Using Groups in Modules with pre_transform Hooks

netlab supports groups generated from BGP AS numbers to simplify setting parameters for all members of an AS. Those groups are calculated in the module_pre_transform hook of BGP configuration module. It’s thus impossible to copy structures into node data before the pre_transform hooks have been executed, as the group membership isn’t fully evaluated until after the BGP module_pre_transform hook completes.

Modules that use pre_transform hooks to modify global- or node data structures must therefore take special precautions to cope with objects that could be defined based on groups.node_data. Two modules that have to deal with this are the VLAN and VRF configuration modules – vrfs or vlans entries could be created from or entries.

Both modules use the same approach:

  • Create empty topology-level VRFs or VLANs from VRF/VLAN names mentioned in vlans or vrfs attributes of at the beginning of pre_transform hook.

  • Copy id/vni (for VLANs) or rd/import/export attributes (for VRFs) into topology-level vlans/vrfs from node_data entries.

  • When needed, auto-generate VLAN/VNI or RD/RT data for those objects in the pre_transform hook

  • Merge topology vlans/vrfs with node vlans/vrfs in the post_transform hook (any hook after the pre_transform hook would do).