| Date: | May 25 2000 08:53:24 EDT |
| From: | "Julio Arruda" <[EMAIL PROTECTED]> |
| Subject: | Re: [redewan] [Fwd: NetBIOS Overview.html] |
|
Bom saber que a docmentacao da Bay esta correta.Como eu havia falado, o NetBIOS nao e considerado do nivel de rede, e sim de sessao, rodando sobre algum outro protocolo, neste exemplo, o IP (na figura que voce enviou attached aparece esta "relacao" das camadas). O NetBEUI por outro lado, e' e considerado e NetBIOS sobre o seu proprio transporte, sem um outro protocolo de rede abaixo, sobre um transporte maluco, inclusive nao possuindo capacidade de roteamento. Este NetBIOS "extended user interface" � o que muitos chamam de NetBIOS, o que nem sempre � verdadeiro (todo NetBEUI � NetBIOS, nem todo NetBIOS � NetBEUI).
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Lista de Discuss�o Rede Wan - http://www.networkdesigners.com.br � << File: C:\WINDOWS\TEMP\nsmailM9.gif >> http://support.baynetworks.com/library/tpubs/search/search.htm> << File: C:\WINDOWS\TEMP\nsmailM6.gif >> http://support.baynetworks.com/library/tpubs/html/router/soft1200/117358AA/B_38.HTM> << File: C:\WINDOWS\TEMP\nsmailFO.gif >> http://support.baynetworks.com/library/tpubs/docsrt.htm> << File: C:\WINDOWS\TEMP\nsmail0A.gif >> http://support.baynetworks.com/library/tpubs/html/router/soft1200/117358AA/B_40.HTM> << File: C:\WINDOWS\TEMP\nsmailR! B.gif >> http://support.baynetworks.com/library/tpubs/html/router/soft1200/117358AA/B_7.HTM> << File: C:\WINDOWS\TEMP\nsmailBV.gif >> http://support.baynetworks.com/library/tpubs/html/router/soft1200/117358AA/B_109.HTM> Chapter2 TCP, FTP, TFTP, Telnet, NTP, and NetBIOS over IP Concepts NetBIOS Overview The�Network Basic Input/Output System (NetBIOS) is a session layer communications service used by client and server applications in IBM token ring and PC LAN networks. NetBIOS provides applications with a programming interface for sharing services and information across a variety of lower-layer network protocols, including IP. Figure 2-7 <http://support.baynetworks.com/library/tpubs/html/router/soft1200/117358AA/B_39.HTM#MARKER-9-57> shows the position of NetBIOS and IP in a simple network architecture. << File: C:\WINDOWS\TEMP\nsmail5I.gif >> Figure 2-7.�NetBIOS over IP There are three categories of NetBIOS services: the name service, the session service, and the datagram service. The NetBIOS name service allows an application to: � � The NetBIOS session service allows an application to conduct a reliable, sequenced exchange of messages with another application. The messages can be up to 131,071 bytes long. The NetBIOS datagram service allows an application to exchange datagrams with a specific application or to broadcast datagrams to a group and receive datagrams from the group. Datagrams allow applications to communicate without establishing a session. When a NetBIOS application wants to send information that does not require acknowledgment from the destination application, the application can transmit a NetBIOS datagram. NetBIOS in an IP Environment The NetBIOS name service and datagram service rely on the capability of the underlying network to broadcast name query requests to all NetBIOS applications. In a NetBIOS over IP environment, it is the responsibility of the IP router to ensure that the broadcast queries reach all appropriate network segments. To do this, the router: 1. Analyzes each NetBIOS packet received on any NetBIOS interface to determine whether the packet is a broadcast packet 2. Rebroadcasts each broadcast packet out all appropriate interfaces, except the one on which it was received (readdressing the packet if required) If alternate paths exist between different network segments, broadcasting loops can occur. To prevent such loops, the router: 1. Stamps the data portion of the IP packet with the IP address of the router from which the packet was rebroadcast 2. Parses the IP addresses included in the data portion of the IP packet to determine if the packet has already been rebroadcast by that router In Figure 2-8 <http://support.baynetworks.com/library/tpubs/html/router/soft1200/117358AA/B_39.HTM#MARKER-9-63>, for example, client C on the network connected to router B wishes to communicate with server S, which is located on the network connected to router A. The following steps occur: 1. The client issues a name query request to NetBIOS on the host, specifying the server application by its NetBIOS name. The IP service on the host broadcasts the name query request. 2. Router B receives the name query request, determines that it is a broadcast message, and rebroadcasts it out each of its NetBIOS interfaces (except for the one on which it arrived). 3. Router A receives the broadcast equest and rebroadcasts to its local network. 4. The server on router A receives the IP broadcast request and recognizes its own name. << File: C:\WINDOWS\TEMP\nsmailG4.gif >> Figure 2-8.�Broadcasting a Name Query Request The server responds to the name query request by issuing a positive name query response, containing the IP address of the server, to NetBIOS on the host. The following steps occur ( Figure 2-9 <http://support.baynetworks.com/library/tpubs/html/router/soft1200/117358AA/B_39.HTM#MARKER-9-64>): 1. NetBIOS sends the response to router A as a unicast message. 2. Router A and router B forward the unicast response to the awaiting client. Now that the client has obtained the server's IP address from the name query response, client and server can communicate by exchanging IP messages. << File: C:\WINDOWS\TEMP\nsmailC4.gif >> Figure 2-9.�Returning a Unicast Name Query Response Forwarding Name Queries over an Unnumbered Interface NetBIOS cannot be configured directly on an unnumbered interface. Because of this restriction, name query requests cannot be broadcast over an unnumbered interface. To forward name query requests over unnumbered interfaces, the network administrator configures a static NetBIOS name entry to the proper NetBIOS name server. In this way, name query requests will traverse the unnumbered interfaces as unicast IP packets. NetBIOS in an IP Environment <http://support.baynetworks.com/library/tpubs/html/router/soft1200/117358AA/B_39.HTM#HEADING39-11> Forwarding Name Queries over an Unnumbered Interface <http://support.baynetworks.com/library/tpubs/html/router/soft1200/117358AA/B_39.HTM#HEADING39-31> _____ <http://support.baynetworks.com/library/tpubs/search/search.htm> <http://support.baynetworks.com/library/tpubs/html/router/soft1200/117358AA/B_38.HTM> <http://support.baynetworks.com/library/tpubs/docsrt.htm> <http://support.baynetworks.com/library/tpubs/html/router/soft1200/117358AA/B_40.HTM> <http://support.baynetworks.com/library/tpubs/html/router/soft1200/117358AA/B_7.HTM> <http://support.baynetworks.com/library/tpubs/html/router/soft1200/117358AA/B_109.HTM> Generated with Harlequin WebMaker <http://www.harlequin.com/webmaker> _____ |
