YANG and XML are central to Clixon. Yang modules are used as a specification for encoding XML or JSON configuration and state data. The YANG spec is also used to generate an interactive CLI, NETCONF and RESTCONF clients, as well as the format of the XML datastore.
The YANG standards that Clixon follows include:
Clixon deviates from the YANG standard as follows (reference to RFC7950 sections in parenthesis):
- augment in a uses sub-clause (7.17) (module-level augment is implemented)
- instance-identifier type (9.13)
- status (7.21.2)
- YIN (13)
- Default values on leaf-lists (7.7.2)
- error-message is not implemented as sub-statement of “range”, “length” and “pattern”
Clixon supports the following extended XPath functions (10):
The following extended XPath functions are not supported (10):
See also support of standard XPath functions XML and XPath
4.1.1 Regular expressions¶
Clixon supports two regular expression engines:
- The default method, The regexps:s are translated to posix before matching with the standard Linux regex engine. This translation is not complete but can be considered “good-enough” for most yang use-cases. For reference, all standard Yang models have been tested.
- Libxml2 uses the XSD regex engine. This is a complete XSD engine but you need to compile and link with libxml2 which may add overhead.
To use libxml2 in clixon you need enable libxml2 in both cligen and clixon:
./configure --with-libxml2 # both cligen and clixon
You then need to set the following configure option:
Clixon implements Defining and Using Metadata with YANG RFC 7952 for XML and JSON.
This means that Yang-derived meta-data defined with:
is defined for attributes so that they can be mapped from XML to JSON, for example.
Assigned meta-data are hardcoded. The following attributes are defined:
- ietf-netconf-with-defaults:default from RFC 6243 / RFC 8040
Clixon implements the following NETCONF RFC:s:
- RFC 5277: NETCONF Event Notifications
- RFC 6241: NETCONF Configuration Protocol
- RFC 6242: Using the NETCONF Configuration Protocol over Secure Shell (SSH)
- RFC 8071: NETCONF Call Home and RESTCONF Call Home. NETCONF over SSH (external) and RESTCONF call home (internal) over TLS are implemented.
- RFC 8341: Network Configuration Access Control Model (NACM). Notification not implemented.
- RFC 6243 With-defaults Capability for NETCONF
The following RFC6241 capabilities/features are hardcoded in Clixon:
- :candidate (RFC6241 8.3)
- :validate (RFC6241 8.6)
- :xpath (RFC6241 8.9)
- :notification (RFC5277)
- :with-defaults (RFC6243)
The following features are optional and can be enabled by setting CLICON_FEATURE:
- :startup (RFC6241 8.7)
- :writable-running (RFC6241 8.2) - just write to running, no commit semantics
Clixon does not support the following NETCONF features:
- :url capability
- copy-config source config
- edit-config testopts
- edit-config erropts
- edit-config config-text
- edit-config operation
Further, in get-config filter expressions, the RFC6241 XPath Capability is preferred over default subtrees. This has two reasons:
- XPath has better performance since the underlying system uses xpath, and subtree filtering is done after the complete tree is retrieved.
- Subtree filtering does not support namespaces yet.
Clixon supports netconf locks in default settings but not if
4.2.1 Default handling¶
Clixon treats default data according to what is defined as explicit basic mode in RFC 6243: With-defaults Capability for NETCONF, i.e. the server consider any data node that is not explicitly set data to be default data.
The :with-defaults capability indicates that clixon default behaviour is explicit and also indicates that additional retrieval modes supported by the server are:.
Clixon supports the two RESTCONF compile-time variants: FCGI and Native. Both implements RFC 8040: RESTCONF Protocol.
The following features of RFC8040 are supported:
- OPTIONS, HEAD, GET, POST, PUT, DELETE, PATCH
- Stream notifications (Sec 6)
- Query parameters: insert, point, content, depth, start-time, stop-time and with-defaults.
- Monitoring (Sec 9)
The following features are not implemented:
- Query parameters: fields and filter
RESTCONF event notification as described in RFC7950 section 6 is supported as follows:
- is not supported by native
- is supported by FCGI
RFC 8072: YANG Patch Media Type is not implemented.
In the native mode, Clixon also supports:
- HTTP/1.1 as transport using a native implementation (RFC 7230),
- HTTP/2 as transport implemented by libnghttp2 (RFC7540),
- Transport Layer Security (TLS) implemented by libopenssl,
- ALPN as defined in RFC 7301 for http/1, http/2 protocol selection by libopenssl
The Clixon-SNMP frontend implements the MIB-YANG mapping as defined in RFC 6643.
4.5 XML and XPath¶
Clixon has its own implementation of XML and XPath. See more in the detailed API reference.
The XML-related standards include:
Clixon XML supports version and UTF-8 only.
The following XPath axes are supported:
The following xpath axes are not supported: preceding, preceding_sibling, namespace, following_sibling, following, ancestor,ancestor_or_self, and attribute
The following XPath functions as defined in Section 2.3 / 4 of the XPath 1.0 standard are supported:
The following standard XPath functions are not supported:
The pagination solution is based on the following drafts:
See Pagination section for more info.
Unicode is not supported in YANG and XML.