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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 ...


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

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: ...


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 ...


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

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 ...


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

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 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

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

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

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

Hopefully, you can control the hardware MAC addresses of your virtual ethernet interfaces. In that case, I had a similar problem, and ISC bind was equally uncooperating with my configuration efforts. The best solution, which I am still using for years reliably, is to edit the leases file so that desired IP addresses get assigned to corresponding hardware ...


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 ...


1

First of all you have to use a managed switch. If you are not using a managed switch, then nothing is stopping a person with sufficient privileges on individual machines from simply spoofing a MAC address of another machine. Once the MAC address is being spoofed, there is no way to tell the difference between the two. With a managed switch you can either ...


1

Try using the samba package. You may need to install libnss-windbind as well. This should enable using WINS as a name service. You will need to add wins to the hosts entry in /etc/nsswitch.conf. I have the bonjour package installed on a Window system, but its address is not available. Media services are announce, but only have the machine name. ...


1

I hate to post and then immediately post my own answer but when I was working on getting the DHCP client configuration and leases file I noticed about half a dozen lease entries. Just to create a clean file to post here I deleted that file and rebooted. After that it grabbed the proper DNS server info. While I feel there was more to it my solution was to ...


1

I am 95% sure the DHCP server in Cisco IOS doesn't record this information at all. You'll need to run your DHCP server somewhere else, or collect the hostnames through some other mechanism.


1

You need a BOOTP and TFTP server. You could set "next-server" to your current DHCP server setting to your TFTP server too. You won't be able to run remote boot without correct BOOTP server set to TFTP server (next-server). First you need a BOOTP/DHCP server to setup the client network configuration and inform what server will be used for PXE/TFTP server. ...


1

Assuming Windows: Run Wireshark. Do ipconfig /release followed by ipconfig /renew on the command line.


1

No, this will not work. Both DHCP Servers must be at least Windows Server 2012. As an aside, you should be removing 2003 from your environment quickly, not tying it in to new infrastructure. It goes end of extended support early next year.


1

Update to dhcpd 4.2.x. Those parameters are user configurable in that version. https://kb.isc.org/article/AA-01193/0/DHCP-4.2.7-Release-Notes.html


1

I can confirm the same issue exists with the Nexus 7 and the isc-dhcp-server. I was able to circumvent the problem to some degree by giving the device's MAC a reserved address. This doesn't help when you have guests connect to the network and they don't have a reservation, however. Following the request/response flow with iptables logging I could see that ...


1

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 ...



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