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Career Advice '08

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Career Advice '08

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Useful Cisco Switch Commands (suitable for a 2950)

 Showing the Running configuration of the Switch. Example commands:
show run ' to see the conplete switch running
confige
show run int f0/1 ' to see running confige on
FastEthernet, slot 0, port 1
show run int vlan x ' where x = the management vlan for the
switch
show int status ' show basic interface configuation
information


Saving the Switch Running Configuation. Example command:
copy run start


Dealing with Switch Logging. Example commands:
service timestamps debug datetime localtime
service timestamps log datertime localtime
logging buffered

clear log ' clear logs if they have been on for a
long period of time
show log ' see see the switch logs


Setting the switch clock:
show clock ' to see the clock settings
clock set hh:mm:ss d m y ' clock set 14:10:55 9 sept 2005


Finding out the general topology of the connecting network. Example
commands:
show cdp ne ' for an overview
show cdp ne de ' to be more specific. This gives the
neighbour IP address


Managing the ARP:
show arp ' to see the ARP table
clear arp ' to clear the ARP table


Troubleshooting connectivity issues:
ping x.x.x.x ' ping a known address 5 times. There should
be a quick response.
ping ' extended ping, followed by return to do an
extended ping test. Can state no. of pings
trace x.x.x.x ' to do a trace route to an IP address


Looking at the Switch counters:
clear counters ' to clear all switch counters
show int counters ' to see all interface counters
show int counters error ' to see errors on all the interfaces
show int fa0/22 ' to see errors on a particular
interface

So how fast are Ports running:
show proc cpu
sh cont util


Making changes:
config t ' to go into configuration mode
int range f0/1 - 10 ' to set changes to be make to a range
of ports
speed 100 ' to set the speed of the port to 100Mb
duplex full ' to set the line duplex to full, half
or auto


Setting up the Banner:
config t
banner motd ^C

^C

Working with VLAN's:
show vlan
show vtp status
vlan database
vtp transparent|server|client ' Choose wisely here!! Swithces come
out of the box in Server mode!!!

The source of the picture above is from here.

Subnetting in your head - What do we know?

What do we know about a /25?
128 mask
1 bits on and 7 bits off (10000000)
Block size of 128
2 subnets, each with 126 hosts

What do we know about a /26?
192 mask
 2 bits on and 6 bits off (11000000)
 Block size of 64
 4 subnets, each with 62 hosts

What do we know about a /27?
 224 mask
 3 bits on and 5 bits off (11100000)
 Block size of 32
 8 subnets, each with 30 hosts

What do we know about a /28?
 240 mask
 4 bits on and 4 bits off
 Block size of 16
 16 subnets, each with 14 hosts

What do we know about a /29?
 248 mask
 5 bits on and 3 bits off
 Block size of 8
 32 subnets, each with 6 hosts

What do we know about a /30?
 252 mask
 6 bits on and 2 bits off
 Block size of 4
 64 subnets, each with 2 hosts

Regardless of whether you have a Class A, Class B, or Class C address, the /30 mask will provide you with only two hosts, ever. This mask is suited almost exclusively—as well as suggested by Cisco—for use on point-to-point links.

If you can memorize this “What Do We Know?” section, you’ll be much better off in your day-to-day job and in your studies. Try saying it out loud, which helps you memorize things—yes, your significant other and/or coworkers will think you’ve lost it, but they probably already do if you are in the networking field. And if you’re not yet in the networking field but are studying all this to break into it, you might as well have people start thinking you’re an odd bird now since they will eventually anyway.

Manage network broadcasts on Cisco switches using storm control

Network broadcasts can create a huge amount of traffic on your organization's network. When one device sends out a single broadcast, that broadcast goes to all devices on the subnet or VLAN.

How can you manage these broadcasts to make your network more efficient? One method is to use Cisco Catalyst broadcast suppression—also known as storm control.

Broadcasts are a natural part of the TCP/IP suite of applications. A broadcast is a packet sent to ALL HOSTS or ALL HOSTS ON A SUBNET.

A packet sent to all hosts has a destination IP address of 255.255.255.255. A packet sent to all hosts on a subnet is a directed broadcast, and it goes to a specific destination—for example, 10.1.1.255.

Some necessary protocols such as Address Resolution Protocol (ARP) and Dynamic Host Configuration Protocol (DHCP) use broadcasts, so they aren't something you can just throw out. What you can do is suppress excessive broadcasts on your network using storm control.

Configure storm control

It's important to protect your organization's LAN from broadcast storms, which can cause network slowdowns if they become severe. With the Cisco IOS, you can easily and quickly protect your network by configuring a single command on each switch interface.

You can configure storm control on most Cisco Catalyst platforms. (On older platforms, Cisco calls it broadcast suppression.) The Cisco IOS disables broadcast suppression by default.

Storm control manages how the receiving port handles the broadcast. You can configure a threshold to drop broadcasts for a certain period of time or until the broadcast flow slows down.

By default, the switch only drops the broadcast packets. In addition, you can shut down the port or send a SNMP trap to your management station.

Here's how to configure storm control on a Catalyst 2950 switch:

Switch(config)# int fa0/19
Switch(config-if)# storm-control broadcast level 50
Switch(config-if)# storm-control action trap

The first command—storm-control broadcast—is the only required command. Thestorm-control action trap command is optional, as is shutting down the port, which requires the storm-control action shutdown command.

This example has nothing to do with regular unicast or multicast traffic. However, you can configure storm control for both unicast and multicast traffic by substituting unicastor multicast for broadcast in the command.

Once you've configured storm control, you can check the status of the configuration with the show storm-control broadcast command. Here's an example of the output:

Switch# show storm-control broadcast 
Interface Filter State Trap State  Upper    Lower  Current  Traps Sent
--------- ------------  ---------  -----    -----  -------  ---------
Fa0/1     inactive    inactive     100.00%  100.00%    N/A     0
Fa0/2     inactive    inactive     100.00%  100.00%    N/A     0
Fa0/3     inactive    inactive     100.00%  100.00%    N/A     0
Fa0/4     inactive    inactive     100.00%  100.00%    N/A     0
Fa0/5     inactive    inactive     100.00%  100.00%    N/A     0
Fa0/6     inactive    inactive     100.00%  100.00%    N/A     0
Fa0/7     inactive    inactive     100.00%  100.00%    N/A     0
Fa0/8     inactive    inactive     100.00%  100.00%    N/A     0
Fa0/9     inactive    inactive     100.00%  100.00%    N/A     0
Fa0/10    inactive    inactive     100.00%  100.00%    N/A     0
Fa0/11    inactive    inactive     100.00%  100.00%    N/A     0
Fa0/12    inactive    inactive     100.00%  100.00%    N/A     0
Fa0/13    inactive    inactive     100.00%  100.00%    N/A     0
Fa0/14    inactive    inactive     100.00%  100.00%    N/A     0
Fa0/15    inactive    inactive     100.00%  100.00%    N/A     0
Fa0/16    inactive    inactive     100.00%  100.00%    N/A     0
Fa0/17    inactive    inactive     100.00%  100.00%    N/A     0
Fa0/18    inactive    inactive     100.00%  100.00%    N/A     0
Fa0/19    Forwarding  Below rising 50.00%   50.00%     0.00%   0
Fa0/20    inactive    inactive     100.00%  100.00%    N/A     0
Fa0/21    inactive    inactive     100.00%  100.00%    N/A     0
Fa0/22    inactive    inactive     100.00%  100.00%    N/A     0
Fa0/23    inactive    inactive     100.00%  100.00%    N/A     0
Fa0/24    inactive    inactive     100.00%  100.00%    N/A     0
Switch#

For more technical information on Cisco Catalyst Storm Control, check out Cisco's "Configuring Storm Control" documentation.

Source of the picture above is from this link.

10 things you should know about creating a resume for a high-level IT position

Building a resume that targets an upper-level IT position, such as architect or consultant, requires a different approach than creating a resume to land an entry-level tech job. Although many of the standard rules still apply, you need to follow some more specialized guidelines. In fact, a few of these tips may actually contradict your previous notions of what your resume should include (and exclude).

 image source

 

 

#1: Keep your list of “core skills” short and sweet

When you’ve worked with a lot of technologies, you want to show the world all you’ve done. However, having a long list of core skills actually gives the impression that you know only a little bit about most of those things and that you’re a generalist, not the specialist that the potential client/employer needs. Keep this list to a handful of key skills or possibly eliminate the list altogether.

#2: Don’t list certification exams

At the very least, minimize the impact of a cert list. The average IT pro might want to list exams passed to build up a resume, but for the IT veteran, this actually marginalizes real-world experience and accomplishments.

#3: Quantify projects and results

For example, if you do an Active Directory implementation, specify how many sites, domains, and servers were involved. If you designed an e-commerce system, specify the increased percentage of sales that resulted from the project. Tell the potential client/employer exactly how you helped a previous company you worked for.

#4: Take advantage of bullets

Don’t use paragraph style writing to describe your projects, tasks, and duties. Bullet-point every major accomplishment or project and leave out the minor things. (Your resume is already going to be too big anyway.)

#5: Include examples of work, if possible

For instance, maybe you’ve written articles for an online magazine or built an e-commerce site. Include links to pertinent examples so that potential clients/employers can see firsthand what you do.

#6: Highlight major accomplishments

If you’re a high-tech consultant, you may have a lot of smaller projects and clients. Maybe you were hired as a “grunt” for a couple of short-term assignments but had a major project last year. You can’t exclude the small stuff or potential clients/employers will question what you’ve been doing. But you can minimize the impact by focusing attention on the bigger things. Some ways of doing this include using a slightly larger font, boldface, or italics, or even drawing a thin border around the major accomplishments. But don’t go overboard — subtlety is still key.

#7: Seek advice from actual managers

Recruiters, agents, brokers, and human resource personnel are all different from managers. Managers want to see results, and they usually know how to spot a weak candidate. If managers think your resume reflects someone who can’t do the job, you’ll never get anywhere. Run your resume by some managers you know and have them critique it for you.

#8: Know when to stop

If you list all your experience from all the jobs, contracts, or projects you’ve handled, your resume will be more like a book. Find a place to stop listing your experience. If you feel you must at least acknowledge previous experience, try making a separate section and just bullet-point where you worked and what your title/function was. Of course, you’ll usually want to do this only for the less-accomplished jobs that you don’t want to highlight on your resume.

#9: Make sure your design is simple, attractive, and readable

As with any resume, you should use a clean font such as Times New Roman or Arial. Be consistent in your use of boldface, underline, or italics to help lead the reader through the document and avoid contrived graphical elements.

#10: Edit, revise, and proofread

Experts suggest that a resume should go through three to seven drafts before it begins to reflect the multidimensional individual on a piece of paper. Be grammatically correct, spell-check the document, and have someone else proofread your resume carefully.

• Date: July 24th, 2007
• Author: TechRepublic

Cisco Catalyst Switch bandwidth limit configuration

In the Cisco IOS on a Catalyst switch (not on a router), there’s an Interface Mode command called shape round-robin queue bandwidth. More specifically, the command is srr-queue bandwidth.

This command has been around since IOS 12.2(25). For these examples, I’m using a Cisco Catalyst 2960 switch.

Entering the command appended with a question mark will display the command options. Here’s an example:

Switch(config)# interface FastEthernet 0/1
Switch(config-if)# srr-queue bandwidth ?
  

limit              Configure bandwidth-limit for this interface
  

shape             Configure shaping on transmit queues
  

share              Configure shared bandwidth

As you can see, the command options are limit, shape, and share. While we’ll focus on the limit option this time, keep in mind that you can also use the srr-queue bandwidth command to shape and share bandwidth.

For example, let’s say you have a 100-Mb Ethernet port on a Catalyst switch. You’re selling the bandwidth on the port, and a customer has bought 10 Mb of bandwidth. Obviously, you want to limit the outbound bandwidth on the port to 10 Mb instead of the full 100 Mb.

To do so, go to Interface Configuration Mode on the switch port, and apply the srr-queue bandwidth limit command. Here’s an example:

Switch(config)# interface FastEthernet 0/1 

Switch(config-if)# srr-queue bandwidth limit 90

The 90 sets the outbound bandwidth limit on the port to 90 percent of the port speed. Since this is a 100-Mb port, this should limit the outbound traffic from the port to 10 Mb.

Variations on bandwidth limiting

As with just about everything in the Cisco IOS, there are multiple ways to accomplish the same thing. One way would be to manipulate the port speed. But if you want to hard-code the port speed on the Ethernet port to 10 Mb, you could also limit the customer to only 10 Mb of bandwidth using the speed 10 command. However, you probably won’t get the same level of performance from the 10-Mb Ethernet port.

What if you want a port speed that’s less than 10 Mb? You could limit the port speed to 10 Mb and then use the srr-queue bandwidth limit 90 command to limit the outbound speed of the port to only 1 Mb.

What if you’re working with a Cisco router instead of a switch? Cisco routers don’t support the srr-queue command. While there are several different QoS options that might accomplish the same thing, a common method that I’ve used is the rate-limitcommand.

For example, on a Cisco router when in Interface Mode, you could limit outbound bandwidth to 1 Mb using the following command:

Router(config-if)# rate-limit output 10000000 2000 2000 conform-action continue exceed-action drop