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Category: NetAcad

Multi tabbed, multi execution telnet/ssh client

Working on our practical networking lessons our students and we, as their teachers, we usually configure several routers and switches (sometime up to ten), which are accessible remotely. For this we welcome the use of multi tabbed and especially multi exection clients.

It allows to efficentienly organize working space and run commands in one task on all connected network euqipments (for example to save running config).

Tclsh script examples: how to generate router loop interfaces with IPv4 addresses

This example shows how to generate 254 loop interfaces with assigned ipv4 addresses up to The code is:

for {set i 0} {$i < 256} {incr i} {
ios_config "int loop $i" "ip address 172.16.$i.1"
ios_config "end"

and you may just simply copy and paste it into a Cisco router CLI. Therefore first run tclsh within of privileged EXEC mode

Keeping PuTTY telnet session alive

Working with my HP Terminal server, which we are using as a remote console acccess solution allows us login into Cisco router console ports remotely, i'm loosing the Putty connection due to inactivity. However the PuTTY client can be configured to maintain a connection and not time it out. All what we need to do is setup built-in keepalive machanism:

CCNP – Route redistribution – Simulating routing loops


Teaching CCNP ROUTE courses and describing the problematic of two-way routing redistribution I need an example describing the case which point out to the process of creating a routing loop. This example shows how such routing loop may arise using badly configured redistribution process andusing bad seed metric. The topology with two redisitributing routers creates routing feedback (two way, multipoint redistribution). The loop is created for packets routed from the ospf network to the destination network.

Display CCNA curriculums locally

Once if we are allowed download zipped version of ccna curriculum (for example as an netacad instructor) we should be able run them locally without web server need. However there is a problem to display these curriculums by default as it contain embeded flash animation. This problem persists in different browsers (firefox, chrome, epiphany) for example.

VTP (+DTP) security threat – myth or fact?

There is some confusion and misunderstanding regarding VTP (VLAN Trunking Protocol)+DTP (Dynamic Trunking Protocol) and this article will hopefully make it all clear. Most of the confusion comes from the statement that VTP is always a security threat to your network. There are even some CCIE material which I find to be wrong on this topic so my advice here is to test everything by yourself.