In preparation of our CCNA exam, we want to make sure we cover the various concepts that we could see on our Cisco CCNA exam. So to assist you, below we will discuss TCPIP Address and Subnetting.
|TCP/IP Address & Subnetting Overview
|In a TCP/IP environment, each node must have a unique 32-bit logical IP address. Each IP datagram includes the source and destination IP addresses in the header.
|Host and Network Address
|Each company listed on the Internet is viewed as a single network. This network must be reached before a host within that company can be contacted. A two-part addressing scheme allows the IP address to identify both the network and the host.
|IP Address Classes
|There are five classes of IP: Classes A through E. Classes A, B, and C are the most common. Class A has 8 network bits and 24 host bits. (So there are few Class A networks, but each has many hosts.) Class C addresses allow for many more networks, each with fewer hosts. This scheme was based on the assumption that there would be more small networks than large networks in the world.
Note: The address range for all five classes is shown in the figure. Class D is used for multicast purposes, and Class E addresses are used for research.
|The example in the figure shows networks A and B connected by a router. Network B has a Class A address (10.0.0.0). The routing table contains entries for network addresses (not hosts within that network). In the example,172.16.0.0 and 10.0.0.0 refer to the wires at each end of the router. Network 10.0.0.0 is a special case of Class A networks. It is typically used in private networks.
|TCP/IP Address Summary
|Implementing Subnet Planning
|Without subnets, the organization operates as a single network. These flat topologies result in short routing tables but, as the network grows, the use of bandwidth becomes inefficient. (All systems on the network receive all the broadcasts on the network.) Network addressing can be made more efficient by breaking the addresses into smaller segments, or subnets. Subnetting provides additional structure to an addressing scheme without altering the addresses. In the figure, the network address 172.16.0.0 is subdivided into four subnets:
172.16.1.0, 172.16.2.0, 172.16.3.0, and 172.16.4.0. If traffic were evenly distributed to each end station, the use of subnetting would reduce the overall traffic seen by each end station by 75 percent.
|A subnet mask is a 32-bit value written as four octets. In the subnet mask, each bit determines how the corresponding bit in the IP address should be interpreted (network, subnet, or host). The subnet mask bits are coded as follows:
|Although dotted decimal is the most common format, the subnet can be represented in several ways:
|The ip netmask-format command can be used to specify the format of network masks for the current session. Dotted decimal is the default.
|Default Subnet Masks
|Each address class has a default subnet mask. The default subnet masks only the network portion of the address, the effect of which is no subnetting. With each bit of subnetting beyond the default, you can create 2n – 2 subnets. These examples show the effect of adding subnet bits.
|How Routers Use Subnet Masks
|To determine an address’s subnet, a router performs a logical AND operation with the IP address and subnet mask. Recall that the host portion of the subnet mask is all 0s. The result of this operation is that the host portion of the address is removed, and the router bases its decision on only the network portion of the address. In the figure, the host bits are removed, and the network portion of the address is revealed. In this case, a 10-bit subnet address is used, and the network (subnet) number 172.16.2.128 is extracted.
|Broadcast messages are sent to every host on the network. There are three kinds of broadcasts:
|Identifying Subnet Addresses
|Given an IP address and subnet mask, you can identify the subnet address, broadcast address, first usable address, and last usable address using this method:
|How to Implement Subnet Planning
|Subnetting decisions should always be based on growth estimates rather than current needs. To plan a subnet, follow these steps:
|Implementing Subnet Planning Summary
|Configuring IP Addresses
|An IP address must be assigned to a switch if you plan to use SNMP or connect to the switch through a Web browser or Telnet. If the switch needs to send traffic to a different IP network, the traffic is routed to a default gateway. Here’s the procedure for configuring a switch IP address:
SwitchA(config)#ip address 10.2.5.10 255.255.255.0
SwitchA(config)#ip default-gateway 10.2.5.2
|The no ip address command resets the address to the default (0.0.0.0).
Each unique IP address can have a host name associated with it. A maximum of six IP addresses can be specified as named servers. Domain Name System (DNS) is a system used to translate names into addresses. If a system sees an address it does not recognize, it refers to DNS, which is enabled by default with a server address of 255.255.255.255. The ip domain-lookup and the no ip domain-lookup commands turn DNS on and off, respectively.
|Router IP Host Names
|When names are used to route traffic, they must be translated into addresses. Routers must be able to associate host names with IP addresses to communicate with other IP devices. The ip host command manually assigns host names to addresses.
|Configuring IP Addresses Summary