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Resizing a VirtualBox Linux VDI Disk under Windows Host – VBoxManage error – Resize hard disk operation for this format is not implemented yet!

Using my VirtualBox linux machines (KaliLinux in my case) together with applying a couple of updates brought a problem, where the VB machine starts run out of disk space and I'm not able to update neither extend the system. This could be an often problem once we are trying to save some host system hard disk space using a small initial size of virtual machine disk partitions (12GB here).

The disk file cmd (df) reports:

CCNP – Route redistribution – Simulating routing loops


Teaching CCNP ROUTE courses and describing the problematic of two-way routing redistribution I need an example describing the case which point out to the process of creating a routing loop. This example shows how such routing loop may arise using badly configured redistribution process andusing bad seed metric. The topology with two redisitributing routers creates routing feedback (two way, multipoint redistribution). The loop is created for packets routed from the ospf network to the destination network.

Using tcpdump for diagnostics of DNS – debian

TCPdump is a powerful command-line packet analyzer, which may be used for analyzing of DNS question/answer process. TCPdump is preinstalled on many linux distributions. For debian it can be installed directly from the debian repository:

apt-get install tcpdump

TCPdump allows write a sniff to file or display it realtime. It provides several ways how to use it for DNS analysis. Now I will write a few examples. Deeper description is at the bottom of the page.

Installing WebRTC2SIP gateway – tutorial

System preparation

apt-get update
apt-get upgrade

As the first step we need to install packages necessary to build the main webrtc2sip gateway:

apt-get install build essential libtool automake subversion git pkg-config screen libxml2-dev / 
libssl-dev libsrtp0-dev

to support for libspeex (audio codec) and libspeexdsp (audio processing and jitter buffer) add

Setting up DNS records for Kamailio 4.x platform

Our IMS clients will use DNS service to resolve which transport protocol to preferr and which server provides that SIP service. Therefore we need for this purpose working DNS server with valid delegated zones. In our case we are administrating own DNS zone named So we will add required resource records, first we add NAPTR records and then valid SRV and A records

So, prepare your DNS records, in our case: