CPTTM Network Admin newsletter issue #16

In order to keep closer contact with IT network administrators in Macau, we've created a network admin newsletter and I've taken the liberty to add you to our netadmin-news mailing list. If you'd like to unsubscribe or recommend friends to subscribe at any time, just email me.

Topics in this issue:

• Must attend: Seminar on Aruba thin AP WiFi enterprise architecture
  
• New releases of Linux distributions
  
• Highly effective spam filter
  
• Become a certified network administrator
• Hard earned lesson on MySQL
• Coming networking related courses at CPTTM

Must attend: Seminar on Aruba thin AP WiFi enterprise architecture

New releases of Linux distributions

Ubuntu Linux 7.0.4. Ubuntu Linux is the most popular Linux distirbution in the world, topping RedHat and SuSE. Ubuntu 7.0.4 is its latest version for the desktop. It is also being preloaded on some Dell desktops and notebooks.

Debian 4.0. Debian is the foundation of Ubuntu.

Highly effective spam filter

At CPTTM we were using spamassassin to filter spam. However, it has several problems:

• The accuracy was not that excellent (about 95%).
• It is based on regular expression rules and the engine is written in perl, so it sucks up a lot of computing resources (in paricular, CPU) in pattern matching.
• The rules need continuous updates.
• The rules can be obtained by spammers and they're fine-tuning their spams to get around those rules.

Therefore, we evaluated another spam filter: dspam. It turns out to be much better:

• For most users it becomes very accurate quickly. For example, for one particular user, it gets to 94% accruate in two weeks. For myself, I have been enjoying 99.2% for a very long time.
• It uses Bayesian filtering instead of rules. So it only performs tokenizing and lookup and thus is faster.
• It is written in C.
• The engine doesn't need updates.
• Every user has its own token database. Spammers can't fine-tune their spams against us.
  

dspam is open source. If you're using a Linux based mail server (sendmail, postfix, etc.), it should integrate with the system easily. If you're using a Windows based mail server (MS Exchange), you can use it as a mail proxy.

Become a certified network administrator

The National Computer Technology and Software Professional Technology Qualification Exam (Network Administrator) was just held on May 26 at CPTTM. There were 13 people taking the exam (many of them were civil servants). It is a good way to get your networking skills recognized. It's easier than CCNA and you just can't beat the low exam fee of just MOP100. If you're not good in English, it is also better for you because it is in Chinese.

If you missed this one, it's OK. In this Nov there will be another round. If you'd like to take the exam, you can join our preparation course that will start in late June. It offers a 75% course fee imbursement.

Hard earned lesson on MySQL

If you are planning to use MySQL, NEVER use the default myisam table type! I learned this lesson the hard way when using dspam. If you use myisam tables and shut down the MySQL server while there are connections writing to the tables, they will become corrupt. Repairing a table could take half an hour if it contains several millions of records.  When it is being repaired, no one else can use it. Another problem with myisam tables is that, when one is writing to a myisam table, the whole table is locked. No one else can read it.

What to use then? The innodb table type. It uses record-level locking. If it needs repairing (rolling back interrupted transactions), it will do so automatically while reads and writes are still allowed. Of course it is a somewhat slower than myisam and takes more disk space, but excessive downtime is probably a bigger enemy.

Coming networking related courses at CPTTM

Archive of the CPTTM Network Admin Newsletter is available at http://www2.cpttm.org.mo/cyberlab/netadmin-news.