Checking system-wide uptime on several Cisco hardware platforms

We all know adding redundant supervisors/CPUs to any given system, we can increase the uptime for that system. With In-Service Software Upgrade (ISSU), Cisco hardware even allow us to upgrade the operating system software on-the-fly without stopping the whole system.

Flowers of Cassia fistula was blooming together in southern Taiwan starting from mid-May.
This photo was taken around this location in Baihe District of Tainan City, Taiwan.

An interesting question might be asked. Does Cisco hardware keep track of system uptime even upon supervisor/CPU failover events? And how to display the system uptime, in addition to individual supervisor/CPU uptime?

I spent some time and I summarize my findings in this post.

Command lines to setup IP address and DNS of Windows PC

When I use my Windows notebook as connectivity tester, I often have to switch the IP address configuration from DHCP to some fixed IP, and back and forth. Also, different customers have different assigned fixed IP addresses.

No more HyperTerminal on Windows 7? Try Putty!

  Bits per sec    :  9600  
  Data bits       :     8 
  Parity          :  none 
  Stop bits       :     1 
  Flow control    :  none 

(This post is re-posted in English from my original post.)

We are all used to start HyperTerminal included in old Microsoft Windows XP to do initial console configurations of routers and switches. However, starting from Windows Vista (and also Windows 7), no HyperTerminal software anymore! Now how can we do console configuration in Windows Vista or Windows 7?

In fact, Putty, the software we use as daily Secure Shell (SSH) client, can also be used to do console configuration on routers and switches.

Have a backup plan before power off your routers, especially for old ones

Entrance of the Taoyuangu Trail (DSCN0349),
originally uploaded by Li-Ji.

Even Cisco routers are reliable enough to run non-stop for several years, it does not guarantee it to power on normally after simply one power off.

How many subnets are in your network? A quick estimate

A quick method to estimate the total number of subnets in your network.

IOS Command "show mac-address-table address" also accepts formats like "00-12-34-56-78-90" and "00:12:34:56:78:90"

Both "00-12-34-56-78-90" and "00:12:34:56:78:90" formats work in IOS.

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!

Client PC's Redundancy: Wireless LAN, also backup Internet's traffic

His happy trip ending, and so was mine (DSC_0237),
originally uploaded by Li-Ji.

Continued from previous post. Have you come up with the answer?

The key is still the "more specific route": we only have to craft some routes more specific than the "default route"! The default route itself is indeed the least specific! Any routes with just one bit more specific, is enough to be more specific!

---

OK! Let me give you the answer: we only have to add two routes 0.0.0.0/1 和 128.0.0.0/1, pointing both of them to Wired LAN's gateway IP address, done! Now the Internet traffic will go through Wired LAN in normal time. It goes through the Wireless LAN only when Wired LAN is broken!

Why these 2 routes? We can clearly see it by looking at its binary form:

33          2          1          0       33          2          1          0
1098765.43210987.65432109.876543210       1098765.43210987.65432109.876543210

00000000.00000000.00000000.00000000, mask 10000000.00000000.00000000.00000000

10000000.00000000.00000000.00000000, mask 10000000.00000000.00000000.00000000

Of course, we can also come up with 4 routes, or even 8 routes to play the same trick! Two is the simplest one!

Interesting, isn't it! This trick is quite useful in many cases! We might see it again very often!

Using TELNET to backup Cisco Router and Switch's configuration

Aboriginal Art and Ponds, in Hualian County, Taiwan

I believe you agree that you hardly attach a console cable to your routers or switches in daily maintenance. Your network devices are always locked up on a rack in a room so far away! TELNET is a more frequently used software on Windows.

To backup configuration of a Cisco router or switch, I share with you a tip using TELNET. (However, this tip is only applicable on Windows XP!) If your PC comes with Windows Vista or 7, you should install TELNET client first.

How to "Resign" your Router role as DR/BDR in OSPF without clearing OSPF process?

Cherry Flower (DSCN0694),
originally uploaded by Li-Ji.

In Cisco IOS, just change that interface priority to zero (0), then it quits the role of DR/BDR immediately.

interface FastEthernet0/0
 ip ospf priority 0

Write (save) your configuration before you logout!

I did have some costly lessen of forgetting to write (save, actually!) the configuration of a IOS router. Recently a post of Brad Reese tells that I am not alone!

.....
Top 25 network problems and their business impact

1. Configuration not saved

Reboot will cause config to be lost
.....

Saving the configuration is easy by simply typing wr followed by <enter>, which is a short version for the write command.

The conclusion: always check and save, before you logout!