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Monday, December 28, 2009

IOS "show clock" results' heading symbols

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

Table 15 show clock Display Leading Symbol Descriptions




Time is not authoritative.


Time is authoritative.


Time is authoritative, but NTP is not synchronized.

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

Friday, December 4, 2009

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

 Primary DNS: 
 Secondary DNS: 
How can you forget the following IP addresses: "" and ""?

It is Google's public DNS resolvers.

Thursday, December 3, 2009

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!

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