Archive for the 'Network' Category

How does traceroute work?

It uses the TTL (Time To Live) parameter and UDP to get the path. Each router which is passed needs to decrease the TTL value of a packet and if it is below 1 the router will discard it and send a ICMP (time exceeded) back to the source. So traceroute sends the first packet with a TTL of 1 to reach the first router and one more with a TTL of 2 to reach the second and so on. You get the picture. But how does it know when the destination is reached? Well it useses another trick for that.  Traceroute sends out a UDP Packet with it with a port higher than 3000. It is very unlikely that this port will be opened at the destination so it will get back from the destination a ICMP packet (port unreachable) which is the answer to the question.

Important: Remember that not all packets are going the same way and it’s likely that they use different paths.

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admin on June 27th 2013 in IT, Network

Important Network Commands you should know

Computer Name

#ping [Computername/IP]
Checks if computer can be reached 4 times

#ping -t [Computername/IP]
Checks if computer can be reached unlimited times

#ping –a [IP]
Name resolution of the IP

Get IP-Adress

#ipconfig /all
Here you can get the MAC-Adress

#ipconfig /release
Removes the IP-Adress

#ipconfig /renew
Gets a new IP-Adress from the DHCP

#ipconfig /registerdns
Renews the registration on the DNS-Server

#ipconfig /displaydns
Shows local DNS-Cache

#ipconfig /flushdns
Deletes local DNS-Cache

#arp –a
Table IP-Adresses / MAC-Adresses

#nslookup [IP/Domainname]
DNS – Name Resolution

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admin on February 8th 2013 in IT, Network, Windows, Windows Server

How to install Nagios 3x updates quickly

Don’t forget to backup beforehand

As always make a backup beforehand. The paths and command options might need to be adjusted to your environment.

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admin on August 6th 2012 in IT, Linux, Network


/usr/local/nagios/bin/nagios -v /usr/local/nagios/etc/nagios.cfg

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admin on May 20th 2011 in IT, Network

Linux Network Settings

Check the state
# ifconfig –a

Activate/Deactivate Network Interface
# ifup eth0
# ifdown eth0

# hostname
# uname -n
# vi /etc/hostname

Get an IP from the DHCP Server
# dhclient

Edit this file to setup a fix IP
#vi /etc/network/interfaces

auto eth0
iface eth0 inet static

# /etc/init.d/networking restart

Edit this file to setup DNS
#vi /etc/resolv.conf

order hotsts, bind
domain mydomain.local

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admin on May 17th 2010 in IT, Linux, Network

How to query mx records in Windows

Open Command Console and type:
set type=mx


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admin on December 3rd 2009 in Internet, Network, Windows, Windows Server

lowid in emule


I spend hours try to find out why I have a lowid in emule. I set port forwarding in my router. Opened the ports in my firewall etc. but I still got a lowid. I scanned with an online portscanner my ports and it told me that it is opened. So what’s the problem?

It wasn’t my settings problem. It’s because there are a lot fake servers in emule and they want to get all the traffic trsough their server. So they don’t allow high ids. After fixing my server list I finally got a high id again;-)

Thanks to this post:

To get a reliable server list free of fake ones, you can follow these steps

  1. Go to Options/Security
  2. Select Filter servers too
  3. In Update from URL, type:
  4. Click on Load.
  5. Go to Options/Server
  6. Set number of errors allowed before removing the server to 9
  7. Click List button that appears next to the option Auto update
  8. In Notepad, that is opened, write this line and remove all others if exists:
  9. Save changes in notepad
  10. Untick the options to update list of servers when connecting to new server and new client
  11. Click on Accept
  12. Go to servers window
  13. Remove all servers from static list
  14. Remove all servers from list
  15. In Update Server.met from URL, type the same URL you did in point #8
  16. Click on Update button
  17. If you have selected Autoconnect only to servers on static list add the servers you want to static list
  18. Double click on any server

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admin on January 26th 2009 in IT, Network

Remote Access to your Home/Work Computer

You need to access your computer at home or company. Or do you need to fix you relatives computer but you are to lazy to get up from you chair and visit them. So you need a remote control software. You could use vnc or remote desktop etc. But usually they are behind a firewall and it needs first a lot of configuration. And not everybody knows how to make a ssh tunnel through port 80 to bypass the firewall. Anyway if you looking for a pretty good and fast solution that most of the time works have a look here:

It is by the way free to use, but there are a couple of limitations. One important feature which is missing in the free version is that you can’t share files. Still this service is great and helped me already a couple of times.

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admin on May 16th 2008 in Network

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