Subject: Re: new version of the dhcp server mib

From: "Bernard Aboba" <[email-masked]>
Date: Sat, 20 Feb 1999 02:52:25 -0500 (EST)

Some comments on the DHCP server MIB:

1. Since MIB counters roll over, they are used for measuring differences and
rates. Can you explain how counters such as bootpStatSumSquaresArrivalTime
would be used to compute a difference or rate? After these counters roll, it
would seem to me that they would be useless for computing the variance and
standard deviation.

2. There are no MIB variables that are relevant to diagnosing authenticated
DHCP. Some of the things you might want to measure include:
a. Bad authenticators by protocol and algorithm
b. Unknown algorithms or protocols

3. There are no MIB variables relevant to DHCP relay agents. While a relay
agent is a separate entity it doesn't seem worthwhile to have a separate MIB
for them. I'd suggest a separate conformance group for variables relevant to
relay agents.

4. This MIB has IPv4 dependencies. Rather than using the IpAddress type,
 it would be preferrable to use the NetworkAddress type, which would allow
 the MIB to be useful for IPv6 as well.

---

From: "Hibbs, R BARR (PB-rbhibbs)" <[email-masked]>
Date: Mon, 22 Feb 1999 12:17:35 -0500 (EST)

----------
From:  Bernard Aboba [SMTP:[email-masked]]
Sent:  Friday, February 19, 1999 11:53 PM
To:  Multiple recipients of list
Subject:  Re: new version of the dhcp server mib

..in particular, all of the sum of squares variables are useful only for
computation of the variance and standard deviation.  While someone,
somewhere might employ statisticians as network administrators, it seems
highly unlikely to the authors that any measures of these statistics that
involve rate of change with respect to time (essentially the second
derivative of message counters) will have practical application.

..for example, the inter-arrival rate for, say, BOOTP messages in general
can be computed from the sum of BOOTP message inter-arrival time and number
of messages received during a measurement interval (the interval itself
calculated from the difference in SysUpTime).  To ensure completely
comparable statistics, the authors proposed that the server capture both the
sum of inter-arrival times and the sum-of-squares.  By making a single
simplifying assumption, that the samples in question represent the entire
series of samples (which, for the interval in question is completely
correct), the variance can be calculated directly from the sum-of-squares
variable and number of messages.

..what more will most system or network administrators want?  In the
authors' experience, if an administrator even asks once a month what the
"average" of some message rate is, that shows a great interest in the
subject.  While we don't intend to be flippant on the topic, our reason for
inclusion of these variables was to give the administrators some reliable
tools for determining server utilization -- the statistics for calculating
mean and variance serve as "confidence builders" for the various first-order
rates that may be calculated from message counters rather than an end in
themselves.

..the authors will re-examine the language used to describe the variables
and their usage to ensure that when counters roll-over all related variables
are appropriately reset (roll over) as well to maintain consistent
statistics 

..I'm not sure what you mean by "authenticated DHCP."  As we have, as yet,
no RFCs to cover authentication of DHCP, it seems inappropriate to introduce
any variables that refer to as yet undefined parameters.

..yes, the MIB was intended only to cover DHCP servers -- if that
limitation was not discussed in the introductory matters, we will correct
the omission

..this is intended only for IPv4 and DHCPv4 servers -- as that limitation
is apparently not clear, we will reexamine the wording of the introductory
matters to clarify the restriction.

--Barr