- By Craig Zacker
- Objective 1.1: Compare the layers of the OSI and TCP/IP models
- Objective 1.2: Classify how applications, devices, and protocols relate to the OSI model layers
- Objective 1.3: Explain the purpose and properties of IP addressing
- Objective 1.4: Explain the purpose and properties of routing and switching
- Objective 1.5: Identify common TCP and UDP default ports
- Objective 1.6: Explain the function of common networking protocols
- Objective 1.7: Summarize DNS concepts and its components
- Objective 1.8: Given a scenario, implement the following network troubleshooting methodology
- Objective 1.9: Identify virtual network components
This section contains the answers to the “Can you answer these questions?” sections in this chapter.
Objective 1.1: Compare the layers of the OSI and TCP/IP models
- The Point-to-Point Protocol (PPP) is the primary TCP/IP protocol operating at the link layer. PPP is designed for use with modems and other direct connections in which there is no need for media access control, as with Ethernet. Because it connects only two systems, PPP is called a point-to-point or end-to-end protocol. On a system using PPP, the TCP/IP protocols define the workings of the entire protocol stack, except for the physical layer itself, which relies on a hardware standard.
- The presentation and the session layers of the OSI model do not have TCP/IP protocols dedicated exclusively to them. In most cases, application layer protocols include the session and presentation layer functions.
- At the transport layer, the Transmission Control Protocol (TCP) provides connection-oriented service and the User Datagram Protocol (UDP) provides connectionless service.
- The OSI reference model is defined in a document published by the International Organization for Standardization (ISO), and the TCP/IP model is defined in a Request For Comments document published by the Internet Engineering Task Force (IETF).
Objective 1.2: Classify how applications, devices, and protocols relate to the OSI model layers
- Encryption devices function as the presentation layer of the OSI model. All of the other listed components are physical, data-link, or network layer devices.
- The cables are the only component listed that is exclusively associated with the physical layer; the switch and the NICs are associate with the data-link layer.
- The data-link layer and the network layer. The basic function of a switch is a data-link layer process, but to accommodate advanced features, such as VLANs, network layer capabilities are required.
- Routers do not forward broadcast traffic; therefore they split a network into separate broadcast domains.
- The addresses associated with the Internet Protocol (IP), running at the network layer, are 32 bits long in version 4 and 128 bits long in version 5.
Objective 1.3: Explain the purpose and properties of IP addressing
- Class A subnets provide over 16 million hosts.
- The subnet mask for a network with a /21 suffix is, in binary notation: 11111111 11111111 11111000 00000000; or in decimal notation: 255.255.248.0.
- APIPA uses the 169.254.0.0/16 subnet when assigning IP addresses.
- The last twelve zeroes in the network address can be compacted as follows: fe80::/64.
- The OUI in the MAC address is the first three bytes: 60-EB-69.
Objective 1.4: Explain the purpose and properties of routing and switching
- A large network connected by switches forms a single broadcast domain that can generate a huge amount of traffic. Splitting the network into VLANs enables you to create multiple, smaller broadcast domains.
- RIPv2 supports the use of multicasts instead of broadcasts. By reducing the amount of broadcast traffic on the network, bandwidth is conserved.
- On network segments with redundant switches, the Spanning Tree Protocol selects one of the switches to be operative, and leaves the others dormant until they are needed. This prevents the switches from forwarding packets back and forth to each other.
- RIPv2 includes a subnet mask field that enables the protocol to support networks that use classless addressing. RIPv2 also supports multicasting, which can help to reduce the broadcast traffic on the network.
- For an internetwork to function efficiently, the routing tables on all of its systems must be current and correct. Convergence is the process by which changes are propagated to all of the routing tables on the network.
Objective 1.5: Identify common TCP and UDP default ports
- DHCP uses well-known ports for both client and server. This is because DHCP transactions begin before the TCP/IP settings on the client computer are configured.
- An email client using IMAP and SMTP would use port 25 for outgoing traffic and port 143 for incoming.
- The client browser connects with the HTTPS protocol, which uses port 443.
- The port numbers below 1024 are reserved for use as well-known ports, so there are 1023 available.
Objective 1.6: Explain the function of common networking protocols
- TCP and UDP are transport protocols.
- SIP and RTP are application layer protocols used by VoIP.
- SMTP, IMAP, and POP3 are all protocols that carry email messages.
- DNS typically uses UDP at the transport layer.
- The ARP protocol operates at the data-link layer.
Objective 1.7: Summarize DNS concepts and its components
- Administrators can create aliases by using CNAME resource records.
- A reverse name resolution request causes a DNS server to supply a PTR resource record containing an address-to-name mapping.
- DNS enables clients to locate AD DS domain controllers on the network.
- A resolver is a DNS client.
- DNS servers typically send iterative queries to other servers.
Objective 1.8: Given a scenario, implement the following network troubleshooting methodology
- The next step would be to escalate the problem to a senior administrator.
- The email server issue appears to have the potential to affect the most people, so you should address that problem first.
- To determine the scope of the problem, try to ascertain whether anyone else is having the same experience.
- You can test whether a problem is limited to a single workstation by trying to reproduce the problem on another workstation.
Objective 1.9: Identify virtual network components
- A Type I hypervisor addresses the hardware directly, while a Type II runs on top of a host operating system.
- Voice over IP is the telephony service that has made the virtual PBX possible.
- By creating identical virtual machines on different host computers, you can leave one VM as an offline backup to the operational one.