/BSD works? looked at the ...
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1answer
152 views

A LOT of connections from my external IP address to my web server

I installed Nagios recently on a Debian machine running an Apache web server among other things. The thing is that lately, Nagios tells me that the HTTP service is failing intermittently and it seems ...
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0answers
278 views

TCP High Send-q coupled with FIN_WAIT1 status

I'm having a problem with one of my webservers, which is taking minutes to completely render a web page. I had a look at the TCP connection and noticed that I have a very high value in the send-q ...
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4answers
7k views

Is there a way to see what is actually filtering TCP port communication?

nmap -p 7000-7020 10.1.1.1 Will output all the filtered ports Starting Nmap 6.40 ( http://nmap.org ) at 2015-03-04 12:18 EET Nmap scan report for 10.1.1.1 Host is up (0.00091s latency). PORT ...
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1answer
424 views

How do I open specific ports on Linux (an AWS instance of RHEL v. 7)?

I'm using RedHat version 7. My AWS instances are in a security group with ample permissions for inbound connectivity. I can do Yum updates. The servers can ping each other. I can transfer files ...
2
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1answer
161 views

How to filter for the most common problems with tcpdump/tshark

I am currently using the following command in Linux to get specifics on network problems. tshark -r file.pcap -q -z io,stat,1,\ "COUNT(tcp.analysis.retransmission) tcp.analysis.retransmission",\ "...
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1answer
43 views

Windows Server 2008 sending regular TCP DNS requests to Forwarders

Our organization's primary DNS server is a Windows Server 2008 which two Forwarders set. I happened to notice on our firewall that this server is sending out regular TCP requests to the Forwarders in ...
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2answers
558 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
183 views

length of Tcp segment exceed MSS

I find a weird behavior in my Linux system, when I curling a web page, the received TCP segments are significant larger THAN the MSS. here is the output of tcpdump: 00:00:00.000000 IP 10.15.71.190....
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0answers
732 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==>>...
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0answers
383 views

Cisco ASA firewall blocking requests to internally hosted DNS server

I have a DNS server behind a Cisco ASA firewall. The Cisco firewall is performing NAT. When inside the network, I can NSLOOKUP directly to the server. When the client is external, requests time out. ...
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1answer
413 views

how to determine client side or server side retransmission from a pcap

I am trying to get some clarification on something I read here: how to calculate packet loss from a binary TCPDUMP file The first answer says that the sequence number will be the same from client to ...
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1answer
380 views

server is not responding on SYN packets

On the attached tcp dump, the first two SYN packets (#21800 and 21801) came to the server, however SYN ACK was sent for the second SYN. Is that correct behaviour? My understanding is that the client ...
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1answer
165 views

How to redirect all incoming packets to sniffer in Linux using iptables?

I need to redirect all incoming tcp packets from eth0 to current host (change ip address from 1.1.1.1 to 1.1.1.2) and outgoing tcp packets from sniffer from eth1 to another host(from 2.2.2.2 to 2.2.2....
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3answers
251 views

how to use tcpdump to log only certain data in real time

I'd like to monitor network interfaces but only log things likes errors, collisions and dropped packets. The send that to stdout. – Can tcpdump be configured to do this?
3
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0answers
110 views

Linux - Outgoing connections from process timeout after the process restarts

banging my head against the wall with this one... I have an Ubuntu Linux server, on top of which our own process which holds 40K persistent connections to external services. When the process starts,...
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1answer
400 views

Concurrent TCP connections on Azure can be upto 500K. Really?

Let me be very clear at the outset that I am new to cloud technology. All I know is cloud servers are easily scalable (i.e. adding physical hardware is transparent to applications and users) and ...
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1answer
759 views

Linux clients can't connect, server and TCP Windows Size / Timestamps issue

We have a problem that a number of clients (all linux Ubuntu) are sometimes not able to connect to a remote server over SSH. If the problem occurs, Windows clients don't have that problem and can ...
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34 views

Split TCP packet - Data layer vs IPv4Layer

What is the different between split TCP packet in the Data layer compare to split the packet in IPv4Layer ?
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1answer
1k views

NetTcpPortSharing process won't start on Windows Server 2012 R2

I have a problem in Windows Server 2012 R2 : I have searched and try everything I know to fix this, but I cannot start NetTcpPortSharing service and therefore I cannot configure Windows Server ...
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0answers
1k views

HAProxy resetting backend connections

I'm in the process of setting up a series of servers as proxies to our application server, primarily to obscure the application server's IP as part of a suite of anti-DDOS measures. My goal is to ...
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1answer
286 views

TCP: out of memory - Nginx

I'm running a high traffic site on a nginx server. Last fews days I'm having problems with my VPS locking up (unable to SSH, and nginx seems to be down). When I look in the logs I can see the ...
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1answer
689 views

TCP packet loss against SQL-server

Where I work, we have had some issues with connections to the database. We get a lot of failures which appear as "recv failed" on the client side. I have used Wireshark to try to debug the problem and ...
1
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1answer
312 views

PHP-FPM TCP connections not terminating in time

I'm serving Wordpress pages via nginx/PHP5-FPM using APC caching (through the W3 Total Cache plugin). Nginx communicates with PHP-FPM via TCP sockets on port 9000. I've adjusted the number of max ...
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0answers
97 views

Bad ping results while testing 6000 TCP clients with 18 mbytes/s total traffic on Windows Web Server 2008

The clients are running on the machine #1. The server is installed on the machine #2. The machines have a gigabit connection through a switch on their private vlan. There are no errors in the switch ...
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1answer
92 views

SNORT only alerting on inbound traffic

I am trying to raise an alert when someone is setting up a connection to PORT 25 (tcp), whatever source or destination. For this i came up with this simple rule: alert tcp any any -> any 25 (msg:"...
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2answers
70 views

Get a website's host machine's OS/server software without access to the server

Is there a good methodology to find the operating system and server software that is being used on a served website that you don't have SSH access to? What I'm doing right now is looking at TCP/IP ...
2
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1answer
444 views

TCP Upload Speeds Slow to the Internet over LFN

I've got two Linux VMs separated by a 50 mbps WAN connection. There is about 70ms of RTT on this WAN link, so it's got some latency. I've been testing my upload throughput to the Internet from each of ...
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1answer
372 views

Hitting Ephemeral TCP Port Exhaustion

We run a high traffic website. Over the past few days, we've had several customers complain of sporadic downtime that we cannot reproduce. We have several web servers elected to receive traffic from ...
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0answers
210 views

Ghost tcp connections: ss sees them, nothing else does

We have a strange problem. Our remote server shows over 900 connections coming from our office over port 80: # ss -n | grep ESTAB | grep $OFFICEIP | grep :80 | wc -l 935 Netstat shows a similar ...