Natv2-MIB has few writable objects, only for control of notifications
and setting of quotas. Thus the module assumes that other means are used
to provision NAT instances and address pools and configure subscriber
data. It seems likely that a mechanism such as the one used to maintain
the integrity of references to ifIndex will be needed to protect
references to NAT instance index, address pool index, and subscriber
index, but that is another topic.
The basic question is how persistent the counter values supported by the
Natv2-MIB should be. Apparently past practice has been to say: "until
the agent restarts", but that isn't really helpful when you are trying
to debug a problem. I distinguish between a counter, which is
cumulative, and a state object, which gives a snapshot at the moment of
reporting.
Would implementors support the following general statement?
"Ideally, counter values are never reset while the parent object (NAT
instance, address pool, subscriber) continues to exist, even across
reboots. Individual implementations may not be able to guarantee this
level of persistence, and SHOULD document the circumstances under which
resets could occur. In any event, all implementations MUST report the
time of last reset in the relevant object in the NAT instance, address
pool, and subscriber tables."
By "reset" I mean setting the counter back to zero. I think that is the
proper action, because it makes discontinuities more obvious than
resetting to a random value.
No comments mean that I will go ahead with this proposal.
Tom Taylor
BACKGROUND
In my present thinking, the conceptual tables in the MIB module come in
two groups, device level, and NAT instance level:
1. Device level: indexed by subscriber index, not by instance index (to
make it easier to reassign subscribers from one NAT instance on the
device to another):
natv2SubscriberTable
-- contains per-subscriber counters
natv2SubscriberIngressInterfaceClassifierTable
-- configuration data only
2. Group indexed by NAT instance, meaningful only while the instance exists:
natv2InstanceTable
-- now incorporates the per-instance counters, thresholds, and
limits that were in separate tables before
natv2NextProtocolTable
-- counters per protocol supported by the NAT instance
natv2PoolTable
-- counters per address pool
natv2PoolRangeTable
-- configuration data only
natv2AddressMapTable
-- state data only
natv2PortMapTable
-- state data only
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