ZyXEL Communications USG110, Руководство пользователя

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Chapter 43 Object
ZyWALL USG Series User’s Guide
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Computers use Transmission Control Protocol (TCP, IP protocol 6) and User Datagram Protocol (UDP, IP
protocol 17) to exchange data with each other. TCP guarantees reliable delivery but is slower and more
complex. Some uses are FTP, HTTP, SMTP, and TELNET. UDP is simpler and faster but is less reliable. Some
uses are DHCP, DNS, RIP, and SNMP.
TCP creates connections between computers to exchange data. Once the connection is established,
the computers exchange data. If data arrives out of sequence or is missing, TCP puts it in sequence or
waits for the data to be re-transmitted. Then, the connection is terminated.
In contrast, computers use UDP to send short messages to each other. There is no guarantee that the
messages arrive in sequence or that the messages arrive at all.
Both TCP and UDP use ports to identify the source and destination. Each port is a 16-bit number. Some
port numbers have been standardized and are used by low-level system processes; many others have
no particular meaning.
Unlike TCP and UDP, Internet Control Message Protocol (ICMP, IP protocol 1) is mainly used to send error
messages or to investigate problems. For example, ICMP is used to send the response if a computer
cannot be reached. Another use is ping. ICMP does not guarantee delivery, but networks often treat
ICMP messages differently, sometimes looking at the message itself to decide where to send it.
Service Objects and Service Groups
Use service objects to define IP protocols.
• TCP applications
• UDP applications
• ICMP messages
• user-defined services (for other types of IP protocols)
These objects are used in policy routes, security policies, and IDP profiles.
Use service groups when you want to create the same rule for several services, instead of creating
separate rules for each service. Service groups may consist of services and other service groups. The
sequence of members in the service group is not important.
43.8.2 The Service Summary Screen
The Service summary screen provides a summary of all services and their definitions. In addition, this
screen allows you to add, edit, and remove services.
To access this screen, log in to the Web Configurator, and click Configuration > Object > Service >
Service . Click a column’s heading cell to sort the table entries by that column’s criteria. Click the
heading cell again to reverse the sort order.