Protocols

What does ‘502 bad gateway’ mean?: Explanation and solution

Error 502 Bad Gateway: Where’s the problem?

HTTP status codes emerge when something isn’t running properly on the internet. In this respect, the 502 Bad Gateway error is no exception. But this familiar error message can be particularly tricky: It’s not actually clear where the source of the problem lies. In the chain of gateways along which internet requests run, the error could occur at a number of different points. This article explains...

HTTP error 500: Internal Server Error

HTTP error 500: Where does the problem lie and how to fix it?

Error messages when surfing the net are a nuisance for everyone involved, but especially for those who have to find out what the problem is. The search for a solution can be particularly tedious if the status code message barely provides any information on the source of the error. The HTTP error 500 (“Internal Server Error”) is a collective status code. We give you tips on where errors could have...

550 requested action not taken: possible solutions

SMTP error 550: how to fix “Requested action not taken: mailbox unavailable” and other SMTP 550 error messages

If you want to send a message with your e-mail client and the sending fails, you’ll receive a corresponding error message from the server, including an SMTP status code. For example, the message “550 Requested action not taken: mailbox unavailable” means that the targeted address couldn’t be reached. Since this problem can have various causes, even more possible solutions exist, some of which you...

PHP 5.6 Support

PHP 5.6: Support stops at the end of 2018

Security support for PHP 5.6 ceases at the end of the year. Although developers had already postponed the end date by a year, many website operators still seem to be unprepared. A large number of websites still run on PHP 5.6. From January onwards, these websites will be at risk. However, many are dreading the update. How can you protect your website?

401 error: What can you do about it?

Error 401: Unauthorised – No access to the website

You’re surfing around on the internet, but instead of getting the desired content you only receive an error message: annoying or even downright frustrating. Especially if you don’t exactly know what the status is supposed to mean. How are you expected to solve the problem, if you don’t know what’s causing it? This also goes for the error 401. Here we explain what the error means and what you can...

The OSI model: a reference for standards and protocols

What’s the OSI model?

Those working with network technology are bound to encounter the ISO-OSI model sooner or later. This system subdivides communication between computer systems into seven different layers. Each of these layers is assigned a certain task. With the help of this layer model, subareas of abstract processes are able to be descriptively explained.

MAC address

MAC address (media access control)

Without a MAC address, nothing in a network will work on your device. Just as your postman needs a valid address to reliably deliver the mail, the transmission of data packets in computer networks is only possible with the unique hardware address of the target device. When it comes to a MAC address, at least there is one address available on each network-compatible device. But what is the MAC...

Bootp protocol

BOOTP: All information on the DHCP forerunner

If you want to connect a computer, smartphone, etc. to a network (LAN or Wifi), you can either assign the IP address manually, or get it automatically. The latter is possible thanks to the DHCP (dynamic host configuration protocol) communication protocol, which has established itself as the cross-platform standard solution for address management. The forerunner was the BOOTP bootstrap protocol...

IGMP snooping

IGMP snooping: eavesdropping for multicast traffic

If a system in IP networks is to send data packets to different target hosts as efficiently as possible, an IP multicasting connection is the perfect solution. When it comes to multipoint transmission, the data packets are able to reach all interested parties thanks to various protocols such as GMP, for example. Switches and internet routers can also use the communication protocol for IGMP...

Network protocol: Standards for data exchange

Network protocol: The basis of electronic data exchange

For computer systems to be able to communicate with each other and exchange information, they need common ground, just like humans must share a common language. But computers don’t rely on foreign language lessons, and instead only need the appropriate network protocol to successfully communicate. This provides guidelines and structures for the data transfer, and so plays a decisive role in the...