DHCP stands for Dynamic Host Configuration Protocol and is an auto configuration protocol used on IP networks and an extension of the Bootstrap Protocol.

learn more… | top users | synonyms

62
votes
11answers
155k views

How do I find if there is a rogue DHCP server on my Network?

What's the best approach towards determining if I have a rogue DHCP server inside my network? I'm wondering how most admins approach these kinds of problems. I found DHCP Probe through searching, ...
43
votes
2answers
147k views

Can I have multiple DHCP servers on one network?

This is a Canonical Question about Redundant DHCP Servers. Is it possible to have more than one DHCP server on the same LAN? What are the implications of doing this? What happens if there is ...
27
votes
5answers
4k views

Locate rogue DHCP server [duplicate]

Possible Duplicate: How do I find if there is a rogue DHCP server on my Network? I know this is a serious long shot, but here we go. In the past week or so, for users connected to a ...
23
votes
4answers
1k views

1 Year DHCP Lease

Just a little background I'm a fairly young I.T. Tech working in a school only and only been working in the as a technician for a few years so I would still consider myself a "newbie" Anyway, My boss ...
21
votes
4answers
3k views

How do I protect a low budget network from rogue DHCP servers?

I am helping a friend manage a shared internet connection in an apartment buildling with 80 apartments - 8 stairways with 10 apartments in each. The network is laid out with the internet router at ...
20
votes
9answers
95k views

Any way to find unused IP addresses on my network?

How can I locate unused IP addresses on my network? The DHCP server keeps assigning the same address and I need a different IP address to test my application with. The software would need to run on ...
20
votes
4answers
25k views

How does a computer obtain an IP address via DHCP?

How does the computer know which device on the network to query? How does the default gateway factor into this? Pretty much, what is the chain of events that occurs when a computer tries to obtain an ...
19
votes
5answers
12k views

Why does it take seconds to obtain IP address via DHCP?

Out of curiosity, why does it often take seconds to obtain network configuration via DHCP when the CPU is capable of processing millions of operations per second and ping to the router takes a couple ...
17
votes
4answers
36k views

How do I request a new IP address from my DHCP server using Ubuntu Server?

I know there is a simple command for this, but how do I tell my Ubuntu server instance to request a new IP address from the DHCP server on eth0?
16
votes
3answers
2k views

Phones on some switches cannot complete DHCP process

Background I have a Windows DHCP server (Server 2008 R2) handing out addresses for several scopes. One of those scopes is for some Mitel IP Phones. The phones are configured to use dhcp option 125 to ...
15
votes
5answers
83k views

How do I determine what my DHCP server is?

I have a sad network left behind by some careless admins - I am in process of figuring out exactly what services are running where, not excluding the possibility that some services are running from ...
14
votes
2answers
17k views

What are the possible issues in using very short DHCP lease time (< 1min)?

We have a network setup for a demo, which lasts about 15mn. Our DHCP server is configured to assign ~ 100 addresses (max number of simultaneous connections or our AP) ... but since people might come ...
14
votes
4answers
4k views

Windows DHCP Server - get notification when a non-AD joined device gets an IP address

SCENARIO To simplify this down to it's easiest example: I have a Windows 2008 R2 standard DC with the DHCP server role. It hands out IPs via various IPv4 scopes, no problem there. WHAT I'D LIKE I ...
13
votes
4answers
1k views

What does a DHCP-client consider to be the “best” answer?

We have training rooms where normally Windows XP is installed (via PXE). The "normal" DNS/DHCP infrastructure are Windows-Servers. The training room has its own VLAN (different from the Windows ...
13
votes
1answer
21k views

dhclient: What does “RTNETLINK answers: File exists” Mean?

I wanted to update the DHCP lease of an Amazon EC2 instance, so I executed the following command: user@host:~$ sudo dhclient Following that, the system's DHCP lease is updated successfully updated. ...
13
votes
8answers
27k views

Command line program to test DHCP service

Is there a simple ping-like command to test whether a DHCP service is running on a network? ...on Linux
12
votes
5answers
14k views

Why can Windows machines resolve local names when Linux can't?

I have a small network with Windows and Linux machines connected to a D-Link DIR-825 router. The Windows machines on the network can reach all other machines by name while the Linux machines only can ...
12
votes
1answer
7k views

How to request dhcp (using dhclient) on a virtual interface (i.e. eth0:1)

This seems to work fine: dhclient eth0 ifconfig eth0:1 192.168.1.105 up But not this: ifconfig eth0 192.168.1.105 up dhclient eth0:1 Is there any way to get dhcp on a virtual address?
12
votes
3answers
13k views

Howto setup Cobbler with PXE if you can't change the dhcp server?

In the past I've setup a PXE server several times by making the normal dhcp server return everything needed for network booting: both the regular ip config AND bootinfo in a single dhcp setup. That ...
12
votes
2answers
9k views

PXE Booting Virtualbox guests in internal networking mode?

I am not sure if this is just specific to my distro's packages or is a vbox limitation. So, any help would be appreciated. Ok, so I have a network of VMs, with one VM acting as a NAT for the other ...
12
votes
1answer
2k views

How to set up Google ShortName service for my domain, so that the FQDN isn't needed

The blog post "A 'tinyurl' service for your domain" explains how to set up a ShortName service for your domain using Google Apps. For example, if your domain is example.com and you use Google Apps, ...
12
votes
3answers
1k views

Use Windows DHCP/DHCPv6 server without setting a static address

You cannot set the Windows DHCP/DHCPv6 server to listen on dynamic addresses or all addresses, only static addresses. Is there a technical reason for this limitation? Is there any workaround? My ...
11
votes
9answers
82k views

What is a good DHCP lease timeout configuration

I have generally seen that DHCP lease times are quite long (a day plus) on most defaults. I have a client that seems to have the following problem. They have a DHCP server in a router that is ...
11
votes
1answer
27k views

VLAN tags not shown in packet capture (Linux) via tcpdump

I am adding a tagged VLAN onto eth0: #ip link add link eth0 name eth0.20 type vlan id 20 This results in: #ip link 2: eth0: <BROADCAST,MULTICAST,PROMISC,UP,LOWER_UP> mtu 1500 qdisc ...
11
votes
4answers
15k views

Register A records for my Linux box on my Windows 2008 DNS/DHCP server

I've a network which is mainly Windows: Windows 2008 server (with DNS/DHCP as well as AD), and various mainly Windows machines (servers, XP, 7). I know trying to add few Linux boxes, and can't make ...
11
votes
2answers
30k views

Multiple VLANs, multiple subnets, single DHCP server?

At my job we are prepping to transition from multiple LANs connected over slow VPN connections to a single MAN connected over fiber, and I've got a few questions. First of all, we are planning on ...
10
votes
6answers
9k views

dnsmasq: mapping 2 MAC addresses to the same IP address

Is it possible to map 2 different MAC addresses to the same IP address? For my backup, I need to connect back from the server to the portable, and I would like to have the same IP both for the ...
10
votes
6answers
22k views

How to make a Macintosh register a Hostname to the DHCP Server?

I have a MacBook running Snow Leopard in our company's internal network, which is basically a Windows domain network. Our TO department complains about my MacBook not specifying a name to the DHCP ...
10
votes
2answers
3k views

DNS and DHCP not agreeing on an IP address

I'm having a problem where our Windows Server 2003 domain controller assigns my Windows 7 computer one IP address (x.x.x.75) via DHCP, but reports another (x.x.x.84) via DNS. This causes some ...
10
votes
3answers
1k views

No internet after dhcp lease renews

Today we had a number of machines stop getting internet access. After a lot of troubleshooting, the common thread is that they all had their dhcp lease renewed today (we're on 8 day leases here). ...
10
votes
1answer
5k views

Is there a downside to always updating DNS from DHCP?

I've got a Windows 2012 Domain Controller running DNS and DHCP servers. The default setting appears to be Dynamically update DNS A and PTR records only if requested by the DHCP clients. (This is ...
10
votes
3answers
3k views

Windows DHCP server - distribute multiple default gateways?

I'm helping a client through the process of configuring a Windows 2012 DHCP server while migrating from Linux ISC DHCP. In the Windows New Scope Wizard dialog, there is an option to: ...specify ...
9
votes
7answers
22k views

Find out the DNS server for a DHCP connection in Linux

I know they're defined in /etc/resolv.conf, but what if it's not there? And more specifically, how do you find the DNS server returned by DHCP? In GNOME you can use the NetworkManager applet to see ...
9
votes
2answers
912 views

MAC addresses on dual-NIC mainboards

Here's a weird problem. We've got a number of devices with dual-NIC mainboards. Some are Realtek NICs, which suck. Some are Intel e1000s, which don't. I've just noticed on 2 machines, one is an ...
9
votes
1answer
260 views

What are the practical risks of enabling the unsecure DNS updates on Windows?

What are the practical risks of enabling the unsecure DNS updates on Windows? As far as I found enabling the unsecure DNS updates is a requirement for enabling DHCP Linux clients from registering ...
9
votes
6answers
7k views

Update hostname from Debian machine with DHCP to a Windows 2008 DNS server

I have a XenServer installation with Debian (lenny) machines created on a daily basis using a script which creates the machine from a template and assigns it with a new hostname. Our network has a ...
9
votes
5answers
3k views

libvirt: Change dhcp-setup without restarting

I'm using libvirt and kvm to virtualize my server. I configured libvirt to start a dhcp-server on the bridge-network-interface to give the vm's their ips. Every VM's gets always the same ip based on ...
8
votes
4answers
1k views

When the internet is down, so is Active Directory?

I am setting up a business server for a small office use with 5 users / 5 devices or so. Nothing elaborate here. I've set up a SINGLE Lenovo TS440 server (single NIC) with Windows Server 2012 R2 ...
8
votes
2answers
3k views

Domain Controller offline for a few days

My primary domain controller died over the weekend, its motherboard is being replaced tomorrow. I have been told that the mac address of the server may change once the new motherboard is installed. ...
8
votes
5answers
13k views

Reverse DNS records not registered when using DHCP

I've stumbled upon a strange behaviour with Windows machines, which seems to be fairly consistent between all Windows versions from Vista/2008 to 8.1/2012 R2; it doesn't happen instead when using ...
8
votes
3answers
13k views

How do you get dnsmasq to specify alternate DNS servers?

I'm working on a network with ~10 kubuntu desktops (and numerous servers and IP phones) and am trying to get dnsmasq to specify another dns server as a failover. I tried using server=192.168.0.90 ...
8
votes
4answers
3k views

DHCP on-the-fly block assignment

We have a large number of clients who connect to our DHCP machine. We want to assign some of them to a different IP block, which is routed with lower priority. Every DHCP lease renewal, we'd like to ...
8
votes
2answers
7k views

IPv6 DHCP Configuration

I want to set up an IPv6 only network for testing. However, I can't find any HOWTOs or information on setting up DHCP to autoconfigure IPv6 DNS server addresses etc. I use radvd on a ubuntu server to ...
8
votes
3answers
21k views

How to configure radvd, dhcpd6, routing and /64 subnet based on delegated prefix by DHCPv6-PD server?

My ISP has just started IPv4/IPv6 dual stack service. In order to connect IPv4/IPv6 internet, almost all users usually use a CPE leased by the ISP. But I want to use my Linux router instead of such ...
8
votes
3answers
7k views

dhcp-snooping option 82 drops valid dhcp requests on 2610 series Procurve switches

We are slowly starting to implement dhcp-snooping on our HP ProCurve 2610 series switches, all running the R.11.72 firmware. I'm seeing some strange behavior where dhcp-request or dhcp-renew packets ...
7
votes
6answers
2k views

DHCP for data center

Can someone provide cons and pros for having DHCP in a data center? I know this is usually a taboo, but maybe there were developments which alleviate the said issues? Thanks.
7
votes
4answers
38k views

Force the DHCP server to renew the IP address of a client machine, without doing anything in client machine

I would like to know, if there is a way I could force the DHCP server to renew the IP address of a client machine instantly, without me going to the client machine? In fact, imagine, I don't have ...
7
votes
4answers
713 views

What happens if the DHCP server comes online after the client devices do?

If I have a Windows PC running a DHCP server. I expect it will take on order of minutes a few to boot. My network will have a variety of other devices from various vendors that will boot within ...
7
votes
7answers
4k views

DHCP addressing vs Static addressing for Servers

I'm having a "lively" debate with a work associate about the reasons for or against using DHCP on servers in a network environment. The network environment in particular is a relatively small network, ...
7
votes
6answers
455 views

Wisdom of switching from Windows to redundant linux boxes for DHCP servers? [closed]

We've had a few issues with our Windows DHCP server failing. I'm a linux guy by nature, but not a systems guy (I'm a programmer who happens to be running IT for ~800 users), but I'm curious: how crazy ...