Writable SNMP

Christopher Morrow morrowc.lists at gmail.com
Tue Dec 6 10:28:04 CST 2011


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 OID
> 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!"

> 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.

Also, who tests snmp WRITE in their code? at scale? for daily
operations tasks? ... (didn't the snmp incident in 2002 teach us
something?)

-chris



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