IOS "show clock" results' heading symbols

 R0>show clock
 *00:20:29.467 UTC Fri Mar 1 2002 
 R0>

We all know by "show clock" command we can know the system time on an IOS host. Do you notice there are some symbols ahead of the result output? Here is my research:

Reference of show clock on Cisco.com

Table 15 show clock Display Leading Symbol Descriptions

Symbol	Description
*	Time is not authoritative.
(blank)	Time is authoritative.
.	Time is authoritative, but NTP is not synchronized.

* NOTE: the above table also applies to log messages!

How can you forget these IP addresses: "8.8.8.8" and "8.8.4.4"?

 Primary DNS: 8.8.8.8 
 Secondary DNS: 8.8.4.4 

How can you forget the following IP addresses: "8.8.8.8" and "8.8.4.4"?

It is Google's public DNS resolvers.

VoIP: simple proof of IP network's quality

Suppose that some remote colleague were complaining about the application performance, and she were assuming "IP network performance" is to blame.

If I could call back by phone and explain to her: "I am calling over the same IP network. What do you think about the voice quality right now?!"

Isn't this quite a simple proof of IP network's quality! I now have a good purpose to implement telephony services on IP networks!

MAC address ranges of virtualized world

Nowadays when several MAC addresses are associated with one switch port, we cannot assume that this port is connected to another switch or hub as before. It might be connected to a Virtual Machine server.

Wi-Fi Blocking Paint

We know that Wireless LAN (Wi-Fi) is riding on non-licensed bands of radio frequencies. It is unavoidable, especially in a metropolitan area, that our facilities are filled with un-wanted wireless LAN radios.

With new strong encryption, we do not have to worry about the information leakage. However, we DO have to worry about effective transmission throughput. The more users in the same channels, the less effective throughput can we get!

How to verify the Secondary Root?

As you know  we can configure the designated switch as the "Primary root role" or the "Secondary root role" using the following commands:

spanning-tree vlan 10 root primay
spanning-tree vlan 20 root secondary
  

Although these commands are just "macros" that we cannot see them in the running configuration, it is still easy to verify the "Primary root role" is correctly configured: We just use "show spanning-tree" command to check the designated switch is really the current "Root Bridge".

Why a "vlan.dat" file for an IOS switch?

It looks to me the "vlan.dat" design will stay a long life on IOS switches.