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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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Recently had a perculiar issue with clients on one of our customers networks that stopped being able to lookup names on the internal network, losing network drives, gpo etc as a result.

DHCP is served by windows server 2008 DC with DNS service also hosted on this with the relevant pointers to this set up in DHCP.

We ended up having to statically set the DC name in the HOSTS file until I looked at this onsite this morning, I noticed a nslookup was resolving the router as the dns service instead of the DC. Powering off the router and running the same nslookup and it resolved to the DC. DNS and DHCP were both disabled on the router.

I made a change to the Interface in DNS as it was set to 'Listen On All IP addresses' I changed this to 'Listen on specific IP' which was the IP of the DC(Itself). Flushed the cache on the clients, restarted them they got the gpo, drive mappings, and I could resolve the server by name.

However, a nslookup still resulted in the router name rather than the DC name, despite obviously being able to resolve hosts on the network.

I then disabled ipv6 on one of the clients nics and hey presto a nslookup resolved to the IP of the DC, if I re-enable ipv6 on the nic it reverts back to resolving the router.

My thoughts are that the client isn't able to resolve the DC by ipv6 so it is reverting to the server for some reason, perhaps because of forwarders/root hints set up in DNS.

They are up and running again but I have noticed …
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I tried to fix this error but but no luck. Below is the question I posted before.

Is there anyone who can assist me to fix this?
Really appreciate
I have a remote site with no local tech support. The gateway is a Fortigate firewall. Recently, when trying to sign in to edit firewall rules, I have started getting a logon prompt describing level 15 access and referencing an IOS certificate that cannot be verified. Sometimes it allows the https Fortinet web page login, and sometimes it produces the logon box- obviously a Cisco device. I have tried using an IP scanner but it doesn't allow to browse that IP (Advanced IP Scanner has a dropdown that allows you to see available resources at an IP, such as web pages and FTP sites), and I have not been able to connect via SSH (The only shell option I have is within the Fortigate web administration, and I can't get the page to load reliably for obvious reasons). This site is 3/4 of the way across the country so traveling there is out of the question. I cannot just re-IP the Fortigate for two reasons: I can't get it to save changes, and I can't take down the plant's production gateway from across the country without any kind of guarantee that I'll be able to rescue the device or limit downtime. My goal is to identify the Cisco device, possibly by obtaining the serial number so I can find out who owns it and have them correct it's IP address. I'll welcome any advice as to how to get to that point... Anyone? I appreciate your help.
Need to refresh DHCP IP address reassign Needed to command
Michelle Phillips
Sometimes clients can lose connectivity with the Lotus Notes Domino Server, but there's not always an obvious answer as to why it happens. Read this article to follow one of the first experiences I had with Lotus Notes on a client's machine, my now good bipolar friendly software.
First, If I am correct:
Standard Access-list  can match traffic based on Source IP address only
Extended Access-list can match traffic based on Source/Destination IP address , port number, protocol, etc...

well, there is also  Named Access-list. We can have Standard Named Access-list and Extended Named Access-list
  Is Standard Named Access-list similar to Standard Access-list, it can match traffic based on Source IP address only ?
Is Extended Named Access-list  similar to Extended  Access-list ,it can match traffic based on Source/Destination IP address , port number, protocol, etc. ?

Thank you
I need to know the difference between :

Access-List 100 permit .....
IP Access-list extended 100.  
  ip access-list extended name

if I have forgotten other access-list types , please list and explain it :)

Thank you
Hello Everyone!

We had some security cameras installed and the installer asked me to open port 8000 for the dvr.  We have a Sonicwall 1260 Pro and I followed the instructions for port forwarding.  I created the service for both TCP/UDP, port 8000 and then created the group.  I used the public server wizard to allow public access to the camera ip.  After everything was complete I used the site,, to check if port 8000 was open.  Unfortunately, the port is still closed.  I'm stuck figuring what I could be doing wrong.  We do have 2 static ips for the site.  The other ip is used for the fax machine line.  i don't know if this could cause the problem.  Any help is appreciated.

Router: SonicWall 1260 Pro
ISP: Cox
Camera IP:
Port: 8000
In the example below, which wildcard mask will cover  the 4 subnets only

I though is correct, but it will cover more than those 4 subnets.

Any wildcard mask calculator link, will be helpful.

We have an odd situation.

It's a hodgepodge network in a franchisor's location.

It's technically administered from head office on the other side of the country but they get me to do some of the work as I'm less annoying than the main IT.

Windows Server 2012 peer-to-peer system

#1. A windows 7 Professional station gave hard drive warnings (failure imminent) and infection notices
#2. Took station, cloned drive onto SSD
#3. autologon for computer was now erroring out. Had no idea what old password was, created new one with autologon in the registry
$4. Disinfected computer via Malwarebytes and installed Barkly endpoint
#5. Find out that the server is used to access 3 shared folders via peer to peer on the station and that it can't access the shares

At this point I figure that the issue is simply related to the password change, but no.

The server is unable to ping the station, either by name or by ip address. However, the station can ping the server by both name and ip address.

It looked to me as if DNS was incorrectly configured on the server (typo), so I fixed. ( to

#1. I've tried repair network on both.
#2. ipconfig /flushdns on both
#3. rebooted one or both after each or every other change
#4. turned off homegroup on station
#5. changed station network type from home to work
#6. created hosts file entry for station name to ip address
#7. tried to ping TCP/ip 6 address (no go)
#8. checked for saved credentials on the …
Building an interactive eFuture classroom
Building an interactive eFuture classroom

Watch and learn how ATEN provided a total control system solution including seamless switching matrix switch, HDBaseT extenders, PDU, lighting control to build an interactive eFuture classroom.

Hi guys,

I am a network engineer and I have a requirement where I was asked to design IP PBX system with  Analog phones
can I use cat6A cable, CAT6A patch panels or I have to consider 110block?

Can anyone please guide here, it's very urgent...........
What is the difference between Internet Protocol (TCP/IP) Enabled or Industrial standard (modbus, profibus, etc) enabled communications with HVAC systems for the data center?
Very bizarre issue. Details:

1. A customer on fibre-optic high speed Internet (via ISP-provided router) cannot connect to nor ping a mail server at
2. I arrived there with my own laptop, tried both LAN and wifi, and also could not ping the mail server.
3. I remoted into 3 other computers from his house, and from those remote computers, pinged the mail server just fine. These two other computers are in the same city as my customer. Two use the same ISP as my customer.
4. The ISP apparently logged in and checked his router - they say all is fine, and they have no idea why this would be happening.
5. Except for the inability to reach the mail server, the connection is completely fine - can get anywhere on the Internet, etc.

I seem to recall having an issue like this years ago, and it had something to do with routing at the ISP, but cannot remember any details.

Has anyone ever encountered anything like this?  I'm going there in two days to do a full reset of his router, but not confident this will be the cure.

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?
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  netmask  broadcast
        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  netmask  broadcast
        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  netmask
        inet6 ::1  prefixlen 128  …
Hello all,
our HTTP packets go via a proxy, unlike the rest of the TCP/IP packets.
so using ping to measure the latency between us and a webserver won't be very accurate. we need to measure latency over HTTP instead of ICMP.
any help ?
System: windows 10

After running windows update i can ping internal and external Ipaddress but kant access any internet pages or internal shares

- Checked Windows Firewall
- Disabled the firewall

No luck
Run the command Netsh

- Netsh int ip reset reset
- Netsh int tcp set heuristics disbled
- Netsh int tcp set global autotuninglevel=disabled
- Netsh int tcp set global rss=enabled

No luck

- Run the command Netsh

- Netsh winsock reset

No luck

- Ipconfig /release
- ipconfig /renew
- ipconfig /flushdns

no luck
Installed telnet and telnet the port neth 3389
commands successvol

issue still there any help or idees will be appreciated
Our school network has the following:
Sonicwall NSA 250 M Router (acts as gateway and also handles a separate VLAN)
Network address / 24 (subnet mask
Single DC running Server 2016 std (ip, handling DNS and DHCP
About 150 endpoints

We're in danger of running out of IPs, so I'm hoping there's a way we can change just the subnet mask and retain the - range while gaining an extra range of IPs on the same, new subnet (for example 192.168.2.x, or .0.x) .  I'm also hoping that changing the subnet mask (but not the IP) of the DC will not cause problems. I know I'll have to reconfigure the subnet mask on any non-dhcp devices (such as network printers and the server).

So I've a couple of questions. What's the best way of doing this?  
Which subnet mask would yield what ranges of IPs?  
Is changing the subnet likely to cause any issues for the server (which I envisage keeping on the same IP?

Thanks in advance.
how to send and receive the message through in tcp/ip using servlet
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When I connect vo my remote SQL Server  via Microsoft SQL Server Management Studio I get the error 121.

A Transport level error has occurred when receiving results from the server.

I'm at spain and my Internet provider is Movistar.

When I open Microsoft SQL Server Management Studio , I can Log on with my credentials, the connection is via SQL login, and the connection is like\Instancename,49888

49888 is the port I'm using.

I can connect to the same server throug other computers form other places with different Router.

If I connect a USB Internet stick to the problematic computer, then it Works fine, then I think is a router issue. But when I call to my internet provider (Movistar) they say that all the outgoing ports are open.

Any idea?
I'm taking over a new network and the IP scheme is set up as 10.10.x.x/8. I want to change it to a/23. Can I do this within my DHCP and on my router without any changes to my printers and dusktop?
What is the importance of this message.
What should I be concerned about? Or When should I be concerned about this?

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
I am able to send email to gmail (of course) although it does show up as spam, outlook flatly rejects the .loc domain... but still cannot send between two .loc domains in lab..

I created two domains, dc2016.loc and dc2016a.loc (using 2016 essentials as DC) I have added both domains to the accepted domains list however, when I attempt to send to either of the two .loc domains, the email gets rejected as, unable to locate a valid address...

Looking at the recipient Information in the Queue Viewer, I am seeing Last Error: [{LRT=};{LED=};{FQDN=};{IP=}] even thought I have added them as accepted domains...Any thoughts?

I have just added a virtual private NIC to both exchange servers, and added appropriate send receive connectors on each

I have both NICs setup to Enable NetBIOS over TCP/IP as well but still having this issue... any thoughts?
I have a url with
what does the 8888 represent?





Articles & Videos



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.