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20

With a very low lease time you will see an increase of network traffic, particularly broadcast traffic as the "discover" and "offer" phases of DHCP are layer 2 broadcasts. How much of an issue this is depends on many factors such as the size and complexity of the network, latency, performance of the DHCP server, etc. Keep in mind DHCP clients do not wait ...


13

Matching the DHCP lease times with the connection limit of your AP doesn't strike me as the best way of handling the issue. The two don't have to match. Lower the DHCP lease time to something like twice the length of the demo (completely arbitrary suggestion) and expand your DHCP scope to accommodate as many leases as you think you'll have in a reasonable ...


9

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 management point of view, I am sorry, but I think it is silly to try and hand-wave away and ignore the practical issues about running your network. Getting a valid ...


6

As MadHatter mentioned in a comment, the leases file is periodically re-created to avoid this problem. While the period isn't mentioned in the documentation, discussions on the dhcp-users mailinglist indicates that it should be done once an hour, and I've checked the source code and found that this is correct. Unfortunately this isn't a configurable option. ...


5

It is possible, as outlined in this technet article. http://technet.microsoft.com/en-us/library/dn495425.aspx This guide describes the steps for migrating existing DHCP server settings to a server that is running Windows Server 2012 R2. Migration documentation and tools ease the migration of server role settings and data from an existing server to ...


5

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 is made in unicast, so the client requests directly the DHCP Server. What if the DHCP changed his original IP address ? The renewal will fail and the ...


5

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 have been able to access everything else that was inside the old /24 network, because the wrong mask will still give the right answer for those addresses. They ...


4

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've seen malware infections that used ARP to effectively bring a network to it's knees due to the volume of ARP broadcasts generated by the malware.


4

Strictly speaking, yes. The client hardware address is a data field that will be in both the DHCPDISCOVER message (which won't leave the LAN) and the DHCPREQUEST message, which will be relayed by the relay agent. Why do you ask?


4

One thing that seems to be rarely suggested is inspecting at one of the clients that has a bad address and looking at where it came from. For example, on a Windows client "ipconfig /all" will tell you immediately what the rogue server address was. For long term monitoring, the check_dhcp plugin for Nagios can be set to warn if you have too many responses, ...


3

If you have DHCP Audit logging enabled you might have the data in the logs. Details on how to set up DHCP Audit Log on Windows Server 2008 including the event types (e.g IP address lease etc) By default the log files would be located in %windir%\System32\Dhcp.


2

OK. So you want all of the traffic to go out the closest gateway, but you can't get there from here. It's all the same layer 2/3 network so there's no way to prioritize the gateways so that clients use the closest one. If you use different subnets on each side then that presents the wrinkle of having to route traffic between the two subnets so you'd then ...


2

The real question is how do I provide two routes to the Internet and ensure my hosts always use the fastest path to get there? The case for routing. You have two locations, each with its own Internet connection. Hosts at each location are best served by using their site's route to the Internet. The two locations are also connected by a single link. This ...


2

Wireshark Try a running a protocol analyzer like Wireshark while connected to the subnet in question. You'll want to filter on bootp messages. If you want to do this in a truly passive manner, you'll have to wait until a client on that subnet initiates a DHCP request, after which you'll see all of the DHCP servers listening on the subnet respond to the ...


2

As long as the routing is in place such that the DHCP relay to Router 0 actually traverses Router 2 & 1 to Router 0 and back, then yes, it will work just fine. It's no different than VLANs across Layer 3 switches with IP Forwarding enabled. You could even think of it as getting a DHCP address across a WAN link from a remote DHCP server if you'd like.


2

You can't control somebody else's computer. If somebody else has "Administrator" or superuser-level access to the machine then all bets are off. You're better off doing this in the network, where you can control things. I see you say "...without the help of the router", but enforcing network policy with the network equipment gives you the best chance to a ...


2

It turns out that the answer to "does the API provide sufficient information to work?" is, as of ISC DHCP 4.3.1, "no, it does not". However, I've just spent a chunk of time putting together a patch set to extend the server to provide (just) enough information to add and remove routes. My changes are available at https://github.com/mpalmer/isc-dhcp, in the ...


2

The DHCP logs are located at %windir%\System32\Dhcp.


2

Just use the DHCP management console to set the router that is set in the DHCP responses (to the address of the Linux server).


2

In short: you can't In order for the DHCP server to know if a device is inside the domain, it have to communicate with a domain controler, thus it first have an IP address. This is why the settings you want are greyed out. A trick can be to name your computer with a special prefix. Then the DHCP server can detect it when the computer negociate it DHCP ...


2

You can deploy batch script over GPO to DHCP servers that will change DNS settings in DHCP scope using netsh utility. A command to set DNS servers in scope with netsh is: netsh dhcp server DHCP_server_IP_or_Hostname scope Scope_Network set optionvalue 006 IPADDRESS DNS1_IP DNS2_IP If 10.10.10.1 is primary DNS, and 10.10.10.2 is secondary DNS, and ...


2

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 additional investigation I found that various computers on our network had Intel nic cards that had a wake on lan function. The computers would sleep and would ...


2

They are duplicate options, applied at different levels. 'Server options' apply to all defined DHCP scopes on the server. 'Scope options' apply to only that specific DHCP scope (you can have more than one scope defined in the DHCP server).


2

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 the "outside"/eth0 side then you have a bridge somewhere between the 2 networks; either your "router" is actually a bridge (do you have an interface called br0 or ...


2

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 service clients. A client will use whichever DHCP server it gets a response from first. So in your scenario, you'll need to enable DHCP on the router when you turn ...


2

While this answer is simple I'm posting it here because if anyone else attempts a DHCP failover setup as I did and they received this error, then hopefully this will help them. Sometimes it's not apparent on the web pages showing a failover configuration that the 'Configure Failover' wizard is not run from the DHCP server that will be the 'failover server'. ...


1

You have option routers 192.158.66.254; in your configuration, which causes the invalid default route in your client configuration. Comment out this line, and you should be left with the correct default router of 192.168.66.254.


1

I think there are 2 different things at play here - The incorrect setting option routers 192.158.66.254; in your DHCP configuration. This would stop external connectivity, but is not actually the cause of your problem. The inability to ping the Windows box from the Linux boxes is most likely due to the TCP stack on the Windows box (or a firewall running ...


1

For small site you can simply remove the DHCP's role from the server and leave it to the router for ever, I seen that often. You setup the DHCP on the router to give the domain dns suffix and to give only the domain dns. Server on or at off, the DHCP will never fail. The problem you will face is more for the DNS. Usually you give only the DC's IP as a ...


1

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 adding a NEW reservation outside of the address pool. It seems the best method is to utilize exclusion zones on your address pool to limit what range of ...



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