During a session with the database, the client uses Oracle Call Interface (OCI) to interact with the database server. OCI is a software component that provides an interface between the application and SQL.

Character set differences can occur if the client and database server run on different operating systems. The presentation layer resolves any differences. It is optimized for each connection to perform conversion when required.

The presentation layer used by client/server applications is Two-Task Common (TTC). TTC provides character set and data type conversion between different character sets or formats on the client and database server. At the time of initial connection, TTC is responsible for evaluating differences in internal data and character set representations and determining whether conversions are required for the two computers to communicate.

The Oracle Net foundation layer is responsible for establishing and maintaining the connection between the client application and database server, as well as exchanging messages between them. The Oracle Net foundation layer can perform these tasks because of Transparent Network Substrate (TNS) technology. TNS provides a single, common interface for all industry-standard OSI transport and network layer protocols. TNS enables peer-to-peer application connectivity, where two or more computers can communicate with each other directly, without the need for any intermediary devices.

On the client side, the Oracle Net foundation layer receives client application requests and resolves all generic computer-level connectivity issues, such as:

• The location of the database server or destination

• How many protocols are involved in the connection

• How to handle interrupts between client and database server based on the capabilities of each

On the server side, the Oracle Net foundation layer performs the same tasks as it does on the client side. It also works with the listener to receive incoming connection requests.

In addition to establishing and maintaining connections, the Oracle Net foundation layer communicates with naming methods to resolve names and uses security services to ensure secure connections.

Oracle protocol support layer is positioned at the lowest layer of the Oracle Net foundation layer. It is responsible for mapping TNS functionality to industry-standard protocols used in the client/server connection. This layer supports the following network protocols:

• TCP/IP (IPv4 and IPv6)

• TCP/IP with SSL

• Named Pipes

• Sockets Direct Protocol (SDP)

• Exadirect

All Oracle software in the client/server connection process requires an existing network protocol stack to establish the computer-level connection between the two computers for the transport layer. The network protocol is responsible for transporting data from the client computer to the database server computer, at which point the data is passed to the server-side Oracle protocol support layer.

Oracle Database supports the standard IPv6 address notations specified by RFC 2732. A 128-bit IP address is generally represented as 8 groups of 4 hexadecimal digits, with the colon (:) symbol as the group separator. For example, the following address is in a valid IPv6 format:

2001:0db8:0000:0000:0000:0000:200C:417A

Each hexadecimal digit in the address represents 4 bits, so each group in the address represents 16 bits. The following addresses represent the first and last hosts in the 2001:0db8:0000:0000 subnet:

2001:0db8:0000:0000:0000:0000:0000:0000
2001:0db8:0000:0000:FFFF:FFFF:FFFF:FFFF

In shorthand notation, consecutive zero fields can be compressed with a double colon (::) separator, as shown in the following equivalent notations:

2001:0db8:0:0::200C:417A
2001:0db8::200C:417A
2001:DB8::200C:417A

• CIDR Notation
  
• IPv6 Addresses in URLs
  
• IPv4-Mapped Addresses
  

http://[2001:0db8:0:0:8:800:200C:417A]
http://[2001:0db8:0:0:8:800:200C:417A]:80/index.html

0000:0000:0000:0000:0000:FFFF:C0A8:0226
0000:0000:0000:0000:0000:FFFF:192.0.2.38
::FFFF:192.0.2.38

A host may have different IPv4 and IPv6 interface configurations. The following configurations are possible for a host:

• Only an IPv4 interface, in which case the host is an IPv4-only host.

• Only an IPv6 interface, in which case the host is an IPv6-only host.

• Both an IPv4 and IPv6 interface, in which case the host is a dual-stack host.

A single host may also use different types of IP address. For example, a domain name server may associate a dual-stack host both by an IPv4 and an IPv6 address or only an IPv6 address. The IP address configurations that are not supported are the following:

• An IPv4-only host cannot use an IPv6 address.

• An IPv6-only host cannot use an IPv4 address.

Figure 4-5 shows possible host and interface configurations. The dual-stack host in the center of the diagram can communicate with IPv4 hosts over IPv4 and with IPv6 hosts over IPv6.

The network connectivity of a host refers to its ability to communicate with another host over a network. For example, if a dual-stack client must communicate with an IPv6-only server, then the network and router must make end-to-end communication between these hosts possible.

A client or server host is IPv6-capable if it meets the following criteria:

• It has a configured IPv6 interface.

• It can connect to other hosts using the IPv6 protocol.

The IPv6 capability of a host is partially dependent on the network and partially dependent on its interface and address configuration. Figure 4-6 shows the possibilities for connectivity in a client/server network. For example, an IPv4-only host can connect to either an IPv4-only or dual-stack server, but not an IPv6-only server. Both dedicated and shared server modes are supported.

Table 4-1 summarizes the IP protocols used for client/server connectivity with different host and network configurations.

Components in this release of Oracle Database 12c support IPv6 in the configurations described in "IPv6 Network Connectivity", with the following exception:

• Oracle Clusterware for private and ASM networks