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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cannot send emails to other Web servers

I'm trying to limit my server's open ports in CSF. The IPv4 port settings include: # Allow incoming TCP ports TCP_IN = "22,25,53,80,110,143,443,587,3654,53343” # Allow outgoing TCP ports TCP_OUT = ...
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1answer
160 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 ...
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1answer
996 views

Linux iptables - reject tcp SYN with RST

I am doing an implementation on a linux machine to reject incoming telnet requests from wan side telnet port 8023. The functionality is achieved by using the below iptables rules. The first rule in ...
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7answers
92k views

How to forcibly close a socket in TIME_WAIT?

I run a particular program on linux which sometimes crashes. If you open it quickly after that, it listens on socket 49201 instead of 49200 as it did the first time. netstat reveals that 49200 is in ...
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0answers
48 views

periodic connection timeouts to nginx server

We have the following setup: One nginx server as a loadbalancer in front of four worker application servers. The nginx server get about 100 requests per second, sometimes more that that, active ...
3
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1answer
135 views

Is net.ipv4.vs.timeout_timewait used also for IPv6?

Does this setting for TCP net.ipv4.vs.timeout_timewait apply only to TCP connections established over IPv4 or does it also apply to TCP connections established over IPv6? I have found this for ...
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0answers
34 views

Want to route NFS response via an interface. What will the source ip of the packets being sent out?

The NFS server is listening on an interface for a new connection, once a new TCP connection is established the NFS operation is carried out. I'd like to send this NFS response via a different ...
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0answers
139 views

Proxy / Squid 2.7 / Debian Wheezy 6.7 / lots of TCP Timed-out

I'm facing a lot of TCP timed-out on a busy cache server and here below my sysctl.conf configuration as well as an output of netstat -st Kernel 3.2.0-4-amd64 #1 SMP Debian 3.2.57-3 x86_64 GNU/Linux ...
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0answers
142 views

Cannot connect to Solaris Server when Oracle GoldenGate process uses the port

I'm trying to test the Oracle goldengate to replicate data between two databases on the same server. So I installed two databases and two goldengate homes in the same machine. The goldengate ...
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1answer
435 views

iptables and TPROXY support

I'm running iptables v1.4.21 on Ubuntu 14.04 and is trying to setup iptables to use TPROXY. How can I check whether my current build of iptables supports TPROXY? I can check TPROXY support for ...
8
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1answer
637 views

TCP packet being retransmitted 7 times when sysctl tcp_retries1 is set to 3 - why?

Ubuntu 12.04 I am trying to better understand how many times TCP will attempt to retransmit a packet when it does not receive confirmation the destination received it. After reading the tcp man page ...
2
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1answer
238 views

remote login failed on windows XP, but remote telnet successful on mac

I recently set up an Oracle DB, started the listener on port 1561, and enabled TCP access. I then opened that port to all incoming connections. When I get on my Mac - I can use telnet remoteserver ...
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1answer
27 views

TCP rsyslogd events showing up as 2000 character continuations

I'm taking syslog events from a proprietary app. This could be the app's fault or it could be rsyslogd. Events are written like: Aug 15 16:00:00 10.11.12.13 Event1 from this wonderful product using ...
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2answers
83 views

When a socket switch to TIME_WAIT state, why I can't see its inode number?

I'm developing a program in python that parses /proc/net/tcp informations, but unfortunately, while I was doing this, I saw a strange thing. Practically, when a socket change in TIME_WAIT state, ...
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1answer
56 views

CentOS 5.10 TCP Sequence Number

We have done a security check on a server and its come back with Linux Kernel TCP Sequence Number Generation Security Weakness. We are looking to correct this being flagged up on the check We are ...
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2answers
76 views

Using (r)syslog's dynamic file generation

I am in the middle of configuring a (r)syslog server as a remote server that receives logs from various clients. I wonder whether there is a nicer way to dynamically generate multiple file names as ...
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0answers
58 views

Is The MaxUserPort Restriction In Windows Server Accumulative Across All Local IPs?

I have a Windows 2003 server with multiple IPv4 addresses assigned to it. Each single IP address doesn't use more than 2000 outbound sockets/connections. Collectively though across all IPs, this adds ...
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1answer
128 views

HAProxy - proxy to webserver via tcp

I have a simple web application, All requests to that application are HTTP based (RESTfull API and standard ajax) I have an haproxy before my tomcat cluster. So now i have clients that http request ...
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0answers
377 views

TCP Connection Issue Between Linux Machine and VMWare Windows Server

I have a TCP connection issue as follows. The setup: VMWare Virtual Machine: Windows Server 2008 R2 DataCenter SP1, IP: 192.168.2.111, DG: 192.168.2.254 Host Machine: Windows 7 Professional SP1, IP: ...
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1answer
656 views

Troubleshooting High TCP Retransmit Rate

I've been attempting to troubleshoot a network issue that presents with very high rate of TCP retransmits. 36 samples (taken with Wireshark 1.10.8 running on 32-bit Windows 7) totaling a little over ...
3
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2answers
453 views

FTP client/server failing on switching to PASV mode

Update The ISP said that they recently added the area where this computer is located to their IPv6 network. Coincidentally, ever since the day they added that area to their IPv6 network, no FTP ...
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3answers
272 views

How does anycast work with tcp?

TCP, being stateful, should require subsequent packets to reach the same server. (Stateless) HTTP runs on top of TCP, and CDN's can use anycast. So how does TCP work with anycast? What if the syn ...
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3answers
605 views

How do I diagnose network corruption on an Internet path?

I run a few hosts on network A that make requests to servers (which I don't own) on network B, somewhere across the Internet. Unfortunately, many of these requests get corrupted. If I make the ...
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2answers
5k views

What is [PSH, ACK] doing during my connection to a global catalog server?

A linux server of mine is trying to establish a LDAPS connection to a global catalog server and the connection is getting dropped (presumably by the GC side). For the purpose of discussion, let's ...
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1answer
1k views

Windows Server 2008 constantly spamming external IP's on outbound TCP port 445

I have a Windows Server 2008 box running as a Domain Controller. I have noticed in my Cisco ASA firewall logs that this box is continuously sending out (like a thousand requests a second) requests on ...
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0answers
76 views

FortiBalancer and IE TCP issues

We are using a Fortibalancer for our web servers (Win2012 with IIS) and we have run into a strange issue. IE users will experience timeouts (~77s) in getting a response from our servers. Packet traces ...
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1answer
461 views

iptables: unknown option “--dport”

When I try to run iptables -A control_in -p tcp --dport 22 -j ACCEPT I get the error message iptables v1.4.20: unknown option "--dport". Everything I've found on the internet and serverfault relating ...
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2answers
205 views

Debugging slow transfer rate from server [duplicate]

I'm trying to explain this as simple but documented as possible. This is not exclusive to this server or my current ISP. I've seen the same exact issue over the years while being with different ISPs ...
2
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1answer
24 views

Why some tcp_[rw]?mem$ voodoo show all equal values?

Looking at TCP optimization guides across the Internet, a common theme is setting the tcp_mem, tcp_rmem, or tcp_wmem three-integer vector to have equal values in the sysctl.conf file. Borrowing from ...
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1answer
169 views

How to Add/Remove New Server behind Haproxy with Minimal Disruption

Haproxy is currently balancing the load between 2 servers, A an B. Clients are connecting to these servers via persistent TCP connections. Question: We want to upgrade from server A to a more ...
3
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1answer
1k views

is it possible to synchronize the states of TCP proxies in real time (for real-high-availability of SLB)?

Consider that there are two server load balancers working in the tcp proxy mode (e.g., for L7 load balancing). Is it possible to synchronize their states in real time so that they can be a backup for ...
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2answers
2k views

is TCP port exhaustion real? [closed]

How fast would one need to allocate ephemeral ports in order to get into the TCP port exhaustion condition? I was told there are ~4k (older Windows), ~16k (newer Windows) or ~28k (RH Linux) ports ...
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1answer
675 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. ...
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2answers
101 views

Strange data in HTTP request

I have a HTTP server that serve many short time connections from many clients, the server logged that there are some invalid HTTP requests, so I decide to capture the network traffic. This is what I ...
0
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1answer
74 views

Prevent TCP Connections from Timing out on Restarting Service

On Ubuntu 14.04, an app communicates with clients at intervals of about 1 per sec to 1 per min. However the service have to be restarted regularly and this causes all the connections to drop/timeout. ...
3
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1answer
1k 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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1answer
100 views

How can my server announce its presence to everyone in the network [closed]

The situation is as follows. I want to have an application running on a server. All of the desktops in the company has to connect to it. But I do not want the IP address of the server to be hard coded ...
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0answers
46 views

OWPING communicating between tcp and tcp6

I am trying to deploy the perfSonar toolkit on my network. I'm testing the one-way ping tool on a local subnet, which contains the monitoring station (in this case, a laptop) and a host ( a cubox-i ...
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2answers
97 views

Incoming tcp SYNs possibilities

This might be a general TCP question. Can I receive TCP SYN packet on an established connection OR a connection in TIME_WAIT state? Is is possible?
2
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1answer
867 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 ...
8
votes
5answers
811 views

dump tcp connections without tcpdump

On a centos box, I like to dump tcp connections - I would like to see if a server tries to send requests to a certain IP. Usually tcpdump would do the trick - but tcpdump is not installed, and ...
11
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3answers
30k views

What does LAST_ACK mean, as a State value in netstat?

If a Windows server has several thousand ports open in LAST_ACK state (as shown by netstat), what could this mean? Is it because one endpoint is waiting for the other to respond?
0
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1answer
109 views

TCP RST from telnet/ssh daemons when connecting from openvpn

I have LAN_1 and LAN_2 interconnected with an openvpn tunnel terminated ona pair of SOHO routers running busybox. One of the vpn purpose is to allow clients on both LAN_1 and LAN_2, to administer the ...
2
votes
1answer
630 views

Cisco ASA 5510 Out-of-Order Packets to Google

We're seeing a large number of packets being dropped due to being Out-of-Order. The numbers are large enough that it may be having an impact on network performance. We've isolated it down to a few ...
1
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1answer
684 views

How to configure SSH client timeout after network failure?

Let's say I connect from a client to a server via SSH, and in the middle of the session I pull the server's network cable. On the client, the ssh connection stays alive for around 15 minutes before ...
6
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2answers
16k 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 ...
3
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2answers
660 views

When a server IP changes, do exising TCP (e.g. http/mysql) connections remain running

We have some PHP-FPM servers and when they need a database connection, they connect to an HAProxy server which selects them a database server to use and the connection opens. When we then want to ...
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0answers
332 views

Improving TCP performance over a gigabit network lots of connections and high traffic for storage and streaming services

I have two servers, Both servers hardware Specification are Processor : Dual Processor RAM : over 128 G.B Hard disk : SSD Hard disk Outging Traffic bandwidth : 3 Gbps network cards speed : 10 Gbps ...
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1answer
1k views

How to send 0x80 byte to a tcp port using netcat or similar tool?

I'm trying to make a Memcached server respond as if I where using binary protocol. If possible just command line answers pls, no code spinet in any programming language.
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1answer
76 views

TCP Server Memory management: #Connections Vs. #Requests

Given that, there is no theoretical limit to number of concurrent TCP connections a Windows 2008 server can handle. Only thing will happen is, with each connection there will be memory consumption in ...