Cisco: Multilink PPP over Frame Relay (MLPoFR)

In this tutorial I propose to show something that is not very used these days, or at least not every day, but which can be tricky if you don’t know how to approach this type of configuration. To understand this, I assume that you know the basics about PPP, FR and Multilink. I will make a short summary here but I will not go into details:

PPP or Point-to-Point protocol is used to establish direct connection between two network points. It can provide authentication, encryption privacy and compression.
FR or Frame-Relay is a telecommunication service used mostly on the WAN side towards your provider or carrier and it relay on frames for data transmission.
Multilink is used for bundle together 2 or more channels / circuits for communication improvement.

Here we will use these 3 technology to create something called MLPoFR. For security we will use authentication. Please download here the topology. Please be aware that in the topology you cannot see actually 2 links there (it a limitation of GNS3), but trust me the links are there. To be more convenient and quick the R1 of the topology is preconfigured.

Please see the tutorial below:

Cisco: Deny false information routing injection into OSPF domain

In a well controlled environment, false information routing should not reach your OSPF domain, as network engineer take care what to advertise and what not into OSPF. But there are cases when you have to deal with 3rd party companies somehow, and you want to be sure that nothing in injected by mistake into your domain. Also this can be a task for CCIE RS lab exam.

And since I specified that this can be an exam task, let take some “DO NOT USE” rule and we have to accomplish the task above without using the command “ip ospf authentication message-digest”. Download the used topology here. R1 from the topology is pre-configured. The OSPF timers have been reconfigured to hello 1 second and dead interval 5 seconds, not to wait “forever” until it rebuilds the adjacency.

Please see the tutorial below:

Interface macro command on a Cisco switch

From the beginning let me tell you that I don’t see very useful this command, as I prefer to use “interface range…” syntax, but since I saw it as a requirement in one of the task for CCIE RS lab exam, and maybe somebody will find it usable in real environment, I said I should put it here in a tutorial.

As many of you already know, you can control a range of interfaces by typing the command “interface range Fa0/1 – 6” (for example), but there is another way to do this by using the interface macro style. For those how are beginners, this interface range or macro syntax spare you from typing 6 commands under 6 interfaces (stick to the example above), but issue only one command under interface range or macro.

Please see the tutorial below:

Limit traffic on a Cisco switch L2 port with minimal configuration

Let’s say that somebody (or some task in a test) ask you to limit the inbound traffic on a switch Layer 2 port by using minimal configuration possible. I must say that in the first steps I failed this task miserable, but actually is very simple to do it.

I will use a plain layer 2 Cisco 2950 switch for this task. I observed that I could not implement this on a Cisco 3500XL. I don’t know if the IOS image was wrong, but I didn’t investigate too much in that area as I cannot stand 3500XL switches and they are actually pretty old piece of hardware.

No topology is needed for this as I will only show how to do it and not testing it with real traffic. I will do testing later when I’ll have some more time, or you can do it on your own.

See the tutorial below:

Cisco hidden tool: test crash

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: