/etc/libnl-3/classid is in libnl-3-200 3.2.29-0ubuntu3.
This file is owned by root:root, with mode 0o644.
The actual contents of the file can be viewed below.
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#
# ClassID <-> Name Translation Table
#
# This file can be used to assign names to classids for easier reference
# in all libnl tools.
#
# Format:
#   <MAJ:>		<NAME>		# qdisc definition
#   <MAJ:MIN>		<NAME>		# class deifnition
#   <NAME:MIN>		<NAME>		# class definition referencing an
#					  existing qdisc definition.
#
# Example:
#   1:			top		# top -> 1:0
#   top:1		interactive	# interactive -> 1:1
#   top:2		www		# www -> 1:2
#   top:3		bulk		# bulk -> 1:3
#   2:1			test_class	# test_class -> 2:1
#
# Illegal Example:
#   30:1                classD
#   classD:2            invalidClass    # classD refers to a class, not a qdisc
#
###############################################################################
# <CLASSID>		<NAME>
# Reserved default classids
0:0			none
ffff:ffff		root
ffff:fff1		ingress
#
# List your classid definitions here:
#
###############################################################################
# List of auto-generated classids
#
# DO NOT ADD CLASSID DEFINITIONS BELOW THIS LINE
#
# <CLASSID>		<NAME>
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