S3SS10N Wednesday – Network Services Part 1

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S3SS10N Wednesday – Network Services Part 1

Published: January 4, 2017 | By: Kelly Handerhan | Views: 4353
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This Weeks S3SS10N Wednesday


In this Session Wednesday video, Kelly Handerhan gives us an overview of common network services. The basics she covers will prepare you for the Network Infrastructure exam. Kelly introduces the four main services that comprise this subject: DNS, DHCP, RADIUS, and NAC. This video discusses the first two. RADIUS and NAC are covered in Part 2 of this series.

DNS or Domain Naming Service provides a mapping of a fully-qualified domain name to an IP address. Kelly points out that people deal in names and machines prefer numbers, as is the case with domain names and IP addresses. The procedure for the mapping process originates with a named request via DNS.

Records managed by DNS specify the services on the network and the location on the network of the servers on which they’re hosted. Examples are authentication servers such as a domain controller in Windows or an LDAP server as is the case with Active Directory. In these examples, a client making a named request requires the IP address of a particular server either to authenticate on the network or locate a particular service.

Formerly, a broadcast was issued as part of the named request, but this generates excessive traffic on the network. It’s now more common for a client to request the IP address of the server closest to it. DNS is an efficient mechanism for mapping named requests to IP addresses, but it is vulnerable to exploits such as cache poisoning and DDoS attacks as in the recent attack on the DYN DNS infrastructure that rendered several major websites unreachable for hours on the East Coast of the United States.

Kelly then moves on to discuss DHCP or Dynamic Host Configuration Protocol. This service provides for the automatic assignment of IP addresses to devices wishing to connect to a network. IP addresses can be either statically or dynamically assigned.

Static assignment has the advantage of being more secure as it allows for more control. The drawback of statically assigned IP addressed is increased overhead and the risk of errors during manual configuration. Things are much easier — especially with a large number of hosts –when using dynamic assignment. IP addresses are “leased” with a dynamic protocol such as DHCP and are released back into the pool once a device goes offline making it available to other devices.

The session concludes with a discussion of DORA, which is an acronym for the process of Discover, Offer, Request, and Acknowledge. It’s the process used by DHCP. A client sends out a broadcast when coming onto the network and in turn, every DHCP server responds. The client is then obliged to accept the first offer it receives. In the case of DHCP, it’s an IP address. This is the default configuration for DHCP. The accepted IP address is then removed from the DHCP server’s scope. Kelly discusses the vulnerabilities associated with this process and points out that they exist because DHCP was built to work, but not to work securely!

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About This S3SS10N Wednesday's Contributor

Kelly Handerhan
Skilled and certified in CISSP, CASP, and PMP, SME Kelly has taught several courses on Cybrary and is highly praised for her ability to effectively communicate important information in a relate-able and understandable way.
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3 Comments
  1. The video kept stopping 13mins into it.

  2. Unable to watch the lesson, having an issue with the streaming not sure.

  3. very good class

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