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Re: Writable SNMP
From: Christopher Morrow <morrowc.lists () gmail com>
Date: Tue, 6 Dec 2011 15:00:27 -0500

On Tue, Dec 6, 2011 at 11:49 AM, Keegan Holley
<keegan.holley () sungard com> wrote:
2011/12/6 Christopher Morrow <morrowc.lists () gmail com>

On Tue, Dec 6, 2011 at 11:16 AM, Jared Mauch <jared () puck nether net>

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
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
as new ones come up.  Writable SNMP seems like an easier way to deal
scripted configuration changes as well as information gathering.
Admittedly, you will have to deal with proprietary mibs and reformat
data once it's returned.  Most people consider it insecure, but in
it's no worse than any other management protocol.  Yes I know netconf
better, but in most circles I'd have problems explaining what netconf
why it's better and that I'm not making it up.  So I'll take what I can

Some of the problems is the bulk nature of some config changes (or
nature on those that support atomic operations) have been harder to

Anyone that has spent any quantity of time with ASN.1 generally would

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
to walk/revisit a large number of elements to make things happen

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

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

I think the general feeling is that snmp is udp so it's spoofable and
your perimeter acls will never be 100% (or rather, are you willing to
risk them not being 100%?)

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 assume.

read is 'painful', write can be downright deadly (to your SLAs).

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

lol, that could be a problem.

yea, I bet the number of people that test, at scale/operations-pace,
snmp WRITE is countable on a single hand.

... (didn't the snmp incident in 2002 teach us

Please elaborate.


oh, 2001... memory lag :(

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