CCNA :) Be a Good Network Administrator

A waste of space 1.1.2  This page will explain how certain address schemes can waste address space. In the past, the first and last subnet were not supposed to be used. The use of the first subnet, which was known as subnet zero, was discouraged because of the confusion that could occur if a network and a subnet had the same address. This also applied to the use of the last subnet, which was known as the all-ones subnet. With the evolution of network technologies and IP address depletion, the use of the first and last subnets have become an acceptable practice in conjunction with VLSM. In Figure , the network management team has borrowed three bits from the host portion of the Class C address that has been selected for this address scheme. If the team decides to use subnet zero, there will be eight useable subnets. Each subnet can support 30 hosts. If the team decides to use the no ip subnet-zero command, there will be seven usable subnets with 30 hosts in each subnet. Cis...

A waste of space 1.1.2  This page will explain how certain address schemes can waste address space. In the past, the first and last subnet were not supposed to be used. The use of the first subnet, which was known as subnet zero, was discouraged because of the confusion that could occur if a network and a subnet had the same address. This also applied to the use of the last subnet, which was known as the all-ones subnet. With the evolution of network technologies and IP address depletion, the use of the first and last subnets have become an acceptable practice in conjunction with VLSM. In Figure , the network management team has borrowed three bits from the host portion of the Class C address that has been selected for this address scheme. If the team decides to use subnet zero, there will be eight useable subnets. Each subnet can support 30 hosts. If the team decides to use the no ip subnet-zero command, there will be seven usable subnets with 30 hosts in each subnet...

VLSM What is VLSM and why is it used?  1.1.1 Certification-level claim: Compute and use Variable Length Subnet Masking (VLSM) techniques to design and implement effective and efficient IP addressing. This module provides essential background information for the CCNA exam. Namely, this is how to configure IP addresses, subnet masks and gateway addresses on routers and hosts, and how to design an IP addressing scheme to meet design requirements. Hands-on skills: None In this lesson students will be introduced to the new topic of Variable Length Subnet Masks (VLSM). It is important for instructors to introduce this topic after they have made sure that students are thoroughly familiar with subnetting. It might be useful to give students the opportunity to demonstrate their skills at subnetting by giving them a series of small network addressing problems. These could be such as ones they have done in CCNA 1 and 2. Instructors should then emphasize that VLSM is an importan...

Semester 3  Module 1: Introduction to Classless Routing Overview Network administrators must anticipate and manage the physical growth of networks. This may require them to buy or lease another floor of a building for new network equipment such as racks, patch panels, switches, and routers. Network designers must choose address schemes that allow for growth. Variable-length subnet mask (VLSM) is used to create efficient and scalable address schemes. Almost every enterprise must implement an IP address scheme. Many organizations select TCP/IP as the only routed protocol to run on their networks. Unfortunately, the architects of TCP/IP did not predict that the protocol would eventually sustain a global network of information, commerce, and entertainment. IPv4 offered an address strategy that was scalable for a time before it resulted in an inefficient allocation of addresses. IPv4 may soon be replaced with IP version 6 (IPv6) as the dominant protocol of the Internet. I...

 Summary Module 11 ACLs This page summarizes the topics discussed in this module. ACLs are lists of conditions that are applied to traffic that travels across a router interface. They can be created for all routed network protocols such as IP and IPX. Packets are accepted or denied based on these lists. Network administrators create ACLs to control network access. ACLs provide the ability to limit network traffic, increase performance, and manage security issues. ACL statements operate in sequential, logical order. When a condition is matched as true, the packet is permitted or denied and the rest of the ACL statements are not checked. If all the ACL statements are unmatched, an implicit deny any statement is placed at the end of the list by default. The invisible deny any statement at the end of the ACL will not allow unmatched packets to be accepted. When first learning how to create ACLs, it is a good idea to add the deny any at the end of ACLs to reinforce the ...

Restricting virtual terminal access    11.2.6 This page will explain how ACLs are created for virtual ports. Standard and extended access lists apply to packets that travel through a router. They are not designed to block packets that originate within the router. An outbound Telnet extended access list does not prevent router initiated Telnet sessions, by default. Just as there are physical ports or interfaces, such as Fa0/0 and S0/0 on the router, there are also virtual ports. These virtual ports are called vty lines. There are five vty lines, which are numbered 0 through 4, as shown in Figure . For security purposes, users can be denied or permitted virtual terminal access to the router but denied access to destinations from that router. The purpose of restricted vty access is increased network security. The Telnet protocol can also be used to create a nonphysical vty connection to the router. There is only one type of vty access list. Identical restri...