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Latest articles in ‘Networking’

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   • career
   • certification
   • networking
   • cisco

   Cisco CCNA Routing & Switching certification review

   The five Ws

   • What: CCNA Routing & Switching is a technical certification about enterprise-grade IT networking from Cisco. It covers the involved devices, protocols and how to implement them using Cisco technologies.

   • When: This is an entry-level certification with no prerequisite.

   • Why: This certification demonstrate a good level of familiarity with enterprise networks and Cisco’s IOS-based devices.

     It is a de-facto standard in terms of IT networking certification, valuable even for employers using different technologies than Cisco, and is also a prerequisite for several other Cisco certifications.

     Note

     Note that Cisco certifications may not have the actual CCNA R&S certification as a prerequisite, but the CCENT instead which is half of the CCNA R&S.

     If you are interested in networking (and I expect you are when you intend to pass a Cisco exam) I warmly encourage you to pass the full CCNA R&S certification instead of …

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    • lab
    • networking
    • cisco
    • gns3
    • virtualization

    How to add Cisco IOS-based devices in GNS3

    GNS3 historical use-case was to act as a GUI around Dynamips to emulate Cisco devices. However, while stable, this emulation may not be as straightforward as it could be and has some limitations.

    To understand the negatives, we first need to understand how IOS-based Cisco hardware work.

    How real gear works

    Professional switch and router devices cannot be reduced to a general purpose small-factor computer with a few additional network interfaces.

    When using a general purpose computer with classical network adapters to build a router/firewall appliance, all the processing occurs at the software level, generally the operating system kernel.

    On specialized hardware such as Cisco switches and routers, the operating system (here IOS) works tightly with some underlying specific (and usually proprietary) hardware and delegates parts or all of the processing to dedicated chips, the Application Specific Integrated Circuits or ASICs, to allow faster processing.

    On general-purpose computers …

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    • lab
    • networking
    • gns3
    • virtualization

    How to add virtual machines (end devices nodes) in GNS3

    Virtual machines can be added in GNS3 topologies as end devices nodes and can play various roles:

    • Lightweight ones are very focused for instance to provide just enough to test the network connectivity or provide a functional browser.

      They start blazingly fast and are very light on resources, meaning you can put several of them to test end-user workstation behavior at several places in your topology with little to no worry about the CPU or memory impact.

    • Dedicated appliances are designed to provide a specific service, like networking (firewall, …), applicative (proxy, email filtering, …) or administrative (monitoring, …) services.

      Resource consumption vary greatly depending on the service and the software used by the appliance. However, professional appliances are usually designed to handle a large number of simultaneous operations: some will support with no issue to see the virtual machine resources settings reduced on test environments (some may require a modification in their …

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    • lab
    • networking
    • gns3
    • virtualization

    How to install GNS3 and VMware Player on Linux (Debian)

    While installing GNS3 and VMware should be easy, it in fact very easy to loose a lot of time on silly issues.

    • If you are interested only in installing VMware Player, feel free to directly go corresponding part.

    • If you are interested in installing GNS3, I also recommend to install VMware player as some appliances may require it.

    RouterGods also shared a few tips on how to setup a more comfortable GNS3 lab. Take a few minutes to check it once you’ve ended the installation!

    Installing GNS3

    GNS3 relies on Linux kernel features. If you are not a Linux user, the recommended way to use GNS3 is to use the GNS3 official virtual machine. This virtual machine may also be a good solution if you are a Linux user but you just want to quickly test GNS3 or do not want to modify your host environment.

    For a regular …

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    • lab
    • networking
    • gns3
    • virtualization
    • pentest

    How to run a CAM table overflow attack in GNS3

    Knowing where difference with real gears lies

    For performance reasons, a lot of switch things are actually not part of the IOS code but are implemented in hardware. This includes the ARL, or Address Resolution Logic, which provides all the methods to add, remove and lookup entries in the MAC address table.

    Therefore, for the NM-16ESW module to work in GNS3, Dynamips had to reimplement all these normally hardware provided services, or at least push this far enough to allow an unmodified IOS to run on it correctly.

    The sad thing is indeed that this is unfinished work, as stated in this module’s source code header:

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    /* * Cisco router simulation platform. * Copyright (c) 2006 Christophe Fillot (cf@utc.fr) * * NM-16ESW ethernet switch module (experimental!) * * It's an attempt of proof of concept, so not optimized at all at this …

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