Ch1 - 1.02 - Understanding TCP/IP Flashcards
Loopback address
The loopback address is used to refer to the local system, also known as the localhost. If you want to verify that the TCP/IP software has initialized on the local system even though you may not have an IP address, you may ping the loopback address, which is typically referred to as 127.0.0.1.
Private address
A private address is an address that can be assigned to a system but cannot be used for any kind of Internet connectivity. The private addresses are non-routable addresses, so any system using them will be unable to function off the network. The following are the three address ranges that are the private address ranges:
- 0.0.0 to 10.255.255.255
- 16.0.0 to 172.31.255.255
- 168.0.0 to 192.168.255.255
Transmission Control Protocol (TCP)
The Transmission Control Protocol (TCP) is responsible for providing connection-oriented communication and for ensuring delivery of the data (known as reliable delivery). Connection-oriented communication involves first establishing a connection between two systems and then ensuring data sent across the connection reaches the destination. TCP makes sure that the data reaches its destination by retransmitting any data that is lost or corrupt.
Initial Sequence Number (ISN)
In the first phase, the sending system sends a SYN message to the receiving system. Each packet sent is assigned a sequence number, which is a unique number assigned to the packet. The SYN message contains the initial sequence number (ISN), which is the first sequence number to be used. In this example, Computer A is connecting to the web site on Computer B, so a SYN message is sent to port 80 on Computer B.
User Datagram Protocol (UDP)
The User Datagram Protocol (UDP) is used by applications that do not want to be concerned with ensuring the data reaches the destination system. UDP is used for connectionless communication (unreliable), which means that data is sent to the destination and no effort is made to track the progress of the packet and whether it has reached the destination.
Internet Protocol (IP)
The Internet Protocol (IP) provides packet delivery for protocols higher in the model. It is a connectionless delivery system that makes a “best-effort” attempt to deliver the packets to the correct destination. IP does not guarantee delivery of the packets—that is the responsibility of transport protocols; IP simply sends the data.
The IP protocol is also responsible for the logical addressing and routing of TCP/IP and therefore is considered a layer-3 protocol of the OSI model. The IP protocol on the router is responsible for decrementing (usually by a value of 1) the TTL (time to live) of the packet to prevent it from running in a “network loop.” Windows operating systems have a default TTL of 128.
Internet Control Message Protocol (ICMP)
Internet Control Message Protocol (ICMP) enables systems on a TCP/IP network to share status and error information. You can use the status information to detect network trouble. ICMP messages are encapsulated within IP datagrams so that they can be routed throughout a network. Two programs that use ICMP messages are ping and traceroute (Linux) or tracert (Windows).
Address Resolution Protocol (ARP)
Address Resolution Protocol (ARP) provides logical-address-to-physical address resolution on a TCP/IP network, which is converting the IP address to a MAC address.
To accomplish this feat, ARP sends out a broadcast message with an ARP request packet that contains the IP address of the system it is trying to find. All systems on the local network see the message and the system that owns the IP address for which ARP is looking replies by sending its physical address to the originating system in an ARP reply packet. The physical/IP address combo is then stored in the ARP cache of the originating system for future use.
Hypertext Transfer Protocol (HTTP)
The Hypertext Transfer Protocol (HTTP) is used on the Internet to allow clients to request web pages from web servers and to allow client interaction with those web servers. HTTP is a stateless protocol, meaning that the web servers are unaware of what a client has or has not requested and cannot track users who have requested specific content. This system does not allow for good interaction with the web server but does allow for retrieving the HTML pages stored on web sites. To aid in tracking client requests, we use cookies—small files stored on the client computer that allows the web server to store data on the client that the client will send back with each request to the server.
Hypertext Transfer Protocol, Secure (HTTPS)
The Hypertext Transfer Protocol, Secure (HTTPS) allows you to connect to a web site and to receive and send content in an encrypted format using Secure Sockets Layer (SSL), or its successor Transport Layer Security (TLS). HTTPS is most commonly used on e-commerce sites to allow you to send personal information, especially credit card numbers and other confidential data, without worrying that an Internet hacker is viewing this information.
Domain Name System (DNS)
The Domain Name System (DNS) service is used to convert fully qualified domain names (FQDNs) to IP addresses. When accessing Internet sites or servers on the Internet, you use names such as www.gleneclarke.com to connect to the system. Before a connection is attempted, your system queries a DNS server over UDP port 53 and asks the DNS server for the IP address of that system. Once your system has the IP address of the target system, it makes a connection to that system by using the IP address.
Simple Mail Transfer Protocol (SMTP)
The Simple Mail Transfer Protocol (SMTP) is used to send or route mail over a TCP/IP network such as the Internet. Most e-mail server products support SMTP (TCP port 25) in order to send e-mail out of the corporation and onto
the Internet.
Post Office Protocol version 3 (POP3)
The Post Office Protocol version 3 (POP3) is the Internet protocol used to retrieve e-mail from a mail server down to the POP3 client over TCP port 110. The e-mail is “popped” or downloaded to the client after the client has been authenticated to its mailbox. POP3 has limited capabilities as far as folder support is concerned. A POP3 client supports only an inbox, an outbox,
sent items, and deleted items. If additional folder support is required, you would need to use an IMAP4 client.
Internet Message Access Protocol version 4 (IMAP4)
The Internet Message Access Protocol version 4 (IMAP4) is another protocol similar to POP3 that allows clients to retrieve messages from a mail server using TCP port 143. IMAP4 allows additional folders other than the four basic ones provided with POP3. For example, you can use an IMAP4 client to connect to public folders stored on a Microsoft Exchange Server.
Simple Network Management Protocol (SNMP)
The Simple Network Management Protocol (SNMP) is an Internet standard that provides a simple method for remotely managing virtually any network device that supports SNMP over UDP port 161. A network device can be a network card in a server, a program or service running on a server, or a network device such as a hub, switch, or router.
