52
votes
Rogue DHCP Server Can't be found
On one of the affected Windows clients start a packet capture (Wireshark, Microsoft Network Monitor, Microsoft Message Analyzer, etc.), then from an elevated command prompt run ipconfig /release. The ...
- 109k
38
votes
Rogue DHCP Server Can't be found
Found it!! It was my DCS-5030L D-Link Network Camera! I have NO idea why this happened. This is how I found it.
I changed my laptop IP Address to 10.255.255.150/255.255.255.0/10.255.255.1 and the DNS ...
- 770
18
votes
Rogue DHCP Server Can't be found
Do a binary search.
Disconnect half the cables
Using '/ipconfig release' test if it's still there
If so, disconnect another half of the remaining and goto 2
If not, reconnect the half of the ...
- 5,406
17
votes
Rogue DHCP Server Can't be found
You could just:
Open the network and sharing center (either from start or right click the network tray icon), click the blue connection link -> details.
find the ipv4 dhcp address (in this example it'...
- 1,222
12
votes
Accepted
Can the network still work when DNS & DHCP go offline?
The network will keep working until your DHCP leases expire. After the leases expire devices may switch to RFC 3927 addresses. But those addresses are not predictable so you'd have to rely on MDNS to ...
- 30.1k
10
votes
Accepted
DHCP: Create a scope within a scope
Ip addresses are meaningless without a subnet mask. When you say the scope encompasses the whole 10.2.0.0 range and then say that range is 10.2.0.0-10.2.63.254 you're implying a subnet mask of /18 (...
- 109k
9
votes
Why does a DHCP server need a static IP address?
A DHCP server must have a configured IP address so that it can know which scopes are locally attached to physical interfaces, and which Scopes can only be served via a DHCP relay.
Ignore a ...
- 130k
7
votes
Accepted
What happens if the DHCP server comes online after the client devices do?
OK, I have a couple thoughts:
There are as many DHCP stacks as there are stars in the sky. OK, not quite, but you get the idea. Embedded networking stacks are especially known for having non-complete ...
- 109k
7
votes
Accepted
VCenter has failed, DHCP server is down
Add the DHCP role to the physical DC. Authorize the DHCP server. Create an appropriate scope with appropriate options.
You'll need to create a Scope appropriate for your network with the appropriate ...
- 109k
6
votes
Accepted
Why does a DHCP server need a static IP address?
My understanding of DHCP is, a client broadcasts a DHCP Discovery
request on the network, and any device on the network can respond.
A client can make an unicast DHCP request too, the renewal request ...
- 775
5
votes
Different subnet mask on router and DHCP server
The subnet mask is mostly used to work out whether another IP address can be accessed on the local network, or if it needs to go through a router. Your workstations with the old /24 subnet mask will ...
- 7,983
5
votes
Accepted
Windows DHCP Reservation Outside of Lease Pool
Well I have pretty much come to a conclusion.
In short, yes, it will work (if the reservation already exists). However like so many things from MS there are some caveats since there can be errors if ...
- 2,077
5
votes
What happens if the DHCP server comes online after the client devices do?
There are three scenarios for a Windows DHCP client that I can think of off the top of my head. I can't speak to non-Windows DHCP clients but I have to assume they operate the same way.
A running ...
- 109k
5
votes
ISC DHCP Server "Dynamic and static leases present"
The error says it all, you have both static and dynamic lease present for the same ip address range.
In the following you have defined a dynamic lease:
# Bekannte Geraete
pool {
range 192....
- 8,941
5
votes
Accepted
dhcp server gives "no free leases" error although there should be available IPs
It looks like you miss either range definition or a specific host entry for those boxes, matching their MACs.
Unless your failing boxes are on the list that "goes on like this", they won't have any ...
- 661
5
votes
Accepted
IPv6 address lifetime: preferred versus valid lease
The best explanation I have seen is in the introduction to RFC 4862 (which you should read in its entirety later):
IPv6 addresses are leased to an interface for a fixed (possibly
infinite) length of ...
- 241k
5
votes
Unusual DHCP activity after power outage
It is not an answer to your question as I feel there is not enough information to really determine what happened.
To prevent issues with DHCP servers many system administrators prefer to give their ...
- 5,607
4
votes
Accepted
Is it possible to bring down a network with DHCP discover?
Any broadcast traffic or switch flooding of a sufficiently high volume could bring a network down. A switching loop is a good example of this very thing. A malware infection is another good example. I'...
- 109k
3
votes
How to block DHCP traffic using iptables
DHCP uses broadcast traffic for it's discovery process. Routers do NOT forward broadcast traffic.
If your VM's on the "inside"/eth1 side of your router are getting leases from your modem/router on ...
- 5,367
3
votes
configure a dhcp server to serve two different scope on the same subnet with multiple interfaces
You defined wrong network mask at, that's why dhcp server is failing to start
iface eth1 inet static
address 192.168.0.1
netmask 255.255.255.0
iface wlan0 inet static
address 192.168.0....
- 357
3
votes
Polycom phone not requesting DHCP offer
I finally found the answer! After a lot of digging into various wireshark captures I noticed that when the problem was happening that there was a lot of IPV6 broadcast and discovery traffic. After ...
3
votes
Accepted
Can I use a router as a backup DHCP if the DC's are offline?
It's not all that difficult. When the servers are being turned off enable DHCP on the router. Disable DHCP on the router when the servers are being turned on.
Any DHCP server on the network can ...
- 109k
3
votes
How to ignore unused network interfaces in dhcpd on Centos 7
I believe /etc/sysconfig/dhcpd indicates how to limit the interfaces listened on on systemd on a ${RHELish}7 system:
cp /usr/lib/systemd/system/dhcpd.service /etc/systemd/system
sed -i '/^ExecStart/s/...
- 1,636
3
votes
How to ignore unused network interfaces in dhcpd on Centos 7
You don't need to add the interface line if it is on a different subnet. The Slackware 14.2 Linux distribution provides the following example:
# No service will be given on this subnet, but declaring ...
- 773
3
votes
Accepted
DHCPD configuration by interfaces
Assuming you are using ISC DHCPd it is based on the subnet:
subnet 10.10.0.0 netmask 255.255.255.0 {
range 10.10.0.1 10.10.0.100;
}
subnet 10.20.0.0 netmask 255.255.255.0 {
range 10.20.0.1 ...
- 7,672
3
votes
Enable DHCPv6 in dnsmasq to distribute fixed range IPv6 addresses but failed
You are making a few different mistakes in your configuration. First of all site-local addresses have been deprecated for many years. Any documentation telling you to use addresses starting with fec0 ...
- 30.1k
3
votes
Accepted
Windows Server 2012 Failover DHCP
Scope options and reservations are not replicated automatically. See this comment from "Microsoft Windows DNS, DHCP and IPAM Team Blog".
There is a Powershell Cmdlet in Server 2012R2:
Invoke–...
- 2,949
3
votes
Does a Windows host correctly interpret dnsmasq parameters?
I found the problem: my DNS settings on the client were static. The IP was assigned via DHCP.
This is not normal and what brought me to check that is that I have had the same issue of the DNS ...
- 3,517
3
votes
Accepted
how dhcpd handles static IPs vs DHCP reservations
Static IPs are normally outside the pool range as you do not want static IPs assigned to other hosts. As long as the static IPs are in an IP range local (or relayed) to the DCHP server they can be ...
- 27.6k
3
votes
how dhcpd handles static IPs vs DHCP reservations
Some DHCP server software operate differently when it comes to reservations:
some require that all reserved addresses be outside the dynamic range but be within the subnet.
some require that all ...
- 2,615
Only top scored, non community-wiki answers of a minimum length are eligible