Question

a) You have installed the DNS server role on a computer running Windows Server 2016 and in the process of configuring forward/reverse lookups. Explain the difference between “ping www.google.com” and “ping the IP address of Google server at 172.217.167.68”. You may want to try both and observe any differences. Your answer should include your explanation, as well as screenshots.

b) Network administrators warn against configuring a file server to use DHCP. Explain what would happen if a file server was configured to use DHCP and, due to a power outage, the file server and DHCP server rebooted at the same time? Justify your answer.

Answer 1

a) DNS Server :A DNS server is a computer server that contains a database of public IP addresses and their associated hostnames, and in most cases serves to resolve, or translate, those names to IP addresses as requested. DNS servers run special software and communicate with each other using special protocols.

When you type a website address into your browsers address bar and press Enter, a DNS server goes to work to find the address that you want to visit. It does this by sending a DNS query to several servers, each of which translates a different part of the domain name you entered. The different servers queried are:

• A DNS Resolver: Receives the request to resolve the domain name with the IP address. This server does the grunt work in figuring out where the site you want to go actually resides on the internet.
• A Root Server: The root server receives the first request, and returns a result to let the DNS resolver know what the address of the Top Level Domain (TLD) server that stores the information about the site. A top level domain is the equivalent of the .com or .net portion of the domain name you entered into the address bar.
• A TLD Server: The DNS resolver then queries this server, which will return the Authoritative Name Server where the site is actually returned.
• An Authoritative Name Server: Finally, the DNS resolver queries this server to learn the actual IP address of the website you're trying to deliver.

Some DNS servers can provide faster access times than others. This is often a function of how close you are to those servers. If your ISP's DNS servers are closer to you than Google's, for example, you may find domain names are resolved quicker using the default servers from your ISP than with an external server.

If you experience connection problems where it seems no websites will load, it's possible there's an error with the DNS server. If the DNS server isn't able to find the correct IP address that's associated with the hostname you enter, the website can't be located and loaded.

The ping is done with its two parameters,namelyICMP and the packet size of each echo request (S.T.Ali,2015).so the command will be like the follows:

ping -n 10 -l 512 www.google.com

Using this ping request,the search is done in the command prompt and the screenshot is shown below:

with this ping request ,echo is done for 10 times as it shows in the footer result in Sent and Received Packet for 10 times .For each time the request is transacted,512 bits are transacted actually.As the internet is connected,so packet loss is Zero.

The ping is done in two ways,primary by usingthe google domain name and secondly by providing the IP address of the google server.So,for the first case,the ping will be as follows:

ping www.google.com

And in the second case,ping will be as follows:

ping 172.217.167.68

Now,the screenshot for theese two pings is as follows:4

For both two cases,the default transation is made by sending and recieving packets 4.The time taken for the first case is lesser when compared to the second one.The average time required for the first ping is 58 ms and for the second case, the average time required is 179 ms.So,the first one is efficient in terms of time consumption.

b) DHCP : Dynamic Host Configuration Protocol (DHCP) is a network management protocol used to automate the process of configuring devices on IP networks, thus allowing them to use network services such as DNS, NTP, and any communication protocol based on UDP or TCP.

What is DHCP?

Anyone with a basic knowledge of computer networking knows that for two hosts to communicate on the same network using TCP/IP model, both hosts need to have a unique IP address. There are two ways on how any given host on your network can obtain an IP address.

One way is to manually configure the network interface and assign an IP address by hand. The manual network configuration is called static configuration, which means that host's IP address does not change its IP address unless changed manually by the user or system administrator. If your company network includes more than 1000 hosts, the job of configuring each host with a static IP address becomes tiresome and more importantly extremely inefficient.
Another way to assign your network hosts with a proper IP address regardless of the actual network size is to assign an IP address to each host automatically. To perform an automatic host's IP configuration is where DHCP ( Dynamic Host Configuration Protocol ) comes handy.

The DHCP protocol lets a DHCP client, that is your network host to lease network configuration parameters such as an IP address. In fact, lease parameters are not limited to IP address only as they may also include the following configuration settings:

• IP addresses and network masks
• Domain Names servers ( DNS )
• Default Gateways
• WINS servers
• Syslog hosts
• Proxy servers
• NTP servers
• X Font servers
• Syslog hosts

Each network host configured to obtain an IP address dynamically via DHCP will upon boot send a DHCP request over the network ( by definition this is a broadcast of all 1's ) to discover whether there is a DHCP server available somewhere on the network and consequently ask for a network configuration. DHCP client is then obligated to maintain communication with DHCP server and renew its IP address regularly as dictated by IP address's lease time expiry. In case that DHCP client fails to renew its IP address ( disconnection, a host is turned off, etc. ) its IP address expires and DHCP server is free to lease this IP address to another DHCP client.

DHCP server keeps a record of all leased IP addresses and stores them in a file called dhcpd.leases within /var/lib/dhcp directory ( location of this file may vary depending on Linux system in use ). Having such a file allows DHCP server to keep track of all IP address leases even after the reboot or power failure.

Here are some advantages of having a DHCP server connected to network:

• No IP address conflicts. DHCP can guarantee that all hosts on the network have a unique IP address. DHCP server keeps a record of all IP addresses assigned and cross reference them with host's MAC addresses.
• Based on the MAC address, DHCP allows for a fixed parameter configuration for a specific host
• minimum local client network configuration, hence Increased efficiency

DHCP server configuration file:

This is a simple dhcpd configuration file, dhcpd.conf . This file includes a subnet range that's dynamically assigned to clients, but also contains two static entries for known servers that are expected to be present at certain IP addresses. One is a printer server, and the other is a network-enabled toaster. The DHCP server configuration isn't specific to wireless networks, and you can apply it to wired networks as well.

ddns-update-style none;

#option subnet-mask 255.255.255.224;
default-lease-time 86400;
#max-lease-time 7200;

subnet 192.168.20.0 netmask 255.255.255.0 {
        range 192.168.20.41 192.168.20.254;
        option broadcast-address 192.168.20.255;
        option routers 192.168.20.1;
        option domain-name-servers 192.168.20.1;
        option domain-name "soho.com";

        host printerserver {
               hardware ethernet 00:50:BA:85:EA:30;
               fixed-address 192.168.20.2;
        }

        host networkenabledtoaster {
               hardware ethernet 00:A0:D2:11:AE:81;
               fixed-address 192.168.20.40;
        }
}

The nameserver, router IP, and IP address will be supplied to your wireless network clients. The router IP address is the IP address of the gateway's wireless network interface that's connected to your wireless network. The nameserver is set to the gateway's wireless network adapter, since the gateway is also handling name serving services. The gateway nameserver will redirect requests for unknown hostnames to the ISP nameserver. The internal wireless network has been defined to be 192.168.20.0. Note that we've reserved IP address range 192.168.20.1 through 192.168.20.40 for static IP address assignment; the dynamic range starts at 192.168.20.41.

Now that we have the configuration file, we need to start dhcpd.

We need to make sure that the directory /var/run exists, as well as /var/state/dhcp. The file /var/state/dhcp/dhcpd.leases must exist. You can create an empty file for the initial start of the dhcpd binary.

When you start dhcpd, you must tell it where to find the configuration file if it isn't in the default location. You also need to pass an interface name, as you want only dhcpd to service your internal wireless network interface. If we used the adapter from the wireless discussion, this would be ral0:

dhcpd -cf /etc/dhcpd.conf ral0

Your DHCP server should now be running. If there are any issues, you can start dhcpd in a debugging mode using the -d option. The dhcpd daemon also logs messages to the system log, slogger

BOOTP Support

ISC DHCP server is backward compatible with BOOTP. The following is a BOOTP client declaration to be defined in DHCP's main configuration dhcpd.conf file:

host bootp {
              hardware ethernet 00:00:2e:55:12:09;
              fixed-address 123.123.1.3;
              filename "/path/to/tftpboot/bootp.boot";
            }

due to a power outage, the file server and DHCP server rebooted at the same time the BOOTP support  backward compatible

if a DHCP server shutdown, doesn't matter if power failure or normal shutdown, the client will keep it's ip address according to the lease time configured in the DHCP scope settings. At the half lease time a client will try to renew it's ip address, if the DHCP server isn't reachable at that time it tries again after the next half (so with a lease time from 8 hours, first try after 4 hours, second try after 2 hours etc.).

If a DHCP server responds the lease will be renewed and should/can be the same, as long as the ip address is still free. If the ip address was chosen from another machine, as it was free on the server because of the crash and now empty database, the machine will get a new ip address. This can be only avoided with fixed ip addresses, which should be always done for critical machines like servers.