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.

Filter by
Sorted by
Tagged with
1 vote
1 answer
3k views

iptables rule to allow only incoming TCP-handshake

I need some iptables rule to allow only incoming TCP-handshake. So I need to allow flags SYN and ACK. But I can't figure out what should be in ??? position in my rule? iptables -A INPUT -p tcp --tcp-...
z0lupka's user avatar
  • 139
0 votes
1 answer
560 views

Are TCP RTO value and RTT value influenced by the packet size?

I am doing troubleshooting in my network. I found some re-transmission by using wireshark. The segment 1400 bytes are well transmitted but The segment 800 bytes are lost and re-transmitted. I know ...
nimdrak's user avatar
  • 139
-3 votes
1 answer
225 views

Who listens to the port

I have a conflict between the mail server and one more service. netstat -ltnp | grep -w ': 25' Conclusion: (Not all processes could be identified, non-owned process info   will not be shown, you ...
hedgehogues's user avatar
3 votes
1 answer
2k views

Why was Windows picking the wrong route when attempting to connect to a TCP server?

I had previously asked this on Stack Overflow and was advised to move the question over to Server Fault. So here I am :) The application I am working with connects to a couple of TCP servers running ...
johnildergleidisson's user avatar
1 vote
0 answers
75 views

Duplicate Local Port in Virtual Guest's /proc/net/tcp

I'd like to understand the following two entries in my VirtualBox's guest's /proc/net/tcp: 6: 00000000:18EB 00000000:0000 0A 00000000:00000000 00:00000000 00000000 0 0 9581 1 ...
jimmytann's user avatar
  • 111
1 vote
2 answers
921 views

I have a loopback traffic in linux involving port 631 and I have no idea what is causing it

So I did some packet capturing in my networking and everything else is actually fine except for this weird communication where source and destination is literally 127.0.0.1, source port is 631, and ...
cmakeislife's user avatar
4 votes
3 answers
5k views

Lots of connections in SYN_RECV, not a SYN flood, is it some reflection attack?

Since at least a few months, issuing a netstat -t command on our web server, which has TCP ports 22, 80 and 443 exposed to the Internet, often reveals dozens of connections in SYN_RECV status: $ ...
Ale's user avatar
  • 1,723
-1 votes
1 answer
2k views

What hardware specs is needed to serve 100,000 clients on OpenVpn? [duplicate]

Serving vpn clients (tcp connections) with OpenVpn server relies on what ? Or how can we calculate the clients count with hardware specs ? Does it rely on server bandwidth speed, like if we have a ...
Khlda's user avatar
  • 1
0 votes
2 answers
615 views

how to get 2 internet connections working

It's either I have a fundamental misunderstanding on how interfaces are suppose to work or I've done something oddly wrong. I have two interfaces: eno1: 10.6.59.203/24 (gateway 10.6.59.1) eno2: 192....
Dellowar's user avatar
  • 133
0 votes
1 answer
544 views

Configuring iptables when operating KVM virtual machines over a VLAN bridge

I am currently setting up a virtualized environment with KVM that spans across two physical host machines (Host1 and Host2). Both are connected to the same VLAN. The network interfaces on both ...
Alexander Richter's user avatar
0 votes
1 answer
699 views

At Iperf3, TCP weird behavior

I am a newbie network engineer. I did a small experiment with iperf3. But I run into a small problem. (1) My question. I think TCP flow do not act properly despite of its congestion control. The flow ...
nimdrak's user avatar
  • 139
0 votes
1 answer
1k views

TCPDUMP, tcp Flag not changing from Flags [S] to other flag values

I need support understanding these lines. when i tried to connect to server in a particular port it shows connecting and gives me timeout error. But in the tcp-dump command the packet flag not ...
VinothRaja's user avatar
1 vote
1 answer
262 views

TCP connection bridge/proxy-alike for logging

The simplified scenario: I have a phone system which logs out every single operation on port 6543. I also have a listener (existing application) which connects to the phone system (a linux box) and ...
MensSana's user avatar
  • 111
0 votes
1 answer
57 views

TCPDump, can't understand these parts

I need help to understand the bold part of this line : 01:04:28.539138 IP 90.2.255.58.37727 > 71.197.145.153.46872: . 9801:11201(1400) ack 0 win 2003 9801:11201(1400) 9801 seems to be the data ...
yeedooz's user avatar
-2 votes
1 answer
68 views

How mail transfer works between the Senders SMTP and the receivers SMTP

when I send an E-Mail it works like this: My E-Mail Client -> My SMTP -> Recipients SMTP -> Recipients E-Mail Client I know the way how my E-Mail client communicates with my SMTP but how do the SMTP ...
Emil Engler's user avatar
0 votes
1 answer
416 views

TCP protocol strange behaviour in my program

I started working recently in IT field and as first assignment they want me to communicate with a remote board with a simple Socket using Java. Today I completed all the job but I noticed that my ...
user3649959's user avatar
1 vote
2 answers
1k views

What should be the next sequence number after a packet with the FIN containing payload?

I was capturing some HTTP traffics and I observed a packet with the FIN flag set and also containing payload data. I searched for this topic and I found some similar questions but none of them ...
mrazimi's user avatar
  • 121
0 votes
1 answer
111 views

I've Encountered A Strange Network Interface. Is This A Standard Practice?

I am currently developing ONVIF software, and one of my test cameras has presented me with a rather odd network interface. The camera in question is an AXIS M3045-WV. It's a fairly low-cost (for AXIS)...
Chris Marshall's user avatar
1 vote
0 answers
110 views

Windows .NET application can't connect after Ubuntu 16.04 upgrade of linux-image to 4.4.0-151

After upgrading Ubuntu 16.04 kernel to linux-image-4.4.0-151-generic some of our clients stopped being able to connect with TCP. Specifically using SSH.NET library from Windows servers with SFTP ...
Tometzky's user avatar
  • 2,729
0 votes
1 answer
891 views

Do outbound TCP connections prevent port binding for listening?

I'm running an application that is trying to listen on port 34002. When it tries to do so, it gets the error: Address already in use When I use lsof to find the culprit, I find that it's an ...
Indigenuity's user avatar
1 vote
1 answer
289 views

How does LDAP Authentication Work at the TCP Layer?

Specifically, how does an LDAP server distinguish a TCP packet containing a SearchRequestOp from an authenticated user, from a TCP packet containing a SearchRequestOp from an unauthenticated user? I ...
Tikiyetti's user avatar
  • 113
1 vote
0 answers
385 views

Mysql has gone away error randomly

I have a web application written in php. In this app, I have a script(CLI) which is really heavy. After this script finishes its job, I get "mysql has gone away" error in my normal http request for a ...
undone's user avatar
  • 177
-1 votes
1 answer
615 views

WebSocket communication error

Trying to understand what is wrong with WebSocket communication since the fact application is trying resend message. The last WebSocket packet contains error: The client frame set the reserved bits ...
vico's user avatar
  • 99
5 votes
1 answer
3k views

socat tun device very low throughput

I was tinkering around with socat and tried to use socat for creating a TUN device for tunneling between two debian stretch servers. However, throughput seemed very low and comparing with iperf ...
1gd_1bs37coua9dd's user avatar
1 vote
0 answers
37 views

the strange value of SRE in a D-SACK packet

I'm troubleshooting a strange network issue in our production environment. The dumped pcap file comes from the full NAT mode LVS , and the toploy of the ip address in the dump file is: 172.19.132.90(...
kongyk's user avatar
  • 111
0 votes
1 answer
81 views

Security for Docker (bridge network)

I am running Docker on Linux (Ubuntu). By default, it uses the docker0 network. docker0: flags=4099<UP,BROADCAST,MULTICAST> mtu 1500 inet 172.17.0.1 netmask 255.255.0.0 broadcast 172....
Paul Draper's user avatar
1 vote
1 answer
107 views

How to Handle Long TCP Sessions deployment in ZDD?

I have an application that forward TCP connection to another App. Currently I am trying to make this application Zero Download Deployment, so I can deploy new version at any time but there is a ...
Penguin_HuHu's user avatar
1 vote
0 answers
73 views

Microsoft tool to see Windows TCP internals (congestion window, etc)

I hope this isn't too vague a question: I remember a tool from Microsoft that was able to show me all kinds of internal TCP variables, like congestion window, etc. I remember that I needed to ...
cxxl's user avatar
  • 123
0 votes
1 answer
1k views

Delayed http response

I am using google api with PHP to query google's API from my server - which uses guzzle to send a regular http request. A high number of requests (~10%) are returning after exactly 63 seconds, while ...
danielb's user avatar
  • 143
1 vote
1 answer
2k views

Linux Log all tcp new connections

On my linux host I want to get per minute logs of all the new tcp connections being created. I have multiple tap devices on my host from which various are trying to create the tcp connections. I ...
Prashant Singh's user avatar
0 votes
1 answer
1k views

Stress-testing for `tcp_mem`

Linux has a tcp_mem setting for the amount of memory it will allocate to TCP connections for all running applications. As per the official documentation: tcp_mem - vector of 3 INTEGERs: min, ...
ketan vijayvargiya's user avatar
1 vote
2 answers
4k views

Windows Server Firewall: Block all incoming traffic except from domain members

I want to secure a Remote-Desktop server farm (running on Windows Server 2019). I run multiple servers with different roles (as Active Directory, Connection Broker, RD Gateway, ...). Now I want to ...
dinnerspoon's user avatar
0 votes
2 answers
3k views

Changing Linux kernel network settings on active live TCP sockets

If I change settings like this for example: # sysctl -w net.core.rmem_default=500000 # sysctl -w net.ipv4.tcp_rmem='4000 90000 10000000' Is it safe to do this in a heavy duty live production ...
Vladimir Ralev's user avatar
1 vote
1 answer
644 views

Kerberos - TCP client wants 1195725856 bytes, cap is 1048572

I'm having some difficulties debugging this error. I'm running nginx as an api gateway built to make a sub-request to kerberos whenever an endpoint gets called using the SPNEGO method. But whenever I ...
Kenpachi's user avatar
0 votes
0 answers
566 views

TCP Retransmissions when packets exceed 1500+

I am currently trying to communicate using NMOS protocol over my network. This is a /30 network. The issue I am seeing is that when I send an http request from my computer to my device over the ...
RAZ_Muh_Taz's user avatar
0 votes
0 answers
705 views

Configuring TCP services with nginx ingress on minikube/k8s

I'm new to k8s/minikube (and to some extent, unix networking in general) so if I ask something that seems to make no sense, I'll be happy to clarify! Goal I want to configure a port-based TCP ...
Ben's user avatar
  • 251
1 vote
1 answer
4k views

how to reach 1M concurrent TCP connections?

I am trying to setup a environment with multiple nodes (1 receiver + 16 senders) to establish 1,000,000 (1M) concurrent TCP connections. Using this tool: https://github.com/Microsoft/ntttcp-for-linux ...
Howard Shane's user avatar
3 votes
1 answer
3k views

Unable to create seemingly simple stunnel configuration

I have a computer at work that is behind a firewall with an internal ip address of 192.168.12.13... the firewall maps ports 40000 - 40019 to matching ports on this local machine. (e.g. 40000 - 40000, ...
Brian Rice's user avatar
-2 votes
1 answer
553 views

most efficient way to block an ip address from connecting to a ubuntu 18.04 server [closed]

Since i do not have access to other layers, i would like to know the most efficient way to block an ip address from connecting to a Ubuntu 18.04 server. To the box itself, they are most likely ...
Dan's user avatar
  • 195
0 votes
1 answer
1k views

nginx reuseport with backlog

In nginx if I specify reuseport and backlog=X stream { server { listen 8080 backlog=X reuseport; will I get a maximum queue length of size X per socket/worker or a max total queue of size X?
andresp's user avatar
  • 151
0 votes
0 answers
1k views

Unable to use VNC when connected to OpenVPN

When I try to VNC to a particular machine #1 (192.168.1.221) from within the network I am able to connect to it without issue. When I try to connect from outside the network from my OpenVPN VPN I am ...
Coldgate32's user avatar
1 vote
0 answers
54 views

Encapsulate udp traffic info tcp with on-disk buffering

My ipfix flow receiver supports only udp (can't be replaced), which is not resistant to network failures and then I'm loosing flow data. To improve this I'm thinking about using socat, mkfifo between ...
Supermario's user avatar
1 vote
1 answer
5k views

Cannot connect to open port in remote server

On my remote server, I installed ElasticSearch, which can be accessed at http://localhost:9200/: I defined an inbound security rule, Port9200, in the firewall for my remote server: As you can see, ...
M.Y. Babt's user avatar
  • 121
0 votes
1 answer
460 views

Trying to connect to a REST API on my LAN using a C# program, but I get a WebException (Timeout). Telnet and browser works fine

I am running a very simple REST service using Flask on a Ubuntu Server on my local area network at home. I am trying to connect to this REST service using a simple .NET Core C# program. When I run the ...
andrerav's user avatar
  • 101
1 vote
1 answer
543 views

Modify source IP from a package dump

I have a dumped several packages udp and I am trying to tcpreplay it. The issue is that the source is from a different network and I want to modify or redump by changing the source IP. I have done ...
max246's user avatar
  • 113
1 vote
1 answer
1k views

HAProxy returns bad Request with send-proxy-v2

Haproxy returns 400 with send-proxy-v2 and without send-proxy-v2 it returns proper result. Config which returns proper result: backend satellites balance leastconn mode tcp retries 3 ...
Harshit Agarwal's user avatar
2 votes
1 answer
5k views

No response from web server in Docker container from host

I am running a web server (Java Spring boot application) inside a Docker container on port 8080, which is exposed to interface 127.0.0.1 also on port 8080. docker ps shows that the port is exposed: ...
Michael Cornel's user avatar
0 votes
1 answer
491 views

iptables ... -j DROP appears to leave connections open?

So forgive me if this is a dumb question, I'm not much of a networking expert. A friends server is being flooded by a certain IP, which is pretty obvious when looking at the output of tcptrace, as ...
DarkWiiPlayer's user avatar
1 vote
0 answers
588 views

Why is Watchguard dropping an open TCP connection?

We are using Watchguard version T35-W. When our system is under heavy load, we sometimes see active TCP client connections are dropped and become black holes. We think that this has something to do ...
Andrew Eisenberg's user avatar
1 vote
1 answer
378 views

TCP port mapping / proxy with AWS

I have several services running on a single AWS instance on different ports: rabbit :5672 rabbitMQ :15672 elastic :9200 a few others I have a jumpbox on AWS which handles all incoming requests. I ...
p-mcgowan's user avatar

1
5 6
7
8 9
34