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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55
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6answers
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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 ...
17
votes
6answers
13k views

Why would a server not send a SYN/ACK packet in response to a SYN packet

Lately, we've become aware of a TCP connection issue that is mostly limited to mac and Linux users who browse our websites. From the user perspective, it presents itself as a really long connection ...
31
votes
11answers
21k views

What is the difference between UDP and TCP?

My router has two protocols (and a "both" option) that I can select when setting up port forwarding: UDP and TCP. What is the difference between these two protocols and when would you select one over ...
4
votes
2answers
1k views

syn/ack sequence number confusion

I was looking at some random traffic in wireshark and came across this (using relative seq/ack numbers): 1. myIP -> 74.125.227.96 [SYN] seq=0 2. 74.125.227.96 -> myIP ...
19
votes
4answers
2k views

Slow Transfers over Distance

From our NY Datacenter, transfers to locations that are farther away are having poor performance. Using speed test to test various locations, we can saturate our 100 mbit uplink to Boston and ...
13
votes
7answers
13k views

traceroute TCP equivalent for Windows [closed]

I'm trying to determine where connectivity to an external host using a specific TCP port is being blocked. Traceroute for Windows only uses ICMP, and telnet will only tell me that the port is blocked ...
12
votes
2answers
32k views

Which is the default TCP connect timeout in Windows?

Which is the default TCP connect timeout in Windows? There is a registry key to configure it or it's set dynamically?
8
votes
2answers
6k views

How can I tune the initial TCP retransmit timeout?

The initial TCP RTO value of 3s is too long for most LAN-based applications. How can I tune it lower? Is there a sysctl?
12
votes
3answers
6k views

What's the difference between Unix socket and TCP/IP socket?

It's from this answer: http://stackoverflow.com/questions/2482411/is-this-pdo-bug-fixed-now/2482424#2482424
4
votes
4answers
550 views

Why was the FTP protocol designed to use more than one port?

The question is in the title. The reason I wonder this is because I'm coding an tcp service and would like to explore some of the reasons as they may shed some light on my work.
3
votes
3answers
719 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) ...
10
votes
3answers
2k views

Is it possible for a TCP connection to remain open when the client has disconnected?

We have a server application which is facing TCP exhaustion problems at around 4000 connections. This will occur every 3 or 4 weeks (approximately). The vendor, which has created this server ...
2
votes
3answers
872 views

Why is it 3-way-handshake and not more?

TCP uses the 3-way-handshake mechanism. I understand how it works pretty well but I wonder why it's not 4, or even 5-way? Is it because that's too much overhead and is not needed?
2
votes
5answers
2k views

I am looking for a good load balancing (or reverse proxy) software for TCP and HTTP, any suggestions? [closed]

I am looking for a good load balancing (or reverse proxy) software for TCP and HTTP, any suggestions?
2
votes
1answer
9k views

Enabling system wide TCP keepalives on a Windows system

Can I change/add the KeepAliveTime and related registry variables to make a Windows machine send TCP keepalive packets on an idle connection? I want to know if anyone has successfully got this ...
0
votes
1answer
1k views

How do i view / enable kernel logs on an ec2 instance (amazon linux)?

I've got a amazon ec2 server that i'm playing around with TCP settings in the sysctl.conf to increase the number of concurrent TCP connections it can handle, and i want to be able to view the kernel ...
0
votes
1answer
686 views

how to enable port 7777

I am initiating file transfer using tcp on openfire server. But I am not able to open the port number 7777, from which I need to send files. I changed the security setting in the admin console panel ...
-1
votes
2answers
1k views

Been up for 2 days please help! SYN flooding Error [closed]

I'm having a problem been working on this for 3 weeks been up the past two days trying to fix this. My server is a busy server If I run netstat -plan | grep :80 | wc -l I get 22717. In my logs I ...
21
votes
5answers
25k views

What is the best way to transfer a single large file over a high-speed, high-latency WAN link?

This looks related to this one, but it's somewhat different. There is this WAN link between two company sites, and we need to transfer a single very large file (Oracle dump, ~160 GB). We've got full ...
14
votes
3answers
53k views

“Possible SYN flooding” in log despite low number of SYN_RECV connections

Recently we had an apache server which was responding very slowly due to SYN flooding. The workaround for this was to enable tcp_syncookies (net.ipv4.tcp_syncookies=1 in /etc/sysctl.conf). I posted a ...
16
votes
3answers
1k views

Troubleshooting Network Speeds — The Age Old Inquiry

I'm looking for help with what I'm sure is an age old question. I've found myself in a situation of yearning to understand network throughput more clearly, but I can't seem to find information that ...
8
votes
4answers
5k views

haproxy + stunnel + keep-alive?

I'd like to put stunnel in front of haproxy 1.4 to handle HTTPS traffic. I also need stunnel to add the X-Forwarded-For header. This can be achieved by the "stunnel-4.xx-xforwarded-for.diff" patches ...
12
votes
5answers
5k views

I'm designing a system to handle 10000 TCP connections per second, what problems will I run into?

I have a relatively new 8-core box running CentOS. I would like to develop a stats server that uses TCP. It's very simple, it accepts a TCP connection, increments a counter and closes the connection. ...
7
votes
3answers
5k views

TIME_WAIT connections not being cleaned up after timeout period expires

I am stress testing one of my servers by hitting it with a constant stream of new network connections, the tcp_fin_timeout is set to 60, so if I send a constant stream of something like 100 requests ...
3
votes
2answers
2k views

dmesg SYN flood on 80 sysctl -p

I am getting a synflood on my server port 80 and i cannot stop it. first i got tables full then i disabled iptables to find out that its a synflood netstat -n | grep :80 |wc -l #returns 1300 - 2000 ...
17
votes
2answers
6k views

What is the “in-the-wire” size of a ethernet frame? 1518 or 1542?

According to the table here, it says that MTU = 1500 bytes and that the payload part is 1500 - 42 bytes or 1458 bytes (<- this is actually wrong!). Now on top of that you have to add IPv4 and UDP ...
28
votes
8answers
228k views

What does “TTL expired in transit” mean on a ping attempt?

We get the message “TTL expired in transit” when we try to ping to a server in a different network segment. When we run tracert, 4 ip addresses repeat themselves indefinitely: 14 60 ms 59 ms ...
23
votes
5answers
2k 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 ...
5
votes
3answers
4k views

tool for splitting pcap files by TCP connection?

Is there tool to split a packet capture file (in pcap format) into separate files for each TCP connection ? (other than a home grown shell script which probably needs to run twice over the ...
4
votes
2answers
5k views

What are the ramifications of setting tcp_tw_recycle/reuse to 1?

I set both tcp_tw_recycle/reuse to 1 in my configuration file. What are the ramifications of doing this? If a tcp socket is re-used, does that pose a security risk? i.e. 2 different connections both ...
4
votes
5answers
5k views

Server not sending a SYN/ACK packet in response to a SYN packet

Using iptraf, tcpdump and wireshark I can see a SYN packet coming in but only the ACK FLAG is set in reply packet. I'm running Debian 5 with kernel 2.6.36 I've turned off window_scaling and ...
4
votes
2answers
1k views

Remote server hangs, gets stuck. How to debug?

I have an vps running on VmWare ESX with Ubuntu 8.04 LTS. It has been running smoothly for the past 3 months, however recently we've notices two strange bugs. a. The server hangs, today was second ...
6
votes
2answers
2k 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 ...
5
votes
2answers
2k views

Duplicate incoming TCP traffic on Debian Squeeze

I have to test a homebrew server that accepts a lot of incoming TCP traffic on a single port. The protocol is homebrew as well. For testing purposes, I'd like to send this traffic both : - to the ...
2
votes
2answers
2k views

Can I test broadcast packets on a single machine?

I want to have a server sending broadcast UDP packets and two other clients, in the same machine, receiving them. Can I do that somehow? What IP address would I use? @gravyface gave me hope but I ...
1
vote
5answers
2k views

Increasing bandwidth with multiple NICs

If I have two NICs in my system and both are connected to different ISP with different IP addresses, can I distribute my network traffic on them to increase my Bandwidth. I have already looked at ...
5
votes
2answers
2k views

apache webserver unresponsible with server-status showing all child processes waiting for connection

My setup: i have 3 nearly identical webserver machines serving the same high loaded dynamic website with simple load balancing over dns. The service has been working for over two ears with the same ...
5
votes
2answers
3k views

Force forwarder DNS requests to TCP mode

I have set up a DNS-server on SLES10 (currently bind 9.6) on a multi-homed server. This server can be queried from all internal networks and delivers answers for all internal networks. We have two ...
5
votes
3answers
580 views

Is SYN flooding still a threat?

Well recently I've been reading about different Denial of Service methods. One method that kind of stuck out was SYN flooding. I'm a member of some not-so-nice forums, and someone was selling a python ...
4
votes
2answers
602 views

VMXNET3 performance on Linux on ESX 5.0

What kind of performance can I expect from VMXNET3 adapter when running two Linux guests on the same VMware ESX private network defined between those guests? I use VMXNET3 adapter for communicating ...
4
votes
2answers
1k views

High Instances of Zero Window Messages

On my web servers I am seeing a high rate (106 over ~13 seconds or 300,000 packets) of zero window update messages sent form my web servers to my database servers during peak traffic. Firmware is ...
3
votes
2answers
857 views

Automatically-reconnecting TCP tunnel

I have an unreliable network connection between two machines: sometimes active TCP connections get dropped for reasons beyond my control. I want to establish a reliable TCP connection between the two ...
3
votes
2answers
2k views

Load Balancing long running TCP connections

I'm trying to research the best way to load balance long running TCP connections for the following scenario: We have multiple servers behind a redundant set of firewalls and clients establish long ...
3
votes
3answers
2k views

Allow X Client Display through TCP on Lucid

On Karmic, to allow other PCs to open and X-Window on a station, one had to edit /etc/gdm.conf and change DisallowTCP to false. That file no longer exists on Lucid. I tried changing an entry in ...
2
votes
1answer
541 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
votes
2answers
2k views

Reduce firewall rules by half - one iptables rule for tcp and udp

I have a number of iptables rules on my firewall that look like this: iptables -A zone_lan_forward -p tcp -d 1.2.3.0/24 -j ACCEPT iptables -A zone_lan_forward -p udp -d 1.2.3.0/24 -j ACCEPT Is ...
2
votes
2answers
548 views

SYN cookies on internal machines

Our system uses Cassandra running on Ubuntu 10.04 and during last spike in traffic we observed the following message in logs: possible SYN flooding on port 9160. Sending cookies. These machines are ...
2
votes
1answer
6k views

How to change receive queue length of a network interface in Linux?

I have a server running Linux (kernel 2.6.18) which is dropping incoming network packets drastically. I thought it is suffering from this because the length of the receive queue of that interface is ...
2
votes
2answers
8k views

How to check TCP timeout in linux / macos?

I have a network problem on my MacOS that i need to troubleshoot. I know that TCP socket has internal timeout that will close connection if remote party is not responding (but no graceful disconnect ...
1
vote
0answers
176 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 ...