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57

Based on this answer, assuming you have installed nmap (sudo apt install nmap): sudo nmap --script broadcast-dhcp-discover Add the -e $interface option if you have more than one network interface. (For example: nmap --script broadcast-dhcp-discover -e eth0) Sample output: Starting Nmap 7.01 ( https://nmap.org ) at 2017-09-27 17:40 CEST Pre-scan script ...


57

If you don't want to do any configuration inside the guest, then the only option is a DHCP server that hands out static IP addresses. If you use bridge mode, that will probably be some external DHCP server. Consult its manual to find out how to serve static leases. But at least in forward modes nat or route, you could use libvirt's built-in dnsmasqd (More ...


26

Basically what happens is that dhclient adds a route to the routing table. It tries this while the route is already in the table. Check ip route for a route which was added by the dhcp server. For having the lease renewed do dhclient -r if thats not enough you can remove all leases by removing the file and getting a new lease sudo rm /var/lib/dhcp/...


25

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 ...


20

I think you should go the multi-VLAN route - and not just because of the DHCP server issue. At the moment, you have one big flat network and while to some degree, users should be expected to take care of their own security, I'd personally find it a pretty unacceptable setup. The only switches that need to be managed are yours. Beyond that, you give each ...


20

You should have your Small Business Server (Server Essentials) doing DHCP and DNS. SBS will automatically disable its DHCP service when it detects another DHCP server on the LAN. (You can verify this by checking the event logs, there will be DHCP errors, and the service will likely be stopped) Since your router is likely handing out the ISPs DNS, your ...


18

Technically there is nothing wrong with this lease time, especially if in the school the computers and devices on the network rarely change. However, the general rule of thumb is that your leases should be long enough to reduced network bandwidth and server load in the event that you have a large amount of devices who could potentially need leases. So ...


18

The domain-name option specifies the client's domain name (of which there can only be one), and is specified in resolv.conf with the domain keyword. This is the domain which will be used when running hostname -f on the client. The domain-search option specifies a list of domains to use when looking up bare hostnames, and is specified in resolv.conf with the ...


18

IANA is the organization responsible for global IP assignments. They assign "blocks" of IP addresses to Regional Internet Registries which are geographically based organizations responsible for allocation within their geographic areas -- there are 5 RIR's: AfriNIC (Africa) LACNIC (Latin America & Caribbean) APNIC (Asia Pacific) ARIN (United States, ...


16

You can't see VLAN tag from tcpdump -i eth0 output on i686/x86_64 architecture because of VLAN acceleration. the VLAN layer will be filtered by kernel so it always looks untagged. Please refer to Bug 498981 - tcpdump cannot deal with 802.1q vlan tag According to your case, you can get VLAN tags via: tcpdump -i eth0 -Uw - | tcpdump -en -r - vlan 20 You ...


16

This seemed like overkill to me, we already wont come close to filling the single /64 but this might be my IPv4 mindset confusing me. Stop counting hosts, that's IPv4 thinking. Subnets come in one size fits all, enormous. A /64 can address every IP device ever made with plenty room to spare. Yet the address space is even bigger such that a single site ...


15

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 ...


15

Determine the IP address that is assigned to your server and then go onto the DHCP and set a DHCP reservation for that server.


14

The solution is checking Use this connection's DNS suffix in DNS registration in the TCP/IP settings of the network interface: As much as it may appear strange, this is the only solution to ensure Windows will register both the A and the PTR records for a DHCP network connection; otherwise, it will only register the A record.


13

One possible reason for this issue is when the machine account password gets out of sync with the domain controller. This can happen, for example, if the computer account in Active Directory is manually removed and re-added, or if the client machine has been restored to an earlier point in time (machine account passwords are automatically changed every 30 ...


13

The machine's MAC address changing won't affect anything. Active Directory isn't concerned with the link layer. Yep you can just plug it back in, and the DC will catch up. (Now on the other hand, if the DC's hard drive was encrypted with something like Bitlocker, replacing the motherboard (and thus the onboard TPM chip) would mean the end of the road for ...


13

virsh net-update is a good command for you (you don't need to restart/destroy your network etc) see: https://www.redhat.com/archives/libvir-list/2012-September/msg01380.html


12

Hanging on to IPs so long, there is a risk as devices move through your system. Anything extra that comes in now has a very long hold on your network. Mostly it should just be your own devices, but things happen: exceptions are granted for presenter laptops, mistakes are made, faculty/students sneak their own equipment in, etc. It would be easy to ...


12

802.1X. This is not something that is trivial to implement, it requires the appropriate security infrastructure to back it up (associated user accounts, etc), but it as far as I know, the only way to even get close to what your auditors are asking for. It is supported by Windows, Linux, iOS (both the Apple and Cisco versions, so its good for iPads and ...


12

When your computer sends a packet of data to 255.255.255.255, it will actually map that to the MAC address FF:FF:FF:FF:FF:FF. The packet is then sent out of your computer to the switch (or whatever your computer is plugged in to) with a destination of FF:FF:FF:FF:FF:FF. Switches know that packets destined for that MAC address should be sent out of all ports ...


12

DHCP only assigns IP addresses. Not only can it not assign MAC addresses, you NEED a MAC address in order to use DHCP. (It's the address used for the lower layer ethernet protocol.) Essentially, to get an IP address, you send a broadcast request, and the response is sent to your MAC address. MAC addresses are usually assigned in hardware, by the ...


11

Would comment p.campbell, but I have only 1 reputation and therefore cannot, first I review installed interfaces: ip addr release IP from selected interface (e.g. eth0, eth1, enp1s0, sit0, wlan0,...): sudo dhclient -r *interface* request new IP from DHCP server (alert on error): sudo dhclient -1 *interface* check IP: ip addr Ubuntu 16.04 LTS ...


11

No it wont traverse routers unless you setup a dhcp relay agent. Broadcast messages are only broadcasted on the broadcast domain of the host (subnet).


11

Setup reservations for the specific hosts using the dhcp-host option. Use tag options to flag those for a special set of options. This is completely un-tested, but I suspect your config might look something like this. Check the man page for full details. dhcp-host=00:15:99:27:f8:98,set:specialhosts,192.168.32.20 dhcp-host=00:51:99:72:8f:89,set:...


11

can I put PowerCLI "code" (Cmdlets, etc.) inside a PS1 file, along with other PowerShell code, and execute it like a normal PS1? Yes. But if you want it to work as expected (as when you use the PowerCLI console) you'll need to initialize the environment. You can see how this is done by examining the shortcut "VMware vSphere PowerCLI.lnk", the target is: ...


11

Apparently there is no such elegant method to accomplish the job. So, let's do it manually. Stop dhcp server. Check your /var/lib/dhcp/dhcpd.leases file and check for the entry. It contains the list of all dhcp leases. Remove the entry carefully and start the dhcp server again.


10

Go to Event Viewer, Applications and Services Logs, Microsoft, Windows, Dhcp-Client, Microsoft-Windows-DHCP Client Events/Operational. By default this trace log will be empty, because you need to enable it by clicking on “Enable log” on the right side. Source: http://texhex.blogspot.be/2011/12/debugging-dhcp-on-client.html


10

VLAN's are a layer 2 feature, while IP/DHCP is a layer 3 one, I just wanted to make that clear but they have a lot to do with each other in this scenario. Basically all you really need to do is ensure that your L2/3 switch/router is configured to allow your DHCP server to not only route to/from all VLANs but provide a 'DHCP Helper' service so that all ...


10

Move your servers to a separate VLAN - this will mitigate although there is nothing preventing the user from setting his IP to that of the gateway. Or better, move the problem user to his own VLAN. This can also be solved by using dynamic arp inspection on a good enough managed switch. This can also be solved by treating it as a disciplinary problem that ...


10

host hostname-primary.my.domain { option host-name hostname; hardware ethernet xx:xx:xx:xx:xx:xx; fixed-address 10.0.1.134; } host hostname-secondary.my.domain { option host-name hostname; hardware ethernet yy:yy:yy:yy:yy:yy; fixed-address 10.0.1.134; } Just for the record... You are opening yourself for an IP address conflict, but I ...


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