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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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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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We have a GPS tracking app
There is one windows app on windows server 2016 which communicates with the gps devices on different ports and accepts the data

We have recent seen problems where the gps devices stop reporting, even though they are constantly sending data every 30 secs  (some are saying 6 hours ago)

When we restart the windows app, they start reporting again within 30 seconds

We have 2 devices working on port a certain port
However, when looking at netstat, its showing 62 connections, and they are all ESTABLISHED
This sounds like its the cause of the issue

C:\Windows\system32>netstat -a -n | find /c "3333"
62

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 TCP    82.113.146.43:3333     41.80.64.186:50270     ESTABLISHED
  TCP    82.113.146.43:3333     105.48.38.41:49817     ESTABLISHED
  TCP    82.113.146.43:3333     105.50.155.210:51853   ESTABLISHED
  TCP    82.113.146.43:3333     105.51.186.160:54257   ESTABLISHED
  TCP    82.113.146.43:3333     105.51.233.133:59692   ESTABLISHED
  TCP    82.113.146.43:3333     105.54.2.101:57306     ESTABLISHED
  TCP    82.113.146.43:3333     105.57.244.173:52367   ESTABLISHED
  TCP    82.113.146.43:3333     105.57.249.109:50983   ESTABLISHED
  TCP    82.113.146.43:3333     105.58.227.38:53840    ESTABLISHED
  TCP    82.113.146.43:3333     105.59.87.117:64881    ESTABLISHED
  TCP    82.113.146.43:3333     105.59.254.162:55759   ESTABLISHED
  TCP    82.113.146.43:3333     105.61.81.156:60019    ESTABLISHED
  TCP    82.113.146.43:3333     

Open in new window

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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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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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Hello , does anyone knwo how to transfer iPhone contacts and messages to Android phone without any loss ? i've tried many ways to transfer them , but always fail ,and i don't how to connect the differen operation phones ,
Pls
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Does anybody know the exact function/meaning of the Windows regedit setting
  HKEY_LOCAL_MACHINE\SYSTEM\CurrentControlSet\Services\Tcpip\Parameters\StrictTimeWaitSeqCheck

I find no real documentation from Microsoft, but some sources state something like:
  "This key tells the system to wait for TCPTimedWaitDelay to pass before reopening a socket."


It sounds like that would be applicable only for creating new outbound connections, not for responding to inbound connections.
Is that correct, does anybody know?

Thus, TCPTimedWaitDelay affects handling of both outbound and inbound connections, but StrictTimeWaitSeqCheck only affects outbound connections?

And if not - why bother with StrictTimeWaitSeqCheck at all. Why not just set TCPTimedWaitDelay to 0?


Also, in addition, I cannot find any formal Microsoft documentation on the default value for TCPTimedWaitDelay. Some sources say 240 seconds and some say 120 seconds. My test results lead me to think that the default value changed at some time (when?) and at least since Win2012 it is 120. Any ideas on this?
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I've got a normal MS (IIS8) web serve (IIS8 on Windows 2012), to which client browsers connect to request html pages.

One client (or rather its proxy) behaves like this:
1) Outbound connections use a quite small port range
2) Connections in time-wait ,or where the other side is supposed to be in time-wait, are reused for new outbound connections after 60 seconds (the web server uses 120 seconds for this setting, hence the incompatibility)
3) New connections initiated from the client do NOT use a TCP sequence number that is always larger than the last packet sequence number on that particular src/dst pair. Instead a completely random value is used as initial sequence number.

Issue 1) means that the client quite often makes the web server run into a "port re-use" situation, such that a new inbound connection is using a src/dst port combination that has already been used before (the server port is always 80, of course)
Nothing bad with this, though.

Issue 2) means that the the port re-use according to 1) sometimes occurs while the web server is still in time-wait state for that particular src/dst port pair.
This is a problem, as the web server will then not accept the request for some more time (until the server time-wait timeout period finishes), and the client will end up retransmitting its SYN connection attempt during that time, delaying connection.
However, that would not be so bad if it wasn't for issue 3)

Issue 3) means that when 2) happens, the web …
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HI,
I have tried almost everything on the Internet, I am not sure what am still missing.
PC: Windows 10
Router: Port forward enabled with UnPnP

The webserver is a Datasnap REST webserver, (might be irrelevant), hosted with IIS on windows 10 PC, and its accessible to localhost as well as different computer on same network, However its failed to get connect to when accessible via public ip:port  even on same pc.
Tested the port which is listening correctly. I put firewall and Antivirus off for the test.

Please help.

Thanks and Regards,
Vijesh
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Hi Networking Gurus,
Sorry if i sound stupid but i am very new to networking.My application work as ESME  for the smsc  and it seems that recently we observing huge delay in ack of submitted  message or ack not coming at all.I can see in netstat output of linux send queue is increasing hugely.Taken a tcpdump in which i can  see to much [TCP Dup ACK],[TCP Out-Of-Order],[TCP Retransmission]

Also i see in wireshark
Smsc send mesg with seq:1 ACK:1 Len: 51 -->"213.132.40.140 -> 192.168.40.8 SMPP SMPP Deliver_sm"
but we reply by
 192.168.40.8 -> 213.132.40.140 TCP 42758 > dynamid [ACK] Seq=4141 Ack=52 Win=128 Len=0
That means are we losing frames.Pls help
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Hello I have a digital signage software server to remote led screens ..its   a web sever run on port   777  and 5222 it was work fine for few months my puplic ip was started by .195.xxx.xx.xx but now  it's stop i cant ping my pulic ip and all the ports is closed when I checked them by can you see me . Com now my public ip start by 63.xx.xx.xx what I can do to run the server again


Thank you
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Hello,

We use an RDP session through a VPN tunnel to connect to our hosted software out of state.

We constantly experience latency through all of our VPN tunnels.  I can run a constant ping from our hosted provider back to our environment to get a small picture how bad the response times of the pings are.

The ping times will be consistent for a little while hovering at 55ms - 67ms and then we will see "request timed out" multiple times and then ping times will rise.  It seems like the ping times fluctuate a lot  (I assume they would as the signal is traveling through multiple possible connections).

When ping times are at 55ms or less everything seems fine.  However, when it goes up from their end users report latency.

We are not hard lined to our ISP as everything is wireless.  Our internet pipe should be sufficient at all locations as we have spoken with our ISP and we do not hit the high water mark on our bandwidth - only rare spikes the main site.  

We are not hitting the high water mark on bandwidth usage at any of our other sites.  Is there a good piece of Enterprise level software that one could use to help get a clearer picture of where the issue occurs?

What kind of architectural questions should we be presenting to our ISP?   To our hosted provider?

1.  Is your VPN Server over-utilized?
2?
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How to enable Mysql server access through TCP/IP
where mysql installed in Centos machine.,.I am trying to access using mysql workbench it through TCP/IP but throwing error .. attached screenshot.
Where as when I select TCP/IP over SSH .. I can able to connect .
mysql-TCPIP.jpg
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I'm receiving this error among others, listed after. I have no idea why this error is coming up! how do I address?

Event 4879 MSDTC Client 2
MSDTC encountered an error (HR=0x80000171) while attempting to establish a secure connection with system SERVERNAME.

More errors that I don't understand and one that Microsoft doesn't even seem to know about (starting with that one)

The error that MS has no info on in Event ID Online help
Event 4230 TCP/IP has chosen to restrict the congestion window for several connections due to a network condition.  This could be related to a problem in the TCP global or supplemental configuration and will cause degraded throughput.
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Need to refresh DHCP IP address reassign Needed to command
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Let me start off by saying I'm in no way shape or form a network engineer. I am an IT Generalist and I'm in the process of trying to figure out why some remote IP phones have stopped working for a client. I don't want to get too into the weeds, but I've looked at and compared traffic from working equipment to this non working system. What I've seemed to have boiled it down to is:

Working: Phone tries to communicate on Port 6801 with server, server sends RST, ACK - phone then tries Port 6802 - same. Finally phone tries port 6800 and everything works fine.

Non-working: Phone tries to communicate on Port 6801, receives back a RST (without ACK). Phone continually tries to communicate on port 6801 until it reboots and starts over.

I've captured traffic at the server, at the firewall and at the phone. It seems like the packets are leaving the server as RST, ACK, leaving the Firewall as RST, ACK but arriving at the remote location as RST.

I'm looking for ideas on what could cause this?
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I have an IPv6 box that is supposed to be routing via HE. I have radvd configured, so it hands out a /64 subnet as follows:

interface enp2s0
{
      AdvSendAdvert on;
      AdvManagedFlag off;
      AdvOtherConfigFlag off;
      prefix 2001:470:1f17:204::/64 {
            AdvOnLink on;
            AdvAutonomous on;
      };
      # This is the DNS server on the internal interface
      RDNSS 2001:470:1f17:204:feaa:14ff:fe53:2eec {
      };
      route ::/0 {
      };
};

I have the interfaces up as follows: enp1s0 (enternal interface), enp2s0 (internal interface to LAN) and hurricane-ipv6 (interface to HE):

enp1s0: flags=4163<UP,BROADCAST,RUNNING,MULTICAST>  mtu 1500
        inet 184.71.193.90  netmask 255.255.255.252  broadcast 184.71.193.91
        inet6 fe80::219:5bff:fe2f:e30  prefixlen 64  scopeid 0x20<link>
        inet6 2001:470:1f16:204::2  prefixlen 64  scopeid 0x0<global> ...

enp2s0: flags=4163<UP,BROADCAST,RUNNING,MULTICAST>  mtu 1500
        inet 169.254.173.107  netmask 255.255.0.0  broadcast 169.254.255.255
        inet6 2001:470:1f17:204:21f:c6ff:fe5e:58b1  prefixlen 64  scopeid 0x0<global>
        inet6 fe80::21f:c6ff:fe5e:58b1  prefixlen 64  scopeid 0x20<link> ...

hurricane-ipv6: flags=209<UP,POINTOPOINT,RUNNING,NOARP>  mtu 1480
        inet6 fe80::b847:c15a  prefixlen 64  scopeid 0x20<link>
        inet6 2001:470:1f16:204::2  prefixlen 64  scopeid 0x0<global>...

lo: flags=73<UP,LOOPBACK,RUNNING>  mtu 65536
        inet 127.0.0.1  netmask 255.0.0.0
        inet6 ::1  prefixlen 128  …
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how to send and receive the message through in tcp/ip using servlet
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Hello-

I have an interesting setup. We switched to a hosted voip solution but for our emergency analogue lines we purchased two fxs vega 3050g gateways.

I have successfully configured the dialplans between the two units without the freepbx box as an in between. It is such a simple setup to just have it dial our security desk the pbx was not needed.

We are getting ready to deploy but have two lingering issues. To route calls between interfaces and the two gateway devices you have to initiate the sip handler to apply codecs and handle advanced features like call waiting. So dialing by IP between devices or loopback on between interfaces.

The one limitation I am running into is only one call at a time will take place between gateway... almost like the port is busy or it can only route one call at a time between gateways. Similar issue happens when trying to use call waiting... the first call connects but when I initiate the second call I get one indicator tone then the call fails with a cause code 41 (temporary network error)

Is this a matter of me needing to use more than the default udp port 5060 or am I just missing something here? I'm not a phone guy so I have a slight learning deficit.

I have combed through sangomas support site and manuals and found nothing like this... their support has yet to offer any solutions (on almost any of the setup.. which is troubling) so I'm turning to the community.

Thank you in advance
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(1) how can i know subnet mask & default gateway of any ipv4?
(2)Explain  dns server in detail?
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devices behind a switch are not able to acquire DHCP. when i assign a static IP it works OK.  the switch is connected by fiber optic to a core switch where the DHCP is configured
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Hello,
we have a TZ-210 wireless that need to change a couple of things on.  

We are connected to a comcast business gateway device.  It has wireless and we use that as an outside wireless,  It is not setup to access the internal network.  When we setup a laptop of phone we use that for VPN testing and remote connectivity.  I have 2 issues.

1. I cannot connect to the management interface on the modem, it is the default 10.1.10.1.  It keeps getting dropped in the firewall.  What rukes do I add to tallow this?
2. We cannot send email from our mobile devices when connected to the Comcast wireless.  I would expect it to be a rule as well, but I'm not sure what to add to make this work.

We want to keep the comcast wireless off the internal network. But we need to access the management interface, plus some of the users need to be able to send via exchange when using devices or phones and sending exchange email.

Thanks.
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I have 5 IP's assigned by AT&T to me on my On Demand Fiber circuit, but I only have 1 public address to the WAN. How do configure my 3 TZ300 to each use one of the assigned IP address and each to be a DHCP server?
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Here's my scenario.  I have two networks and I need to combine them, ideally using Cisco SG300.  
Basically, LAN1 nodes need to be accessible to the LAN2 devices.  
To be exact, LAN2 computers need to be able to "talk" (TCP inbound and outbound) to the LAN1 computers on different ports.

Please see the diagram.  

I think I need to create two VLANS but not sure about the details.  Is this even possible with this switch?

2017-03-14-22_58_37-SG300-switch.odg.png
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Hi

I have TDA200  I have made no restriction for Landline & Mobile and restrictions for International calls

I want to know...for dialing an international call it should be in such a way that they should be able to dial it with Code only. I want

to know the steps how to do it
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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.