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TCP/IP

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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.

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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 192.168.56.1

Sure, something is wrong. Could you help?

RegardsVBOXerr1.txt


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 10.0.2.15  netmask 255.255.255.0  broadcast 10.0.2.255
        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 127.0.0.1  netmask 255.0.0.0
        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  …
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9 Comments
CompTIA Security+
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Learn the essential functions of CompTIA Security+, which establishes the core knowledge required of any cybersecurity role and leads professionals into intermediate-level cybersecurity jobs.

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Regedit \ RouterManager can be configured ?

Regedit \ TCPip6 every modified would be return to previous state, as motherboard changed, DUID mac info inside needed to , RFC3315 required .

When the OEM vga driver latest supported driver updated to Nov. 2018, whatever way tried, the computer Driver Manager can not see the latest date of the offering ?
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6 Comments
I HAVE A HAEMTALOGY ANALYZER WITH RJ45 PORT. I NEED TO RECEIVE DATA FROM THAT MACHINE TO MY VB.NET PROGRAM. KINDLY SHARE THE CODE FOR THE SAME SO THAT I CAN GET THE DATA AND RESTRUCTURE THE SAME AS PER MY REQUIREMENT.
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17 Comments
I am having trouble using the Mitov Openwire VCL components TVLIPCamera.
I am writing a Windows 32 C++ application using Embarcadero XE10.2 to stream video from an IP camera.
I have a single for Form1 with a TVLIPCamera and VLImageDisplay component, the output pin of the TVLIPCamera component is connected to theinput pin of the
VLImageDisplay. I have set the URL property of the camera component to http://username:password@192.168.1.65/mjpg/1/video.mjpg
the code compiles and runs but there is no video displayed. Mitov advertises the TVLIPCamera component as suitable for use with a "generic IP" camera although the term "generic" is not defined.

I can test the camera with an web browser using the following URL  http://192.168.1.65 Which then prompts me for a user name and password,
after entering both, live streaming of video from the camera is displayed in the browser.
 I have monitored the network traffic to the camera with Wireshark and when the RAD C++ builder application runs, a TCP connection is made with the camera and Wireshark shows 9 TCP packet exchanges but then communication stops.
Any suggestions as to what the URL should be or otherwise what the problem might be would be greatly appreciated ?

The IP camera is a SANNCE Security Cameras Wifi 1080P which is manufactured by ANNKE
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4 Comments
Hi Experts.

Got a question we seem to disagree on amongst colleagues.

In "modern" Windows environment (2008, 2012, 2016) with multiple DNS servers within unique AD (let's keep it simple for argument sake and not talk multi AD or forests), what is the best practice when it comes to IP assigning.

#1. Each DNS server has itself (loopback) as unique DNS entry in the TCP/IP settings, and any second DNS is declared in the Name Servers tab.
#2. Each DNS server has itself (loopback) as Primary DNS entry AND any second DNS is declared as Secondary DNS entry in the TCP/IP settings.
#3. Each DNS server has the secondary DNS declared as Primary AND itself (loopback) in the TCP/IP settings.

All three scenarios seem to work 99% of the time, when it comes to AD replication mostly, but at times, we like to point fingers at each others config for any downtime that occurred, and subsequently buy a round of coffees for the team :)

Any Experts wish to comment ?
Cheers.
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7 Comments
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
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15 Comments
What is the purpose of in-addr.arpa within Server 2016 DNS?

in-addr.arpa
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6 Comments
Within Server 2016 DNS Manager what are SRV records used for?

SRV records
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3 Comments
Within DNS manager, what are the values in the brackets "[ ]" within the Data column?

Data values
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2 Comments
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

tcpdump:

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 [.], …
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8 Comments
Rowby Goren Makes an Impact on Screen and Online
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Rowby Goren Makes an Impact on Screen and Online

Learn about longtime user Rowby Goren and his great contributions to the site. We explore his method for posing questions that are likely to yield a solution, and take a look at how his career transformed from a Hollywood writer to a website entrepreneur.

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We just switched to a different ISP provider a few days ago. Since then, there have been several Bad Address entries in the DHCP server (Windows server 2012). After deleting them, they'll appear again in an hour. Their Mac addresses are not shown in the address lease.

I used the DHCPFind to check if there's any other DHCP server on the network. The result is attached.

How do I find out what device(s) is causing the issue? Or How to fix this issue?
DHCPFindResult.JPG
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13 Comments
Dear EE,

I have found warning at DB server when user has reported Application dis-connectivity.
 
1)  User reported Application Dis-connectivity Error as attached.
SQL Error

2) We investigate the issue and look in to the Event logs and found below WARNING. Event Id : 4227

TCP/IP failed to establish an outgoing connection because the selected local endpoint was recently used to connect to the same remote endpoint. This error typically occurs when outgoing connections are opened and closed at a high rate, causing all available local ports to be used and forcing TCP/IP to reuse a local port for an outgoing connection. To minimize the risk of data corruption, the TCP/IP standard requires a minimum time period to elapse between successive connections from a given local endpoint to a given remote endpoint.


Please confirm will user application error is due to this above error.

Thanks
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1 Comment
I am having problem with using arpspoof on my kali linux box.  i am receiving the following error " arpspoof: couldn't arp for host 10.10.9.5(windows 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  10.10.6.1 (which is the SVI), and the cisco switch arp table is populated.  

Below is the command Im using.

arpspoof -i eth0 -t 10.10.9.5 10.10.9.1

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
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1 Comment
Hi!  anyone have any luck with a "TELNET" like connection with MS ACCESS?    I send simple text commands to a connected unit via TELNET.    By TELNET I mean using a communications application that converses with a connected device via IP address.     Something like sending "readbuffer01" and a response like "0,00.4,2" is returned by the conneted device.   I do this over a TELNET application like Tera Term set up for IP of the connected device xxx.xxx.xxx.xxx format for IP and TCP/IP port 3602 emulating a VT100 terminal.   Any way that ACCESS can send commands and listen for a response like these terminal programs.   I am basically trying to automate data collection over the tcp/ip connection and store in a form/table.

Thanks!
Brian
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7 Comments
Hi Experts,
How to grep connected tcp IP & Port connection then forcefully kill using batch.

example;-
netstat -a output is

Active Connections

  Proto    Local Address                        Foreign Address                State
  TCP       192.168.1.101:49366            192.168.1.55:65000          ESTABLISHED
  TCP       192.168.1.101:49475            192.168.1.55:64000          ESTABLISHED
  TCP       192.168.1.101:49384            192.168.1.55:63500          ESTABLISHED
  TCP       192.168.1.101:49396            192.168.1.55:22                 ESTABLISHED

Need to forcefully kill all TCP connection which is connected with 192.168.1.55
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5 Comments
I bring my (Windows 10 Pro) laptop around to do support in a few different networks - some with DHCP and some where a fixed IP-address is needed. Have tried to find a way to make shortcuts to set the fixed addresses (or set the network adapter back to dhcp), but haven't found a way to do it. Thinking of commands in a batch-file. Any suggestions?

-Olaf-
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9 Comments
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?

Thanks
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2 Comments
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

…
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0 Comments
Cisco Network Question:  2 vlans and one Internet connection

I need to set up a guest network for access to the Internet-only.  The network configuration is:
-  COX Internet
-  RTR_FW: Meraki MX64
-  Core_Switch: WS-C2960X-48FPD_L:  LAN-base
-  Distribution_Switches: WS-C3560CG-8PC-S: IP-base

We presently have one external IPv4 address and use 192.168.168.0/24 internally for operations.

The 2960X is a layer 3 capable switch.

Is there a way to route another network VLAN, something like 172.16.168.0/24, to the Meraki RTR Internet connection.  The Meraki is presently port mapping the external address to the 192.168.168.0/24 network with the Default router of 192.168.168.1.  I used a trunk to the Meraki RTR-FW from the 2960X and it works....

Or do I need to add a RTR and use two virtual interfaces?
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9 Comments
OWASP: Threats Fundamentals
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Hello,
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?

Thanks
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5 Comments
Hi All,

i need to listen on port for testing on a windows server. Do anyone know of a utiltiy? i used one before however unfortunetely i didnt keep a note of it.

Regards,
kay
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8 Comments
Today we faced the Email Delay issue on Exchange environment. Emails were delivering with 5 to 7 minutes delay. On investigation, we found following errors on server. It appears from the first error there could be some connectivity issue between the Exchange servers, but both the servers are located on same chassis, the chances of connectivity issue is very low. After restart the issue gone it also shows there was no connectivity issue. What could be the issue?

Error on Server Queue:
{LED=441 4.4.1 Error encountered while communicating with primary target IP address: "Failed to connect. Winsock error code: 10048, Win32 error code: 10048. "Attempted failover to alternate host, but that did not succeed. Either there are no alternate hosts, or deliver failed to all alternate hosts. The last endpoint attempted was x.x.x.x:475]

Warning on Server Log:
TCP/IP failed to establish an outgoing connection because the selected local endpoint was recently used to connect to the same remote endpoint. This error typically occurs when outgoing connections are opened and closed at a high rate, causing all available local ports to be used and forcing TCP/IP to reuse a local port for an outgoing connection. To minimize the risk of data corruption, the TCP/IP standard requires a minimum time period to elapse between successive connections from a given local endpoint to a given remote endpoint.
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10 Comments
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!!

Brian
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7 Comments
How can I completely disable IPv6 from all network adapters on a Windows 7 Pro. computer?  The use this method to roll-out that configuration change to hundreds of computers?  Is there perhaps a script?

What I am looking for is to disable or un-check the ipv6 settings.

ipv6_1
I want it to be grey'd out or disabled.

ipv6_2
According to web page: https://techjourney.net/disable-turn-off-ipv6-support-in-windows-10-8-1-8-7-vista/

I have tried opening a command prompt as administrator and running 
reg add "HKEY_LOCAL_MACHINE\SYSTEM\CurrentControlSet\Services\Tcpip6\Parameters" /v DisabledComponents /t REG_DWORD /d 0x000000FF /f

Open in new window


But after I run this command I think IPv6 is disabled partly; but, I still see the check mark on the adapters indicating that it is still enabled.  

Question1: How can I disable the ipv6 for all adapters on a windows 7 Pro. PC?  My manager specifically asked me to do the un-check box, to make it look disabled.

Question2:  How can I use that method for a mass deployment to change the config on hundreds of devices?

Question3:  How can I verify that IPv6 is indeed disabled?

Before the registry changes, if I ran an ipconfig all, under "Ethernet adapter Local Area Connection"  I saw
IPv4 Address. . . . . . . . . . . :  ###.##.##.###
Then I saw
DHCPv6 Client DUID. . . . . . . . : ##-##-##-##-##-##-##-##-##-##-##-##-##-##

After the Registry changes, I do not see any reference to DHCPv6 Client DUID. . . . . . . . : ##-##-##-##-##-##-##-##-##-##-##-##-##-##
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19 Comments
Hi... Can anyone tell me what is this Simple Network Audio Protocol running on port 4752 ? Thanks
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1 Comment

TCP/IP

11K

Solutions

6

Content

i
The collection of articles, videos, and posts on this topic.

17K

Contributors

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.