Client-7.2-7.4 PDF Networking Concepts

As you study this section, answer the following questions: - Which IP configuration issues should you be aware of? - How can an incorrect subnet mask cause IP communication issues? - Which issues can prevent a Dynamic Host Configuration Protocol (DHCP) server from properly issuing an IP...

As you study this section, answer the following questions: - Which IP configuration issues should you be aware of? - How can an incorrect subnet mask cause IP communication issues? - Which issues can prevent a Dynamic Host Configuration Protocol (DHCP) server from properly issuing an IP address to a host? - What does the **/release** switch do when you use it with **ipconfig** ? - How can you tell if a rogue DHCP server is active on a network? - How do you know if a host is using Automatic Private IP Addressing (APIPA)? In this section, you will learn to: - Explore IP configuration - Troubleshoot IP configuration - The key terms for this section include: Automatic Private IP Addressing (APIPA) The Windows function that provides DHCP autoconfiguration addressing. Dynamic Host Configuration Protocol (DHCP) A protocol used to centrally manage the distribution of IP addresses within a network. Domain Name System (DNS) (DNS) A system that translates domain names into IP addresses, which computers can understand. Rogue DHCP server An unauthorized DHCP server on a network. **TCP/IP Required Configuration Settings** The IP address identifies both the logical host and the logical network addresses. - Each host on the entire network must have a unique IP address. - Two devices on the same subnet must have IP addresses with the same network portion of the address. - Two devices on the same subnet must have unique host portions of the IP address. - You cannot use the first or the last host address on a subnet address range. The subnet mask identifies the portion of the IP address that is the network address and the portion that is the host address. Two devices on the same subnet must be configured with the same subnet mask. The default gateway identifies the router to which communications for remote networks are sent. The default gateway address is the IP address of the router interface on the same subnet as the local host.\ \ Without a default gateway set, most clients cannot communicate with hosts outside of the local subnet. Domain Name System (DNS) server: The DNS server address identifies the DNS server that is used to resolve host names to IP addresses. The hostname identifies the logical name of the local system. As you study this section, answer the following questions: - What is the difference between **netstat** and **arp** ? - What does a failed **ping** test signify? - When should you use **tracert** ? - What does **tcpdump** do? In this section, you will learn to: - Use **ping** and **tracert** - Explore network communications ping A command that sends an ICMP echo request/reply packet to a remote host. A response from the remote host indicates that both hosts are correctly configured and a connection exists between them. Address Resolution Protocol (ARP) A protocol that hosts use to discover a device\'s MAC address. **Ping Troubleshooting Process** Identifying the scope of a problem is a critical step in the troubleshooting process. To help you understand the troubleshooting process, consider the following reported connectivity problem. A Workstation (on the local network) cannot communicate with another Workstation. The following table lists tasks to troubleshoot the reported connectivity problem. These steps trace the problem backward from the remote host to the local host. Depending on the situation, you might be able to troubleshoot the problem more efficiently by skipping some tasks or changing the order in which you perform them. You might even complete them in reverse order. Ping Often, the best way to troubleshoot a problem is to ping the host you are trying to contact. This verifies the reported problem. If the ping is successful, the problem is not related to network connectivity. In that case, check other problems, such as name resolution or service access. If you have access to another computer, try pinging the destination host from that computer. If the ping is successful, skip the remaining tasks and troubleshoot the local host configuration or physical connection. Ping another host on the same subnet as the unreachable host If you cannot contact a specific remote host, try pinging another host in the same remote network. If the ping is successful, the problem is with the remote host. For example, the problem could be a misconfiguration, a broken link, or an unavailable host. If you cannot contact any host in the remote network, try pinging hosts on other remote networks (try several other networks). If the pings are successful or if you can contact some remote networks and not others, the problem is with the routing path between the network and the remote network. Use the tracert (Windows) or traceroute (Mac) command to check the path to the problem network. If you cannot contact any remote network, ping the default gateway router. If the ping is successful, but you still cannot contact any remote host, have the router administrator verify the router configuration. Check for: - Broken links to the remote network. - Interfaces that have been shut down. - Access control lists or other controls that might be blocking traffic. If you cannot contact the default gateway router, ping other hosts on the local network. If the pings are successful, check the default gateway router. If you cannot communicate with any host on the local network, the problem is likely with the local host or its connection to the network. Troubleshoot by doing the following: - Check physical connectivity. - Validate the TCP/IP configuration on the local host. - Validate IP configuration settings. The route command can be useful in troubleshooting. You can use the route command on the router to view directly connected routes that have been set up. You can also use it on the default gateway of the local subnet to verify that the router has a route to the remote subnet. Additionally, you can use the route command to: - View the routing table; this helps you see the networks the router knows about. - Display additional networking information not provided by ifconfig. One special ping test you can perform is pinging the local host. By doing this, you are verifying that the TCP/IP is correctly installed and configured on the local host. You are verifying that the workstation can communicate with itself. To ping the local host, use the following command: ping 127.0.0.1 If this test fails, check to ensure TCP/IP is correctly configured on the system. This test does not check physical connectivity. The ping can succeed even if the host is disconnected from the network. As you study this section, answer the following questions: - Why is IPv6 needed? - What is the format of an IPv6 address? - How can an IPv6 address be simplified? - What are the two parts of an IPv6 address? - What allows IPv6 hosts to communicate over a IPv4 network? - What is the difference between stateful autoconfiguration and stateless autoconfiguration? In this section, you will learn to: - Configure a DHCP6 server - Configure an IPv6 address Prefix ID The first 64 bits of an IPv6 address. The prefix can be divided into parts that identify things such as geographic region, ISP, network, and subnet. Interface ID The last 64 bits of an IPv6 address. This is a unique identifier for each device, similar to a MAC address. Tunneling A communication method that allows IPv6 hosts or sites to communicate over the existing IPv4 infrastructure. Unicast address A network address assigned to a single interface for the purpose of allowing one host to send and receive data. Packets sent to a unicast address are delivered to the interface with that address. Multicast address A network address that represents a dynamic group of hosts. Anycast address A unicast address that is assigned to more than one interface. The interfaces it is assigned to typically belong to different hosts. Loopback address An IP address you can use to verify that the TCP/IP protocol stack is properly installed on the host. The local loopback address is not assigned to an interface. For a device to communicate on a network, it must have its Internet Protocol (IP) information configured. This can be done either manually or dynamically (automatically). - A *static IP* is an IP address that has been manually configured. This means the address will not change even if the device disconnects from the network. - A *dynamic IP* is an IP address that is automatically assigned. The IP configuration is handled by the Dynamic Host Configuration Protocol (DHCP). This lesson covers the following topics: - Role of DHCP - DHCP configuration - DHCP process **Role of DHCP** Implementing DHCP on a network allows the IP configuration to be assigned automatically when a device connects to the network. The IP configuration can include: - Unique IP address. - Subnet mask. - Default gateway. - Domain Name System (DNS) server (only if needed). - Windows Naming Service (WINS) server (only if needed). **DHCP Configuration** To implement DHCP, the DHCP scope must be defined. This is the configuration information that will be applied to each device receiving an IP configuration through DHCP. Depending on the network, different devices can serve as the DHCP server, such as: - SOHO router - Windows or Linux server The IP range defines the range of IP addresses that the DHCP server can assign. When a new device connects to the network, the DHCP server assigns the next available address. When defining the IP range: All available addresses in the network can be assigned. Only specific ranges can be assigned (e.g., 192.168.5.50 - 192.168.5.100). Specifying a limited number of addresses can help limit the number of connections to the network. The subnet mask defines the network ID and host ID. The subnet mask must be defined. Exclusions are IP addresses that the DHCP server will not assign. Be aware that exclusion addresses: - Are typically used for devices such as servers, printers, routers, or other network devices that must have a static IP address. - Must be manually configured on each device. It is important to remember that the exclusion addresses must fall within the configured IP range of the scope. Reservations are static IP addresses not dynamically assigned by the DHCP server. - Reservations are assigned by the DHCP server using the device\'s MAC address. - Whenever the device with the specified MAC address connects to the network, the DHCP server assigns it the reserved static IP configuration. When a device is assigned an IP configuration, it is for a specified amount of time. This is the DHCP lease. - While a lease is active, that IP address cannot be reassigned, even if the device disconnects from the network. - When the lease is half over, a device still connected to the network will attempt to renew the lease. A lease can be set for a few hours up to many days, weeks, or months. - If the device stays connected to the network, set the lease to last for days. - If clients are connecting for only a short period of time (e.g., a guest network), set the lease accordingly so available addresses are not tied up. The default gateway defines where data packets leaving the network should go. An example is packets going to the internet are sent to the default gateway. DNS server If a specific DNS server is being used, define it in the scope. WINS server Most networks do not use WINS anymore. If it is needed, you can define it in the DHCP scope. DHCP Process When a new device connects to the network, it goes through a four-step process to obtain the IP configuration from the DHCP server. The four steps in the process are: discover, offer, request, and acknowledge. The acronym DORA is a useful memory aid. The following table describes the DORA process. DHCP discover (D) The client begins by sending a DHCP discover frame to identify DHCP servers on the network. DHCP offer (O) A DHCP server that receives a discover request from a client responds with a DHCP offer advertisement that contains an available IP address. If more than one DHCP server responds with an offer, the client usually responds to the first offer that it receives. DHCP request (R) The client accepts the offered address by sending a DHCP request back to the DHCP server. If multiple offers were sent, the DHCP request message from the client also informs the other DHCP servers that their offers were not accepted. They can make the IP address in the offers available to other clients. DHCP ACK (A) The DHCP server whose offer was accepted responds to the request by sending a DHCP ACK (acknowledgment). At this point, the IP address is leased to and configured on the DHCP client. The DHCP renewal process occurs when fifty percent of the device\'s lease time has expired. This process skips the DHCP discover, and DHCP offer steps. The client sends the DHCP request packet to the server, which responds with the DHCP ACK packet and renews the IP configuration. When the client attempts to renew its lease, the DHCP server will try to reassign the same IP information. However, if the client is off the network for an extended period and the lease expires, that address goes back into the pool and can be reassigned to another device.