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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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I have two questions about "under the hood" processes executed by Webrequest and the getresponse method.

1) I have noticed while packet capturing that, when doing a webrequest with a payload, packets starting a TCP/IP connection are sent and received *before* the getresponse method?  I would have expected the payload to be cached and sent only when the getresponse was called?

2) I have a webrequest case that has me puzzled.  It is an HTTPS URI.  All proceeds as expected (443 TCP/IP connection made before getresponse called) until the getresponse is called.  When that happens, the process attempts to create a new TCP/IP connection to the server, this one being on port 80 (not HTTPS).  Since the request is not HTTPS, the server ignores it and the process times out with a "no response from server".

What would cause the getresponse method to spawn a new connection, and why would it send it via HTTP when the original connection was made via HTTPS?  The certificate for the server is valid, and I have tried turning off the check-certificate functionality.

Thanks for any insight on both questions.

Bryan Hunt
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my network is as follows:

Comcast 10.1.10.1

Sonic Wall - 10.1.10.2 (gateway 192.168.1.1)


Just double checking, I want the SonicWALL subnet to be private.  I am a little concerned because when I am on a workstation behind the sonic wall I can ping the Comcast gateway, and navigate to the admin portal.

However, when I am directly plugged into the Comcast gateway I cannot ping the 1.1 gateway subnet.  So the SonicWALL subnet is not visible to the main comcast network.  Is my network setup and secured as intended?
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Hello Experts,

We have an application which is login on CentOS 6.8 64 bit (GUI Interface) & after login generate tcp port 50000 for make connection with user.
Behind that port there are many connection connected with different-different IP (192.168.207.11, 207.12, 207.13) & user name (user1, user2, user3):

Example Output:-
[root@CC ~]# lsof -i :50000
COMMAND    PID USER   FD   TYPE DEVICE SIZE/OFF NODE NAME
TCPServer 3647 rajat  245u  IPv4 156532      0t0  TCP 192.168.207.125:50000->192.168.207.15:49277 (ESTABLISHED)
TCPServer 3647 rajat  261u  IPv4  23354      0t0  TCP *:50000 (LISTEN)
TCPServer 3647 rajat  387u  IPv4  24955      0t0  TCP 192.168.207.125:50000->192.168.207.13:49271 (ESTABLISHED)

From this cmd i only check which IP is connected behind port 50000, but i want to check user name also. Please suggest.
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Hi,

Is there such an application that can scan ports between two devices so see there which ports are open/closed/listening?

We have two devices, each one on different sides of wireless link, on the same network, and we wish to confirm there is no issue of ports not working.

The type of app I am think is iperf but for ports.

Thanks,
Col
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This morning when I got to work a couple of machines could not access the internet, including my own. The only common thing is that they have all got static IP addresses for RDC connections.

main subnet => 192.168.16.1/21
DHCP scope => 192.168.18.10 - 192.168.18.255

my static IP => 192.168.19.3

On the PC's which have a static address if i change them to DHCP everything works. If they are static they are not able to access anything external. Internal Sites work fine. DNS lookups work fine for both internal and external sites.

I have tried getting a dhcp address on my PC, then setting the exact same IP address manually and see the same restrictive behaviour. Everything was fine yesterday evening when we left, nothing has been changed. i cant see any updates have occurred. i have checked router settings and rebooted several times. still no joy.

Any Help would be appreciated.

Thanks

Michael
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Hello Experts,
I just installed sonicwall tz400w and everthing is going well except printer. Printer disconnect automatically after few minutes. I have to connect them manually again and again. I am using commercial printer by konica minolta and i use fiery app on Konica. Its working fine without the firewall.  Please help
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Need to access an application on a company Windows Server from outside using an iPad, Server has a private Static IP (10.x.x.x). The office router has Public Static IP interface. How can I access the server from outside on an iPad? Can I access the server using a public IP is this situation? Please advise.
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We use a service to route calls for our call center. There are about 100 call center agents and everyday, four or five will have trouble launching the soft phone application. We connect to the call manager and soft phone system via and MPLS.

Sometimes restarting the PC fixes it. Sometimes resetting the browser fixes it, sometimes disabling / re-enabling the NIC fixes it. Sometimes it magically fixes itself.

The attached packet capture image from Wireshark typifies what a TCP stream looks like from a PC experiencing  a failed application launch.

NOTE: In the attached file, the TCP RST flag is not always seen. Many times I only see the TCP re-transmissions or TCP SEQ Out Of Order.

Questions 1: Am I right to believe my problem is, either a reset is being thrown or the other side stops responding for some reason, hense the re-transmissions

Since this is over an MPLS, I am not able to get a capture from the other side.

Question 1. What troubleshooting steps should I take to identify why I am getting these re-transmission, and or Resets.

Question 2: Is it possible that some traffic might be routing out the MPLS, while other is getting lost in the network? If this were possible, and I wanted to capture the packets on the Switch, would I SPAN the both the interface connected to the PC and the Interface connected to the router, or just the router?

Note: I don't have trouble logging into the portal, I have trouble launching the softphone, which uses a browser …
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I have a client/server TCP .Net application. I am getting exceptions on NetStream.Read or Write operations, no data received, if there is a delay of about 10 minutes or longer.

The client app contacts the server. The client may send blobs (many reads and writes back and forth for each blob) of data to the server. The server may then send blobs of data back to the client. There can be a processing delay before each sent blob. Everything works with even large blobs going back and forth. The problem occurs when the processing delay before starting to send a blob becomes around 10 minutes.  For example: Connect, client sends a blob, server process for about 10 minutes, server tries to send a blob, error on first TCP write (read error on first TCP read on client). This problem does not occur if the client and server are on the same LAN. It only occurs when a client outside of the LAN connects through the Router via port forwarding to the server.

Is there some kind of router timeout setting I should be considering? Or maybe an "idling" parameter to tell the TCP connection to stay active for long periods of time?
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I have a Juniper QFX. My infosec team wants me to disable the TCP timestamp as per the ID: 80091

Now I know how to disable ICMP timestamps, but not the TCP timestamps. And I don't want to disable it for the whole QFX. If it can be done for an interface, that will be awesome.

Any help will be appreciated.
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For some reason this virtual machine running Windows 2003 Std SP2 started to bluescreen and reboot non-stop, it will stay up for a few minutes and them it crashes, the mini dump contains the following. This server is a stand-alone server. Any ideas will be welcome.


==================================================
Dump File         : Mini120817-08.dmp
Crash Time        : 12/8/2017 7:29:59 PM
Bug Check String  : IRQL_NOT_LESS_OR_EQUAL
Bug Check Code    : 0x0000000a
Parameter 1       : 0x00000000
Parameter 2       : 0xd000001b
Parameter 3       : 0x00000001
Parameter 4       : 0x808312e7
Caused By Driver  : tcpip.sys
Caused By Address : tcpip.sys+1ce7a
File Description  : TCP/IP Protocol Driver
Product Name      : Microsoft® Windows® Operating System
Company           : Microsoft Corporation
File Version      : 5.2.3790.4573 (srv03_sp2_gdr.090815-0925)
Processor         : 32-bit
Crash Address     : ntkrnlpa.exe+8c9eb
Stack Address 1   : ntkrnlpa.exe+312e7
Stack Address 2   : ntkrnlpa.exe+28191
Stack Address 3   : afd.sys+153f
Computer Name     :
Full Path         : C:\WINDOWS\Minidump\Mini120817-08.dmp
Processors Count  : 8
Major Version     : 15
Minor Version     : 3790
Dump File Size    : 85,344
Dump File Time    : 12/8/2017 7:31:29 PM
==================================================
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Hi all - Will try to explain carefully ... thanks for reading ...  

My problem:
I am experiencing intermittent issues when watching a movie, which is a 7GB file on a local network drive of mine. Downstairs all works fine. Upstairs, when the issue occurs, the movie will play for 10 seconds, then I get a wait-icon (hourglass or what have you) for about 10 second, back & forth over & over.
Sometimes it behaves this way, and other times is perfect.

My Network:
Fast Ethernet service (Time Warner) from the street into my Modem. All over Downstairs it clocks at 110 Mb download and 13 Mb upload, using speedtest.net.
UPSTAIRS I have an Apple Airport Express, setup as a Bridge "Extend an existing network", which worked fine downstairs until I moved it upstairs.  Then connected to that is an Apple TV connected wirelessly, using the same netwk name (SSID).  It clocks at 30 Mb down & 8Mb up, way slower than Downstairs, but I thought would still be fast enough to watch a movie without speed issues.

Note that the data/movie is coming over my LAN ... that I have saved on a local network drive in my house. It is *not* being streamed from any services!  The 7GB Movie is on an ext hard drive plugged directly into the Airport Extreme Base Station.

Can anyone suggest how to troubleshoot this? It's been a long time since I broke a perfectly working network and had to do this!  I am thinking:
- Get a meter or Util to measure exact bandwidth/signal strength?
- Change to use …
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When a client initiates an SFTP upload to a server - is the size of the file to be coming included in the early part of the conversation? It would be helpful to know in some instances. Thank you.
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Hello,

Recently we have begun observing some SMB errors logging on our 2k12 R2 servers indicating a failure connecting to a share.  We have a NAS appliance servicing the share(s) in question via SMB3.  Thus far we have bee unable to identify an issue at either the client nor the server level, so it has been very frustrating.  

One thing I can say is that the issue only occurs sporadically and not on all machines, so my inclination is that it is something on the Windows side, but I'm just not certain.

Below is an example of the error.

The network connection failed.

Error: The transport connection is now disconnected.

Server name: \xxxxxxxxxxxxxx
Server address: xx.xx.xx.xx
Connection type: Wsk

Guidance:
This indicates a problem with the underlying network or transport, such as with TCP/IP, and not with SMB. A firewall that blocks port 445 or 5445 can also cause this issue.


Thanks in advance!
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So im given a subnet range of x.x.54.128 /27

Does this mean any address from 54.128 - 54.254? With a subnet mask of 255.255.255.224

That sound about right? I need to static assign a few servers within that range.
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Hello,

       I am running through the securing TCP/IP of the N10-06 certification and having difficulty understanding the use of Hash. I get the process of using the algorithm to change the data, but what I don't understand is how that is applied and how it is decrypted on the receiving side to get the data. I have read that it is a One-Way system and cannot be decrypted, but if that is the case how does the recipient decrypt it? Is there a public key sent with the hash and what portion of my computer actually does the decryption. I've been Googling on this a while and reading Mike Myers book as well as Professor Messers video on it, but I am only getting vague descriptions on the intent and concept but not how its staged and executed. Does anyone have any sage advice on this?

Thanks!
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I've got a client that is running the DHCP role on their domain controller. They are running a 192.168.1.0/24 network and they are running out of addresses. What they would like to do is move to a /23 network so they have a larger pool of addresses. What needs to be done to convert the /24 to a /23 network on the server? Once the /23 network is setup, do I just need to reconfigure the subnet mask on everything static? A reboot to dynamically assigned hosts fix their network connections, right?
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We have seen that SNMP uses UDP as its transport protocol.  Why was UDP chosen over TCP?
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One of the first steps in configuring a device to be managed is to give it an IP address. Why?
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hi experts,

 I changed my printers ip address and I'm on the server and trying to change the ip address and while I try to add a standard tcp/ip port I get access denied, I'm logged on as administrator. see picture
printer.png
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I am trying to install  Dell Laserjet 5210n on our school network server so it can be shared across all clients. I have assigned a static IP address to the printer and I can ping it. When I try to install the drivers I downloaded from the Dell website I get the attached error.
I have tried installing as a network printer using the TCP/IP port and also as a local printer also using the TCP/IP port. Either way I get the same result.
The Server on the network is running Windows Server 2008R2 and all of our clients are Windows 7 Pro.  I did try to install it using a PCL driver found in Windows and I was able to print one test page but after that the printer went offline and will not come back on line even though I can ping still ping it.

Please Advise.

Thank you!

Robert
Dell-Printer.jpg
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if I disable ipv6 will it cause a problem on my network?
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hi experts,

 please see screen shot, sometimes my computers get one ipv4 address and I can go online but sometimes I get TWO of them and unable to go online??
ipv4.png
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Visited a client site and ran various ‘my ip address’ site to determine what is the External IP address the provider assigned.  Noticed that each device resulted a different value.  For example their phone and their tablet gave different values where that last segment changed (xxx.xxx.xxx.19 and xxx.xxx.xxx.20), yet when we ran myipaddress in our device gave a whole different value in all segments.

We understand that the internet provider assign the cable modem or location a single dynamic external ip.  The location router managed a total different internal ip sequence values and assigns it to each device connecting to the wifi or router within the location.  Thus the cable modem has 1 IP address and the devices within the location has different ip address.

Why would the “my IP address” website display different IP address in all devices connected to the same wifi?
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When adding the DNS server address of a server (and the server itself is a DNS server), is it preferable to add the IP address as "127.0.0.1" or should the server's actual IP address of 192.168.10.20 be used?

I have seen both types of IP addresses used and am wondering if there is an advantage of using one over the other or if there are any problems with using one IP address format over the other one.

This is in a Server 2016 environment.
1

TCP/IP

11K

Solutions

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.