Routing protocols - How to configure static routes and more

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   I've mentioned in the previous post that routing tables can be updated by either dynamic or static routing mechanisms. In this post I will show you how to configure and troubleshoot static routing on a Cisco intermediary device. I hope you've watched my last Cisco Packet Tracer video tutorial, because in the next one I will use the same topology and we will continue expanding and configuring our network. You already know how to make the basic router configuration, how to configure interfaces and connection between devices, that's why I am going to add only the things that we've not talked about.
   After we have configured connection between devices, verify connectivity by pinging between them. Also you can type in show ip interface brief or show running-config to see the interfaces status and configuration. As an example, an interface must display the message "fastethernet 0/0 is up, line protocol is up" for fast Ethernet interfaces or "serial 0/0 is up, line protocol is up" for Serial interfaces. Remember that the difference between configuring a fastethernet and a serial interface, is that on a serial interface you have to add the clock rate command. The following image displays a configured serial interface :
show ip interface brief

   Serial interfaces must be configured with a clock signal to synchronize communications. There are two parts involved in a serial communication, the DCE on one side and the DTE on the other side:
From Wikipedia (
Data terminal equipment (DTE) is an end instrument that converts user information into signals or reconverts received signals. data circuit-terminating equipment (DCE) is a device that sits between the data terminal equipment (DTE) and a data transmission circuit. It is also called data communications equipment and data carrier equipment. Usually, the DTE device is the terminal (or computer), and the DCE is a modem.
To determine who is the DCE/DTE device use the show controllers command. The following images are showing the difference between these two types:
                                for DTE device:
show controllers command
                                 for DCE device:
show controllers

   I will add a video tutorial with all the new things we will talk about in this post, don't worry, you will understand everything after watching it. Remember that you can see the available routes by typing show ip route:
show ip route

From this output we can see that the network is directly connected on the Serial 0/3/0 interface.
   A very powerful protocol used to discover neighbouring devices, is the CDP (Cisco Discovery Protocol) protocol. As the name suggests, CDP protocol is a Cisco proprietary protocol that can be configured only on Cisco devices. It is manly used to monitor and troubleshoot network activity. If you are using Cisco devices in your network you should always use this protocol but ONLY inside your network. I will show you how to activate CDP on certain interfaces and deactivate it on others. CDP is enabled by default on Cisco devices, but if for whatever reason is not, you can enable it by typing cdp run from the global configuration mode. You can disable CDP globally by typing no cdp run. To display the information that CDP can provide, type show cdp ?:
show cdp command

OK, now let's type show cdp neighbors and show cdp interface:
show cdp neighbors

We can continue further by typing show cdp neighbors detail:
show cdp neighbors detail

To enable or disable CDP on an interface do the following. First select the desired interface then type in cdp enable or no cdp enable:
enable cdp on Cisco device

I recommend disabling CDP on the interface that connects the network to the Internet. The following image will make you understand this:

   For troubleshooting purposes you can use the debug command. Type in debug ? to see the available commands. To disable a debug command use no debug command or undebug all to disable all debugging messages.

   Static routes can be configured manually by network administrators. They are mainly used to announce networks that do not have a dynamic evolution in time. For example, you have a small network that does not changes it's IP or you want to create a route for a stub network (a network that is accessed by one route). Read more about stub zones on Wikipedia: To configure a static routes use the command ip route network-address subnet-mask { next-hop address or exit interface }.
The following image displays the ip route command parameters:

After entering ip route, you'll have to write the Destination network IP Destination prefix mask and then the next hop address or the exit interface. There are other types of static routes, default and summarized static routes. The default static route looks something like this ip route { next hop or exit interface } (the default route is used when no other route exists to forward a packet).
   To understand how to summarize networks and announce static summarized routes, let's take the following example:
suppose we have the following networks
The boundary where the last 1 bit exist is at /22, that's the network mask you'll have to use to announce these 3 networks. the route would look something like this: ip route fastethernet 0/0. Let's take the following example:
To summarize all these networks use the network with /16 or subnet mask. It is actually really simple to summarize networks. The route would look like this: ip route fastethernet 0/0.
   To view configured networks use the show ip route command. Try to remember all commands that we have learned so far because you will need almost all of them when troubleshooting router/routing configuration.
   That is all for this post folks, I will post soon a video tutorial with all the new things we have learned so far.
Have a wonderful day.
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