Network definition

Networks connect different systems with each other to enable data exchange between these systems. This not only has the advantage that the systems can exchange information with each other, but a network also enables the sharing of resources. Another advantage of networks is that communication between different systems becomes possible even over a large physical distance. For example, a company with two locations and a data centre in the cloud can still be connected to each other in terms of communication systems.

Characteristics that define networks

Networks can be differentiated according to their spatial extent, i.e. their size.

  • The PAN (Personal Area Network) has a circumference of approximately 10m and refers to the networking of devices in the direct personal environment, such as the home network in the living room or the connection of PDA and computer.
  • The LAN (Local Area Network) has an extension of up to 900m and is mostly used in companies.
  • The MAN (Metropolitan Area Network) covers up to 60 km. The MAN is a city or regional network.
  • The WAN (Wide Area Network) is the long-distance network and is designed for long distances and stretches across countries as well as continents.

Networks are also differentiated by the type of line routing (topology), by type of transmission or by transmission speed.

Latest concept posts Latest blog posts Concept Page Blog Page

Blog entries

Palo Alto PA-200 Attacks

overview of file blocking profiles

The firewall uses file blocking profiles to block specified file types over specified applications and in the specified session flow direction (inbound/outbound/both).

Palo Alto PA-200 Attacks

Protection against ransomware (filtering of Windows PE files)

To protect against ransomware, Windows PE executables should be filtered by content and not just by extension.

Palo Alto PA-200 Factory reset

How to perform a factory reset on a PA-200?

The following steps describe how to perform a factory reset on a PA-200.

Security guidelines


Security guideline "Voice over IP (VoIP)"

This security guideline considers the security aspects of VoIP end devices and switching units (middleware). The components described here are similar in terms of their functionality to the telecommunications systems described in the security guideline "PBX". The specifications of the BSI module NET.4.2 "VoIP" from the Compendium 2020 were observed in the creation of this security guideline.


Security guideline "PBX"

The objective of the security guideline is to protect the information that is transmitted via PBXs as well as to protect the system from external intervention and manipulation. The specifications of the BSI module NET.4.1 "PBXs" from the Compendium 2020 were observed in the creation of this security guideline.


Security guideline "VPN"

This security guideline defines requirements with which a VPN can be planned, implemented and operated in a targeted and secure manner. When creating this security guideline, the requirements of BSI module NET.3.3 "VPN" from the Compendium 2020 were observed.


Cisco IOS NX-OS Hardening

Hardening recommendations for IOS and NX-OS

This article provides configuration recommendations for Cisco IOS and NX-OS systems and enables the overall security of the network to be increased.

Some information about IPv6

IPv6 Notation

Compared to the familiar notation of IPv4, the notation of IPv6 takes some getting used to. Separated by a colon, IPv6 addresses consist of 8 blocks of four-digit hexadecimal numbers. Thus an IPv6 address looks like 2001:db8:838a:1349:42db:8371:3050:ff34

As with almost everything, there are certain special rules for IPv6 to facilitate spelling and readability. The following notations are also legitimate:

  • Leading zeros within a segment can be omitted, but at least one digit must remain.
  • If one or more segments have the value 0, they can be omitted and replaced by a second colon. Thus, the IPv6 address 2001:db8:0:0:0:4ab:3054 can also be shortened as follows 2001:db8::4ab:3054. However, a shortening may only be made once in an address, otherwise the uniqueness would be lost.

So that the spelling is not associated with the port in IPv4, the IPv6 address is placed in square brackets http://[2001:db8:db34:a::34:8420]/ in a URL notation.

IPv6 network notation

Networks are subdivided into network prefix and subnet, just as with IPv4.

The subnet always has the size of a power of two. From this, the following notation is common for networks 2001:db8:94::/48. In this example, the IP address space ranges from 2001:db8:94:0000:0000:0000:0000:0000 to 2001:db8:94:ffff:ffff:ffff:ffff:ffff, whereby the mask of the subnet in this example is ffff:ffff:ffff::. This means that this network contains a total of 280 IP addresses.

Networks of this size are usually allocated to end customers. As a result, the previously known division from the address space of IPv4 will no longer be necessary.

The Internet Service Provider ISP usually receives a /32 network from the RIR, for end customers either a /48 or /56 sized network is provided.

IPv6 address ranges

Loopback address: ::1/128

Probably the simplest and also very important IP address is the loopback address. It has an identical task to the IPv4 address

Link Local Unicast address space: fe80::/10 -- fe80:: - febf::

All addresses in the Link Local Unicast range are not forwarded by the router and are therefore only accessible in the LAN. This means that a network interface does not have to be specified. The Link Local Unicast address is mainly used for autoconfiguration, i.e. it is only used if no other address is bound.

Unique Local Unicast address space: fc00::/7 -- fc00:: - fd00

The local unicast addresses are used for local address allocation, i.e. within a LAN. For IPv4, the ranges for this purpose are, and Currently, only the network fd00::/8 is used for locally generated addresses, but the prefix fc00 will be used in future for the unique assignment of Local Unicast addresses. After the 8 bits used for fc or fd, 40 bits follow for the unique site ID, then 16 bits as the subnet. The last 64 bits are the interface identifier.

Multicast address space: ff00::/8 -- ff00:: - ffff::

Multicast addresses serve as distributors, thus several devices are addressed via one IP address. Since IPv6 does not have its own broadcast address, two multicast addresses are used for this purpose ff01::1 and ff02::1 Furthermore, three IP addresses are important, as these multicast addresses are used to address all routers in a range ff01::2,ff02::2 and ff05::2

Global Unicast Address Space

All other address spaces are basically Global Unicast addresses. However, only four ranges have been defined so far, the remaining addresses have not been assigned yet.

  • 0:0:0:0:ffff::/96 -- IPv4 mapped (mapped)
  • 2000::/3 -- networks assigned by IANA to the RIRs
  • 2002::/4 -- for the tunnel mechanism 6to4
  • 2001:db8::/32 -- for documentation purposes

The first address range is used for the temporary transition from IPv4 to IPv6. The 32 bits after the prefix represent the IPv4 address, so that a router can switch between the two protocols while still recognising the IPv4 address.

IPv6 Privacy Extension

With the autoconfiguration function, IPv6 provides a convenient and quick way to automatically obtain a unique IP address. The IP address is automatically generated on the basis of the interface identifier in this case.

By including the MAC address, anonymity is lost. In other words, all data can always be assigned to an IP address. To prevent the exact assignment, the "Privacy Extension" was designed. This prevents the IP address from always remaining the same.

By inserting randomly generated bytes in the address, the uniqueness is broken. Of course, this does not ensure that the user can call up data on the net completely undetected, but it is a step in the direction of meeting data protection regulations. Nevertheless, many operating systems do not yet use it by default.

IPv6 autoconfiguration

The Dynamic Host Configuration Protocol (DHCP) manages the network configuration of IT systems within a network. By using DHCP, a new IT system in the network does not have to be configured manually. Instead, it makes a request via the IPv4 broadcast address of the network segment. In the case of IPv6, the DHCP request is made to the multicast address ff01::1. Depending on the configuration of the DHCP server, it can assign the following parameters to the requesting hosts, for example.

  • IP address with netmask
  • Gateway
  • DNS server
  • Time and NTP server
  • WINS server (for Windows clients)

With IPv6, the automatic distribution of IP addresses is originally handled by autoconfiguration, so this task is not necessary for a DHCPv6 server. However, it is possible to change this behaviour and to allocate the configuration parameters via DHCPv6. An important new feature of DHCPv6 is that only authorised clients have access to the DHCP server.


The Dynamic Host Configuration Protocol (DHCP) manages the network configuration of IT systems within a network. By using DHCP, a new IT system in the network does not have to be configured manually. Instead, it makes a request via the IPv4 broadcast address of the network segment. In the case of IPv6, the DHCP request is made to the multicast address ff01::1. Depending on the configuration of the DHCP server, it can assign the following parameters to the requesting hosts, for example.

  • IP address with netmask
  • Gateway
  • DNS server
  • Time and NTP server
  • WINS server (for Windows clients)

With IPv6, the automatic distribution of IP addresses is originally handled by autoconfiguration, so this task is not necessary for a DHCPv6 server. However, it is possible to change this behaviour and to allocate the configuration parameters via DHCPv6. An important new feature of DHCPv6 is that only authorised clients have access to the DHCP server.

6to4 Tunnel

Especially for the transition phase from IPv4 to IPv6, there is the possibility of "tunneling" IPv6 packets through IPv4 networks. The 6to4 mechanism was developed to make this possible. The procedure documented in the RFC3056 standard specifies a special procedure for converting an address to an IPv6 tunnel network. The network is first prefixed with the prefix for 6to4 tunnels ("2002") followed by the IPv4 address in hexadecimal and the interface identifier.

For the IPv4 address "", this would result in the following 6to4 tunnel network:

  • 2002 - prefix
  • cb00:7140 - IPv4 address in hexadecimal
  • The network thus looks as follows: 2002:cb00:7140::/48.

The local host or router with public IPv4 address nested an IPv6 packet into an IPv4 packet. Should the packet reach a native IPv6 network, it was sent to a 6to4 relay. At the relay, the IPv6 packet is unpacked again and sent to the actual objective. If the remote host sends something back to the local host, the reply packet is not necessarily routed through the same 6to4 relay again, but could be routed through any 6to4 relay.

Public 6to4 relays provide easy access to the IPv6 network. For further simplification, the next public 6to4 relay can be reached via the anycast address (or 2002:c058:6301::).


The Internet Control Message Protocol for IP version 6 is used to exchange error and information messages. It takes over the same tasks as its predecessor for IPv4, with the decisive difference that an IPv6 connection can only be established if the operation of ICMPv6 also functions. This is mainly due to the fact that the Neighbor Discovery Protocol (NDP) is dependent on it.

The IPv6 header refers to an ICMPv6 packet in the Next header with a protocol number 58. As with the IPv6 header, the ICMPv6 header provides more detailed information about the content of the message.

Neighbor Discovery Protokoll (NDP)

The Neighbour Discovery Protocol (NDP) provides a function comparable to the Address Resolution Protocol (ARP) of IPv4 and is also used for communication between neighbouring hosts within a local network. In addition, NDP is used to determine the "gateway router" that could forward packets into a "foreign" network. The exchange of this information takes place by means of different ICMPv6 packet types. For example, routers are requested via type 133 (Router Solicitation) to respond with type 134 (Router Advertisement). As a result, the default router list can be created or renewed.

typical network attacks

What are the effects of a successful DDoS attack?

A successful DDoS attack is tantamount to an invitation for further attacks. Those affected must expect further attacks to follow until more reliable defences are implemented.

What is meant by high-volume attacks?

High-volume attacks are attempts to increase bandwidth consumption in the targeted network/service or between the targeted network/service and the rest of the Internet. This type of attack leads to congestion and bottlenecks.

What are application layer attacks?

These attacks are directed against specific aspects of an application or service at the application layer (layer 7). This is the most dangerous type of attack, as a very efficient attack can be carried out with only one attacking device generating a low data rate (for this reason, proactive detection and mitigation is extremely difficult). These attacks have increased significantly over the last three to four years and simple application level flooding attacks (HTTP GET etc.) are among the most commonly observed DDoS attacks.

What is a TCP State Exhaustion Attack?

This attack attempts to overload the connection capacity of state tables that are present in many infrastructure components such as load balancers, in firewalls and in the actual application servers. Even high capacity devices capable of storing and managing the state of millions of connections can be disabled by this type of attack.

In accordance with the legal requirements of data protection law (in particular the BDSG as amended and the European Data Protection Regulation 'DS-GVO'), we inform you below about the nature, scope and purpose of the processing of personal data by our company. This privacy policy also applies to our websites and social media profiles. With regard to the definition of terms such as "personal data" or "processing", we refer to Art. 4 DS-GVO.

Name and contact details of the person(s) responsible

Our responsible person(s) (hereinafter "responsible person") within the meaning of Art. 4 fig. 7 DS-GVO is:
Jens Mahnke
Karl-Kunger-Str. 56
12435 Berlin Germany
Email address:

Types of data, purposes of processing and categories of data subjects

Below we inform you about the type, scope and purpose of the collection, processing and use of personal data. 

1. types of data we process
Usage data (access times, websites visited, etc.), communication data (IP address, etc.),

2. purposes of the processing according to Art. 13 para. 1 c) DS-GVO 
Technical and economic optimisation of the website, optimisation and statistical evaluation of our services, improving user experience, compilation of statistics,

3. categories of data subjects according to Art. 13 (1) (e) DS-GVO
Visitors/users of the website,

The data subjects are collectively referred to as "users".

Legal basis for the processing of personal data

Below we inform you about the legal basis for the processing of personal data. 1. if we have obtained your consent for the processing of personal data, Art. 6 para. 1 sentence 1 lit. a) DS-GVO is the legal basis. 2. if processing is necessary to comply with a contract or to carry out pre-contractual measures in response to your request, Art. 6 (1) sentence 1 lit. b) DS-GVO is the legal basis. If the processing is necessary to comply with a legal obligation to which we are subject (e.g. statutory retention obligations), Art. 6 (1) sentence 1 lit. c) DS-GVO is the legal basis. If the processing is necessary to protect the vital interests of the data subject or another natural person, the legal basis is Art. 6 (1) sentence 1 lit. d) DS-GVO. If the processing is necessary to protect our legitimate interests or the legitimate interests of a third party and your interests or fundamental rights and freedoms are not overridden in this respect, Art. 6 para. 1 sentence 1 lit. f) DS-GVO is the legal basis.

Disclosure of personal data to third parties and order processors

As a matter of principle, we do not pass on any data to third parties without your consent. However, if this should be the case, then the data will be passed on on the basis of the aforementioned legal grounds, e.g. when data is passed on to online payment providers for the fulfilment of a contract or due to a court order or because of a legal obligation to hand over the data for the purpose of criminal prosecution, to avert danger or to enforce intellectual property rights. We also use processors (external service providers e.g. for web hosting of our websites and databases) to process your data. If data is passed on to the processors as part of a contract processing agreement, this is always done in accordance with Art. 28 DS-GVO. In doing so, we select our processors carefully, monitor them regularly and have been granted a right to issue instructions regarding the data. In addition, the processors have to have taken suitable technical and organisational measures and comply with the data protection regulations according to the BDSG n.F. and the DS-GVO.

Data transfer to third countries

The adoption of the European General Data Protection Regulation (GDPR) has created a uniform basis for data protection in Europe. Your data is therefore predominantly processed by companies to which the GDPR applies. However, if processing is carried out by services of third parties outside the European Union or the European Economic Area, these have to fulfil the special requirements of Art. 44 ff. DS-GVO must be complied with. This means that the processing takes place on the basis of special guarantees, such as the officially recognised determination by the EU Commission of a level of data protection corresponding to the EU or the observance of officially recognised special contractual obligations, the so-called "standard contractual clauses". Insofar as we obtain your express consent to the transfer of data to the USA due to the invalidity of the so-called "Privacy Shield" in accordance with Article 49 (1) sentence 1 lit. a) DSGVO, we point out in this regard the risk of secret access by US authorities and the use of the data for monitoring purposes, possibly without any legal remedy for EU citizens.

Deletion of data and storage period

Unless expressly stated in this data protection declaration, your personal data will be erased or blocked as soon as you revoke the consent given for processing or the purpose for storing the data no longer applies or the data are no longer required for the purpose, unless their continued storage is necessary for evidence purposes or is contrary to statutory retention obligations. This includes, for example, retention obligations under commercial law for business letters in accordance with § 257 para. 1 of the German Commercial Code (HGB) (6 years) and retention obligations under tax law for receipts in accordance with § 147 para. 1 of the German Fiscal Code (AO) (10 years). When the prescribed retention period expires, your data will be blocked or deleted unless the storage is still necessary for the conclusion or fulfilment of a contract.

Existence of automated decision making

We do not use automated decision making or profiling.

Provision of our website and creation of log files

1. If you use our website for information purposes only (i.e. no registration and no other transmission of information), we only collect the personal data that your browser transmits to our server. If you wish to view our website, we collect the following data:

  • IP address;
  • Internet service provider of the user; 
  • Date and current time of the request;
  • browser type;
  • language and browser version;
  • Content of the retrieval;
  • Time zone;
  • Access status/HTTP status code;
  • Amount of data;
  • Websites from which the request came;
  • Operating system.

This data is not stored together with other personal data about you.

2. This data serves the purpose of user-friendly, functional and secure delivery of our website to you with functions and content as well as its optimisation and statistical evaluation.

3. The legal basis for this is our legitimate interest in data processing in accordance with Art. 6 (1) sentence 1 lit. f) DS-GVO, which also lies in the above purposes.

4. For security reasons, we store this data in server log files for a storage period of 70 days. After this period, they are automatically erased, unless we need to keep them for evidence purposes in the event of attacks on the server infrastructure or other legal violations.

Contacting us via contact form / email / fax / post

1. When contacting us via contact form, fax, mail or email form, your data will be processed for the purpose of handling the contact request.

2. If you have given your consent, the legal basis for processing your data is Art. 6 (1) sentence 1 lit. a) DS-GVO. The legal basis for the processing of data transmitted in the course of a contact request or email form, letter or fax is Art. 6 para. 1 p. 1 lit. f) DS-GVO. The responsible party has a legitimate interest in processing and storing the data in order to be able to answer users' enquiries, to preserve evidence for liability reasons and, if necessary, to be able to comply with its statutory retention obligations for business letters. If the objective of the contact is the conclusion of a contract, the additional legal basis for the processing is Article 6 (1) sentence 1 lit. b) DS-GVO.

3. We may store your details and contact request in our Customer Relationship Management System ("CRM System") or similar system.

4. The data is erased as soon as it is no longer required to achieve the purpose for which it was collected. For the personal data from the input mask of the contact form and those sent by email form, this is the case when the respective conversation with you has ended. The conversation is ended when it is clear from the circumstances that the matter in question has been conclusively clarified. We store enquiries from users who have an account or contract with us until two years after termination of the contract. In the case of legal archiving obligations, deletion takes place after their expiry: end of commercial law (6 years) and tax law (10 years) retention obligation.

5. You have the option to revoke your consent to the processing of personal data at any time in accordance with Art. 6 para. 1 p. 1 lit. a) DS-GVO. If you contact us by email form, you can object to the storage of personal data at any time.

Rights of the person concerned

1. Objection or revocation against the processing of your data

Insofar as the processing is based on your consent pursuant to Art. 6 para. 1 sentence 1 lit. a), Art. 7 DS-GVO, you have the right to revoke your consent at any time. This does not affect the lawfulness of the processing carried out on the basis of the consent until the revocation.

Insofar as we base the processing of your personal data on the balance of interests pursuant to Art. 6 (1) p. 1 lit. f) DS-GVO, you may object to the processing. This is the case if the processing is not necessary, in particular, for the compliance with a contract with you, which is shown by us in each case in the following description of the functions. When exercising such an objection, we ask you to explain the reasons why we should not process your personal data as we have done. In the event of your justified objection, we will review the merits of the case and either cease or adapt the data processing or show you our compelling legitimate grounds on the basis of which we will continue the processing.

You can object to the processing of your personal data for the purposes of advertising and data analysis at any time. You can exercise the right to object free of charge. You can inform us of your advertising objection using the following contact details: Jens Mahnke
Karl-Kunger-Str. 56 12435 Berlin Germany
Email address:

2. Right to information You have a right to information about your personal data stored by us in accordance with Art. 15 DS-GVO. This includes, in particular, information about the processing purposes, the category of personal data, the categories of recipients to whom your data has been or will be disclosed, the planned storage period, the origin of your data if it has not been collected directly from you.

3. Right to rectification You have the right to have inaccurate data corrected or correct data completed in accordance with Art. 16 DS-GVO.

4. Right to deletion You have the right to have your data stored by us deleted in accordance with Art. 17 DS-GVO, unless legal or contractual retention periods or other legal obligations or rights to further storage prevent this.

5. Right to restriction

You have the right to request a restriction in the processing of your personal data if one of the conditions in Art. 18 (1) a) to d) DS-GVO is complied with:

  • If you contest the accuracy of the personal data concerning you for a period of time which enables the controller to verify the accuracy of the personal data;
  • the processing is unlawful and you object to the erasure of the personal data and request instead the restriction of the use of the personal data;
  • the controller no longer needs the personal data for the purposes of the processing but you need them for the establishment, exercise or defence of legal claims; or
  • if you have lodged an objection to the processing pursuant to Art. 21 (1) DS-GVO and it is not yet clear whether the legitimate reasons of the controller outweigh your reasons.

6. Right to data portability You have a right to data portability in accordance with Art. 20 DS-GVO, which means that you can receive the personal data we hold about you in a structured, common and machine-readable format or request that it be transferred to another controller.

7. Right to complain You have the right to complain to a supervisory authority. As a rule, you can contact the supervisory authority for this purpose, in particular in the Member State of your place of residence, your workplace or the place of the alleged infringement.

Data security

In order to protect all personal data transmitted to us and to ensure that data protection regulations are complied with by us as well as by our external service providers, we have taken appropriate technical and organisational security measures. Therefore, among other things, all data is transmitted between your browser and our server via a secure SSL connection.

Status: 09/09/2022

Jens Mahnke
Karl-Kunger-Strasse 56
12435 Berlin
Email form:

Disclaimer - legal information 

§ 1 Warning about content 

The free and freely accessible contents of this website have been created with the greatest possible care. However, the provider of this website accepts no responsibility for the correctness and up-to-dateness of the free and freely accessible journalistic advice and news provided. Contributions identified by name reflect the opinion of the respective author and not always the opinion of the provider. The mere fact of calling up the free and freely accessible content does not create any contractual relationship between the user and the provider; in this respect, the provider's intention to be legally bound is lacking. 

§ 2 External links 

This website contains links to third-party websites ("external links"). These websites are subject to the liability of the respective operators. When the external links were first created, the provider checked the external content for any legal violations. At that time, no legal violations were apparent. The provider has no influence on the current and future design and content of the linked pages. The inclusion of external links does not imply that the provider adopts the content behind the reference or link as its own. It is not reasonable for the provider to constantly monitor the external links without concrete indications of legal violations. However, such external links will be erased immediately if legal violations become known. 

§ 3 Copyrights and ancillary copyrights

The contents published on this website are subject to German copyright and ancillary copyright law. Any use not permitted by German copyright and ancillary copyright law requires the prior written consent of the provider or the respective rights holder. This applies in particular to the copying, editing, translation, storage, processing or reproduction of content in databases or other electronic media and systems. Third-party content and rights are marked as such. The unauthorised reproduction or transmission of individual contents or complete pages is not permitted and is punishable by law. Only the production of copies and downloads for personal, private and non-commercial use is permitted. The display of this website in external frames is only permitted with written permission. 

§ 4 Special terms of use

Insofar as special conditions for individual uses of this website deviate from the aforementioned paragraphs, this will be expressly indicated at the appropriate place. In this case, the special terms of use shall apply in the respective individual case.