README.netns

This text comments on the partial support for network namespaces in net-snmp.

Background:
	When you move one of your Linux network interfaces into a network namespace,
	net-snmp will no longer be able to collect data on that interface.
	This modification starts to add some network-namespace awareness to the
	if-mib part of net-snmp.
	The new behaviour is disabled by default. You can enable it by setting
	environment variable $SNMP_NETNS to "1".

Approach:
	* enumerate namespaces by accessing /var/run/netns/
	* wrapping the appropriate netlink and ioctl action into a pair of setns() calls
	* prefixing exposed interface names with the name of the netns and a "/"
	* limit interface indices to SNMP_IFINDEX_BITS bits and use the remainder to
	  store the netns index; this is done to achieve uniqueness for interface indices
	  (namespace names are lexicographically sorted to get some persistence)

Example Output:
	.1.3.6.1.2.1.2.2.1.2.1 = STRING: lo
	.1.3.6.1.2.1.2.2.1.2.2 = STRING: em1
	.1.3.6.1.2.1.2.2.1.2.3 = STRING: docker0
	.1.3.6.1.2.1.2.2.1.2.5 = STRING: tap0
	.1.3.6.1.2.1.2.2.1.2.1025 = STRING: test3/lo
	.1.3.6.1.2.1.2.2.1.2.1028 = STRING: test3/tap0
	.1.3.6.1.2.1.2.2.1.2.2049 = STRING: test2/lo
	.1.3.6.1.2.1.2.2.1.2.2052 = STRING: test2/tap0

	(In this example there are 2 non-global namespaces "test2" and "test3".)

Author / Copyright:
	Travelping GmbH (http://travelping.com) -- Tobias Hintze <tobias.hintze+ip@travelping.com>