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Category: NetAcad

Multi tabbed, multi execution telnet/ssh clients

Working on our practical networking lessons our students and I, as their teacher, we are usually configuring several routers and switches (sometimes up to ten), which are accessible remotely. For this, we welcome the use of multi-tabbed and especially multi execution clients.

They allow us to eficiently organize working space and run commands in one task on all connected network equipments (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

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.

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:

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