Transmission Control Protocol/Internet Protocol (TCP/IP) is the set of networking protocols that define end-to-end connectivity specifying how data should be packeted, addressed, transmitted, routed and received at the destination. This functionality is organized into four abstraction layers which are used to sort all related protocols according to the scope of networking involved.

Share tech news, updates, or what's on your mind.

Sign up to Post

We have an AIX unix server we need to connect to and then run two commands using C# or something in SSIS. How can we do this? Ultimately we are working to automate what is currently a manual task for us.

cd /strbus/fw
sh job/edid2c
OWASP: Threats Fundamentals
LVL 13
OWASP: Threats Fundamentals

Learn the top ten threats that are present in modern web-application development and how to protect your business from them.

ISP uses router in front of my firewall and They use dedicated public IP block  (WAN and GW) for the connectivity.

My firewall WAN IP and other external IPs are in completely different range.

With traceroute , Router's LAN IP is getting listed as the first hop and next is ISP GW IP. The public IP assigned in router (WAN) is not getting listed.

Is this common situation with traceroute or what is the theory behind this ?
I have a rsh command to connect to a UNIX box from a Windows XP box via TCP/IP. I replaced the rsh with PLINK after the Windows box migrated to Windows 10. Below is the example of the command. I still used the same PORT ID but got connection refused error. Then I added the parameter "-P xxx" but still failed.

rsh [unixHost] -l [hostlogin] mv [file_1] [file_2] ===> PLINK [unixHost] -l [hostlogin] mv [file_1] [file_2]

1. For this kind of conversion, can we use the same TCP/IP PORT ID?
2. It seems that PLINK has more security restrictions than rsh. Need help on how to solve this problem.

Thanks for the help.
Trying to figure out a better way to manage IP addresses.

In a typical scenario, let's say a DHCP server is given a scope that is a subset of usable IPs. For example, - 250. IPs less than 50 are not in the scope because those numbers will be manually/statically assigned to servers and networking equipment. Now, fast-forward a few years and you wish you had more non-DHCP addresses because you have new devices that you want to assign static IPs to.

So, spin up a new VM, let DHCP assign it an IP address right smack in the middle of your DHCP scope; then right-click on that record in DHCP and convert it to a reservation.
That I suppose would be sufficient, but there's something about leaving the server's network adapter set to DHCP forever so my preference/tendency is to remote into the server and change it to manual, and then manually type in the IP address that I just reserved. But now that IP address is no longer a reservation. It's static! So in the DHCP server I change the IP address to an exclusion rather than a reservation.

Seems like the proper(ish) thing to do, but now I have all of these holes in my DHCP scope and the exclusions you set on the DHCP server are nothing more than a list of IP addresses with no clue as to what they were used for. I like the 'reservation' method because it will literally tell you the name of the computer you reserved it for, its MAC address and it falls nicely into place when you view the list of IPs. But as I …
Hi Experts!

Now after battling with the “POST” method under http to send data for tax purposes assessments, finally it is dropped, we are given another option which I thought was more straight forward. However, I still need some guidance on how to use the TCP/IP port system in Ms Access VBA code
Below are the port system sample:
Module IP:
Port: 10009860Y
Baud Rate: 96089
Data Bits: 8
Parity: None 
Stop bits: 1 

Open in new window

How do declare the above stuff into the VBA code below so that the converted Json data string can be sent to Port: 10009860Y????????

Private Sub CmdSales_Click()
'  Const SQL_SELECT As String = "SELECT * FROM Qry3;"
  Dim coll As VBA.Collection
  Dim dict As Scripting.Dictionary
  Dim db As DAO.Database
  Dim rs As DAO.Recordset
  Dim fld As DAO.Field
  Dim qdf As DAO.QueryDef
  Dim prm As DAO.Parameter
  Set db = CurrentDb
  Set qdf = db.QueryDefs("Qry4")
For Each prm In qdf.Parameters
    prm = Eval(prm.Name)
Next prm
Set rs = qdf.OpenRecordset()

Set qdf = Nothing
  Set coll = New VBA.Collection
'  Set db = CurrentDb
'  Set rs = db.OpenRecordset(SQL_SELECT, dbOpenSnapshot)
  If Not rs.BOF And Not rs.EOF Then
    Do While Not rs.EOF
      Set dict = New Scripting.Dictionary
      For Each fld In rs.Fields
        dict.Add fld.Name, rs.Fields(fld.Name).Value
      Next fld

      coll.Add dict
  End If

  Set fld = Nothing
  Set rs = Nothing
  Set db = Nothing
  Set dict = 

Open in new window

Hi, I have Windows Fail Over  Cluster configured as below in VMware vSAN environment:

Production Network:

Cluster Heartbeat Newark: (Communication only between two cluster nodes, no gateway, DNS specified, only IP and mask)

vSAN iSCSI shared storage network:  (Communication only between vSAN and Windows iSCSI initiator, no gateway, DNS specified, only IP and mask)

Windows cluster is configured, and the cluster test is passing. I can restart the servers and cluster switching is working fine.

The problem is, that we have an application, which is supposed to bind to the Production network (usually it does it automatically), where it can communicate with other servers in the network, however, it always binds to Heartbeat network. How to get the nic priority level sorted. I followed the steps in the below link, but no luck.

We need urgent help.
I’m not sure why but I cannot seem to get Secure Print to work for a Canon iR-ADV C3530 III network printer. We have the badge authentication part working (there’s a card reader that in top of printer that reads badge mapped to an AD fax attribute for identification) but it’s useless this far since there are no way to secure print and require authentication at printer.  
When I do straight prob tit works. But if I choose Secure Print in output method from printing it goes through a pin code prompt and says it prints but nothing gets to the printer. Anyone know how this typically works and is setup? I’ve tried GPO deploy to my machine, doing direct TCP/IP connection as well.
My application consists of  GUI application, an  application which resides on controller  and the server application. I am developing my application with C++ for the Poco libraries. The controller should communicate with the GUI and the server through the TCP /IP protocol. So My question here is whether I need to setup my GUI as server? If some one can forward me the sample of TCPServer created with Poco libraries which listens to specific ip adress and port.
HI, we have a customer that uses unmanaged switches and has used all of thir 254 IP address on the local network.
What is the best way to achieve more local IP addresses on the LAN
I have SCO Unix 5.0.5
I am trying to Add LAN Adapter
Using netconfig program
Add Hardware Lan Adapter finds the Intel/100b on the motherboard.
Add Protocol finds no Protocols to add

tcp, ifconfig, and other basic programs for working with TCP/IP cannot be found

Does SCO 5.0.5 require a separate installation package and maybe a separate license?

Introduction to R
LVL 13
Introduction to R

R is considered the predominant language for data scientist and statisticians. Learn how to use R for your own data science projects.

Hello i am trying to do an asynch server tcp in c# and i get this error and can not resolve it please

Request for the permission of type 'System.Net.DnsPermission, System, Version=,

thanks for your help

my code :
 public static void StartListening()
        Console.WriteLine("started point");
            // Establish the local endpoint for the socket.  
            // The DNS name of the computer  
            // running the listener is "".  
	    string host = Dns.GetHostName();
	    IPHostEntry ipHostInfo = Dns.GetHostEntry(host);
            IPAddress ipAddress = ipHostInfo.AddressList[0];
            IPEndPoint localEndPoint = new IPEndPoint(ipAddress, 11000);

            // Create a TCP/IP socket.  
            Socket listener = new Socket(ipAddress.AddressFamily,
                SocketType.Stream, ProtocolType.Tcp);

            // Bind the socket to the local endpoint and listen for incoming connections.  

                while (true)
                    // Set the event to nonsignaled state.  

                    // Start an asynchronous socket to listen for connections.  
                    Console.WriteLine("Waiting for a connection...");
                        new AsyncCallback(AcceptCallback),

Open in new window

I had this question after viewing Getting postfix to send out a specific interface.

I'm running Debian Linux with postfix installed, the server is also an apache web server .. there are a total of 19 interfaces not including the loopback ..

The issue is that our hostname resolves to a specific IP address and postfix sends from a different address.. this causes some servers to reject our mail since the forward doesn't match the reverse.

In my the two relevant lines are:

inet_interfaces = all

The issue is that when I set smtp_bind_address, outbound mail no longer works .. I get the following error:

postfix/smtp[16332]: 9C82836712: to=<>, relay=[]:10025, delay=0.13, delays=0.12/0/0/0, dsn=4.4.2, status=deferred (lost connection with[] while receiving the initial server greeting)

The moment I disable that line and restart postfix, mail starts flowing again ..  the interesting thing to note is that postfix appears to be binding to the last interface, I could swap those but I'm hesitant to do that..

What is the solution? I've searched but can't find the answer
2 Recently installed HP elitebook laptops with windows 10.
Client has windows server 2012 which is the DNS server in their domain.
They have a Meraki access point, and when one of the laptops leaves the wifi network, it doesn't work on other wifi networks.
Upon investigation, the wireless adapter's properties had the IP address of their domain server in the TCP/IP properties under: use the following DNS server addresses:  instead of obtain automatically, as it should be.  We removed it and changed to obtain automatically, but every time she's in that network, it changes back.  
The other laptop does not have this issue.
I've never encountered this before, and not sure what is changing it or how to stop that behavior.
I have OpnSense (Another version of Pf Sense) Firewall installed. I can not get out to the Internet on my second, 3th, 4th LAN ports.
I have an OpnSense Firewall PC box I made which has the following inside…
OpnSense 18 (latest version) 
-G.SKILL Ripjaws V Series 16GB (2 x 8GB) 288-Pin DDR4 SDRAM DDR4 2400 (PC4 19200) Desktop Memory Model F4-2400C15D-16GVB
-King Spec SATA III 3.0 2.5" 60GB MLC Digital SSD Solid State Drive for PC B5Y1
-AMD Athlon 200GE 2-Core, 4-Thread, 3.2 GHz Base, Socket AM4 35W YD200GC6FBBOX Desktop Processor
-ASRock A320M-HDV AM4 AMD A320 SATA 6Gb/s USB 3.0 HDMI Micro ATX AMD Motherboard
-80 plus bronze certified power supply 380Watt
-Dell Intel PRO/1000 VT Quad-Port Gigabit Ethernet Card Standard Profile YT674
-IOCrest 4 Port Gigabit Ethernet PCI-e x1 Network Interface Card SI-PEX24042
This is inside a 4U server Case, inside an APC 48U Server Rack

My goals are the following...

-      I want to one 4 Port NIC using different IP Addresses such as --- Web server Network Entertainment Network Work Network --- Web server Network
I already setup these networks inside my box but I am willing to START from the beginning if you need me too.

-      I want the networks not to be able to talk to each other.
-      I have 5 block of Public static IPs which I want to use.
-      104.XX.xx.1--- This is assigned to the OpnSense itself
-      104.xx.xx.1 talks to …
We have a system that is meant to send out data and messages to an external system (via 443/tcp 80/tcp). This extract system was working perfectly well when our internal system was hosted on Server 2008 R2. We have recently upgraded to 2012R2 and the extract is unable to send outbound data except we have an active browser session by launching the browser and visiting an external website (any website at all as long as it is on the internet). Once the Browser session is closed, the outbound transfer of data becomes impossible.

Thank you
Hi All,

I recently upgraded our Cisco ASA 5545 to version 9.9(2)36.  Since the upgrade we are not able to transfer files to/from our Azure tenants via the site to site vpn we have setup.  Here is an example:  

Local Server:
Azure server:

We can ping both ways fine, but file trans are failing.  It just hangs when I try a transfer.  For the monitoring I am seeing TCP Reset-I from inside.  Could this be the reason the file transfers are failing?  If so, anybody have any idea how to remedy that reset??

Jan 08 2019      08:25:33      302014      445      51178      Teardown TCP connection 38499637 for outside: to inside: duration 0:05:53 bytes 5384 TCP Reset-I from inside

Thanks in advance.

If I am running a tcp ping tool on a virtual windows server that is hosting my website also, would it be possible to use the tcp ping tool to ping the visitor of my website to record the latency/round trip time without the stateful firewall blocking it?

The issues I came up with would be that all/most home-based firewalls are stateful firewalls, tcp communication can use only one IP and one port(if I am correct?) per application (website in this scenario). So I would have to have the tcp ping application listen in on the port using another IP, or open a new port (and IP) to communicate with the same website user. So my second question would be: would the stateful firewall block this communication since it is from a different port and/or IP even though it's on the same web server?
VBOXerr1.txtSSH connection refused when running SSH (putty) from my WINDOWS PC a  an ORACLE LINUX running on the same PC on Oracle Virtual BOX.

PUTTY displays the error:
PUTTY Network  error:  Connection refused  on

Sure, something is wrong. Could you help?


I already attached a log from the Windows8  machine (ipconfig ).
What I am ryng to do is connect from Windows using putty (SSH) to the VM Linux running on the same machine .
Someone can give any advice?

See below the ifconfig of the VM Linux machine:

root@ServidorLinux7 ~]# ifconfig
enp0s3: flags=4163<UP,BROADCAST,RUNNING,MULTICAST>  mtu 1500
        inet  netmask  broadcast
        inet6 fe80::52d0:9ddb:1f83:48f2  prefixlen 64  scopeid 0x20<link>
        ether 08:00:27:5d:46:25  txqueuelen 1000  (Ethernet)
        RX packets 6787  bytes 4818007 (4.5 MiB)
        RX errors 0  dropped 0  overruns 0  frame 0
        TX packets 4517  bytes 617833 (603.3 KiB)
        TX errors 0  dropped 0 overruns 0  carrier 0  collisions 0

lo: flags=73<UP,LOOPBACK,RUNNING>  mtu 65536
        inet  netmask
        inet6 ::1  prefixlen 128  scopeid 0x10<host>
        loop  txqueuelen 0  (Local Loopback)
        RX packets 46  bytes 7314 (7.1 KiB)
        RX errors 0  dropped 0  overruns 0  frame 0
        TX packets 46  bytes 7314 (7.1 KiB)
        TX errors 0  dropped 0 overruns 0  carrier 0  …
Something is going on with our network and I don't know where the issue is.  Many downloads (but not all) consistently halt with a [RST] but always the same ones, like PowerISO download.  Windows update fails with a Network Error on all PCs.  This is happening on both Windows and Linux.  Attached is a wireshark capture (it opens in Wireshark is you have it installed and double click it) and the jpeg screen shot.

We have COX as the internet provider but I don't know what is causing the problem.  

Can someone please take a look?  Thank you.

Wireshark Screen capture of [RST] download failed.RST_during_Windows_Update2.cap
CompTIA Cloud+
LVL 13
CompTIA Cloud+

The CompTIA Cloud+ Basic training course will teach you about cloud concepts and models, data storage, networking, and network infrastructure.

I a running an HTTP server on Ubutnu which handles GET requests.  I want to send the payloads to the client in as large of packets as possible.  However, when I look at tcpdump output, I see the payload being broken up into many small packets, typically between 1448 and ~6000 bytes.  I have tried turning off tcp_window_scaling on both client and server, but that did not work.  What settings should be adjusted on server and client to get as large of packets as possible?

Server: Ubuntu SMP Thu Aug 16 16:21:21 UTC 2018 x86_64 x86_64 x86_64 GNU/Linux
Client: Ubuntu SMP Mon Sep 24 16:19:09 UTC 2018 x86_64 x86_64 x86_64 GNU/Linux


13:03:31.227151 IP serverIP.port > clientIP.port: Flags [.], seq 1452077:1453525, ack 4279, win 60032, options [nop,nop,TS val 43798667 ecr 1911733405], length 1448
13:03:31.227154 IP clientIP.port > serverIP.port: Flags [.], ack 1453525, win 65529, options [nop,nop,TS val 1911733424 ecr 43798667], length 0
13:03:31.227161 IP serverIP.port > clientIP.port: Flags [.], seq 1453525:1454973, ack 4279, win 60032, options [nop,nop,TS val 43798667 ecr 1911733405], length 2896
13:03:31.227162 IP clientIP.port > serverIP.port: Flags [.], ack 1454973, win 65529, options [nop,nop,TS val 1911733424 ecr 43798667], length 0
13:03:31.227184 IP serverIP.port > clientIP.port: Flags [.], seq 1454973:1456421, ack 4279, win 60032, options [nop,nop,TS val 43798667 ecr 1911733405], length 1448
13:03:31.227186 IP clientIP.port > serverIP.port: Flags [.], …
I am having problem with using arpspoof on my kali linux box.  i am receiving the following error " arpspoof: couldn't arp for host host). I am able to ping to all my network devices and SVI's. I have bulilt out my own Network lab that have cisco routers, swithches, and firewalls. All my devices are receiving ip's from my DHCP server, and able to get on the internet. But for some strange reason the kali linux box arp table isn't populating and it's showing only (which is the SVI), and the cisco switch arp table is populated.  

Below is the command Im using.

arpspoof -i eth0 -t

I have 4 vlans in my network (User's, Server's, Management,and kali)

10.10.9.x/24= users
10.10.8.x/24= servers
10.10.7.x/24= managment
10.10.6.x= kali
Can someone explain to me where consensus algorithms fit within the TCP/IP model?  Let use Raft as an example.  Does it use multicast?  Does it use it's own transport number or TCP/UDP?  Does it live on the application layer?

Hello Experts,
Seemingly out of the blue (starting July 29th), though possibly corresponding with installing VMware Tools on the server (7/22), or, less likely I think, updating our ERP software including telnet server (7/21) and OS updates (7/21 - see attached), our Server 2012 R2 VM has been acting up.

I have been rebooting a telnet server service daily for two years+ to kick out clients that didn't log out and had their then sessions hang, which frees up licenses for new clients to log on in the morning. Recently, this has caused the server to not accept new connections on port 23. Nothing seems to fix it except for an OS reboot. The corresponding message in the Event Viewer is from AFD:

Closing a TCP socket with local port number 23 in process 16584 is taking longer than expected. The local port number may not be available until the close operation is completed. This happens typically due to misbehaving network drivers. Ensure latest updates are installed for Windows and any third-party networking software including NIC drivers, firewalls, or other security products.

Open in new window

This happens reliably now every time the telnet service is restarted. The process ID corresponds to the telnet server. Killing the process (that was restarted initially and caused this error) does not then allow connections on 23 - the OS must be rebooted. Disabling and then enabling the network adapter does not help. I reinstalled VMware tools which did not help.

Another error from Tcpip may be related started happening about a week later (8/7) and has been occurring daily or up to six times a day since:

Open in new window

I would like to convert HTTP streaming HLS  to UDP or RTP, I  have tried VLC  and it works only in windows 10, does anyone  have any other software example that is validated  and is working properly?

I had this question after viewing Need to kill an application that is auto starting on Windows CE 5.0.

I have a remote device running Windows Embedded CE 6.   I would like to add some bench automation to this unit, but like most target devices ti has an autostart routine that puts an app on a touch screen with limited functions.    I am confident I can get the automation I need if I can only poke around in the file system of the target device.   I am trying to connect to the device remotely with a Windows10 machine, so activesync is out.  I did try a windows XP machine and activesync failed, so the target device is not set up for that.   That leaves TCP/IP I guess and a connection with Visual Studio tools?   Is there a better tool?   VS requires that I install Corecon files to the target, but if I could install files to the target, I would not need Visual Studios.....  The unit can be attached with OEM software to run remotely as well as firmware updates are installed via USB connection, so I am pretty sure there is an agent installed to the target that allows this.   The unit installs to devices under Windows10 as "USB Remote NDIS Network Device".  I apologize for my novice approach here, but I am more of a hardware gy than software.   I am willing to hire this hel pout if anyone knows a contractor that works with embedded windows.     Thanks so much for reading!!







Transmission Control Protocol/Internet Protocol (TCP/IP) is the set of networking protocols that define end-to-end connectivity specifying how data should be packeted, addressed, transmitted, routed and received at the destination. This functionality is organized into four abstraction layers which are used to sort all related protocols according to the scope of networking involved.