Managing IOS Configuration Snippets

Tim Durack tdurack at
Thu Feb 27 14:36:54 UTC 2014

On Thu, Feb 27, 2014 at 8:58 AM, Saku Ytti <saku at> wrote:

> On (2014-02-26 17:37 -0500), Robert Drake wrote:
> > Consider looking at Tail-F's NCS, which according to marketing
> > presentations appears to do everything I want right now.  I'd like
> > to believe them but I don't have any money so I can't test it out.
> > :)
> Tail-F is probably least bad option out there.
> In configuration management, this is super easy:
> DB => Template => Network
> This is super hard:
> Network => DB
> The first one keeps all platform specific logic in flat ascii files filled
> with variables from template.
> When you introduce new product, feature, vendor to network, you only add
> new
> ascii templates, extremely easy, no platform-specific logic in DB.
> The second one every little change in network, requires parser changes
> trying
> to model it back to DB. This is not sustainable. We can kid ourselves that
> NetCONF/YANG will solve this, but they won't. SNMP is old technology, when
> new
> feature comes to vendor, it may take _years_ before MIB comes. There is no
> reason to suspect you will be able to get feature out via NetCONF just
> because
> it is there. And if you can't do it 100% then you have to write parser
> which
> can understand it.
> You only need the second one, in case 100% is not from DB. But it is
> actually
> trivial to produce 100% from DB. You don't want DB to model base
> configuration, that's lot of work for no gain, that'll come from template
> or
> at most DB vendor-specific-blob.
> Then after you push configuration from DB to network, you immediately
> collect
> configuration and create relation of DB-config 2 network-config, now you
> can
> keep ensuring network has correct config. If it does not have, you don't
> know
> why not, you can't fix the error itself, but you can repovision whole box,
> so
> you do get configuration conformance check, it's just very crude.
> But the alternative, trying to understand network config, is just never
> ending
> path to to pain. If someone is going to do it, model it to python or ruby
> and put it in github so others can contribute and we don't need to do it
> alone.
> --
>   ++ytti
Agree with this.

We started out with rancid, quickly moved to a homebrew scp and git backed
system with webgit/cgit as the user interface. If you are lucky your
network equipment supports "advanced features" like ssh keys. If not, you
might be stuck using sshpass to ease config collection.

Built a config parsing system that would decompose monolithic configs into
configlet files. Md5sum the file and use as part of the filename. You can
then see "version" information for parts of the config tree. Quickly
realized that maintaining this system is a full time job, due to the
advanced status of network equipment software...

Now looking at Tail-F NCS. Demo is impressive. I'm hopeful.

Stating the obvious: the software running on most network equipment is of
poor quality. The tools to manage this are a combination of high quality
engineers and homebrew tools. Vendor tools are of a similar quality to the
equipment software. I'd like to think "SDN" is an attempt to improve this,
but I have my doubts.


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