TCP/IP Addresses

IP addresses are broken into 4 octets (IPv4) separated by dots called dotted decimal notation. An octet is a byte consisting of 8 bits. The IPv4 addresses are in the following form: 192.168.10.1 There are two parts of an IP address: Network ID Host ID The various classes of networks designate more or less octets to designate the network ID versus the host ID. Class 1st Octet 2nd Octet 3rd Octet 4th Octet Net ID Host ID A Net ID Host ID B Net ID Host ID C Leading bit patterns for classes of networks: Class Pattern Max Networks Max Nodes A 0 126 16777214 B 10 16384 65534 C 110 2097152 254 Subnet masks Subnetting is the process of breaking down a main class A, B, or C network into subnets for routing purposes. When doing subnetting, the number of bits in the subnet mask determine the number of available subnets. Two to the power of the number of bits minus two is the number of available subnets. When setting up subnets the following must be determined: Number of segments Hosts per segment Subnetting provides the following advantages: Network traffic isolation - There is less network traffic on each subnet. Simplified Administration - Networks may be managed independently. Improved security - Subnets can isolate internal networks so they are not visible from external networks. A 14 bit subnet mask on a class B network only allows 2 node addresses for WAN links. A routing algorithm like OSPF or EIGRP must be used for this approach. These protocols allow the variable length subnet masks (VLSM). RIP and IGRP don't support this. Subnet mask information must be transmitted on the update packets for dynamic routing protocols for this to work. The router subnet mask is different than the WAN interface subnet mask. One network ID is required by each of: Subnet WAN connection One host ID is required by each of: Each NIC on each host. Each router interface. Types of subnet masks: Default - Fits into a Class A, B, or C network category Custom - Used to break a default network such as a Class A, B, or C network into subnets. IPv6 IPv6 is 128 bits. It has eight octet pairs, each with 16 bits and written in hexadecimal as follows: 2b63:1478:1ac5:37ef:4e8c:75df:14cd:93f2 Extension headers can be added to IPv6 for new features. Supernetting Supernetting is used to help make up for some of the shortage if IP addresses for the internet. It uses Classless Inter-Domain Routing (CIDR). If a business needs a specific number of IP addresses such as 1500, rather than allocating a class B set of addresses with the subnet mask of 255.255.0.0, a subnet mask of 255.255.248.0 may be allocated. Therefore the equivalent of eight class C addresses have been allocated. With supernetting, the value of 2 is not subtracted from the possible number of subnets since the router knows that these are contiguous networks. 8 times 254 = 2032. SNMP SNMP stands for simple network management protocol. It is used to monitor the state of the network. SNMP collects information two ways: The devices on the network are polled by management stations. Devices send alerts to SNMP management stations. The public community may be added to the alert list so all management stations will receive the alert. SNMP must be installed on the devices to do this. SNMP terms: Baseline - A report outlining the state of the network. Trap - An alert that is sent to a management station by agents. Agent - A program at devices that can be set to watch for some event and send a trap message to a management station if the event occurs. The network manager can set the threshold of the monitored event that will trigger the sending of the trap message. SNMP enables counters for monitoring the performance of the network used in conjunction with Performance Monitor. SNMP Name Resolution SNMP supports the use of DNS, WINS, HOSTS file, and LMHOSTS file for name resolution. SNMP Communities An SNMP community is the group that devices and management stations running SNMP belong to. It helps define where information is sent. The community name is used to identify the group. A SNMP device or agent may belong to more than one SNMP community. It will not respond to requests from management stations that do not belong to one of its communities. SNMP default communities are: Write = private Read = public SNMP Security SNMP should be protected from the internet with a firewall. Beyond the SNMP community structure, there is one trap that adds some security to SNMP. Send Authentication Trap - When a device receives an authentication that fails, a trap is sent to a management station. Other configuration parameters that affect security are: Accepted Community Names - Only requests from computers in the list of community names will be accepted. Accept SNMP Packets from Any Host - This is checked by default. Setting specific hosts will increase security. Only Accept SNMP Packets from These Hosts - Only requests from hosts on the list of IP addresses are accepted. Use IP, or IPX address or host name to identify the host. SNMP Installation SNMP is installed from the control panel network applet services tab. The service is called "SNMP Service". Two parameters are specified at installation: Send Trap with Community Names - The name of the community that traps are sent to. Trap Destination - The name or IP address of hosts traps are to be sent to. SNMP Configuration Clicking "SNMP Properties" brings up a menu with the following three parts: Agent - The contact for where traps are sent is configured here. This is an e-mail address. Service checkboxes include: Physical Applications Datalink/Subnetwork Internet End-to-End Traps - The community name(s) where traps are sent are specified here. Trap destinations are specified by host name or IP address. Security - Includes: Send Authentication Trap checkbox is checked by default. Accepted Community Names box from where requests are accepted from. Accept SNMP Packets from Any Host radio button. Only Accept SNMP Packets from These Hosts. SNMP Use NT Server cannot be an SNMP manager by default without special software. SNMP errors are viewed from the system log of Event Viewer. SNMP Commands GetRequest - The manager requests information from the agent. GetNextRequest - This is used to get information that is contained by an array. GetResponse - Used by the agent to satisfy a request sent by the manager. SetRequest - The manager changes the value of an agent's parameter. Trap - A command or message used by the agent to inform the manager of a certain event. Information collection methods: The agent will send trap message alerts to the SNMP manager. The SNMP manager will poll the network devices.