Cisco hidden tools: Testing TCP connection

Sometimes you have a connection between 2 routers that you want to test with something more than a ping. Cisco devices have a hidden command which is actually a very powerful testing tool for your TCP connection.

The command is “ttcp” and you will not find it in the the default list of commands of a Cisco device. So, even if you use help ( “?” mark at the router prompt) this command will not be showed to you.

For our testing we will use the same topology as in the previous posts. If you do not have it please download it here. Since this is a point-to-point TCP connection testing we will not use any fancy routing protocol or other networking protocols.

See the tutorial below:

How to force Loopack interface to be advertised with a /24 netmask

Many of you already know that usually when you advertise a Loopback interface into OSPF it is advertised with /32 netmask (one IP address) even if the IP address under Loopback interface is with a /24 netmask. If you checked my previous post, you’ll see at the end that I’m right, and the Lo0 address is advertised with /32 netmask.

But what if you have to advertised as a /24 subnet (task require or some testing) ? There is “dirty little trick” to do it. I will use the same topology and design like in the post before. If you do no have the topology please download it here.

Watch the movie:

How to advertise subnet into OSPF without network or redistribution command

During my CCIE R&S preparation for lab exam, I encounter a task that requested me to advertise a subnet into OSPF routing protocol, but without using network statement or redistribution command. Since back then I was a little confuse about this, I said to post here maybe it help others.

Please download the topology used in this example here. We have already OSPF prepared and the task request to advertise interface Loopack0 from R0 to OSPF without using network statement or redistribution command.

See how to do it here:

Dynamips: How to save vlans after switch reload

Most of you already know that in Dynamips after a reload of a switch all the vlans and vtp configurations are gone. There is a way how to save the vlan and vtp configuration even in case of a reload of the switch and I will show you below how to do it. For switch emulator I used a Cisco 3640 IOS image with a NM-16ESW module to have Layer 2 port on the device.

Click below to see the movie and explanation:

How to save vlans after switch reload
How to save vlans after switch reload