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Alias IOS Command

When configuring a router I often use different show commands to check or troubleshoot the configuration. I always hate to type in the whole show command, so I use aliases instead. Aliases are also used in the Open Source community, when working with a terminal.

There are multiple options for the alias command, lets take a closer look:

• Alias exec: for Privileged Mode (for Router# prompt);
• Alias configure: for Global Configuration Mode (for Router(config)# prompt);
• Alias interface: for Interface Configuration Mode (for Router(config-if)# prompt;

Cisco IOS includes some built-in command aliases (of course, the Cisco IOS always accepts the shortest unique command). Default command aliases are for example:

Next are some alias command, which I use very often:

ALIAS EXEC

Router(config)# alias exec s show ip int brie | exclu unass

Router(config)# alias exec si show int status

Router(config)# alias exec r show run

Router(config)# alias exec rr show ip route

ALIAS CONFIGURE

Router(config)# alias configure vl1 interface vlan1

Router(config)# alias configure eigrp router eigrp 1024

ALIAS INTERFACE

Router(config)# alias interface ns no shutdown

Router(config)# alias interface load load-interval 30

DSL Terminology

When configuring DSL or other analog connection, I sometimes have problems with the specific terminologies used in these technologies.  I found a post explaining the terminology used for understanding Cisco DSL statistics. Reading this post helps me remember the terminology.

Taken from the post:

To troubleshoot Layer 1 problems, you can use the show dsl interface atm 0 command to verify that the Cisco 877 router is trained to the DSLAM. If the Cisco 877 router is successfully trained to the DSLAM, this command will also display the trained upstream and downstream speed in kbps.

 

Noise Margin (also signal-to-noise ratio)
When DSL service is provisioned in a DSLAM, the minimum acceptable noise margin is usually specified. CAP DSL service is typically provisioned with a downstream margin of 3 dB and an upstream margin of 6 dB. Research has shown that the optimum margins for DMT service are 6 dB downstream and 6 dB upstream.

 

Avoiding configuring a DSL service with more noise margin than appropriate is important because the system will train to an unnecessarily low DSL rate to provide the specified margin. It is also important to avoid specifying an exceptionally low margin, such as 1 dB downstream and 1 dB upstream because a small increase in noise level on the transmission line would probably result in excessive errors and a subsequent retraining to a lower DSL rate.

 

Increasing the transmit power levels will also improve the noise margin but at the cost of interfering with other services in the same cable.

 

Most DSLAMs and CPE report both the provisioned and actual noise margins for each DSL line. If the actual margin is higher than the provisioned margin, the line should provide an acceptable error rate at the present DSL line rate. As the actual margin drops below the provisioned margin, there is a high probability of an excessive error rate and subsequent retrain to a lower DSL rate.

 

Attenuation
Attenuation generally refers to any reduction in the strength of any type of signal, whether digital or analog. More precisely in the case of DSL, attenuation is the normal loss of signal strength over distance. Attenuation specifically is a logarithmic function of the power setting. As power increases, attenuation increases logarithmically. Also called simply loss, attenuation is a natural consequence of signal transmission over long distances. The extent of attenuation is usually expressed in units called decibels (dB).

 

Capacity Used
Percentage of the capacity that is being used.

 

Here are ranges for these values that I received from an AT&T provisioning engineer.

 

For Noise Margin: (the higher this value, the better)
8-13 Average
14-22 Very Good
23-28 Excellent

 

For Attenuation: (the lower this value, the better)
20-30 Excellent
30-40 Very Good
40-60 Average

Tools Page updated

I added a new tool to the Tools page, called Interface Traffic Indicator. The tool can be compared to STG, but needs to be installed on a workstation. The tool can be used to measure the throughput of a specific interface. To use the tool, you need at least the IP address of the device and a SNMP Read-Only string.

Tools like this can come in handy when measuring the used bandwidth of an interface in real-time. Appliance, like Cacti and Nagios, often poll ones in five minutes, which is very useful for establishing a baseline, but not for troubleshooting real-time.

More information about the Interface Traffic Indicator can be found here.