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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4
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2answers
169 views

Optimizing OS for HTTP requests

We make a lot of HTTP requests. Recently, we've started thinking about optimizations at the OS level to make more requests from a single machine. In order to check the performance of our OS, I've ...
3
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2answers
275 views

once in a while windows / .net application ignores the tcp fin flag

i've run into a network problem which i cannot solve. on a few computers running windows 8.1 and communicating with linux http server tcp connections dangle on the windows side instead of being ...
0
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2answers
297 views

VMWare NAT releasing SYN packets from guest but not admitting SYN/ACK packets to guest

VMWare Server 2.0.2 Host OS is Windows Server 2008 R2 Standard Guest OS is Windows XP I am using VMWare VMNet8, the NAT network. The VM guests can't see out to the network around the VM host. Packet ...
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0answers
154 views

How can i detect and diagnose local network problems on a multi-server environment?

I'm a software engineer who trying to detect (and solve if possible) weird local networking problems since 2 weeks on multi-server hosting environment. We bought 3 dedicated boxes with 32GB ram 8 ...
2
votes
1answer
113 views

How do you change tcp_congestion_control on OpenVZ?

I have a network of OpenVZ machines that I am testing various congestion control methods on. I need to know how to change the congestion control. Currently I get nothing but permission denied. Is it ...
-1
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1answer
680 views

How to enable/disable TCP DELAYED ACK parameter on SUSE linux?

I want to disable TCP DELAYED ACK parameter on SUSE Linux Enterprise Server for some performance tuning operations. I have used sysctl command but it does not list this parameter. also in SUSE ...
1
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1answer
60 views

routed network, subnetwork clients has broken tcp connection

I manage a linux server which works also as a router, and route between following networks: PPPoE (to connect to ISP) (default gw) wired network 2x VPN networks (PPTP and openVPN) wireless AP (DHCP) ...
0
votes
1answer
60 views

Routing between two PC

I have two computers connected by wire directly: PC-1 ============= PC-2 PC-1 configuration: IP Address: 192.168.1.1 netmask: 255.255.255.0 PC-2 configuration: IP Address: 192.168.1.2 ...
0
votes
1answer
216 views

Oracle 11g TNSLSNR LAST_ACK connection flooding

We have Windows 2k3 EE SP2 with Oracle 11.2.0.1.0 DB installed. The DB is used by different applications (including web-apps and services). From time to time, we have some problems with the web ...
0
votes
1answer
2k views

TCP port numbers reused and TCP Retransmission

Facing issues due to TCP Port Reuse and Retransmission for HTTP traffic. My deployment is as follows: enter image description here I have a squid proxy installed on a unix machine which is sending ...
0
votes
1answer
85 views

What packet to ignore to not have ssh terminated on brief connectivity loss?

It seems like sometimes there are some connectivity problems around the edge of our network to certain other networks, and my ssh sessions with some remote servers, which themselves have no ...
3
votes
1answer
580 views

Troubleshoot Broken TCP From OpenVPN Client To Server; But ping, traceroute Work

I'm troubleshooting an OpenVPN Server setup on OS X Mavericks. Prior to the 10.9 upgrade, this all worked, and I'm trying to isolate the problem to something fundamental or my server/client setup. ...
2
votes
1answer
7k views

Root cause of “curl: (56) SSL read: errno -5961” errors

I was evaluating some SSL failures, and noticed that when I use curl to one of the failing sites, I got curl: (56) SSL read: errno -5961; however, my google queries for that error didn't show the ...
0
votes
0answers
249 views

How to forward UDP and TCP traffic from one IP to another

I have a server with two LAN cards installed. I have one server in U.S and one in India. I have created a GRE tunnel to route all traffic from the U.S Server to my Indian Server. My traffic has ...
0
votes
1answer
164 views

Several Server Errors (No database connect, can't create TCP/IP socket etc

My server stops taking requests on my website today. It works for some time, but then the server just stops working and throws several errors: 500 Internal Server Error Warning: mysql_connect(): ...
2
votes
1answer
251 views

How to configure tcp wrapper

I have a server with ip-address 192.168.0.1 and a client with ip-address 192.168.0.2 both of them are able to connect with each other. Now the problem is I have configured TCP Wrapper on my server ...
1
vote
1answer
140 views

Prevent Linux from processing incoming ICMP Host unreachable packets

I have a test setup with one host on a network (10.1.0.0/16) talking via TCP to another one on another network (10.2.0.0/16) and a gateway in the middle. Sometimes, the TCP connection is lost and ...
0
votes
1answer
512 views

Random TCP Resets

We got randomly TCP "reset" error when we send request to remote server. Log from remote server Cisco TCP Connection Terminated,Nov 05 14:43:39 EST: %ASA-session-6-302014: Teardown TCP connection ...
2
votes
1answer
60 views

Request to server x Reply from server y

I need some advice from you guys: I'm dealing with a custom loadbalancer/software for which we will use 2 main servers and about 8 slave servers. In short: User sends request to main server, main ...
1
vote
2answers
352 views

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 ...
1
vote
1answer
119 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? ...
2
votes
0answers
391 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 ...
1
vote
0answers
915 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
votes
1answer
123 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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votes
1answer
686 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 ...
1
vote
2answers
488 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 ...
0
votes
1answer
316 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 ...
0
votes
7answers
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 ...
0
votes
1answer
327 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 ...
2
votes
2answers
10k 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 ...
-1
votes
1answer
352 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 ...
1
vote
1answer
238 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 ...
1
vote
2answers
95 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 ...
0
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0answers
266 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 ...
1
vote
1answer
105 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: ...
2
votes
1answer
1k 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
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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 ...
3
votes
1answer
803 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 ...
1
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0answers
407 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 ...
0
votes
1answer
64 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, ...
0
votes
3answers
172 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. ...
1
vote
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 ...
4
votes
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 ...
3
votes
1answer
111 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 ...
1
vote
1answer
414 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. ...
1
vote
1answer
653 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 ...
0
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0answers
731 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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votes
1answer
116 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 ...
0
votes
1answer
158 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 ...
0
votes
0answers
394 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 ...