Exchanging <hello> Tag Elements

The NETCONF server and client application each begin by emitting a <hello> tag element to specify which operations, or capabilities, they support from among those defined in the NETCONF specification. The <hello> tag element encloses the <capabilities> tag element and the <session-id> tag element, which specifies the UNIX process ID (PID) of the NETCONF server for the session. Within the <capabilities> tag element, a <capability> tag element specifies each supported function.

The client application must emit the <hello> tag element before any other tag element during the NETCONF session, and must not emit it more than once.

Each capability defined in the NETCONF specification is represented in a <capability> tag element by a uniform resource name (URN). Capabilities defined by individual vendors are represented by uniform resource identifiers (URIs), which can be URNs or URLs. The NETCONF API for JUNOS Release 9.4 emits the following <hello> tag element (each <capability> tag element appears on three lines for legibility only):

(For information about the ]]>]]> character sequence, see Generating Well-Formed XML Documents.)

The URIs in the <hello> tag element indicate the following supported capabilities:

• urn:ietf:params:xml:ns:netconf:base:1.0—The NETCONF server supports the basic NETCONF operations and tag elements defined in this namespace.
• urn:ietf:params:xml:ns:netconf:capability:candidate:1.0—The NETCONF server supports operations on a candidate configuration. For more information, see Requesting Information from the Committed or Candidate Configuration and Committing Configurations.
• urn:ietf:params:xml:ns:netconf:capability:confirmed-commit:1.0—The NETCONF server supports confirmed commit operations. For more information, see Committing the Candidate Configuration Only After Confirmation.
• urn:ietf:params:xml:ns:netconf:capability:validate:1.0—The NETCONF server supports the validation operation, which verifies the syntactic correctness of a configuration without actually committing it. For more information, see Verifying a Configuration Before Committing It.
• urn:ietf:params:xml:ns:netconf:capability:url:1.0?protocol=http,ftp,file—The NETCONF server accepts configuration data stored in a file. It can retrieve files both from its local filesystem (indicated by the file option in the URN) and from remote machines by using Hypertext Transfer Protocol (HTTP) or FTP (indicated by the http and ftp options in the URN). For more information, see Referencing Configuration Data Files.
• http://xml.juniper.net/netconf/junos/1.0—The NETCONF server supports the operations defined in the JUNOS XML API for requesting and changing operational information (the tag elements in the JUNOS XML API Operational Reference). The NETCONF server also supports operations in the JUNOScript API for requesting or changing configuration information, but NETCONF client applications must use only native NETCONF operations for configuration functions. The semantics of corresponding JUNOScript and NETCONF operations are not necessarily identical, so using JUNOScript configuration operations can lead to unexpected results.

To comply with the NETCONF specification, the client application also emits a <hello> tag element to define the capabilities it supports. It does not include the <session-id> tag element:

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