Tag: IOS

Cisco IOS replace running config instead of merge

By default, if you do

# copy startup-config running-config

the startup config would be merged to the running one. The same happens if you use tftp:// or flash:// instead of startup-config. Eventually, there is a way to replace the running config. The command is:

# configure replace

Bringing Cisco IOS CLI to Linux CLI

There are few people on the globe who loves to work with Cisco and Linux via CLI. These people might have issues with trying to apply Bash/Vim syntax to IOS and vice versa. I’m certainly one of them. That’s why I can do the followng in my Bash:

$ show .bashrc | i return
[[ "$-" != *i* ]] && return
#     return 0
#     [[ -z $adir ]] && return 1
#   [[ $? -ne 0 ]] && return 1
#     [[ $? -ne 0 ]] && return 0
#   return 0

It’s very handy for checking Cisco configs, stored on a Unix machines, without inverting your mind out. In fact, if you are in rush and tried to apply IOS syntax to Bash, you won’t be distracted by an error message, but you’d get a result you reqired.

$ show samle_conf.cfg | i spanning-tree
spanning-tree mode rapid-pvst
spanning-tree etherchannel guard misconfig
spanning-tree extend system-id
spanning-tree pathcost method long
 spanning-tree portfast
 spanning-tree portfast
 spanning-tree portfast
spanning-tree bpduguard enable

It’s achieved very easily. You need to add some aliases to your ~/.bashrc file and relogin:

echo 'alias show="cat"' >> ~/.bashrc
echo 'alias i="grep --color"' >> ~/.bashrc

Dynamips, Dynagen and GNS3 as a Best Free Tools for Cisco IOS Learning

Boson NetSim and Packet Tracer are two examples of good Cisco networks emulators. They provide you with an opportunity to build networks of switches and routers, interconnect them and deploy several features of IOS. Good enough for beginners, but they have a huge drawback – their IOS simulation is limited. It does not implement a real set of functions real IOS has on board.

Several years before, the only opportunity to play with IOS was interconnection of real Cisco switches/routers. I still consider it was and still is a best way to learn Cisco. Unfortunately, not many people have access to networking hardware and even if they have it, the hardware is usually quite old or outdated. It means that you can run old versions of IOS there.

There is another approach of getting access to operational IOS – running it on a virtual machine. Emulating router’s hardware is not a straightforward task – Cisco uses different architectures in their devices. However, the task was accomplished in Dynamips/Dynagen project. It emulates Cisco hardware in a way so you can real IOS images on top of it. It is suitable to support 3600, 3700 and 2600 series hardware. Both pieces of software are closely interrelated and running together, providing users with a robust CLI interface.

Do not be frightened – CLI is not the only way of controlling your Cisco virtual machines. The tools have a graphical interface – GNS3. GNS3 runs on the top of Dynamips/Dynagen packages and provides GUI for controlling every virtual machine, machines interconnection, their modules and graphical network topology representation. It simply does everything that other graphical simulators can do.

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