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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0answers
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How does server-side `TIME_WAIT` really work?

I know there are quite a few SE questions on this, and I believe I read as many of them as it matters before coming to this point. By "server-side TIME_WAIT" I mean the state of a server-side socket ...
23
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7answers
21k 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 ...
1
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3answers
1k views

Windows Server 2008 - unable to bind any TCP port

OS: Win Server 2008 RC2 Windows firewall on (no effect when off) I have suddenly been plagued by an issue in which I cannot find any similar ones with a search. I am running about 20 game servers ...
1
vote
1answer
887 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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2answers
3k 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 ...
11
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7answers
2k views

Why is it good practice to compare checksums when downloading a file?

Websites which supply ISO files for download will often give the md5 checksums of those files, which we can use to confirm that the file has downloaded correctly, and has not been corrupted. Why is ...
7
votes
2answers
125 views

Extreme UDP packet loss at 300Mbit (14%), but TCP > 800Mbit w/o retransmits

I have a linux box I use as the iperf3 client, testing 2 identically equipped Windows 2012 R2 server boxes with Broadcom BCM5721, 1Gb adapters (2 ports, but only 1 used for the test). All machines are ...
0
votes
1answer
312 views

Effects of IW10 (initcwnd 10 initrwnd 10) on high speed LAN based TCP/IP communications?

What does changing the number of packets sent during the initial congestion window to 10 have on LAN connections? Via: ip route change default via GATEWAY dev INTERFACE initcwnd 10 initrwnd 10 Is ...
0
votes
1answer
13 views

Upgrading Web Application's Systems' Kernels for IW10 & other related improvements - upgrade all machines? LB first? Most important?

Stackers - We're making the push to upgrade the systems for our web app to take advantage of the various TCP improvements becoming more readily available (e.g. ...
3
votes
1answer
124 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. ...
2
votes
0answers
24 views

How to enable SYN Cookies on Debian 7.5? [migrated]

How do I enable SYN Cookies on Debian 7.5? nano /etc/sysctl.conf #net.ipv4.tcp_syncookies = 1 remove here the # sysctl -p service network restart Is that the correct way? Or what must I look ...
2
votes
1answer
49 views

Outgoing packet has NATed src address

Configuration/Topology: There are 3 machines hadoop2 | hadoop | driver eth0 10.10.15.3 | eth0 10.10.15.2 | tap0 192.168.0.199 ...
1
vote
1answer
32 views

No response to TCP SYN packet when padding is not 0's or F's

I have this client which initiates a 3 way handshake with a SYN packet but there is no SYN ACK response. We figured out that it was because the client did not pad the end of the TCP headers with 0's ...
3
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 ...
-2
votes
0answers
58 views

TCP/UDP traffic forwarding to a different IP

I have the following configuration. Several remote clients are sending some data packet via TCP and/or UDP to a legacy server beyond an ADSL router. The router has a static public IP and forward ...
0
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0answers
50 views

Nginx TCP Fast Open Issue

I have configured Nginx and Apache on one of my servers. The nginx server listens on port 80 and Apache on port 81. Nginx works as a reverse proxy. In nginx I configured TCP Fast Open: server { ...
1
vote
0answers
24 views

What happens if a machine gets a SYN/ACK packet without sending initial SYN packet?

I'm thinking of a situation where an attacker manipulates a SYN packet that was sent from A's source IP address to B. The server will receive the packet and think it's a legitimate packet, and send a ...
0
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0answers
7 views

How to make TCPFlow to not store package body?

Is it possible to configure tcpflow to store only package headers without package body? My log simply explodes in production.
1
vote
1answer
2k views

option http-server-close on HAProxy haproxy-1.5-dev19 will result in Connection: close header sent in response

I basically have the following issue: whenever I add option http-server-close to the haproxy config (either in frontend or backend section), haproxy will send a Connection: close header in the ...
2
votes
1answer
227 views

Why do I get connection timeouts to private services in Azure?

I seem to be seeing this with both my SQL Server, and my MongoDB replica set. I only get a handful a day, but it still concerns me. I am getting a timeout when trying to open a new connection to the ...
0
votes
0answers
29 views

haproxy get ssl interrupt error, how haproxy tell server to close ssl or tcp?

I use haproxy 1.5 and a windows server build site. my site work under the https protocol, so for haproxy I use tcp mode since I think the ssl can not work on http mode. my problem is the ssl ...
-1
votes
1answer
53 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 ...
0
votes
1answer
1k views

ffmpeg simple RTMP streaming

I am trying to launch up a rtmp transcoder server using ffmpeg; that receives udp MPEG-TS streams as input, transcodes it; and generates an rtmp output to a URL, that can be accessed by users to ...
35
votes
6answers
8k views

Windows TCP Window Scaling Hitting plateau too early

Scenario: We have a number of Windows clients regularly uploading large files (FTP/SVN/HTTP PUT/SCP) to Linux servers that are ~100-160ms away. We have 1Gbit/s synchronous bandwidth at the office and ...
3
votes
4answers
3k views

Need help troubleshooting intermittant TCP timeout in HAProxy

I have an application where the client connects to a server via a simple TCP based protocol over TLS/SSL. In development, this has worked great for many months while we were building our application ...
6
votes
4answers
3k views

How do I check how many connections are open currently on a specific TCP port?

I'm doing some comet benchmarks and would like to see how many open connections I have. Actually I use netstat: netstat -ant | grep 8080 | grep EST | wc -l But it needs around 4-6 minutes to list ...
0
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0answers
21 views

Can I use a domain name for a TCP process hosted in IIS?

I'm trying to set up a WCF service hosted in IIS 7.5, with TCP bindings. I also need to use a SSL certificate for security. From what I have read, I can add net.tcp as a binding type. However when I ...
0
votes
1answer
25 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 ...
0
votes
0answers
111 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 ...
0
votes
1answer
34 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 ...
1
vote
5answers
3k 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 ...
6
votes
1answer
203 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 ...
20
votes
6answers
33k views

How to capture ack or syn packets by Tcpdump?

I want to use a filter rule to capture only ack or syn packets. How do I do this?
-1
votes
0answers
64 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 ...
1
vote
3answers
239 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 ...
6
votes
4answers
2k 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 ...
1
vote
1answer
109 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 ...
1
vote
1answer
26 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 ...
0
votes
1answer
41 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 ...
6
votes
2answers
158 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
vote
3answers
2k 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 ...
0
votes
1answer
76 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 ...
1
vote
0answers
41 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 ...
-3
votes
1answer
62 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 ...
-2
votes
1answer
72 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 ...
1
vote
0answers
50 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 ...
1
vote
2answers
71 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 ...
3
votes
1answer
173 views

Low throughput on Debian + nginx/apache

On the same LAN/WAN I have a Windows server 2012 server running IIS 7.5 and a Debian (wheezy) server running Nginx 1.4.5. Both servers are connected to the same LAN/WAN. When I download a 10MB file ...
2
votes
1answer
76 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",\ ...
0
votes
1answer
30 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 ...