Questions tagged [tcp]

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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Spurious Retransmission after few days

we have strange situation with our client-server platform. On filed we have 10 clients with same firmware version but on different networks. Client sends 50 bytes of payload to server every 15sec. ...
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nginx redis upstream lots of TIME_WAIT to some servers after adding a new bunch to upstream

I have nginx upstream of redis servers (5 servers with 4 redis instances on every) like following: upstream redis_cluster { server 10.0.1.8:6379 fail_timeout=0; server 10.0.1.8:6380 ...
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NFS stuck in ack loop

I have a situation where one of three different NFS clients will break after a period of time (some number of days). I find that the broken host and server are continually sending 'ack' packets (to ...
Josh's user avatar
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How to see + group a list of active tcp connections on a windows server

A client has asked me to take a look at their windows 2008 server because it is running extremely slow. The server is running behind the Windows Firewall (yes, i know) and I believe the application ...
Jim's user avatar
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What is causing RST ACK in my connections?

75% of calls to a 3rd party API are getting dropped. When this happens is propagates up to my calling code as a The request was aborted: Could not create SSL/TLS secure channel error. Here is a ...
Crippeoblade's user avatar
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ESTABLISHED connection recycle after system ip changed

System is CentOs sudo netstat -ntp | grep 103.235.244.98 tcp 0 0 ::ffff:61.184.232.47:35650 ::ffff:103.235.244.98:80 ESTABLISHED 41792/java tcp 0 268800 ::ffff:61.184....
armnotstrong's user avatar
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SOCKS Proxy maintain source IP

I am trying to maintain the source IP going through my socks proxy into the DMZ. Since my connection is TCP I can't use the typical XFF header method for reverse proxies. Is there any standard way to ...
asdf's user avatar
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rsync extremely slow, huge amount of TCP Dup ACK

In our network I have several PCs which sync files from an rsync server (without encryption) to their local hard disk. Often (not always) it is really slow. In sum it took 33 min for 2 GB to transfer ...
Michael's user avatar
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Unable to establish network connection between two servers

I have 7 Ubuntu 14.04.4 servers running in EC2. One server is hosting memcached (port 11211) and the other 6 are clients. Of the 6 clients, 5 are able to connect and one is not (see note). I've ...
John Naegle's user avatar
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Troubleshooting connection timeouts and SYN_RECV

My DigitalOcean droplet fails very often to connect to different resources, like making a REST call with curl or establish SSH connection. Every time it happens, I can see sockets with SYN_RECV state ...
aguyngueran's user avatar
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SYN flooding on port 443 while nginx reload

While reloading nginx, I started getting errors in messages log "possible SYN flooding on port 443", and it seems like nginx becomes completely irresponsive at that time (quite for a while), cause ...
d.ansimov's user avatar
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TCP tuning for DPM on Windows 2012

I've got a pair of servers on opposite ends of a fast (1-10Gb depending on the server) but higher latency (40-60ms) link. Various network tuning options have been set resulting in iperf3 yielding ...
Nathan Neulinger's user avatar
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Measure goodput before sending a response

My idea is to make it possible for web applications working on slower connections to fallback on alternative smaller asset versions(like images, videos, etc.). HTTP Live Streaming has similar behavior ...
Dieter Pisarewski's user avatar
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Server socket sitting in FIN_WAIT_1 whilst network doesn't see its traffic

We've been trying to get a grip on a really weird problem where we can wget a page from Apache 2.2.19 on solaris 10 and some permutations of requests reliably take various fixed lengths of time to ...
Chris Phillips's user avatar
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Iperf Tcp Client and Server

I'd really like to know why the bandwith in the client is higher than the server, i can´t find the answer explaining why this happens. Thank you, Tiago Melancia Values of the bandwidth: Client ...
Tiago Melancia's user avatar
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A small puzzle about routing

This is a followup to this question I saw on SuperUser, to which no answer has been provided. A user deleted the second route in his routing table, # ip route show default via 192.168.73.1 dev ...
MariusMatutiae's user avatar
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Configure a websocket server in front of HAProxy

I have a small python server script which creates a websocket connection and accepts base64 encoded IP packets (very similar to this). As of now my script decodes the IP packet and sends it out into ...
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Why might a connection stay in TIME_WAIT for hours or even days?

Our environment is ubuntu 12.04 on EC2. I know TIME_WAIT is a good thing, and I know generally it's OK to see connections remain in TIME_WAIT for up to 2 minutes according to all the reading I've ...
Joshua Buss's user avatar
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Wireshark RST against TCP Zero Window

During application sharing with Microsoft Lync Client (Mac OS X), TCP ACK with RST flag is sent from my application end to Lync end against TCP Zero Window packets and call gets dropped. Image Link. ...
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tcp previous segment not captured when NAT

I have a client request web service on a server behide NAT. My client IP is 10.54.10.193 NAT address: 10.54.28.183 Server address: 62.209.39.203 When client request web service on server we have TCP ...
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Inconsistency in TCP and HTTP connection management

I observe following scenario in WireShark: The problem I see here is that after receiving [FIN, ACK] from server (4090) and acknowledging it (4092), http client attempts to send another HTTP request ...
Yaroslav Admin's user avatar
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What technology do data center use to guarantee low RTT?

I was reading about data-center-tcp DCTCP and the paper was talking about the low retransmission timer (RTT) of about 250µs, but didn't state how that is being done. Somewhere else I read that DCTCP ...
Ratin Nind's user avatar
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How to fix the amount of bandwidth of iperf in tcp mode?

I'm working on some experiments about my master's degree project. I'm studying some load-balancers (I'm not supposed to cite them here) and the aim is to get for each bandwidth the cpu % usage of a ...
user2567806's user avatar
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Spurious retransmission, Dup ACK and HTTP 408

I have a server which serves as sms gateway (using kannel) and have multiple client connecting to it, but recently this one client with their particular IP said that they can't send to my server and ...
Eins's user avatar
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Citrix NetScaler sending FIN, ACK for SSL VPN Clients

I realise that it's unlikely anyone here has a definite "Check this box to resolve this" answer, but I'm struggling with this issue and I'm hoping that someone with more knowledge than me can give me ...
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Debian limit number of TCP sockets for a process (especially tor) on OpenVZ

I have a debian 7.8 server, running on OpenVZ. On this server I'm running a tor relay and some other network services (like apache and mysql). However the tor service seems to eat up all my available ...
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Should I disable the Nagle Algorithm for Outlook / Exchange RPC/HTTP communication?

I'm investigating reasons why several Outlook clients in non-cached mode are having delays communicating... resulting in Outlook hanging. My suspicion is that a Netscaler, or intermediate device (? ...
makerofthings7's user avatar
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SSH stalled after a while

I am executing some commands over SSH from a linux client (centos 7) toward a server (wind river linux) and for a reason it always stopped ( not completed ). If i executed a command that take short ...
heric's user avatar
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Web sites freeze after clicking link - unexplainable ACK packet

We have a sporadic problem accessing some internal links on websites. (Windows Firefox, Internet Explorer, Chrome) Behaviour On first clicking a link, the browser will load infinitely. The second ...
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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 ...
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How do I cap each individual tcp stream, to a fixed maximum rate?

I've read but not in depth all the various traffic shaping docs and seen the long question on HSFC scheduling Does anyone really understand how HFSC scheduling in Linux/BSD works? looked at the ...
user2603628's user avatar
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TCP High Send-q coupled with FIN_WAIT1 status

I'm having a problem with one of my webservers, which is taking minutes to completely render a web page. I had a look at the TCP connection and noticed that I have a very high value in the send-q ...
StephenC's user avatar
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tcp connection reset [RST, ACK]

getting this errors looks like server is restating the connection because of some packet loss any possible suggestion's to figure out this 37713 591.925575000 Sourceip==>>...
user310685's user avatar
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1 answer
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server is not responding on SYN packets

On the attached tcp dump, the first two SYN packets (#21800 and 21801) came to the server, however SYN ACK was sent for the second SYN. Is that correct behaviour? My understanding is that the client ...
sidorvm's user avatar
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Split TCP packet - Data layer vs IPv4Layer

What is the different between split TCP packet in the Data layer compare to split the packet in IPv4Layer ?
ner aredob's user avatar
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988 views

Ghost tcp connections: ss sees them, nothing else does

We have a strange problem. Our remote server shows over 900 connections coming from our office over port 80: # ss -n | grep ESTAB | grep $OFFICEIP | grep :80 | wc -l 935 Netstat shows a similar ...
Mediocre Gopher's user avatar
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delay in ACK packets for ldap abandon request

we have migrated from an openldap server on linux to a DirX on windows 2008. The ldap server und normal serch request behaves as expected. However with some applications (weblogic deployed webapps) ...
malaprop malaprop's user avatar
1 vote
3 answers
4k views

Limit Number of TCP connections in Linux Server, to avoid attack

I want to limit the number of TCP connections in Linux server, I have used the following command. iptables -A INPUT -p tcp --syn --dport 80 -m connlimit --connlimit-above 25 --connlimit-mask 32 -...
Mani's user avatar
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TCP Window Size Allocation, TCP Window Zero Errors and Network Latency

My mind is about to explode as everyone is always blaming the network guys for disconnections and slowness in the networks, but Solarwinds Reports that all utilization in the network devices and links ...
Rufi's user avatar
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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 ...
Malax's user avatar
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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 ...
Nyxynyx's user avatar
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trying to reach a port forwarded server from the subnet using the public IP not working

I set up a server which is connected to my router. The router forwards a port of my server. So when I scan that port using http://www.t1shopper.com/tools/port-scan/ I got: 188.143.126.14 is ...
laplasz's user avatar
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Multipath tcp application level performance measurement

I am working on a project related to Multipath tcp and I want to measure the goodput and the RTT at the application level. I don't want to use a traditional tool(netperf, iperf, ...) and I want to ...
evelina's user avatar
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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 ...
Linux Guy's user avatar
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339 views

Network flooded with LLC packet

Recently my network has been slow. From Tcpdump i found lot of frame with protocol LLC. A complete packet capture can been here tcpdump result Any hints on interpreting these packet?
riizzz's user avatar
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Increase number of connections per socket

How do I increase the number of connections each socket can accept? I know that you can increase the total number of connections using: # sysctl kern.ipc.somaxconn=4096 But each connection is then ...
cheesesticksricepuck's user avatar
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1 answer
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iperf test in reverse direction gives different result

I used iperf to measure the max throughput for TCP connection between two ubuntu machines. Both the machines were directly connected be means of a 1Gbps cable. When I performed iperf tests i obtained ...
kishore's user avatar
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Linux MIPS box: ICMP (ping) works, but TCP does not - how to fix it?

I'm trying to set up MIPS Linux box network. Here is it's configuration: ~ # ifconfig eth0 Link encap:Ethernet HWaddr CC:5D:4E:FF:45:7F inet addr:192.168.0.2 Bcast:192.168.0.255 ...
S-trace's user avatar
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TCP load balance authentication

Impala is a piece of Cloudera software which implements an ODBC driver on a desktop, which then connects directly to a Hadoop cluster. In our implementation, our Hadoop cluster sits behind a DMZ, in ...
user2858556's user avatar
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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 ...
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