Network Devices and Services Overview for the CCENT Certification Exam

By Glen E. Clarke

Part of CCENT Certification All-In-One For Dummies Cheat Sheet

You can be sure to get a few questions on the CCENT certification exam that test your knowledge of types of devices and different network services. The following are some key points to remember about devices and services:

Network devices

  • Hub: A hub is a layer-1 device that is used to connect systems together. When a hub receives data in the form of an electrical signal, it sends the data to all other ports in hopes the destination system is at one of those ports. All ports on the hub create a single collision domain and a single broadcast domain.

  • Repeater: A repeater is a layer-1 device that is used to amplify the signal. As the signal travels along the network, it gets weaker due to interference, so the purpose of the repeater is to regenerate that signal so it can travel more distance.

  • Bridge: A bridge is a layer-2 device that creates multiple network segments. The bridge maintains a table in memory of what systems reside on what segments by their MAC addresses. When data reaches the bridge, the bridge filters the traffic by only sending the data to the network segment that the destination system resides on. The purpose of the bridge is that it filters traffic by sending the data only to the segment where the destination system resides. Each segment on the bridge creates a separate collision domain, but it is all one broadcast domain.

  • Switch: The switch, another layer-2 device, is an improvement on a bridge in the sense that each port on the switch acts as a network segment. The switch filters traffic by sending the data only to the port on the switch where the destination MAC address resides. The switch stores each MAC address and the port the MAC address resides on in an area of memory known as the MAC address table. Each port on the switch creates a separate collision domain, but all ports are part of the same broadcast domain.

  • Router: A router is a layer-3 device that handles routing of data from one network to another network. The router stores a listing of destination networks in the routing table which is found in memory on the router.

Network services

  • DHCP: The DHCP service is responsible for assigning IP addresses to hosts on the network. When a client boots up, it sends a DHCP discover message, which is a broadcast message designed to locate a DHCP server. The DHCP server responds with a DHCP Offer, offering the client an IP address. The client then responds with a DHCP request message asking for the address before the server responds with a DHCP ACK to acknowledge that the address has been allocated to that client.

  • DNS: The DNS service is responsible for converting the Fully Qualified Domain Name, (FQDN) such as to an IP address.

  • NAT: Network Address Translation is responsible for converting the internal address to a public address that is used to access the Internet. NAT offers the benefit of being able to purchase only one public IP address and have a number of clients on the network use that one IP address for Internet access. NAT also offers the security benefit that the internal addresses are not used on the Internet — helping to keep the internal addresses unknown to the outside world. There are two types of NAT to know for the CCENT certification exam:

    • Static NAT: Static NAT is the mapping of one internal address to one public address. With static NAT, you will need multiple public addresses to allow internal clients to access the Internet.

    • NAT overloading: A more popular form of NAT, NAT overloading is the concept that all internal address get translated to the one public address on the NAT device.

  • Web services: There are a number of Web services you should be familar with for the CCENT certification exam:

    • POP3/IMAP4: POP3 and IMAP4 are the Internet protocols for receiving email over the Internet.

    • SMTP: SMTP is the Internet protocol for sending email over the Internet. SMTP servers are also known as email servers.

    • HTTP: HTTP servers are also known as Web servers and are used to host Web sites. HTTP is a protocol that is used to send the Web page from the Web server to the Web client.

    • FTP: FTP is an Internet protocol used to transfer files over the Internet. The files are hosted on FTP servers, which are then downloaded to any clients on the Internet.