Re: number of ip addresses through a router

On 24 March 2011 17:31, Jaime Lozano <[email protected]> wrote:
> Hi again,
> Scott I'm not such optimistic. I don't know if there is any MIBs guru listening.

I'm not sure that I'd claim to be a MIB guru,
but I'll offer some general thoughts.

Whenever there's a question about
   "how can I find a MIB for X?"
       the first thing to consider is whether the system in question is likely
to be keeping track of X in the first place.

Remember that SNMP isn't some "black box" that will magically provide
all of the management data that you might be interested in.  It essentially
just provides a way of getting hold of whatever information the underlying
system might have.   If the box doesn't record something, then SNMP
won't let you see it.

One useful way of checking this might be to see if the system has a
Command Line Interface - and if so, whether the information of interest
is visible there.   If it is, then there's a reasonable change that it may
also be available via SNMP (either using a standard MIB, or a vendor
specific one).   But if that information is not visible via the CLI, then
that's a possible indication that the system simply doesn't keep track
of this information, and hence it won't be available via SNMP either.

Other things to consider are whether this information is necessary for
the basic operation of the equipment - if so, then it *must* be stored
somewhere, in order for the box to do its primary job.  And hence
it's not unreasonable to hope that it might be accessible as management
information as well.

Also, think about the overheads involved in holding this information
(particularly if you're looking at detailed historical records).   The
larger the amount of data concerned, the less likely this is going to
be retained.
   Keeping track of the number of packets going through a router is
fairly simple, and the overheads are pretty small - so it's not a problem
in maintaining this information.    Keeping a list of all the hosts that
this box has ever talked to (perhaps with per-host counters) is a
somewhat more onerous task, and it's a matter for debate as to whether
the benefits outweigh the cost.
   Keeping track of who has been talking to who (i.e. a full connection
matrix) is probably going to be too much of an overhead to be worth
while.  Certainly for historical data - though a snapshot of the currently
active connections (however that is defined) *might* be needed for proper
operation, and hence perhaps be accessible via SNMP.


Now I haven't looked at any of the information that Juniper provide
(either MIBs or administrator manuals), so I've no feel for what information
is likely to be available.  But hopefully these comments should give you
some idea of the issues involved, and what is realistic to expect (or not!)

Dave

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