Blog ala Vidar

SQL, AppFrame and other cool technologies

Networking for dummies

Since I started in Omega I have got a couple of questions over and over again which clearly states that they’ve misunderstood networking. I’m not saying they’re stupid or anything… We all misunderstand some things… Here I will give a quick and superficial overview of terms and how they’re used.

IP – Internet Protocol (IPv4)
You have probably heard the term “IP address”. This is your address on the network. When you type in your browser, your computer asks your DNS server which IP this refers to. In this case it’s This is VG’s (unique) internet address. If you do start –> run –> cmd –> ipconfig, you’ll see your IP address(es). If it starts with any of these, you’re on a private network (which cannot be connected to from the internet!)
127.*.*.* – Loopback (used internally on your computer)
172.16.*.* to 172.31.*.*
Btw, if you haven’t understood the joke before: “There’s no place like”. is ALWAYS your computer.. I’ve only covered IPv4 (version 4) of this protocol. There’s a new version called IPv6 which is in use by default by Vista+ and 2008+.

TCP – Transmission Control Protocol
This is the most used protocol on the internet (combined with IP.. TCP/IP). With this you send packets on specific ports. For instance when you use your browser to go to you’re accessing TCP port 80 on a specific server in Omega. When you set up your web server you can set it to any port you’d like (between 0 and 65535), but then people have to add this port, for instance Popular services running on TCP/IP: FTP (port 21), SMTP (25), HTTP (80), POP3 (110), IMAP4 (143), HTTPS (443)

UDP – User Datagram Protocol
The main difference between TCP and UDP is that UDP is used for streams. When connecting to a web site you need all packets to view the site. If you don’t have all packets, the html-code may be corrupt. TCP ensures that ALL packets get from sender to receiver, even if it has to send the same packet 1000 times. UDP on the other hand doesn’t care to check if the packet is received. It sends a stream of packets.. If you watch TV on the internet, and there’s suddenly a packet loss, the packet is invalid after 5 milliseconds anyways, so why send it? Popular services running UDP: IPTV, VoIP (Voice over IP).

ICMP – Internet Control Message Protocol
This protocol is used for ping, traceroute and other network specific things. Many think that if you don’t get a ping result from a server, it’s down. THIS IS BULLSHIT. A SQL Server needs to answer on (at least) TCP 1433. But, you can block ICMP calls to the server. This is actually pretty common, because ping can be used for DDoS (Distributed Denial of Service) attacks. So, if you’re outside the Omega network you cannot ping any of our servers. That doesn’t mean they’re down. Instead of doing this, you can telnet the server on a port you know is open.

Before, everyone was using hubs, but the big problem with hubs is that all signals are broadcasted to all devices connected to it. So, if I, JanCB and 8 others are on the same hub, and I’m sending a packet to JanCB, it will be sent to all 10 on the hub. This is where a switch is much better. In the beginning a switch was called a smart hub. Instead of sending the packet to all devices, it sends it to the actual receiver. And then we got routers. The difference between switches and routers are that a router has a table witch says where to send the data AND if it’s allowed. (Yes, I know there’s something called managed switch etc, but this blog post is a quick and dirty introduction to networking).

DHCP – Dynamic Host Configuration Protocol
This is a network application protocol that has a predefined configuration for all devices that connects to it, so that all devices gets an IP address, a gateway, DNS servers etc.

SMTP – Simple Mail Transfer Protocol
This protocol has been in use for more than 25 years (and is running on TCP port 25 ;)! As the name says, it’s a protocol for sending mails. The big problem with it is spammers. Since some of us (NOT ME!) click on links in spam, we’ll never get rid of this problem. But, to be sure spammers don’t use SMTPs there’s one solution: SMTP relaying. This means that you can set which IPs can send mail using this server. In Omega there are only a couple of servers that are allowed to use our SMTP server. This is not a problem since we’re using a web-mail system. All ISPs (Internet Service Provider) have their own SMTP server, so when you’re for example connected at home and want to send mail using outlook, use your ISPs SMTP server. We will NEVER open SMTP for IPs that is outside Omega, so please stop asking about this 🙂 Here’s a list of SMTPs you can use:


By now I’m sure you’ve understood it’s (normally) just adding SMTP before your ISPs URL.

I will try to make JanCB write a couple of blog posts (since he’s the network alpha male in Omega) about the details of these topics. Please ask him on MSN, or mail him at if there are any topics you’d like to hear more about.

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