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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Using proxy server to redirect MySQL traffic to multiple servers using standard port?

Is it possible to redirect MySQL (tcp) traffic to multiple servers based on domain name alone? Our DNS is setup to point several sub-domain aliases to one proxy machine. (running haproxy and ...
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1answer
106 views

TCP syn cookie calculation on Windows Server

Windows Server uses uses TCP syn cookies to protect itself from syn-flooding attacks. Is it known, how the operating system (Windows Server 2008 R2 and Windows Server 2012) calculates the syn cookie? ...
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0answers
360 views

Should I set rto_min for a route inside data center?

We have a few dedicated server rented in a data center with debian 7, kernel 3.2. We use one of those servers as a database server. The network between our application server and database server is ...
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0answers
790 views

How to stop NAT dropping idle connections?

I have a TCP connection that can be idle for many hours. The traffic is flowing from the server to the client only. One might say it's kind of push notification. My home router, however, tends to ...
4
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1answer
117 views

Change TCP wait for ACK timeouts in Win7/WinServer

Is there any possibility to change default wait for ACK timeout in TCP network on Windows 7 or Windows Server ? I'm using very slow network ( 1200 bps ) and want to tweak TCP. When using default ...
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1answer
641 views

How do routers combine WAN and LAN traffic (packet data over wifi and ethernet)? [closed]

In my office, we have a leased line connection which is shared by some 20 users over wi-fi. This causes congestion on the router's end, resulting in slow speed due to high packet drops (and consequent ...
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2answers
428 views

DHCP serving has stopped working

Something happened in our server room over the weekend that had me in the office late Saturday night replacing two switches. After powering down both racks, I have an issue where none of the computers ...
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1answer
302 views

TCP packets larger than 4 KB don't get a reply from Linux

I'm running Linux 3.2.51 in a virtual machine (192.168.33.15). I'm sending Ethernet frames to it. I'm writing custom software trying to emulate a TCP peer, the other peer is Linux running in the ...
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6answers
1k views

Is it possible to redirect/bounce TCP traffic to an external destination, based on rules?

I'm not even sure if this is possible... Also, please forgive my ignorance on the subject. What I'm looking for is for "something" that would allow me to redirect all TCP traffic arriving to host A ...
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1answer
295 views

Bind9 as a caching resolver fails with mismatch ID on localhost but not external IP

I'm running Ubuntu 12.04 LTS on a machine on my private network. I have bind9 installed (v9.8.1-P1) via aptitude, so it appears to have put all the bits in the right places and the service starts ...
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2answers
9k views

How to troubleshoot connectivity when curl gets an *empty response*

I want to know how to proceed in troubleshooting why a curl request to a webserver doesn't work. I'm not looking for help that would be dependent upon my environment, I just want to know how to ...
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1answer
334 views

TCP DOS: How to terminate CLOSE_WAIT connections? [closed]

One of my servers is getting DOS'ed - there are a large number of connections in the CLOSE_WAIT state which are preventing legitimate users from connecting to the system. So is there any way to close ...
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1answer
231 views

SSL Connect timing out during handshake (client exchange re-transmission)

We have a Java LDAP client making SSL connection to AD. Some times the connect hangs with client and server re-transmitting Client Key Exchange and ACK packets continuously as shown below and ...
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2answers
93 views

How to map an ephemeral port to a pid?

I have a RHEL server with several apps on it and I am attempting to figure out which one of them is making calls to an external web service. I have TCP dumps that show the calls being made and through ...
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0answers
253 views

SSH attempt keeps failing, syn+ack does not reach machine

1 0.000000 10.0.0.1 10.1.1.0 TCP 66 49285 > ssh [SYN] Seq=0 Win=8192 Len=0 MSS=1260 WS=256 SACK_PERM=1 2 0.001160 10.1.1.0 10.0.0.1 TCP 66 ssh > 49285 [SYN, ACK] Seq=0 ...
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1answer
104 views

MongoDB cloneCollection between Azure hosted CentOS servers times out at 2 hours

I'm trying to clone a MongoDB collection from CentOS server A to CentOS server B. Both are running 2.4.6. The copy works great until exaxctly 2 hours, at which point I get a 9001 socket exception: ...
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1answer
933 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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2answers
1k views

NAT Gateway - Maximum connection limit

I know just enough networking to be dangerous. The nitty gritty low level details of NAT are not something I am particularly knowledgeable about. I accidentally found myself in a discussion earlier ...
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1answer
716 views

Linux - TCP Source Port Reuse (and delay)

We have an application making a lot of calls to a remote web server/service. Client app is JBoss/Java on Linux (Red Hat 5), remote server is Windows 2008. There is a Cisco ACE in the way but there ...
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0answers
384 views

TCP connections in FIN-WAIT-2 state on linux not timing out according to tcp_fin_timeout

We run a service with lots of embedded devices in the field, their tcp stack is a bit buggy and sometimes does not close connections properly, resulting in some connections being stuck in FIN-WAIT-2 ...
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1answer
63 views

No ssh connection to vServer possible; numtcpsock value is 1,024

my virtual server is used as a mailserver (with Zimbra 7.2.0_GA_2669) and webserver. Yesterday the Zimbra web interface was not accessible anymore, though all services were running. Since two hours, ...
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3answers
155 views

Tunneling ports through different routes without the knowing of the local programs

I need to set up the following scheme: server1: Generic program connects locally to proxy, which then connects to proxy to server2. Everything is ok, until the connection between the servers. ...
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2answers
1k views

How to globally limit total number of TCP connections with iptables?

I'm having quite a difficult time figuring out how to REJECT both inbound and outbound connections from a machine with iptables once the total number of TCP connections hits a global maximum without ...
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1answer
4k views

Unexpectedly shrunk window

I run a major media upload/download site and I noticed these: Is this serious or background noise due to the big file sizes and is there any tweaks I can add to /etc/sysctl.conf to improve and ...
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1answer
110 views

three-way handshake & sequence number

Looking at the image below, taken from the book of Ilya Grigorik - High Performance Browser Networking, I can understand that the SYN packet picks a random sequence number which is incremented in SYN ...
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1answer
364 views

Reasons for a TCP Timeout scenario

I am actually currently investigating long running connections of a Java/Tomcat based Web application. After ruling out any internal or application based reasons, I am now down to the network layer. ...
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1answer
580 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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0answers
664 views

Window Size goes to zero

We are seeing an issue with our web servers where a client is doing a HTTP POST and sending xml files. We are seeing weird behavior where we are sometimes only receiving part of the data. (Sometimes ...
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1answer
112 views

Is their an official tool to tweak Windows 2008 server TCP configurations?

We are running scripts that initiates numerous TCP connections and disconnects right away. It's just to test if the remote report is opened and responsive. But we are having random strange issues ...
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1answer
142 views

TCP packet filter based on TCP sequence

I need to build a test environment with a very precise packet loss based on specific TCP sequence or, optionally, on payload content. I couldn't figure out how to do it with tc or iptables. What tool ...
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0answers
368 views

Blocking a TCP Syn Attack

I have recently experienced a TCP Syn attack and since it was from a software like LOIC, it kept happening until I banned the IP Addresses or stopped my system from making output to them. Here is what ...
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5answers
3k views

Can TCP and UDP packets be split into pieces?

Can TCP packets arrive to receiver by pieces? For example, if I send 20 bytes using TCP protocol, can I be 100% sure that I will receive exactly 20 bytes at once, not 10 bytes then another 10 bytes ...
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0answers
193 views

snmp MIB-TCP::tcp not showing any usage

I am trying to configure MRTG on all of my servers for making a network weathermap, this requires running SNMP which MRTG gets the information from. So, I installed it on two servers the exact same ...
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3answers
1k views

How do high traffic sites service more than 65535 TCP connections?

If there is a limit on the number of ports one machine can have and a socket can only bind to an unused port number, how do servers experiencing extremely high amounts (more than the max port number) ...
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2answers
982 views

Test a server using MTR through TCP

Is it possible to use MTR over TCP? If not is there an alternative? I have done some research and I am not finding any way to do such a thing, so I'm wondering if anyone has had any experience with ...
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0answers
39 views

Apache process 100% with IPV4 TCP 10u

Today i got strange http ussage. All apache processes woks ok but after some time i found few processes stocked at 100% and they are like that long time. After i checked that process id at webmin ...
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2answers
243 views

Unable to POST/Upload files to a PHP page

I have a weird problem when I try to post contents or upload files by php to my server. After submitting the form it sleeps for a while then shows a page loading error. I tried different contents and ...
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1answer
117 views

Is there a Windows utility to create a TCP server to server link?

I two systems that I need to connect, but both act as servers. The first is a scale controller that does not have the ability to open a connection before sending a weight. It will send weights if a ...
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1answer
197 views

VMware - Host two VPS with same IP

I have: 1 Dedicated server, Windows server 2008. 2 Virtual machines inside the server. (VMware, Windows too) 1 example IP address: (0.0.0.1) 1 example IP address: (0.0.0.2) I need: 1 Dedicated ...
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0answers
58 views

Linux + OpenVPN + SNAT + Failure on client grab the reply to it's own generated traffic

Ok, I'm really desesperate I need to release an openvpn deploy to get rid of a dying server. On the subject: I installed OpenVPN with a routed interface (tun0) into a server with a public IP + 3 ...
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1answer
76 views

Fixed TCP payload Size [closed]

I have an aplication that need to have a fixed (516 byes) payload size in the TCP packet. The application itself can't be modified to adjust it settings, therefore i need to tune the TCP Buffer Size ...
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0answers
131 views

Strange dropped packets coming from port 8888 and with ACK or ACK+PSH set

Background During an incident on a small privative network (1 router/FW + 1 server) my server got accidentally exposed to the internet. Fortunately it was protected by it's own UFW to allow only 1 ...
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1answer
22 views

Information about SYN [closed]

I'm new to socket programming and i read that SYN packet can be created through a raw socket .But windows api doesn't allow the creation of a raw socket .I know that ICMP packet doesn't have any port ...
2
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1answer
545 views

How to edit TCP window size from iptables?

There is TCPMSS target to edit MSS value of connections (including forwarded). How to edit window size (for example, cap to some maximum value) by iptables rule? Expecting something like iptables ...
2
votes
1answer
2k views

How to capture retransmitted packet info with tcpdump?

TCP retransmission rate on a host are often a good indicator of network problems. How do I find out the source and destination IPs for the packets that are being retransmitted? For context, on hosts ...
3
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3answers
2k views

How to prevent TCP ZeroWindow on writing a large file to a Windows share?

I've been given access to a share on a Windows Server 2003 SP1 system (10.a.bbb.ccc) which is a file and printer server, and regularly large files get copied to that share. However, occasionally such ...
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1answer
4k views

Too many TCP connections causes disconnections

I have a game server which runs with TCP connections. Server disconnects users randomly. I think its related with TCP settings of server. In local development environment written code can handle ...
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3answers
13k views

Excessive 'TCP Dup ACK' & 'TCP Fast Retransmission' causing issues on network. What's causing this?

I'm getting excessive TCP Dup ACK and TCP Fast Retransmission on our network when I transfer files over the MetroEthernet link. The two sites are connected by one sonicwall router, so the sites are ...
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1answer
3k views

What is msrpc needed for on a Windows 7 workstation

I just ran an nmap scan against our network, and many Windows 7 machines have several high ports listening with Microsoft Windows RPC. Example: Port Serv Process name 49152, msrpc [wininit.exe] ...
3
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1answer
1k views

Is ECN (Explicit Congestion Notification) turned on by default on Windows Server 2012?

In a company network I noticed that all examined Windows Server 2012 machines had ECN turned on: > netsh interface tcp show global TCP Global Parameters ...