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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How should a long-lived connection behave when there is a DNS change?

Scenario: Connector.com connects to server.net, which resolves to 20.30.40.50 Connector.com and 20.30.40.50 keep the connection open DNS is updated so that server.net now resolves to 7.8.9.10 ...
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1answer
105 views

Nginx TCP stream routing based on source IP

I have configured nginx as a reverse proxy for a TCP (non-http) stream. I'd like to apply different routing for a particular source IP address - can this be done, and how? I'm aware of recomendations ...
8
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2answers
1k views

How to configure iptables so an unwanted port is not reported as filtered

I'd like to stop others from seeing my ports as filtered in the nmap standard scan (unprivileged). Let's say that I have the following ports open: 22, 3306, 995 and a firewall configured like this: -...
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1answer
88 views

Nginx TLS Performance Optimization

I switched a busy site to TLS-everywhere and HTTP/2 last week. Performance hasn't improved as much as hoped. In fact, depending on how you measure it, you can argue it has degraded. There is plenty ...
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1answer
60 views

Ephemeral port reuse for TCP connections to different IP addresses

I know that a web server running a website on TCP port 80 can receive TCP connections from many different IP addresses sourced from many different ephemeral ports. Can a client initiate multiple ...
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1answer
96 views

Sonicwall: cannot send email (outlook) and drops connection (google drive)

I will start by saying Im a web developer and my networking knowledge is very limited, please be patient =) . We dont have network/sysad in our company. We are having problem with our connection. We ...
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1answer
44 views

Can I trust a TCP segment with a payload of 255 bytes will be delivered in a single Ethernet frame?

I'm writing some server software that upgrades the firmware on an electronic device. It's a tricky task, because currently these devices don't have enough memory to hold a full firmware before ...
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1answer
42 views

Long lived TCP connection to DNS servers

Typically the TCP connections to DNS servers are expected to be short lived, ie: the client connects, sends the query and disconnects on getting the response. If a client wants to keep a long lived ...
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1answer
29 views

How to open entire subnet with iptables [closed]

I want to enable the entire subnet 192.168.1.0/24 which is connected to eth0 in input. I'm very unfamiliar with iptables. If I add the rule: # iptables -A INPUT -s 192.168.1.0/24 -p tcp -m tcp --...
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1answer
44 views

What is a TCP Relay and when is it used? [closed]

Tcprelay is a TCP connection forwarder with load balancing capabilities. If compiled with TLS support, it may be used as SSL encryption wrapper. What are some practical applications of TCP relay?
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1answer
26 views

Is it possible for SYN/ACK to not be immediately proceeded by a SYN in a network trace

I'm writing a simple program to calculate initial RTTs from a network capture I took using Wireshark. To do this I wan't to calculate the difference in time between the SYN and the SYN/ACK. I don't ...
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0answers
46 views

What happens when connecting to port in TIME_WAIT state?

I'm trying to understand the effect of TIME_WAIT on subsequent TCP connections. I understand how TIME_WAIT behaves when net.ipv4.tcp_tw_reuse = 1, as explained by this answer. But what happens when ...
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0answers
36 views

TCP Handshake fails when ICMP Redirects are enabled

So it seems that due to ICMP redirects it's not possible to connect to a server behind a VPN connection. It immediately responds with a TCP RST (with manifests itself in SSH as ...
6
votes
4answers
660 views

ran out of tcp udp ports [closed]

How to resolve a Windows or Linux system that runs out of the tcp/udp ports on a single server? I have over around 65000 tcp/udp ports being used on a single server as a result of SQL connections, ...
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0answers
25 views

tcp receive buffer size min value seems not work

I tried to increase tcp min receive buffer size to 87380, so in my test it would OOM quickly with a little connections. net.ipv4.tcp_rmem = 87380 87380 6291456 net.ipv4.tcp_wmem = 87380 87380 ...
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2answers
35 views

Bad throughput for single tcp connections

I have a server with a Gigabit Uplink, and testing with iperf3 with 100 parallel connections i get at least 600 MBit/s, depending on the other server (i tried some public test servers). But when i run ...
5
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3answers
370 views

How to fine tune TCP performance on Linux with a 10Gb fiber connection

We have 2 Red Hat servers that are dedicated for customer speedtest. They both use 10Gb fiber connections and sit on 10Gb links. All network gear in between these servers fully support 10Gb/s. Using ...
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0answers
20 views

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 ...
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1answer
99 views

TCP connection; ACK not received

I am having trouble sending mail from Linux to Exchange server. When I telnet from Linux to Windows on port 25, I am not receiving any message from Exchange. The connection is automatically terminated ...
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0answers
37 views

Kamailio CPU usage very high and not accepting new registrations

I am facing a very strange issue with Kamailio, our Azure VM is D2 configuration with 2 cores and 7 GB of RAM, Ubuntu 14.04 LTS, through-out the day we see high CPU usage from Kamailio, and ...
0
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1answer
54 views

rsyslog server listen only on tcp 514

I'm trying to set rsyslog client- server to listen to tcp messages with port other then 514, however it doesn't work. Only when using 514 it receives messages. I'm using EC2 vms. input(type="imtcp" ...
15
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1answer
618 views

Under HTTP2, how often are new TCP connections initiated?

I understand that HTTP2 aims to keep everything under a single TCP connection, and I was wondering how often TCP connections would be torn down. For example, if I visit youtube, do some browsing, ...
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0answers
18 views

ss vs iftop. send XMbps doesn't match

I'm troubleshooting a cross data center network issue, and I found this mismatched. In most case, the data is send from A to B, the port on B is 38790. @Host A [root@**** zhifan]# watch "ss -ati '(...
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0answers
23 views

TCP ACK delay by app / windows on VirtualBox Windows VM

I have a .NET windows service that uses an open source library (Asterisk.net - C#) to listen to TCP connections on a specific port. This service is deployed on a number of VM instances of Windows 7 ...
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1answer
172 views

Server send TCP ACK with wrong number after receiving SYN

I have a client establish new TCP connection then sends request to a server per second. Both client and server are on the same linux box (via loopback interface). The client periodically reports ...
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0answers
45 views

Why my firewall rules aren't working in my NanoStation m2?

I have two NanoStation m2 as AP and Repeater for a wireless network (make them device1 and device2), both working in BRIDGE mode. Both devices are connected as WDS pairs to each other because they ...
0
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1answer
43 views

kill tcp port binding by deleting proc/[0-9]/net/… in linux

I have a script to call syscall Kill the process that holds a certain TCP port in Linux (ubuntu). But even if I do that, sometimes the port still remains in /proc/[0-9]/net directory binding the port. ...
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1answer
717 views

RST ACK with Reset cause

We have a device that connects over Wired LAN (Ethernet) to our cloud servers. At certain customer locations, when the device tries to send data, we are getting RST ACK from the customer server to ...
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1answer
328 views

What are the ports needed for L2TP VPN on Mac OS X Server 5.0.15?

I'm configuring a Mac as a server with a VPN service. So, I opened the ports listed as used by VPN in Apple documentation: UDP 500 -> 500 (+ESP and AH) UDP 4500 -> 4500 Any UDP -> 1701 (I got to ...
3
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2answers
4k views

TCP Messages Merged?

I have an application that sends 100 of 186-byte (excluding headers) TCP messages back to back without gap from host A to host B. I ran tcpdump to capture the packets on host A (where the sender is), ...
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0answers
39 views

Determine which equipment is causing packet loss

I'm connecting from my office to two servers (server 'A' and server 'B') hosted by two different providers. Since a few days, my connection speed to server 'A' has dramaticaly slowed down. Even when ...
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1answer
119 views

Linux: How to configure TCP wrappers in /etc/hosts.allow for manually started processes?

An internal server in the company I work for has been compromised and I would like to harden CentOS machines in the organization in order to avoid any future incidents so I've been reading about ...
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0answers
34 views

nginx monitoring failed to load status page under load

Nginx monitoring script so-called ztc failing to load nginx test page (mostly under highest load to nginx about 2000 rps, which used as proxy), causing errors like "nginx is down" on zabbix, and, in a ...
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0answers
51 views

socat Resource temporarily unavailable

I am using socat as a bridge between some devices and running socat (a couple hundreds of instances) like this: socat -d -d -d -x -d -lf "/var/log/some_log_file" TCP4-LISTEN:6126,fork,max-children=1,...
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0answers
33 views

How does TCP PSH and HTTPS works?

Right now I monitor traffic on my VPN server. I'm using tcpdump for it and it works pretty good. sudo tcpdump -n host SENDER_IP In this example you can see one HTTPS request from SENDER_IP to ...
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0answers
205 views

Why would Windows Server 2012 not respond on ports above 6000?

This is a new question but similar to this previous one. I've inherited the management of a Windows 2012 Server (not R2) and I'm unable to get a response from any ports above 6000. I have services ...
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0answers
47 views

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 ...
3
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0answers
45 views

TCP buffer sizes and ethernet bonding

(This question was originally posted on stack overflow; Andy told me that I could get faster help here, so it is re-posted here now.) I am experimenting with TCP buffer size tuning on Linux, but ...
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0answers
117 views

How to change tcp's window size?

I've tried changing the tcp's window size by modifying net.ipv4.tcp_wmem and net.ipv4.tcp_rmem values, however the changes which I make have no effect on actual window size which I can check using a ...
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1answer
76 views

Why does data sit in Send-Q? TCP sessions freezing

Issue I run an IRC server for 20-50 users. We sometimes have issues with messages not arriving in a timely fashion or at all. After some packet captures we determined that messages sit in the server'...
0
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1answer
45 views

Reduce TCP send buffer

I have a windows 2008 R2 server, an app is constantly polling another server (using a Flash Socket) while waiting for a certain event to occur on that server. We are talking about milliseconds. When ...
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0answers
72 views

Too Many TIME_WAIT Connections [duplicate]

We have issue that our application sometime can not connect to DB server which is a separate server. The application server and DB server communicate locally. So I search and found out that we have ...
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2answers
89 views

Does UDP includes of source address?

Both UDP and TCP does not include source address, but how does it say UDP IP spoofing is easier than TCP? For example, the following webpage also says about UDP vulnerability. "Unlike TCP, UDP does ...
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0answers
113 views

TCP RST/ACK packets not being sent back to NAT client with Forefront TMG

With Forefront TMG, we have an issue where all TCP connections to allowed ports work just fine when the connection is accepted with SYN/ACK, but when they are rejected with RST/ACK, the response does ...
4
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1answer
2k views

Why are connections in FIN_WAIT2 state not closed by the Linux kernel?

I have an issue in a long-lived process called kube-proxy being part of Kubernetes. The problem is that from time to time a connection is left in FIN_WAIT2 state. $ sudo netstat -tpn | grep ...
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1answer
131 views

TCP connection not established: Can't Connect to MySQL Server on Remote Connection (10060)

I'm running MySQL 5.6 on a WinServer 2012 system. It works great. The server is on our office intranet, not accessible to the outside world. I normally administer MySQL remotely from my office on my ...
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0answers
21 views

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 ...
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2answers
44 views

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 ...
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0answers
69 views

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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1answer
301 views

Access to Proxy Protocol address within HAProxy

I am running HAProxy that is receiving layer 4 proxy protocol from an upstream source. I have a need to create a custom HTTP header with the address contained there. I can't seem to find how I can ...