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.
1,655
questions
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-...
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 ...
-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 ...
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 ...
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 ...
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 ...
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:
$ ...
-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 ...
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....
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 ...
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 ...
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 ...
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 ...
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 ...
-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 ...
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 ...
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 ...
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)...
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 ...
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 ...
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 ...
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 ...
-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 ...
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 ...
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(...
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....
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 ...
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 ...
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 ...
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 ...
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, ...
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 ...
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 ...
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 ...
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 ...
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 ...
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
...
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, ...
-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 ...
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?
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 ...
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 ...
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, ...
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 ...
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 ...
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
...
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:
...
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 ...
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 ...
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 ...