Writable SNMP

Keegan Holley keegan.holley at sungard.com
Tue Dec 6 16:49:05 UTC 2011

2011/12/6 Christopher Morrow <morrowc.lists at gmail.com>

> On Tue, Dec 6, 2011 at 11:16 AM, Jared Mauch <jared at puck.nether.net>
> wrote:
> >
> > On Dec 6, 2011, at 11:07 AM, Keegan Holley wrote:
> >
> >> For a few years now I been wondering why more networks do not use
> writable
> >> SNMP.  Most automation solutions actually script a login to the various
> >> equipment.  This comes with extra code for different vendors, different
> >> prompts and any quirk that the developer is aware of and constant
> patches
> >> as new ones come up.  Writable SNMP seems like an easier way to deal
> with
> >> scripted configuration changes as well as information gathering.
> >> Admittedly, you will have to deal with proprietary mibs and reformat the
> >> data once it's returned.  Most people consider it insecure, but in
> reality
> >> it's no worse than any other management protocol.  Yes I know netconf is
> >> better, but in most circles I'd have problems explaining what netconf
> is,
> >> why it's better and that I'm not making it up.  So I'll take what I can
> get.
> >
> > Some of the problems is the bulk nature of some config changes (or
> transactional
> > nature on those that support atomic operations) have been harder to
> automate.
> >
> > Anyone that has spent any quantity of time with ASN.1 generally would
> agree.
> >
> > I recall some bay networks gear you could only program with the proper
> > as the cli was basically a SNMP-SET operation on the device.
> yea... same with cascade devices... icky things (both bay and cascade!)
> > The errors/feedback tends to be very poor over SNMP as well as you may
> need
> > to walk/revisit a large number of elements to make things happen
> properly.
> fun story/fact, you can send an snmp write to the broadcast address of
> a network of NT (at least, probably also post-nt versions of the OS)
> machines, and set their default-ttl to some arbitrary number. "Your
> network is too chatty... not anymore! now your internet is 5 hops
> across!"

Let's leave the legacy boxes out of this.  Remember that SNMP bug that
could keel over a cisco router?  I forget the details other than the guy
who wrote c code at black hat to kill routers after cisco refused to patch.

> > Have you had a good experience with using SNMP-Write?  I have not.
> long ago, in a network far away (not on the interwebs) we used snmp
> write to trigger a tftp config load. It worked nicely... I'm fairly
> certain I'd not do this on an internet connected network today though.

I can see the other comments about interactive commands and bulk
read/writes, but what's the harm of doing it on internet connected boxes
vs. non-internet boxes.  Just about everyone uses snmp reads in the
interwebs and as such filters it at their edges and hopefully on each
platform.  You'd secure it the same way you'd secure readable SNMP I

> Also, who tests snmp WRITE in their code? at scale? for daily
> operations tasks?

lol, that could be a problem.

> ... (didn't the snmp incident in 2002 teach us
> something?)
> Please elaborate.

> -chris

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