CompTIA® Network+ Exam Notes : Network Services

1. Networking Concepts

1.8 Network Services

DHCP Service: DHCP scopes enables ranges of IP addresses, to be defined on a system running a DHCP server application. When a network device is assigned an IP address from an appropriate DHCP scope, that assignment is not permanent. Rather, it is a temporary assignment referred to as a lease . A specific MAC address is mapped to a specific IP address, which will not be assigned to any other network device. This static addressing approach is referred to as a DHCP reservation .

The Internet Protocol Helper (IP Helper) API enables the retrieval and modification of network configuration settings for the local computer.

DHCP scopes enables ranges of IP addresses, to be defined on a system running a DHCP server application.

DHCP relay forwards DHCP requests between the server and the clients.

When a network device is assigned an IP address from an appropriate DHCP scope, that assignment is not permanent. Rather, it is a temporary assignment referred to as a lease .

DNS Services: The core administrative unit in DNS is called a "zone". A zone is a physical file composed of resource records that define a group of domains. A domain is a node in the DNS name-space and all sub-domains below it. DNS is used for host name to IP address resolution.

Any web server can be made to be present on the public Internet by using an external DNS name and a public IP address. Of course, you need to ensure physical connectivity to the Internet, and a broadband router with ISP connection is a good solution for this. Web server listens to port 80, therefore, you need to enable port 80 (incoming) on the router. HOSTS file is used like DNS for resolving Domain names, whereas LMHOSTS file is used like WINS for resolving NetBIOS names. Note that, if you are using HOSTS file for resolving Domain names, you need to load the HOSTS file on all computers on the network that need to access the domain names. This is in contrast with DNS, which is located on a central server.

The IP address and domain name go in one line for ex: 196.54.202.16 ns.dname.com

Also note that the HOSTS file is an ASCII file and can be edited using Notepad or any other text editor. HOSTS file resolves the domain name to corresponding IP address. The DNS server needs to be specified for connecting using FQDN (Fully Qualified Domain Name).

The most common type of DNS record is a Host record (also called an A record). In the Internet, a Host record is used to associate a domain name (FQDN - Fully Qualified Domain Name) with an IP address.

An MX record stores the IP address of your SMTP server, so e-mail clients can determine where a message should be sent. They perform a DNS query against a domain's MX record to get the IP address of the organization's SMTP server.

An Alias record's job is to associate an alternate name with a computer for which there is already a Host record. For example, suppose that the host record for relevant looked like this: Relevant Host (A) 200.100.100.199

Alias record is like a redirect. For example, you have a site mydomain.com. However, someone enters www.mysite.com, You want him or her to be directed to the web.mysite.com. Since there is no server on the network named "www," set up an Alias record that associates www with mysite.com. The Alias record looks something like this: www Alias (CNAME) mysite.com

WINS resolves NetBIOS names to IP addresses.

DNS Record Types:

A - specifies IP addresses corresponding to your domain and its subdomains

MX - specifies where the emails for your domain should be delivered

CNAME - specifies redirects from your domain's subdomains to other domains/subdomains

TXT - these records are used to store text-based information related to your domain. One of their most common uses is for SPF data. SPF, or Sender Policy Framework

SRV - Each SRV record has the following form:

where each of the attributes should have a specific value:

- service - the name of the service in question.

- proto - the protocol of the service (usually TCP or UDP).

- name - the domain name that the record should be valid for (Note: it should end with a dot).

- TTL - time to live

- priority - lower values mean more preferred.

- weight - used for records with the same priority (higher value means more preferred).

- port - the number of the port.

- target - the hostname of the machine where the service is running (Note: it should end with a dot).

TTL, Priority, Weight, Port and Target are straight forward and easy to fill out. The values will be given by the company that will generate the SRV Record for you.

Here is an example of an SRV record: _sip._tcp.example.com. 3600 IN SRV 10 60 5060 bigbox.example.com.

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WINS is used for NetBIOS name resolution. DHCP is used for assigning IP addresses to client computers dynamically. SNMP is used for remote monitoring of a TCP/IP network.

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