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NetAcad, Exercises, CCNA, CCNP

How to find a right server - nslookup and dig dns command line tools

 A simple comparison of the nslookup command, the Microsoft DNS tool, and dig, the linux/win based command alternative.


Configuring reflexive ACL (IP session filtering)

In this article I will configure reflexive ACL. This technique is described during CCNA4 Exploration, and I'm using it during the lab exercises.

About Reflexive ACL (IP session filtering)

Description from the cisco web, regarding IOS 15.1.

How and where to find and download the Cisco SDM manager

The Security Device Manager, or SDM is possible to find on www.cisco.com on the following web link


The Cisco Connection online (CCO) user guest account is needed, which we may create for free.

DHCP configuration using SDM

The flash animation explains how to configure DHCP server on a cisco router using the SDM. Where to find and how to install the SDM is described in this article.


Cisco Catalyst 2960 switch IOS recovery

Sometimes in my lab happens that students delete IOS of the switch from its flash. Unfortunately switches does not have rommon to realize quick IOS recovery over tftp. Only one way is over Xmodem.

Cat 2960 switchIOS recovery

To speed up the process of the recovery we may setup Xmodem speed to higher rate as default 9600 bits:

Set the speed rate to 115200 baud on the switch prompt of the switch:

Configuring complex dynamic ACL (Lock-and-Key)

In this article I will configure dynamic complex ACL (Lock and Key). This technique is described during CCNA4 Exploration.

About Lock and Key

Description from the cisco web

Configuration of the RIPv2 authentication

In this article I will configure, debug and shows the process of RIPv2 authentication.


Authentication methods

  1. Plain text
  2. MD5


Note 1: When using plain text authentication mode, make sure that the following parameters are matching on neighboring routers for successful authentication.

  • Key-string

  • Authentication mode

Zmena preddefinovaného telnet klienta v dynagene za putty

Dynagen obsahuje cmd príkaz, ktorý umožňujú pripojenie na konzolu virtuálnych routrov priamo z jeho príikazového riadku, je to príkaz telnet. Tento príkaz v dynagene spustí preddefinovaného klienta a pripojí ho na lokálny, v net konfigu zadefinovaný port. Vo windows to znamená že sa spustí windows telnet klient. Toto predefinované nastavenie môžeme zmeniť tak, aby bol spúšťaný iný klient, napr. preferované Putty.

Possible bugs/limitations encountered in Cisco's RIP implementation

  1. Default route origination not working reliably.
  2. Automatic summarization turned on causes major networks to be propagated throughout the RIP domain with a metric of 1.
  3. Using RIPv2 on NBMA hub-and-spoke topology causes the hub router to rewrite the next hop field in the RIPv2 update to the IP address of the spoke router advertising the originalupdate, thereby creating reachability issues

IOS recovery using other Cisco router as the TFTP server and tftpdnld

The students in our labs oftenly delete not just startup configuration but the whole IOS of a router. Then the IOS of the router have to be recovered. There is one way using the COM port, but it takes time (tens of minutes). The second way is to use an another router with the same IOS as the TFTP server.




R1 will serve as the tftp server, R2 we have to recover. Routers are connected back-to-back using the cross cable.

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