Fritzbox: Easy USV UPS AVM 7490 Battery Power

If you use a Router with IP Phones you perhaps want to have a Power Storage for up to 60 Minutes to use IP Phone or WIFI on Power Failures??

usv fritzbox 7490

Major Info:

  • Check the Router DATASHEETS! the Battery Voltage on loading should never go over maximum!!
  • Some Trafo wind up to 14Volts and more! This DESTROYS the DSL MODEM CHIP !!!!
  • The 10 Cell AA Batterholder allow to connect 9 Cells! Connect the Wire to only 9th Connector 9x AA 1,26V let the Router work
  • The Modem is protected cause the Circut runs under 12 Volts! 11,25 – 11,5V, the 0,5V lost on the Fuses and Diode.
  • 2 Fuses is a MUST HAVE! use always Fuses of 85% of the Router max Power (1,2Amps take 1A), it let the Fuse act faster!
  • The Trafo is the original Part. 12V 1,2A

Security: Harden DSL Routers and Networks against attacks

Last days there was a high count of news about the Bot Attacks against T-Com Telekom Router devices. To understand the behavior about this up comming security problems you should know following points :

  • Every network supported device can be a goal for a attack ( Routers, Modems, PC, Fridges,IP-TV, IP Switches, IP-Cams…)
  • You have to update the OS for each device monthly, if not supported by the manufacter, then dont buy!
  • Try to get Opensource Hardware with Opensource Software for full access (ssh / console) to have full control
  • Reduce the count of devices who are connected direct to the web!
  • If you must use a ISP Modem / DSL Router of your ISP Provider, then install a second Opensource Router with Firewall behind for more security
  • Use small Firewalls to seperate WIFI and LAN Networks!
  • DISABLE if possible „auto update“ and „ISP Remote Control“ at the DSL Router / Modem cause more and more comfort functions are hacked to break the systems.
  • Updates must be tested on non productive Routers!
  • Keep clean backups of fresh installed Routers / Modems and restore the backup every 3 month to overwrite bad possible changes!!
  • Connect the Routers to a clocktimer to unplug and hard reboot the Router every night! (againts RAM Hacks)
  • Control every month the Router logs and ISP-Settings ( IP-Phones) cause hackers want to route calls to asia!
  • Dont trust blind every commercial hardware! much bugs like open doors, default passwords are set!
  • Test your System with free tools like „nmap“ Portscan and „iftop“
  • Change Passwords, WIFI Passwords, Wifi-IDs! min. 12 signs

Fritzbox: Freezing Wifi if USB 3.0 is used

Today i was touched by a Bug of my fritzbox 7490, after installing a USB 3.0 Stick as NAS the Wifi connect was broken to all devices!

After some search on net i found this post:

The high magnetic frequency’s of USB 3.0 data transfer inside the cable or stick hangup the WIFI chips! It works like a WIFI JAMMER!!

DONT USE A ROUTER AS NAS! If it fails or overheat all devices are offline!! It’s a really big joke that most Manufacter sell devices without TESTING!! I call it Banana Hardware..

Fritzbox: DHCP-IP Problems

Problem:Probleme mit IP-Adressvergabe ueber DHCP, wenn auf dem gleichen Rechner unterschiedliche Betriebssysteme laufen 

Wird ein Rechner mal unter Linux und mal unter Windows betrieben, so kann es passieren, dass der Rechner unter einem der beiden Systemen keine IP-Adresse mehr zugewiesen bekommt.

Waehlt man sich per Telnet auf der Fritzbox ein, so sieht man dort die Fehlermeldung „DHCPD no lease found“. Um dieses Problem zu vermeiden, muss der DHCP- Client unter Linux wie folgt korrekt konfiguriert werden:

Loesung :
In der dhclient.conf des Client-Rechners muss „send dhcp-client-identifier 01:Error-Report: Under the fritzbox router is a Bug appeared

If you run two different OS on one and the same pc, working with DHCP-Clients, the router will stop sending the updated ip addresses to the pc, cause its logged in leases-file.

To solve it edit dhclient.conf and add lines above with the pc mac address-forcing, clear data inside multid.leases and reboot the router.

Fritzbox: DNS lookup slow


Wenn man mit einem PC hinter eine Router z.b. fritzbox 7170 sitzt kann das anfordern von Internetseiten (http://www.usw…) länger dauern. Grund Ihr Internetprovider besitzt DNS-Namensauflösungsserver die unter hoher Last z.B. viele DSL-Kunden leiden.

Das Problem besteht weiter darin das Ihr DSL-Router dynamisch diese DNS-Server mitgeteilt bekommt und Sie diese nicht manuell ändern können (ander Fabrikate ausgenommen)


Sie richten auf Ihrem PC unter Netzwerkeinstellugen neue zusätzliche DNS Servereinträge ein und nutzen diese an erster Stelle

öffenen Sie die Datei /etc/resolv.conf (für Windows Nutzer siehe Netzwerk)

und einfügen

nameserver #Router

nun sollten Sie das Verhalten in den nächsten Tagen testen.

Behind a dsl-router you have the problem with slow internet site requests in your browser, this is a result of the poor performance of the provider dns servers. In fact that your router hardware does not have the possibility to setup own dns-server adresses, your are forced to setup additional dns addresses in your pc.on linux edit /etc/resolv.conf see above with opendns power server addresses