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35

It doesn't know what device to query. Thus it broadcasts its request to the entire subnet. The DHCP server is listening for a certain type of communication and when it hears that specific broadcast it begins the DHCP conversation with the device that broadcasted its request. Take a look at the DORA process for more information. DORA stands for: D iscovery ...


19

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 ...


12

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 ...


10

fedora seems to have the following package in the repos "dhcp_probe" Description : dhcp_probe attempts to discover DHCP and BootP servers on a directly-attached Ethernet network. A network administrator can use this tool to locate unauthorized DHCP and BootP servers. Looks like the man dhcp_probe has some good pointers for DHCP discovery strategy ...


8

Let's not confuse the word "official" with the concept of "generally accepted method". One generally accepted method would be to issue a DHCPDiscover packet and look for a response.


8

Assuming the router is still acting as a DHCP relay and forwarding the request to your original server, then the reason it did that is simply because that Windows DHCP server told it to go ahead and use the IP. In this instance the DHCPNACK from the new server is irrelevant, as a DHCP client will consider all responses, and since it got an offer from the ...


7

DHCP Option 43 is a bit of an odd beast. Vendors can treat it however they want - some expect the option numbers to match with the DHCP option numbers, others do not. The basic structure is 1 byte for an option ID, 1 byte for the length of the option data (n), then n bytes of the actual option data - and, rinse and repeat. Let's take the example from ...


7

It will get the address. In one network I manage all of the reservations are in the excluded range. From the technet docs. http://technet.microsoft.com/en-us/library/cc737055(v=WS.10).aspx Reservations can be created using any IP address in the scope’s address range, even if the IP address is also within an exclusion range.


7

Welcome to serverfault! Yes, you can issue IP Addresses for subnets on which the server itself does not have an interface. When a client tries to obtain an IP Address, it sends a broadcast looking for a DHCP server. When there is no DHCP server available on the local network, a router can be configured as a DHCP helper such that when it receives a DHCP ...


7

You can't thru DHCP itself. It doesn't have provisions for this. The only thing you can do is to force the client into a disconnect/reconnect. - Pull the cable. - If the client is on a managed switch to which you have access you can disable/enable the switchport. - If you can login remotely to the client and you have the required authorisations on the ...


6

Yes, this is possible and will not cause problems as long as it's configured properly. To setup the second DHCP server as a "failover" you will want to divide up the scopes DHCP 1 is serving. To do this you would configure the same scopes on DHCP 2 as there are on DHCP 1. You would then exclude a percentage of the scope on DHCP 1 and then exclude the ...


6

None of the above - you're confusing Lease Time with a DHCP client releasing the address. The client should always renew the IP address well before the lease is up, meaning that there are no problems so long as the client remains active. The only real problem with a short lease from an ISP is that you have no guarantee that you'll get the same IP back if ...


6

While product recommendations are off-topic for ServerFault and I expect your question to be closed by the community in short order, I can offer two suggestions: Limiting yourself to a GUI-based system is limiting your ability to implement the best solution for your situation. Perhaps a system with a GUI will work well, or perhaps not. In spite of the ...


6

There's an official Technet guide for this that I'd use, rather than that one. The process below is a "merge," rather than what would normally be called an "import", and will only modify existing scopes if you import scopes that exist on the target server. If that is the case, you'll need to selectively import scopes, instead of just using the /all switch. ...


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

If users assign IPs to their systems, they'll choose whatever they fancy, and no amount of begging, asking, shouting and threatening is going to change this. Therefore, the safest way would be to separate subnets of servers and users. In that setup a user can conflict only with another user and disrupt one person at worst. What is more, if they assign ...


5

I'm not sure why you are using superscopes at all since you're using VLANS.. You should try to use dhcp relay on the router that connects all these VLANS - I'm pretty sure it will work out for you.


5

Step 1: make sure you have production-quality IPv6 connectivity Step 2: configure your routers/firewalls Step 3: let your routers/firewalls send out RAs (Router Advertisements) advertise not-managed, no-other-configuration advertise the routed prefix with (a)utoconfiguration flag enabled Now you already have IPv6 connectivity. You don't need ...


5

This sounds like a network mis-configuration, plain and simple. "networks that are routable to each other" typically means there is a router in between them, whose job is to filter stuff like DHCP. If systems on one network are getting addresses from the DHCP server that is supposed to be on the other network, then either the router is forwarding DHCP ...


5

Yes this can be done. However, it can't be done with the equipment you currently have. The crux of the problem is Router A. The DI-624 does not support DHCP relay / forwarding / helping (depending on what the equipment manufacturer feels like calling it). You'll need to use a router that can pass DHCP across subnets. As Zoredache reminded me, you can have ...


5

When a router or other device relays a DHCP request, it sends along with it the subnet information of the interface that it received the request on. In other words, the point of relay is that your DHCP server does not need an interface on each VLAN to serve multiple subnets. Are you trying to override that behavior and issue an IP address in a different ...


5

Generally a DHCP relay is supposed to pick up a broadcast from a client and forward it to a specific server (read: unicast) address. Given that the packet sent by the relay to the server can be routed anywhere, the idea of cascading relays doesn't make a lot of sense. In practice it would be more likely to have some kind of intermediary DHCP server that ...


5

The problem is that your client is not talking DHCP but bootp. Not all dhcp servers handle bootp as well due to design limitations or configuration settings.


5

You need to change the subnet on your computers from a /24 to a /23. 255.255.254.0. On computers that have static addresses, such as your servers, you'll need to do it by hand.


5

Everything you want to do (but the billing system) can be done by pfsense out of the box. Including load balancing - just add another NIC to your box.


5

With much thanks to ErikE and the others here, I've gone down a path...I won't say it's the right path, but the Powershell script I've come up with does the trick. The code is below if anyone wants it. Just run it manually pointing at each DHCP server or schedule it (again pointing to each DHCP server in the script). What the script does: Gets lease ...


5

What needs corrected or cleaned up with the order of operations? Nothing Is there any AD data (including logs, though their location is usually pretty standard) that I need to clean up from the decommed DHCP servers? No. There's no AD data in the DHCP database, AD data is in the AD database. Will there be any references to the domain account ...


5

Set the value for option 51 to 4294967295 seconds and it will show up in the GUI as unlimited. C:\Users\EAnderson>netsh dhcp server scope 10.0.0.0 show optionvalue Changed the current scope context to 10.0.0.0 scope. Options for Scope 10.0.0.0: DHCP Standard Option : General Option Values: OptionId : 51 Option Value: ...


4

Identifying the clients (Windows, 'nix, etc.) would help provide a better picture, as well as the DNS server in use. It sounds like you may have mixed Windows (maybe across multiple versions) along with other OS types in your environment. Within Windows, against Windows DNS (since Windows 2000), the DNS tab within the TCP/IP "Advanced..." properties - ...


4

The configuration file is one of /etc/dhcp/dhclient-${DEVICE}.conf, /etc/dhclient-${DEVICE}.conf, or /etc/dhcp/dhclient.conf in that order. The first one that exists is used. From /etc/sysconfig/network-scripts/ifup-eth (Fedora 14; RHEL6 may be similar): # allow users to use generic '/etc/dhcp/dhclient.conf' (as documented in manpage!) # if per-device file ...



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