[Product update] Infrastructure Analysis Tool is now available with Business Accounts.Learn More







The Dynamic Host Configuration Protocol (DHCP) is an auto configuration protocol used on IP networks and an extension of the Bootstrap Protocol. DHCP allows for computers to be configured automatically to communicate with each other over an IP network without the need for manual setup by a network administrator. The implementation of DHCP relies on a DHCP server to hand out network configuration information to DHCP-capable clients that request an IP address (and other information required or useful in communicating with other devices on an IP network). In addition to an IP address, common configuration information served over DHCP includes a default gateway, subnet mask and DNS sever(s).

Share tech news, updates, or what's on your mind.

Sign up to Post

Hello experts,

I am at a site and they use cisco WLC 5500 wireless controller and they have defined all the SSIDs , one of the SSID is the guest and I am checking the interface defined and it is clearly showing that it is on VLAN 50 the IP of the interface is given, plus the gateway which is same as the primary DHCP

I checked the core switch and there is VLAN 50 but just the vlan is defined but there is no SVI for vlan 50 and there are no DHCP services on the core, I checked the Microsoft servers and I do not see the scope for vlan 50. I am wondering how the clients are getting a dhcp IP when they access the guest SSID. I can not find this gateway or primary DHCP

This client also uses cisco ISE, I have access to the cisco ISE but it uses different IP and I do have access to it but I am not getting clarity on this network, Any suggestions on how to find this dhcp server or service will be great help.
OWASP: Threats Fundamentals
LVL 12
OWASP: Threats Fundamentals

Learn the top ten threats that are present in modern web-application development and how to protect your business from them.

We have a windows server 2008 with DHCP enabled. The scope properties display [] with start IP, end IP, subnet We want to know the easiest way to increase the number of IP addresses (example 1000 max) that can be given out by the DHCP server and make sure that everything is still routeable. For example, if one of the new IP addresses let's say is 172.22.2.x will that device be able to see the server at and access the gateway at We want to know how to do this and set it up properly.
Routing problem.... I do not think so.  What do you think?

I am trying to setup a new Wireless setup.  We are currently using HP MSM760; but, it is E.O.L. and we purchased an Aruba Wireless system to replace it.  I have never worked with either Wireless Systems and I am charged with:

1.  Learning how the HP System currently works.

2.  Duplicating the setup in the Aruba system.

I have been reading Aruba user guides  and setup you tube videos and I have everything connected and I have begun testing the SSID's.  The problem is that when I get any laptops or wireless devices connected they get authenticated and the device receives and IP address from the correct VLAN.  The Device shows up in the DHCP server and the IP address is associated with the Computer name; but, those wireless devices cannot ping anything on the network nor can anything on the network ping them.

I think that there must be a configuration setting that needs to be enabled.  Something that is unique to Aruba and outside the instructions I was given.  Aruba Support is stating that this is a network routing issue and they cannot help unless the main router can communicate with the wireless device.  I personally think that the reason there is a routing issue is because the Wireless Client is getting Authenticated into the Aruba system and a configuration setting is required to allow routing.

The thing is that the Aruba controllers can ping  devices that are on all of the required VLans.  The…
I want to detect non-domain computers in my network. Found scripts for this purposes. Which one - detects online workstations via Ip range and next one detects are they joined to domain or not. But i cant join them for properly working ) can anyone help?
$firstThree = "10.20.51"

1..254 | ForEach-Object {

    $address = "$($firstThree).$_"

    If (Test-Connection -ComputerName $address -Count 1 -Quiet) {

        Write-Host "$address is up" -ForegroundColor Green

    } Else {

        Write-Host "$address is down" -ForegroundColor Red



Open in new window

if (Test-Connection -ComputerName $computer -Count 1 -Quiet)
  if ((gwmi win32_computersystem).partofdomain)
    write-host -fore green "I am domain joined!"
    write-host -fore red "Ooops, workgroup!"

Open in new window

Have a small environment with no networking engineers. About 30 laptops on and off the wired and wireless throughout the day. It makes it difficult for deploying applications and scripts to them (like with PSexec or PDQ). Both DHCP and DNS are on 2 windows servers replicated.
Is there a recommended approach to updating a laptops IP when it goes from wired to wireless faster?
I have a VLAN network that is out of IP addresses. We have to stay on IPv4 for a number of reasons, so I think the best way to fix the issue is to add a subnet range. The current subnet is and I would add a subnet, then move all of the statically assigned devices to that network.... which should avoid the complexities of setting up DHCP and IP helpers on the switches. There are some other subnets and VLAN's configured as well, and the switches are stacked. The switches are Aruba L3 switches. Here are the VLAN setups- Subnets's 3rd octets match the VLAN ID for the 192.x.x.x networks:
VLAN ID         Name              IP
1                       DEFAULT
         Tagged:  1/37,1/43-1/44,2/45-2/48,3/4,3/6
         Untagged: 1/1-1/10,1/12-1/17,1/19,1/21-1/34,1/36,1/38-1/42,1/45-1/48,1/A1-1/A2,2/1-2/44,3/1-3/3,3/5,3/7-3/24
2                       VoIP                 172.16.x.xx
         Tagged: 1/1-1/48,1/A1-1/A2,2/1-2/48,3/1-3/3,3/7-3/24
         Untagged: 3/4,3/6
5                       Facility2 
         Tagged: 1/17
         Untagged: 1/11,1/18,1/20,1/37
7                       Facility3 
          Tagged: 1/45
          Untagged: 1/35
8                       Facility4 
          Tagged: 1/46
          Untagged: 1/43

So, I am not touching the VoIP network.
The 5 VLAN is the one I have set up, but I am unclear on the whole tagging versus …
Can you change the IP addressing on Netgear Jetpack-the DHCP uses the same IP address scheme as internal network so VPN won't connect
Need some help in tracking down an IP conflict that I have.  DHCP servers are Windows 2016 servers (setup in a failover scenario) but I have a MacBook that has had this happen twice in the last month.  He will get a popup saying:

Another device on the network is using your computer's IP address (  

I'm not sure if this IP was for his wired connection or his wireless but only seems to affect his MacBook.  With DHCP servers there shouldn't really ever be IP conflicts (unless someone adds a static IP which I don't think this is the case here - it could be but I doubt it).  In DHCP servers, logs don't show anything...

Anyway at this point to track down what grabbed the .204 IP?
I am planing to install DHCP fail-over in our Windows 2012 R2 environment. The current DHCP is on a DC.

There are so many article over the internet. Experts out there must have implemented DHCP fail-over. Have you had any problem with it?
I would appreciate if you could advice me  the best practice etc.
hi guys

We have a load of Watchguard Access Points and they are connected to a Draytek 1100 PoE switch. This switch is then connected to our backbone switch which is a Cisco 3750.

We have set DHCP on the WiFi network that the access points are on in a way to be from on wards and the management IP of this Draytek PoE being Every single day, people complain about not being able to access the internet properly and then it fixes itself again. Then it happens again.

When they do complain, I end up not being able to access the management IP page of the Draytek on This makes me believe that it is in fact this particular PoE causing the issues we are having.

Could that be the underlying problem?

Thanks for helping
Fundamentals of JavaScript
LVL 12
Fundamentals of JavaScript

Learn the fundamentals of the popular programming language JavaScript so that you can explore the realm of web development.

I have a 2012 r2 DHCP server . we are currently only using static reservations .   Why do we need a lease time if the static reservation is permineat?
When deploying an image over PXE I'm getting errors PXE-T04 and PXE-P36.  I have tried to start from scratch on the imaging server with no luck.  I'm have installed DHCP and WDS on the imaging server.
I have a Ubiquiti USG device here.

Its a quite simple setup.

-  Its WAN1 port is connected to my modem-router.
-  its LAN 1 port is connected to an Ubquiti Edge Switch

I can get internet perfectly if i plug cable from modem into switch. However, when internet goes thru the USG device to Switch - I get no internet.

It is as if the USG is blocking internet to the switch.

The USG is acting as DHCP server. What could be blocking the internet in the USG? Any suggestions would be much appreciated.
Server 2012 Standard
Windows VPN
The VPN is set up and working. The issue is that I do not seem to be able to find where to get it to use a static local IP instead of a DHCP address.
Hence, every time the server reboots it grabs a different one.
I have a remote user overseas that maps a drive by IP.

Is someone would be kind enough to point me to the setting, I would be thankful.

My company will be moving in a few weeks and as part of the move, I'll be phasing out two old domain controllers. Before I do that, I plan to move DHCP services to the new DCs. I tried to set this up while at our current location, but then realized that the IP Helper on our switch points to the old domain and this was (likely) preventing our new one from responding to and distributing addresses.

So my question is - if I just set up the new office with the IP helper for my VLANs on new switch hardware pointing to the new DC/DHCP server, am I likely to run into issues? (The old DCs would still be available but I'd hope not responding to DHCP/ DNS requests.)

Or, should I really look to tweak the switch settings in the current location to include the new DHCP server before I move?

Question from a Quallys report QID is 119518
I am missing configuration info in the network dialog box.
MissingThe computer used to get on the Internet but was using a rogue router that had been set up with DHCP.  We turned off DHCP on that router so we can use our main router.
Now the Ubuntu 18.04 machine won't grab an IP address.
I have just configured a LAMP on my 10.1.1.x network.

The LAMP hits the Internet but shows an IP address of (eno1).

Cable (Arris) modem is providing DHCP.

How is it possible for this to happen?  I'm thinking that I want the LAMP to have a 10.1 address.
Experts - have what should be a fairly simple setup, comprising an HP 1920S switch - a Ubiquiti Access Point - and a TZ-400 Sonicwall. Trying to get public/guest WiFi running on VLAN-100, but users not pulling an IP address. Works fine on the Private WiFi network, running on default VLAN-1.

I have this near same setup working at other locations I've done so far - with the only difference between this non-working site and the working sites, is the switch in this non-working site is an HP 1920S switch - whereas other sites have rebranded Aruba switches installed that support CLI.

I've worked with Sonicwall support earlier today and they're not seeing the guest wifi DHCP request hitting the Sonicwall X0:100 interface when a user attempts to connect to the public wifi. They've confirmed the configuration is correct on the Sonicwall.  SHould be OK as it's basically a mirror configuration from other sites that are working.

So this is what I have so far:

**DHCP**   Managed by Sonicwall

DHCP assignment for private internal/wifi office 10.10.x.x and is working,
DHCP assignment for public WiFi is 172.16.1.x and is not working.

** VLAN Info **

Private WiFi and internal office traffic all running on default VLAN-1
Public WiFi is configured to run on VLAN-100.

** Switch Info **

Port #1 is the Sonicwall
Port #2 is the Ubiquity Access Point

Sonicwall support thinks it's an issue upstream, most likely the 1920S switch.  The 1920S only allows GUI. …
CompTIA Cloud+
LVL 12
CompTIA Cloud+

The CompTIA Cloud+ Basic training course will teach you about cloud concepts and models, data storage, networking, and network infrastructure.

I have Server 2008R2 and wish to change our DHCP scope from - to -

Is there a way to do this?
Dear Experts,

i am using ESXi 6.5 with VCSA, I have multiple vlan environment and my dhcp server is a windows  vm. my problem is that broadcast from other vlan does not reach to dhcp server.

so i am thinking that if i make port of the vm as trunk so that it can receive requests from other vlans as well.

Please advise how can i do that, or if someone has some other way to do it.
OK, I am way out of my league here. I am working on a Novell 6 network and need to make some DHCP reservations. There is a DHCP app on one of the connected machines where the scope is setup but what we need to do is make our IP phones a different range other than our regular range that the scope is handing out. Because of that, we would like to take the MAC addresses and reserve them to a lower range to preserve the number of IPs we are able to give up.
I am familiar with Windows DHCP servers and don't see any of the usual steps to perform these tasks on the Novell app. I have the MAC addresses I need, just need to know where to make the settings.
Thanks.Screen shot of DHCP appScreen shot of DHCP app
Migrating the DHCP role from 2008 -> 2012R2 using the basic: netsh dhcp server import / export commands. The new server shows green over IPV4 and all the scope info moved over, and is authorized. I stopped the DHCP service on the source server as well but can't get the new server to issue addresses. Everything I've read makes it seem pretty seamless, so I'm not sure what step I'm missing
IP address shortage on Class C network.
The company is in manufacturing business. They have Windows servers, office PCs, production PCs, network switches, internal WiFi, IP phones, machines, etc. They all consume IP addresses. Now they wanna add 40 more production PCs while there are only 20 free IP addresses.
What should be done in order to release more IPs on this network?
One thing we are considering is to create a separate network for all 20 IP phones which are used in the "sub-site". (Please see the attached diagram). We are not good at VLAN, but we can learn. Will VLAN help in this situation?  
Are there any other things we can do?
Set up a new server 2016 yesterday.
Server 2016 Clients cannot open websites when DHCP assigned.
The server is assigning the right IP's.
The only way a client get to open web pages is if i put in a public DNS IP.
I can remote control clients using teamviewer, regardless the DNS settings,

Im quite sure, that there is a problem with the setup of the server, but I cannot find out where.
I have tried running the Routing and remote access wizard.

Can anyone help?






The Dynamic Host Configuration Protocol (DHCP) is an auto configuration protocol used on IP networks and an extension of the Bootstrap Protocol. DHCP allows for computers to be configured automatically to communicate with each other over an IP network without the need for manual setup by a network administrator. The implementation of DHCP relies on a DHCP server to hand out network configuration information to DHCP-capable clients that request an IP address (and other information required or useful in communicating with other devices on an IP network). In addition to an IP address, common configuration information served over DHCP includes a default gateway, subnet mask and DNS sever(s).