Topology File Transformation

netlab performs a complex data transformation of the lab topology file to get device-level data that is then used to create output files (Ansible inventory, Vagranfile…).

The data transformation has three major steps:

• Setup

• Global, node and link data transformation

• Final Steps and Cleanup

Setup Phase

• Read topology file

• Read customer and system default settings (topology-defaults.yml) and merge them with the topology file (netsim.read_topology.load)

• Perform the basic sanity checks (netsim.augment.topology.topology_sanity_check)

• Check minimum netlab version (netsim.utils.versioning.check_topology_version)

• Adjust the nodes data structure: transform list of strings into a dictionary with empty values (netsim.augment.nodes.create_node_dict)

• Check basic group data structures and auto-create nodes from group members (augment.groups.precheck_groups)

• Initialize plugin system: load all plugins listed in the plugin top-level element (netsim.augment.plugin.init)

• Execute plugin topology_expand hook (netsim.augment.plugin.execute) for plugins that augment lab topology structures (example: Build a Leaf-and-Spine Fabric)

• Initialize the link list (netsim.augment.links.links_init)

  • Transform strings or lists of nodes into link dictionaries (netsim.augment.links.adjust_link_list)

  • Set link names (netsim.augment.links.set_linknames)

  • Expand link groups (netsim.augment.links.expand_groups)

  • Set linkindex attributes (netsim.augment.links.set_linkindex)

• Expand topology components (netsim.augment.components.expand_components)

• Execute plugin init hook (netsim.augment.plugin.execute)

• Process external tools (augment.tools.process_tools)

• Check for the presence of required top-level topology elements (netsim.augment.topology.check_required_elements)

• Initialize attribute validation (netsim.data.validate.init_validation)

• Complete node group initialization (netsim.augment.groups.init_groups):

  • Check the attributes in the group data structures

  • Add group members based on nodes’ group attribute

  • Check recursive groups

  • Copy group device and module attribute into nodes

  • Copy group node_data into nodes

  • Process bgp.as_list to get bgp.as node attributes

  • Create BGP autogroups (groups based on BGP AS numbers)

  • Copy node_data from BGP autogroups into nodes

• Adjust global parameters (netsim.augment.topology.adjust_global_parameters):

  • Set provider top-level element

  • Merge provider-specific device and addressing defaults with global defaults

• Load provider plugin (netsim.providers._Provider.load)

• Augment node provider data: set node device type, select VM/container image, copy provider-specific node data into node dictionary (netsim.augment.nodes.augment_node_provider_data)

• Augment node data with global defaults that are not part of configuration modules (example: MTU) (augment.nodes.augment_node_system_data)

• Setup addressing pools (netsim.addressing.setup)

Global Data Transformation

• Execute pre_transform plugin hooks (netsim.augment.plugin.execute)

• Execute pre_transform module adjustments (netsim.modules.adjust_modules)

• Execute pre_transform node- and link-level module hooks

• Validate top-level topology elements (netsim.augment.topology.check_global_elements)

Node Data Transformation

• Execute pre_node_transform plugin hooks (netsim.augment.plugin.execute)

• Execute pre_node_transform module hooks (netsim.modules.pre_node_transform)

• Set unique ID for every node

• Get loopback IP addresses, management MAC address, and management IP addresses (netsim.augment.nodes.augment_mgmt_if) from loopback and mgmt address pools

• Execute augment_node_data provider hook (example: set hostname for containerlab nodes)

• Execute post_node_transform plugin and module hooks

Link Data Transformation

• Execute pre_link_transform plugin hooks (netsim.augment.plugin.execute)

• Execute pre_link_transform module hooks (netsim.modules.pre_link_transform)

• Check link attributes (netsim.augment.links.check_link_attributes)

• Set link type based on the number of devices connected to the link (netsim.augment.links.get_link_type)

• Augment link and node interface data (netsim.augment.links.augment_p2p_link and netsim.augment.links.augment_lan_link):

  • If the link does not have a prefix attribute, get link prefix from the corresponding address pool

  • Set node interface IP addresses to first and second subnet IP address for numbered P2P links.

  • Calculate node interface IP addresses from node ID and link prefix for all other links unless the on-link node data contains static IP addresses.

  • Copy link-level configuration module data into node interface data (example: OSPF area)

  • Create interface data for all nodes connected to the link (details).

• Execute post_link_transform plugin and module hooks

Final Steps and Cleanup

• Transform the lab validation data structure (netsim.augment.validate.process_validation)

• Execute post_transform module functions (netsim.modules.post_transform):

  • Check whether the lab devices support modules configured on them (netsim.modules.check_supported_node_devices)

  • Merge select node data into interface data (netsim.modules.copy_node_data_into_interfaces) – this is how interfaces get default ospf.area from the node.

  • Execute post_transform node-level module hook

  • Execute post_transform link-level module hook

  • Sort node module lists in order of module dependencies – a module dependent on another module will be configured after it (netsim.modules.reorder_node_modules)

• Execute post_transform plugin hooks

• Merge group-level and node-level custom deployment templates (netsim.augment.groups.node_config_template)

• Cleanup node data in augment.nodes.cleanup function – at the moment, the function prunes the _daemon_config dictionary.

• Execute post_transform primary provider hook and node-specific node_post_transform provider hooks.

• Process device quirks

• Cleanup links: remove empty links list and _linkname attribute from individual links

• Cleanup groups: remove settings (keys starting with ‘_’) from groups dictionary

• Delete temporary data structures from the topology: list of plugin modules, addressing pools, and pointers to provider modules.

Configuration Module Transformations

netsim.modules module contains these transformations

Adjust Global Module Parameters

• Add global modules to all nodes that do not have a module parameter (augment_node_modules)

• Adjust global module settings: add node-specific modules to global list of modules (adjust_global_modules)

• Execute module-level init hook

• Adjust node module parameters (merge_node_module_params):

  • Add global module parameters to node data

  • Add device-specific module parameters to node data

  • Add system default settings to node data

  Note: In all cases, skip module attributes listed in module no_propagate attribute.

• Adjust global module parameters (merge_global_module_params)

  • Copy system default module settings into topology settings, skipping module attributes listed in module no_propagate attribute.

  • Reorder the global list of modules based on transform_after module attribute

  Note: global module parameters have to be adjusted after node parameters to get the desired node/global/device/default precedence.

• Enable additional module parameters specified in the lab topology

• Check global-, node- and link-level module parameters against the list of allowed module attributes (specified under module settings in system defaults) (check_module_parameters)

• Check module dependencies (for example: SR-MPLS module can only be used with IS-IS module) (check_module_dependencies)

• Execute module-level module_pre_default hook

• Execute node_pre_default hooks

• Execute link_pre_default hooks

Node-Level Module Hooks

For every node using the specified module, execute node_ hook (node_pre_default, node_pre_transform, node_post_transform).

Link-Level Module Hooks

For every link that has at least one node using the specified module, execute link_ hook (link_pre_default, link_pre_transform, link_post_transform).

Debugging the Transformation Process

netlab create command (the primary user of the transformation process) has a hidden --debug option that sets numerous debugging flags, allowing you to debug a subset of transformation components.

The following debugging flags can be used in netlab release 1.6.4[1] to debug the core components:

• all: turn on all debugging flags

• addr: debug addressing pools

• addressing: debug IPAM logic

• cli: debug CLI actions

• defaults: debug user/system defaults

• groups: debug netlab group processing

• links: debug the core link transformation code

• modules: debug generic configuration module routines

• plugin: debug plugin loading process and plugin calls

• template: debug common Jinja2 templating routines

• validate: debug the data validation logic

Some modules are so complex that we gave them separate debugging flags:

• vlan: debug VLAN module

• vrf: debug VRF module

You can also debug components involved in lab management process:

• external: debug invocation of external programs

• libvirt: debug libvirt provider

• status: debug the ‘lab status’ code

• quirks: debug device quirks code

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[1]

Execute netlab create --debug help to display the up-to-date set of debugging flags. The error message will tell you help value is an invalid choice for the --debug argument but also display the valid values.