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37

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 ...


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 ...


10

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.


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 ...


10

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 (255.255.192.0) because that's the only subnet mask that gives you that ip address range, but we wouldn't know that is the subnet mask you're using because you ...


9

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 ...


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 ...


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.


7

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 ...


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

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

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.


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 ...


7

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 "standards" implementation. As such, it's highly likely that your devices will end up booting before your DHCPd is ready, will APIPA, and won't ever retry ...


6

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 ...


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

IF you really want to you can disable rogue DHCP server detection by setting the REG_DWORD value DisableRogueDetection to 1 under HKEY_LOCAL_MACHINE\System\CurrentControlSet\Services\DHCPServer\Parameters. As an aside: It kinda sounds like you installed the Hamachi adapter directly on the Windows SBS 2003 computer. If that's the case then you're probably ...


6

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 ...


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

There's no problem with having 2 DHCP servers. In fact, it gives you some redundancy in case one of them goes down. It just needs to be setup correctly. Make sure they both have a different range of addresses to hand out and the same reservations created on each. Of course, if you don't need or want the redundancy and uptime, then just turn one of them off. ...


5

The only real pro's and con's are the ones you've already addressed, which is continuity of the network. I usually put DHCP on the primary server (DC,DNS) so that DNS records can be automatically updated if/when a client's DHCP lease expires and it is issued a new IP address. It would take additional configuration to accomplish this task using the Sonicwall ...


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

The FORCERENEW provides the mechanism for the server to indicate to the client to re-new. Not sure if it is implemented in your distro.


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 ...



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