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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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.
Python 3 Fundamentals
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Python 3 Fundamentals

This course will teach participants about installing and configuring Python, syntax, importing, statements, types, strings, booleans, files, lists, tuples, comprehensions, functions, and classes.


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
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.

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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:

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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!!

Bootstrap 4: Exploring New Features
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Bootstrap 4: Exploring New Features

Learn how to use and navigate the new features included in Bootstrap 4, the most popular HTML, CSS, and JavaScript framework for developing responsive, mobile-first websites.

Hi... Can anyone tell me what is this Simple Network Audio Protocol running on port 4752 ? Thanks
In the environment I am supporting for NGO's there are 2 Exchange Servers, an Exchange 2003 and an Exchange 2010 Server. On the Exchange 2010 Server since few days the router address is added to the IP Block List on the Hub Transport Server. Even after disabling IP Block Listing on the Organization Level the router address is added regularly to the IP Block List within Hub Transport on Server Configuration Level. Any ideas how to prevent this. Blocking does really block complete incoming mail traffic.

I started receiving TCPIP Event ID 4227 on two servers.  One server is an SBS 2011 domain controller and the other one is a Server 2016 Standard virtual machine on completely different hardware that only hosts a reporting software program.  These errors will occur at completely different times on each server so they don't seem to be related to one another at all.  The SBS 2011 server is running on it's own physical hardware, and the Server 2016 server is a virtual machine on a Hyper-V host which also has 6 other server virtual machines that are not experiencing this problem.

For troubleshooting, I have set the 'TcpTimedWaitDelay' to 30 in the registry on both servers and that did not fix the error.  I have also set up a script to run a netstat and get-process capture exactly when the error is logged in Event Viewer and I have collected the logs which are attached.  When looking through those logs I cannot determine what the issue really is since it doesn't seem to be related to the 'TcpTimedWaitDelay' setting.

At this time the error doesn't seem to be affecting any functionality on either server so I'm not sure how concerning this really is.

Any information is appreciated and if you need any further clarification on anything please let me know.

Thank you
I have two sites, both of which are connected to an MPLS that provides the VOIP and site-to-site data communications. The main site has dedicated internet (ASA 5520 and 2800) and is where the other site goes through via the MPLS. All of this is on the private side.

Both sites have regular 100MB/s cable internet for the public Wi-Fi in addition to the EOF/MPLS.

I want to add some redundancy for both locations in the event the MPLS or internet at the main site goes down and utilize the existing public cable internet service.

Looking for some suggestions for failover, using existing equipment or minimal equipment for site-to-site VPN connections. Not too worried if I cannot keep the voice traffic running, mainly a data/internet issue.

Thank you in advance.
dns3.jpgps assist why can't change dns ip address and apply register dns settings.
Issue with high number of  TCP CLOSE_WAIT socket connections on Hortonwork(HDP2.6.4) NameNodes & Metastore Server.
We frequently have very high number of CLOSE_WAIT  socket connections on hadoop servers, as a result hadoop services are unavailable on Namenode servers. This happen after heavy ingestion of data in cluster. As a result, I need to restart the cluster after re-booting concerned servers.
I tried re-setting  value of several TCP attributes on the servers, but this had not solve the problem.
Using lsop | grep CLOSE_WAIT, I can identified concerned processes which had CLOSE_WAIT socket connections, I killed the concerned process & try to re-start hadoop services but this had also not solve the problem.
I had monitored the servers for number of CLOSE_WAIT socket connections & whenever number of these keep rising , it's point to symptom that the hadoop services on NameNode are going to down in couple of minutes.
Any idea to solve this issue is welcome.
I am needing a revolving server system that changes IP address once it starts getting hits from sever filters. It needs to be seamless and use the same email address that we establish to send emails out from, but configures a different IP with every 50 to 100 emails. This is what we need to get a marketing job done and the email messages we want to send have to fit the character count specifics and font type. The subject line is the most important and the size cannot exceed X kilobytes for the total email to reach target market.

Can you please advise why IP of server is changing like

Pinging with 32 bytes of data:
Reply from Destination host unreachable.
Reply from Destination host unreachable.

Open in new window

Recently, our W2012R2 RDS server has started giving users problems logging in. The message is:
The number of connections to this computer is limited and all connections are in use right now. Try connecting later or contact your system administrator.

I'm having a hard time finding any helpful information on how to resolve this issue other than on desktop versions of Windows.

In a bid to get around this issue, I've opened more ports (HKLM\SYSTEM\CurrentControlSet\Control\Terminal Server\WinStations\RDP-Tcp 339x), and this has given some temporary reprieve.

It seems to me that the issue is pervasive. By that I mean that the message does not disappear even if existing users log off from their RDS sessions.

This RDS server has been working fine for years, and now, suddenly, this happens.
Become a Microsoft Certified Solutions Expert
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Become a Microsoft Certified Solutions Expert

This course teaches how to install and configure Windows Server 2012 R2.  It is the first step on your path to becoming a Microsoft Certified Solutions Expert (MCSE).

We run a small network with less than 256 devices so we use static IP addressing (IP subnet
We recently expanded our equipment so I changed the subnet to on all existing servers, workstations, printers, switches, routers, etc to accommodate new workstations in the 192.168.1.? range.

Any workstation (new or old) that I change to the 192.168.1.* range has communications problems. Most notably drive mapping on logon and being accessed by remove viewing products like VNC. Each time I change a machine back to the 192.168.0.* range the problems go away.

Any direction on how to troubleshoot this issue would help !
Please include the detailed explanation of the following:
Physical layer
Data link layer
Network layer
Transport layer
MAC address
IP address
TCP port
Checksum check
Routing table
Hello All,

I have integrated Kamailio 4.4 with asterisk 13 LTS and I think its been properly integrated. It also shows me the registered users but when i call from 101 to 102 it gives me the below error

[May  7 12:43:14] NOTICE[19838][C-00000000]: chan_sip.c:25545 handle_request_invite: Call from '101' ( to extension '102' rejected because extension not found in context 'public'.

I have followed the below for installation and configuration.

The user database is fetching from remote host in which kamailio has been installed. Users are showing in asterisk node as well

asterisk*CLI> sip show users
Username                   Secret           Accountcode      Def.Context      ACL  Forcerport
101                                                          public           No   No
102                                                          public           No   No

So how can i debug this or is there any clue that what might be wrong. Please find below  the extension.conf details as well.

exten => _1XX,1,Dial(SIP/${EXTEN})
exten => _1XX,n,Voicemail(${EXTEN},u)
exten => _1XX,n,Hangup
exten => _1XX,101,Voicemail(${EXTEN},b)
exten => _1XX,102,Hangup

Thanks and looking forward for some clues from this community

Atif Ramzan
Public IP configuration for two different network. I got error when I assign public ip address on port 1 and 2 with same subnet. for port 1 and i got error when I try to set up on port 2, "same subnet on port 1" I am using Cisco 1926.  How do I make this work? Any advise?
I am getting error 1m ipv4 tcp listen drops
"the number of TCP listen socket drops during the last minute"
Last night i tried to enables https on server with following steps
Added virtual host file but i reverted the changes.
I also executed the following commands: is it efected something on server.
sudo iptables -A INPUT -p tcp -m tcp --dport 443 -j ACCEPTED
sudo lsof -iTCP -sTCP:LISTEN -P
I'm sure this is simple, but I can't remember and I don't have time to figure it out, so...

I have a Windows 10 "All In One" lenovo computer.

The PC needs to connect to a small personal NAS via Ethernet, AND, the only way it can get Internet is Via Wireless.

The PC has both wireless and Standard RJ45...

I just can't remember how to do both at the same time.

Or, am I over thinking things: Just set a common IP for the RJ45 and the NAS , and then connect the wireless and I'm done...

Just not sure, and when I get there to set it up, it'll be too late to figure it out.







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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