The Network Security. Org

Networking 101: Subnets Realized (Including IPv6)

An oft-asked question in networking classes is "why can't we just put everyone on the same subnet and stop worrying about routing?" The reason is very simple. Every time someone needs to talk, be it to a router or another host, they have to send an ARP request. Also, there are broadcast packets that aren't necessarily limited to ARP, which everyone hears. When there are only 255 devices on a /24 subnet, the amount of broadcast packets is fairly limited. It is important to keep this number low, because every time a packet destined for a specific host or a broadcast address is seen, the host must handle the packet. A hardware interrupt is created, and the kernel of the operating system must read enough of the packet to determine whether or not it cares about it.

Broadcast storms happen at times, mainly because of layer 2 topology loops. We'll explain layer 2 topology issues in excruciating (actually, enlightening) detail in a future edition. When thousands of packets hit a computer at a time, slow and fast computers alike can become very slow. The kernel spends so much time handling interrupts that it doesn't have much left for dealing with "trivial" things like making sure your Web browser process gets a chance to run. So that, my friends, is why subnets are very important. This is also known as a broadcast domain, because it limits the amount of broadcasts that you will hear.

What's the point of creating subnets anyway? How do I remember those strange looking subnet masks? How the heck does this work with those crazy looking IPv6 addresses? This edition of Networking 101 will expand on the previous Subnets and CIDR article, in the interest of promoting a thorough understanding of subnetting. Networking 101: Subnets Realized (Including IPv6)

More News

• Website infection rate triples
  



• How to Use Honeypots to Improve Your Network Security
  



• Microsoft Patch Tuesday Targets 26 Application Flaws
  



• SSL VPNs might not be as secure as you think
  



• 8 tips to filter spam effectively
  



• Onus on IP address owner to prove innocence
  



• How to install an SSH Server in Windows Server 2008.
  



• Several vulnerabilities closed in the Linux kernel
  



• 8 Best Practices for Encryption Key Management and Data Security
  



• Free Honeypot Client Could Sting Malware
  



• What Firewalls Do & Donot Do
  



• Symantec fingers D Link for bot attacks
  



• WhiteHat: 90% of Sites Still Vulnerable
  



• Red Hat releases free security code
  



• A new type of Bluetooth security
  



• Dude, where is my perimeter?
  



• Scaring users into IT security
  



• VMware fixes security bugs
  



• The top 10 security land mines
  



• Encrypt volumes through a cross platform GUI with TrueCrypt 5.0