Posts Tagged ‘MAC’

Deny DHCP Address by MAC on Linux

Thursday, October 8th, 2020

Deny DHCP addresses by MAC ignore MAC to not be DHCPD leased on GNU / Linux howto

I have not blogged for a long time due to being on a few weeks vacation and being in home with a small cute baby. However as a hardcore and a bit of dumb System administrator, I have spend some of my vacation and   worked on bringing up the the www.pc-freak.net and the other Websites hosted as a high availvailability ones living on a 2 Webservers running on a Master to Master MySQL Replication backend database, this is oll hosted on  servers, set to run as a round robin DNS hosts on 2 servers one old Lenove ThinkCentre Edge71 as well as a brand new real Lenovo server Lenovo ThinkServer SD350 with 24 CPUs and a 32 GB of RAM
To assure Internet Connectivity is having a good degree of connectivity and ensure websites hosted on both machines is not going to die if one of the 2 pair configured Fiber Optics Internet Providers Bergon.NET has some Issues, I've rented another Internet Provider Line is set bought from the VIVACOM Mobile Fiber Internet provider – that is a 1 Gigabit Fiber Optics Line.
Next to that to guarantee there is no Database, Webserver, MailServer, Memcached and other running services did not hit downtimes due to Electricity power outage, two Powerful Uninterruptable Power Supplies (UPS)  FPS Fortron devices are connected to the servers each of which that could keep the machine and the connected switches and Servers for up to 1 Hour.

The machines are configured to use dhcpd to distributed IP addresses and the Main Node is set to distribute IPs, however as there is a local LAN network with more of a personal Work PCs, Wireless Devices and Testing Computers and few Virtual machines in the Network and the IPs are being distributed in a consequential manner via a ISC DHCP server.

As always to make everything work properly hence, I had again some a bit weird non-standard requirement to make some of the computers within the Network with Static IP addresses and the others to have their IPs received via the DHCP (Dynamic Host Configuration Protocol) and add some filter for some of the Machine MAC Addresses which are configured to have a static IP addresses to prevent the DHCP (daemon) server to automatically reassign IPs to this machines.

After a bit of googling and pondering I've done it and some of the machines, therefore to save others the efforts to look around How to set Certain Computers / Servers Network Card MAC (Interfaces) MAC Addresses  configured on the LAN network to use Static IPs and instruct the DHCP server to ingnore any broadcast IP addresses leases – if they're to be destined to a set of IGNORED MAcs, I came up with this small article.

Here is the DHCP server /etc/dhcpd/dhcpd.conf from my Debian GNU / Linux (Buster) 10.4

 

option domain-name "pcfreak.lan";
option domain-name-servers 8.8.8.8, 8.8.4.4, 208.67.222.222, 208.67.220.220;
max-lease-time 891200;
authoritative;
class "black-hole" {
    match substring (hardware, 1, 6);
    ignore booting;
}
subclass "black-hole" 18:45:91:c3:d9:00;
subclass "black-hole" 70:e2:81:13:44:11;
subclass "black-hole" 70:e2:81:13:44:12;
subclass "black-hole" 00:16:3f:53:5d:11;
subclass "black-hole" 18:45:9b:c6:d9:00;
subclass "black-hole" 16:45:93:c3:d9:09;
subclass "black-hole" 16:45:94:c3:d9:0d;/etc/dhcpd/dhcpd.conf
subclass "black-hole" 60:67:21:3c:20:ec;
subclass "black-hole" 60:67:20:5c:20:ed;
subclass "black-hole" 00:16:3e:0f:48:04;
subclass "black-hole" 00:16:3e:3a:f4:fc;
subclass "black-hole" 50:d4:f5:13:e8:ba;
subclass "black-hole" 50:d4:f5:13:e8:bb;
subnet 192.168.0.0 netmask 255.255.255.0 {
        option routers                  192.168.0.1;
        option subnet-mask              255.255.255.0;
}
host think-server {
        hardware ethernet 70:e2:85:13:44:12;
        fixed-address 192.168.0.200;
}
default-lease-time 691200;
max-lease-time 891200;
log-facility local7;

To spend you copy paste efforts a file with Deny DHCP Address by Mac Linux configuration is here
/home/hipo/info
Of course I have dumped the MAC Addresses to omit a data leaking but I guess the idea behind the MAC ADDR ignore is quite clear

The main configuration doing the trick to ignore a certain MAC ALenovo ThinkServer SD350ddresses that are reachable on the Connected hardware switch on the device is like so:

class "black-hole" {
    match substring (hardware, 1, 6);
    ignore booting;
}
subclass "black-hole" 18:45:91:c3:d9:00;


The Deny DHCP Address by MAC is described on isc.org distribution lists here but it seems the documentation on the topic on how to Deny / IGNORE DHCP Addresses by MAC Address on Linux has been quite obscure and limited online.

As you can see in above config the time via which an IP is freed up and a new IP lease is done from the server is severely maximized as often DHCP servers do use a max-lease-time like 1 hour (3600) seconds:, the reason for increasing the lease time to be to like 10 days time is that the IPs in my network change very rarely so it is a waste of CPU cycles to do a frequent lease.

default-lease-time 691200;
max-lease-time 891200;


As you see to Guarantee resolving works always as expected I have configured – Google Public DNS and OpenDNS IPs

option domain-name-servers 8.8.8.8, 8.8.4.4, 208.67.222.222, 208.67.220.220;


One hint to make is, after setting up all my desired config in the standard config location /etc/dhcp/dhcpd.conf it is always good idea to test configuration before reloading the running dhcpd process.

 

root@pcfreak: ~# /usr/sbin/dhcpd -t
Internet Systems Consortium DHCP Server 4.4.1
Copyright 2004-2018 Internet Systems Consortium.
All rights reserved.
For info, please visit https://www.isc.org/software/dhcp/
Config file: /etc/dhcp/dhcpd.conf
Database file: /va/home/hipo/infor/lib/dhcp/dhcpd.leases
PID file: /var/run/dhcpd.pid
 

That's all folks with this sample config the IPs under subclass "black-hole", which are a local LAN Static IP Addresses will never be offered leasess anymore from the ISC DHCP.
Hope this stuff helps someone, enjoy and in case if you need a colocation of a server or a website hosting for a really cheap price on this new set High Availlability up described machines open an inquiry on https://web.pc-freak.net.

 

How to debug failing service in systemctl and add a new IP network alias in CentOS Linux

Wednesday, January 15th, 2020

linux-debug-failing-systemctl-systemd-service--add-new-IP-alias-network-cable

If you get some error with some service that is start / stopped via systemctl you might be pondering how to debug further why the service is not up then then you'll be in the situation I was today.
While on one configured server with 8 eth0 configured ethernet network interfaces the network service was reporting errors, when atempted to restart the RedHat way via:
 

service network restart


to further debug what the issue was as it was necessery I had to find a way how to debug systemctl so here is how:

 

How to do a verbose messages status for sysctlct?

 

linux:~# systemctl status network

linux:~# systemctl status network

 

Another useful hint is to print out only log messages for the current boot, you can that with:

# journalctl -u service-name.service -b

 

if you don't want to have the less command like page separation ( paging ) use the –no-pager argument.

 

# journalctl -u network –no-pager

Jan 08 17:09:14 lppsq002a network[8515]: Bringing up interface eth5:  [  OK  ]

    Jan 08 17:09:15 lppsq002a network[8515]: Bringing up interface eth6:  [  OK  ]
    Jan 08 17:09:15 lppsq002a network[8515]: Bringing up interface eth7:  [  OK  ]
    Jan 08 17:09:15 lppsq002a systemd[1]: network.service: control process exited, code=exited status=1
    Jan 08 17:09:15 lppsq002a systemd[1]: Failed to start LSB: Bring up/down networking.
    Jan 08 17:09:15 lppsq002a systemd[1]: Unit network.service entered failed state.
    Jan 08 17:09:15 lppsq002a systemd[1]: network.service failed.
    Jan 15 11:04:45 lppsq002a systemd[1]: Starting LSB: Bring up/down networking…
    Jan 15 11:04:45 lppsq002a network[55905]: Bringing up loopback interface:  [  OK  ]
    Jan 15 11:04:45 lppsq002a network[55905]: Bringing up interface eth0:  RTNETLINK answers: File exists
    Jan 15 11:04:45 lppsq002a network[55905]: [  OK  ]
    Jan 15 11:04:45 lppsq002a network[55905]: Bringing up interface eth1:  RTNETLINK answers: File exists
    Jan 15 11:04:45 lppsq002a network[55905]: [  OK  ]
    Jan 15 11:04:46 lppsq002a network[55905]: Bringing up interface eth2:  ERROR     : [/etc/sysconfig/network-scripts/ifup-eth] Device eth2 has different MAC address than expected, ignoring.
    Jan 15 11:04:46 lppsq002a network[55905]: [FAILED]
    Jan 15 11:04:46 lppsq002a network[55905]: Bringing up interface eth3:  RTNETLINK answers: File exists
    Jan 15 11:04:46 lppsq002a network[55905]: [  OK  ]
    Jan 15 11:04:46 lppsq002a network[55905]: Bringing up interface eth4:  ERROR     : [/etc/sysconfig/network-scripts/ifup-eth] Device eth4 does not seem to be present, delaying initialization.
    Jan 15 11:04:46 lppsq002a network[55905]: [FAILED]
    Jan 15 11:04:46 lppsq002a network[55905]: Bringing up interface eth5:  RTNETLINK answers: File exists
    Jan 15 11:04:46 lppsq002a network[55905]: [  OK  ]
    Jan 15 11:04:46 lppsq002a network[55905]: Bringing up interface eth6:  RTNETLINK answers: File exists
    Jan 15 11:04:47 lppsq002a network[55905]: [  OK  ]
    Jan 15 11:04:47 lppsq002a network[55905]: Bringing up interface eth7:  RTNETLINK answers: File exists
    Jan 15 11:04:47 lppsq002a network[55905]: [  OK  ]
    Jan 15 11:04:47 lppsq002a network[55905]: RTNETLINK answers: File exists
    Jan 15 11:04:47 lppsq002a network[55905]: RTNETLINK answers: File exists
    Jan 15 11:04:47 lppsq002a network[55905]: RTNETLINK answers: File exists
    Jan 15 11:04:47 lppsq002a network[55905]: RTNETLINK answers: File exists
    Jan 15 11:04:47 lppsq002a network[55905]: RTNETLINK answers: File exists
    Jan 15 11:04:47 lppsq002a network[55905]: RTNETLINK answers: File exists
    Jan 15 11:04:47 lppsq002a network[55905]: RTNETLINK answers: File exists
    Jan 15 11:04:47 lppsq002a network[55905]: RTNETLINK answers: File exists
    Jan 15 11:04:47 lppsq002a network[55905]: RTNETLINK answers: File exists
    Jan 15 11:04:47 lppsq002a systemd[1]: network.service: control process exited, code=exited status=1
    Jan 15 11:04:47 lppsq002a systemd[1]: Failed to start LSB: Bring up/down networking.
    Jan 15 11:04:47 lppsq002a systemd[1]: Unit network.service entered failed state.
    Jan 15 11:04:47 lppsq002a systemd[1]: network.service failed.
    Jan 15 11:08:22 lppsq002a systemd[1]: Starting LSB: Bring up/down networking…
    Jan 15 11:08:22 lppsq002a network[56841]: Bringing up loopback interface:  [  OK  ]
    Jan 15 11:08:22 lppsq002a network[56841]: Bringing up interface eth0:  RTNETLINK answers: File exists
    Jan 15 11:08:22 lppsq002a network[56841]: [  OK  ]
    Jan 15 11:08:26 lppsq002a network[56841]: Bringing up interface eth1:  RTNETLINK answers: File exists
    Jan 15 11:08:26 lppsq002a network[56841]: [  OK  ]
    Jan 15 11:08:26 lppsq002a network[56841]: Bringing up interface eth2:  ERROR     : [/etc/sysconfig/network-scripts/ifup-eth] Device eth2 has different MAC address than expected, ignoring.
    Jan 15 11:08:26 lppsq002a network[56841]: [FAILED]
    Jan 15 11:08:26 lppsq002a network[56841]: Bringing up interface eth3:  RTNETLINK answers: File exists
    Jan 15 11:08:27 lppsq002a network[56841]: [  OK  ]


2020-01-15-15_42_11-root-server

 

Another useful thing debug arguments is the -xe to do:

# journalctl -xe –no-pager

 

  • -x (– catalog)
    Augment log lines with explanation texts from the message catalog.
    This will add explanatory help texts to log messages in the output
    where this is available.
  •  -e ( –pager-end )  Immediately jump to the end of the journal inside the implied pager
      tool.

2020-01-15-15_42_32-root-server

Finally after fixing the /etc/sysconfig/networking-scripts/* IP configuration issues I had all the 8 Ethernet interfaces to work as expected
 

# systemctl status network


2020-01-15-16_15_38-root-server

 

 

2. Adding a new IP alias to eth0 interface


Further on I had  to add an IP Alias on the CenOS via its networking configuration, this is done by editing /etc/sysconfig/network-scripts/ifcfg* files.
To create an IP alias for first lan interface eth0, I've had to created a new file named ifcfg-eth0:0
 

linux:~# cd /etc/sysconfig/network-scripts/
linux:~# vim ifcfg-eth0:0


with below content

NAME="eth0:0"
ONBOOT="yes"
BOOTPROTO="none"
IPADDR="10.50.10.5"
NETMASK="255.255.255.0"


Adding this IP address network alias works across all RPM based distributions and should work also on Fedora and Open SuSE as well as Suse Enterprise Linux.
If you however prefer to use a text GUI and do it the CentOS server administration way you can use nmtui (Text User Interface for controlling NetworkManager). tool.
 

linux:~# nmtui

 

centos7_nmtui-ncurses-network-configuration-sysadmin-tool

nmtui_add_alias_interface-screenshot

Restart hung Mac OS application – How to kill programs in Mac OS – alternative of Windows CTRL + ALT + DEL

Friday, May 23rd, 2014

mac-kill-hung-application-killing-freezed-application-on-mac-osx
If you happen to have the rare case of having a hung MAC OS X application and you're coming from a Linux / Windows background you will be certainly wonderhing how to kill Mac OS X hung application.
In Mac OS the 3 golden buttons to kill crashed application are:

 

COMMAND + OPTION + ESCAPE

Command + Option + Escape

while pressed simultaneously is the Mac Computer equivalent of Windows CTRL + ALT + DEL

mac-os-force-kill-hung-application-force-program-exit-mac-OSX

Holding together COMMAND  + OPTION + ESCAPE on MAC OS brings up the Force Quit Window showing and letting you choose between the list of open applications. To close freezed MAC application, choose it and Press the Force Quit Button this will kill immediately that application.  

To directly end application without invoking the choose Force Quit Window menu, to force a hanging app quit right click on its icon in Dock (CTRL + Click) and choose "Force Quit” from context menu.

A little bit more on why applications hung in MAC OS. Each application in MAC OS has its event queue. Event queue is created on initial application launch, event queue is buffer that accepts input from system (could be user input from kbd or mouse, messages passed from other programs etc.). Program is hanging when system detects queued events are not being used.

macOSX-EventQueue-reason-for-application-hung-in-macs
Other reasons for Mac OS hanging program is whether you're attaching detaching new hardware peripherals (i.e. problems caused by improper mount / unmounts), same hang issues are often observed on BSD and Linux. Sometimes just re-connecting (mouse, external hdd etc.) resolves it.
Program hungs due to buggy software are much rarer in Macs just like in IPhones and Ipads due to fact mac applications are very well tested until published in appstore.

Issues with program hungs in Mac sometimes happen after "sleep mode" during "system wake" function – closing, opening macbook. If a crashed program is of critical importance and you don't want to "Force Quit" with COMMAND + OPTION + ESC. Try send PC to sleep mode for a minute or 2 by pressing together OPTION + COMMAND + EJECT.

An alternative approach to solve hanging app issue is to Force-quit Finder and Dock to try that, launch Terminal

And type there:

# killall Dock

Other useful to know Mac OS keyboard combination is COMMAND + OPTION + POWERHold together Command and Option and after a while press Power – This is a shortcut to instruct your Mac PC to reboot.

Howto Change MAC address in Linux and Windows 2000, XP and Vista (Mac Spoofing :)

Sunday, September 20th, 2009

MAC stands for (Media Access Control) and stands for the computer physical address in LAN networks.
Ethernet MAC is a six byte number, usually expressed as a twelve digit hexadecimal number.
IPs are translated to Mac via a protocol called ARP (Address Resolution Protocol).
Let’s say Computer with IP 10.10.10.1 wants to send information to another system on the LAN with anIP of 10.10.10.2.
10.10.10.1 will first send broadcast to all stations on the LAN asking who has the address of 10.10.10.2.
Then the box possessing 10.10.10.2 will respond to 10.10.10.2 with it’s MAC address which would be temporary stored
in 10.10.10.2′s ARP’s table in order to make 10.10.10.1 recognize 10.10.10.2 later on.

Host 1 (10.10.10.1): Hello everyone on the LAN (FF:FF:FF:FF:FF:FF), who has the IP 10.10.10.2? My MAC is DE:AB:BE:EF:FF:FE so you can respond back to me.Host 2 (10.10.10.2): Hello DE:AB:BE:EF:FF:FE, I have IP 10.10.10.2 and my MAC address is 1C:43:B6:F8:9B:1E so you can send your IP packets to me.
There are a plenty of reasons that might force to wish for changing your mac. Though I’ll mention only one
1. To get across MAC filtering set on a router. Or in other words to bee able to access your internet withall your computers at home (don’t try them simultaneously!). For example recently a cousin of mine bought a secondnotebook for her daughter.
They desired to be able to access the internet with both the PCs. I contacted the ISPwith a request to add me a second MAC address, just to find that this wasn’t possible with this exact ISP.
Their computer ran dual boot install of a GNU/Linux system as well as Windows Vista, thus I needed to change their existing MACaddress in both Windows and Linux
Here is how I achieved that:
1. In Linux
Really simple:/sbin/ifconfig eth0 hw ether 00:00:00:00:00:00 (substitute here with your desired MAC)/sbin/ifconfig eth0 up
2. On BSD
/sbin/ifconfig xl0 link 00:00:00:AA:AA:AB (subst with MAC here), xl0 is your interface name/sbin/ifconfig xl0 up
3. In Windows XP
There are a couple of ways to go in Windows. The hardest way is to use regedit and to look and substitute some obscure values.
Another a bit easier way is to use either MacMakeUp , Smac or EtherChange
The classic way to change Mac in Windows XP is:
Go to Start->Settings->Control Panel and double click on Network and Dial-up Connectionsa) Right click on the NIC you want to change the MAC address and click on properties.b) Under “General” tab, click on the “Configure” buttonc) Click on “Advanced” tabd) Under “Property section”, you should see an item called “Network Address” or “Locally Administered Address”, click on it.e) On the right side, under “Value”, type in the New MAC address you want to assign to your NIC. Usually this value is entered without the “-” between the MAC address numbers.f) Goto command prompt and type in “ipconfig /all” or “net config rdr” to verify the changes are applied.
4. In Windows Vista
Go to Control Panel -> Network Connections -> Properties (on Connection using …) Configure -> Advanced -> Network Address (Then type your MAC Here)
All the credits for this post go to the article Changing Your MAC Address In Window XP/Vista, Linux And Mac OS X which explains what you read above even more thoroughly.
Most of the information here is originally found in the above article.END—–