This is pretty old trick, so maybe you already know it, but for the rest of you, it can be interresting.
You just had a crash on you Cisco hardware and you have the logs, but don’t know exactly what caused this crash. You tried to have the device crash again, to compare the logs maybe you’ll find the cause, but your device won’t crash (of course, it will crash only when don’t want that to happen).
There is a hidden Cisco command: “test crash”. This can help you if you are lucky enough to have the real crash exactly like one of those you can test with “test crash” command.
Note: As you can see in the previous posts I do my tutorials based mostly on Dynamips, when it is possible. This is not the case. So, please do not use Dynamips for this test, as it will go into errors since the device is simulated and not a real one.
Please see the tutorial below:
Let’s say that you have a link configured with Frame-Relay and from time to time you observe that the link is having some strange problems. Since you cannot be sure that the link is provided 100% error free you want to do your own tests. You want to see if the Frame-Relay between R0 and R1 is correctly configured. In order to verify this you want to set up the R0 to test the PVC to R1, by sending traffic to its own IP address.
Please download the topology here. The Frame-Relay between R0 and R1 is already configured.
See the tutorial below:
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:
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:
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: