Network Layer | Layer 3 | OSI Model | TCP/IP Model

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Wildcard mask in EIGRP

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  NOTE This topic is not included in the latest version of the CCNA exam (200-301). If you are studying for the exam feel free to skip this article.   The  network  command in EIGRP uses a classful network as the parameter by default, which means that all interfaces inside the classful network will participate in the EIGRP process. We can enable EIGRP only for specific networks using  wildcard masks . The syntax of the command is: (router-eigrp)#network IP_ADDRESS WILDCARD_MASK We will use the following example network: The router is directly connected to three subnets. Let’s say that we want to advertise only the 10.0.0.0/24 subnet in EIGRP. We can use the wildcard mask of 0.0.0.255 to do this: R1(config-router)#network 10.0.0.0 0.0.0.255 Using the  show ip protocols  command we can verify that only the subnet 10.0.0.0/24 is included in EIGRP: R1#show ip protocols Routing Protocol is "eigrp 1 " Outgoing update filter list for all interfaces is not s...
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Ports on an IOS device

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  Cisco uses the term  interface  to refer to physical ports on an IOS device. Interfaces can be configured with different settings, depending on the type of the interface and whether you are configuring an interface on a router or on a switch. For example, the  Cisco 7201 Router  has four GE physical ports (image source: Cisco): To display the router interfaces in IOS, use the  show ip int brief  command from the privileged exec mode: In the output above we can see that this router has 2 physical interfaces – FastEthernet0/0 and FastEthernet0/1. Consider the output for the  Fa0/0  interface: Here is a brief description of each column: Interface  – displays the type of the interface, in this case Fast Ethernet 0/0. The first zero specifies the physical slot on the router, while the second zero specifies the port number. IP-Address  – displays the interface’s IP address. OK?  – YES in this column signifies that the IP address is...
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IOS command modes

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  We’ve already learned that IOS has three main command modes: the user exec, privileged exec, and the global configuration modes. Each of these modes serves a different purpose and has its own set of commands. In this lesson we will describe each of this modes in more detail. User EXEC mode commands Initially, a user logs into the User Exec mode. This is the mode with the least number of commands. You can get a list of all available commands by typing the character  ? . As you can see, most of the commands available are used to show statistics and perform some basic troubleshooting. The prompt on the left side of the screen always displays the device hostname (R1 in this case), followed by the character >. All commands can be abbreviated to their first letters of the command name. For example, you can abbreviate  ping  by typing  pin , because no other command in the User EXEC mode IOS mode begins with these letters. Privileged EXEC mode commands This IOS mo...
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