Subnet Calculator

A nice tool to experiment with subnets. Link to Subnet Calculater

The Subnet calculator start of with mask /25. If you are using 25 bits, your subnet mask is (check the lower part of the tool) 255.255.255.128, you can divide a old Class C network into two parts. Now slide the network address slider past 127, you will see that the Network Address changed from 192.168.0.0 to 192.168.0.128. You can also see that the broadcast address changed. If you want to make a list of all possible CIDR networks from the chosen mask/address press the Generate subnet list.

Hopefully this will give you an idea of how sub netting works

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UNIX Tips and Tricks!

Learn the basics of the UNIX shell and discover how you can use the command line to combine the finite set of UNIX utilities into innumerable data transforms.

Speaking UNIX, Part 1: Command the power of the command line

Speaking UNIX, Part 2: Working smarter, not harder

Speaking UNIX, Part 3: Do everything right from the command line

Speaking UNIX, Part 4: UNIX ownership and permissions provide for privacy and participation

Speaking UNIX, Part 5: Data, data everywhere

System Administration Handbook

It is not uncommon that every system administrator has a copy of system maintenance tasks checklist. Although, not every system administrator will follow.

As a competent system administrator, he or she, should aware few of these system administration baseline

  • Implement/revise backup strategy and conduct backup-data restoration test on a regularly basis.There is no points to have system backup in place, if no one is able to confirm that the backup strategy is works as it said. For example, some data or files might have been left out from backup strategy after a system upgrade, or the backup media becomes faulty over the time, etc.
  • Discuss with system owners and key personnel about their business needs, from time to time, in order to come up with a disaster recovery strategy that is really works, or meets the business requirement that change rapidly!
  • Be alert and pay attention to any warning signs.The purpose of warning is to alert system administrators, about the potential of developing critical errors in later stage. Although, not every warning sign is significant. For example, a server that suddenly reboots recently, intermittent network connection problems, etc.
  • Serious about system documentation!No one could really remember every minor system parameter change. Without complete system change records, it is hard to recover a failed system to full operational state before system crash. It is not efficient to troubleshoot system failure that might only arise after few of the minor changes.
  • Adopt the philosophy of “Everything that can be logged should be logged.“.Disk space is relatively cheaper than before, while the hard disk capacity is getting bigger and bigger. So, it is not wise to turn off system or application logging! Without sufficient logging information, system administrators will likely take longer time to troubleshoot a system failure!
  • Take time to evaluate patches released by respective system vendors, and apply the patches as soon as possible if applicable. Ignore or delay applying patches might end up a painful system administration life, when the system crash or get attack.
  • Enforce rigid password policy, such alphanumeric password, secondary authentication (such as time token) to complement password, educate system users the importance of keeping password securely to themselves, etc.