tailieunhanh - CCNP Routing Study Guide- P5

CCNP Routing Study Guide- P5:T his book is intended to help you continue on your exciting new path toward obtaining your CCNP and CCIE certification. Before reading this book, it is important to have at least read the Sybex CCNA: Cisco Certified Network Associate Study Guide, Second Edition. You can take the CCNP tests in any order, but you should have passed the CCNA exam before pursuing your CCNP. | Extending IP Addresses 83 28 29 30 Notice that the CIDR list starts at a minimum of 8 and can t go higher than 30. This is because the mask must at least be a Class A default and you must leave two hosts at a minimum. Let s now take a look at how Cisco handles CIDR. Cisco and CIDR Cisco has not always followed the CIDR standard. Take a look at the way a Cisco 2500 series router asks you to put the subnet mask in the configuration when using the Setup mode Configuring interface EthernetO Is this interface in use yes return Configure IP on this interface yes return IP address for this interface Number of bits in subnet field 0 8 Class A network is 8 subnet bits mask is 16 Notice that the router asks for the number of bits used only for subnetting which does not include the default mask. When dealing with these questions remember that your answers involve the number of bits used for creating subnets not the number of bits in the subnet mask. The industry standard is that you count all bits used in the subnet mask and then display that number as a CIDR for example 25 is 25 bits. The newer IOS that runs on Cisco routers however runs a Setup script that no longer asks you to enter the number of bits used only for subnetting. Here is an example of a new 1700 series router in Setup mode Configure IP on this interface no y IP address for this interface Subnet mask for this interface Class A network is 16 subnet bits mask is 16 Notice that the Setup mode asks you to enter the subnet mask address. It then displays the mask using the slash notation format. Much better. Copyright 2001 SYBEX Inc. Alameda CA 84 Chapter 3 IP Addressing Route Summarization In the Design Considerations with VLSM section we briefly mentioned the concept of route summarization. So what is it and why do we need it On very large networks there may be hundreds or even thousands of .