Month: February 2021

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Is Your Network At Risk – Automating the Cisco PSIRT with Genie and Ansible

The security of my network keeps me up at night. Honestly it does. We live in a world where enterprise networks are defending themselves against state-sponsored attacks. But what do attackers look for? Typically, open, well-known, vulnerabilities.

Well, at least to the hackers, attackers, and even script-kiddies, these vulnerabilities are well-known. Those playing defense are often a step or two behind just identifying vulnerabilities – and often times at the mercy of patch-management cycles or operational constraints that prevent them of addressing (patching) these waiting-to-be-exploited holes in the network.

What can we do about it?

The first thing we can do is to stay informed ! But this alone can be a difficult task with a fleet of various platforms running various software versions at scale. How many flavours of Cisco IOS, IOS-XE, and NXOS platforms make up your enterprise? What version are they running? And most importantly is that version compromised?

The old way might be to get e-mail notifications (hurray more e-mail!), maybe RSS-feeds, or go device-by-device, webpage-by-webpage, looking up the version and if it’s open to attack or not.

Do you see why, now, how an enterprise becomes vulnerable? It’s tedious and time-intensive work. And the moment you are done – the data is stale – what, are you going to wake up every day and review threats like this manually? Assign staff to do this? Just accept the risk and do they best you can trying to patch quarterly ?

Enter: Automation

These types of tasks beg to be solved with automation !

So how can you do it?

Let’s just lay out a high level, human language, defined use-case / wish list.

  1. Can we, at scale, go get the current IOS / IOS-XE / NXOS software version from a device?
  2. Then can we send that particular version somewhere to find out if it has been compromised ?
  3. Can we generate a report from the data above?

Technically the above is all feasible; easy even!

  1. Yes, we can use Ansible and the Cisco Genie Parser to capture the current software version
  2. The Cisco Product Security Incident Response Team has incredible, secure, REST APIs available that we can automate with the Ansible URI module
  3. Using Jinja2 templates we can craft business-ready reports

Getting Started

First you need to setup your Cisco.com REST API suite access

Pre-Ansible Development

As with any new REST API I like to start with Postman and then transform working requests into Ansible playbooks.

First, under a new or existing Cisco.com Collection, add a new request called IOS Vulnerabilities

Cisco.com uses OAuth2 authentication mechanism where you first must authenticate against one REST API (https://cloudsso.cisco.com/as/token.oauth2) which provides back authorization Bearer token used to then authenticate and authorize against subsequent Cisco.com APIs

Your Client ID and Secret are found in the API portal after you register the OpenVuln API

Request and use a token from the API in Postman:

Now add your request for IOS

https://api.cisco.com/security/advisories/ios?version=

Test it out!

Let’s hard code a version and see what flaws it has

Ok so it has at least 1 open vulnerability!

Does it tell us what version fixes it?

Ok let’s check that version quickly while we are still in Postman

This version has no disclosed vulnerabilities!

One interesting thing of note – and our automation is going to need to handle it – is that if there are no flaws found we get a 404 back from the API not a 200 like our flawed response!

The Playbook

For the sake of the example I am using prompted inputs / response but these variables could easily be hardcoded and Ansible Vaulted.

So first prompt for your Cisco hosts username and password and your Cisco.com ClientID and Client Secret

Register the response

Then in the IOS.yml group_vars I have my Ansible network connections

I’ve put all IOS-platforms in this group in the hosts file to target them

Next step run the show version ios_command and register the reponse

Genie parse and register the JSON

Now we need, just like in Postman, to go get the OAuth2 token but instead of Postman we need to use the Ansible URI module

Then we have to parse this response and setup our Bearer and Token components from the response JSON.

Now that we have our token we can authenticate against the IOS open Vulernability API

There are a couple of things going on here:

  1. We are passing the Genie parsed .version.version key to the API for each IOS host in our list
  2. We are using the {{ token_type }} and {{ access_token }} to Authorize
  3. We have to expect two different status codes; 200 (flaws found on a host) and 404 (no flaws for the host software version)
  4. I’ve added until and delay to slow down / throttle the API requests as not to get a 406 back because I’ve overwhelmed the 10 requests per second upper limit
  5. We register the JSON response from the API

As always I like to create a “nice” (easy to read) version of the output in a .json file

Note we need to Loop over each host in our playbook (using the Ansible magic variable ansible_play_hosts) so the JSON file has a data set for each host in the playbook.

Lastly we run the template module to pass the data into Jinja2 where we will create a business-ready CSV file

Which looks like this broken apart:

Like building the JSON file first we need to loop over the hosts in the playbook.

Then we check if the errorCode is defined. You could also look at the 404 status code here. Either way if you get the error it means there are no vulnerabilities.

So add a row of data with the hostname, “N/A” for most fields, and the json.errorMessage from the API (or just hardcode “No flaws” or whatever you want here; “compliant”)

Now if the errorCode is not defined it means there are open flaws and we will get back other data we need to loop into.

I am choosing to do a nested set of two loops – one for each advisory in the list of advisories per software version. Then inside that loop another loop, adding a row of data to the spreadsheet, for each BugID found as well (which is also a list).

There are a few more lists like CVEs for example – you can either loop of these as well (but we start to get into too much repetition / rows of data) – or just use regex_replace(‘,’,’ ‘) to remove all commas inside a field. The result is the list spaced out inside the cell sorted alphabetically but if you do not do this it will throw off the number of cells in your CSV

The results

What can you do with “just” a CSV file?

With Excel or simply VS Code with the Excel Preview extension – some pretty awesome things!

I can, for example, pick the ID field and filter down a particular flaw in the list – which would then provide me all the hosts affected by that bug

Or pick a host out of the list and see what flaws it has, if any. Or any of the columns we have setup in the Jinja2

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Included in the report is also the SEVERITY and BASE SCORE for quick decision making or the Detailed Publication URL to get a detailed report for closer analysis.

Which looks like this:

Automation is much more than configuration management. It can be used to manage, understand, and mitigate risk as well.

Together we can secure our enterprise networks and hopefully sleep a little more sound knowing they are safe.

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By Popular Demand – Automating the Cisco Identity Services Engine (ISE) External RESTful Services (ERS) API Suite

My last post, which has turned into one of my more popular posts, covered automating the Cisco ISE MnT Nodes REST API with Postman and Ansible. We also discovered there is an XML limitation with the MnT REST API.

I’ve been asked by several people if a similar approach can be used with the Cisco ISE ERS. Not only can it be done – because ERS returns XML or JSON – it can be done much easier without the additional XML-to-JSON conversion step.

Cisco ISE ERS

Unlike the MnT, which has a very small subset (3 Session APIs for example) of available APIs, ERS has a lot of available APIs to work with!

First you have to enable ERS

You need a User with ERS permissions

To reach the ERS Software Developer Kit (SDK) then visit:

https://ise.my.domain.com:9060/ers/sdk

Now this, which can be a bit misleading, will launch the Quick Reference tab

In the bottom left – there are other panels of information – namely the API References

Now go API-shopping!

This is a pretty incredible list of APIs available to us, each with a dedicated documentation guide, and a rich set of XML or JSON data sets for a single record or all records.

REST API Development

Let’s use the Authorization Profile API to start with, partially to compliment the MnT Session information API documentation we have, let’s enumerate our AuthZ profiles.

First let’s explore the documentation!

Side note – I am usually a do-it-first then read-the-docs-later type of developer but in this case I need the particular URL to actually get to the API.

It’s also good practice !

Various ways to interact with the API are listed – for this example we are interested in the Get-All API

Each API will provide the resource definition – which helps you understand the returned data structure and is it valuable to capture

For example vlan nameID in this returns the name of the VLAN each of my AuthZ policies places authorized clients. This is very valuable to me.

Then check out the actual XML and JSON sample responses so you can see what to expect back in Postman and eventually your JSON files

And then, and this is what we are after, the JSON

Now the key here is the Get-All we still need to go find the request details, which look like this:

So we have the method (GET) , the URI (https://ise.my.domain.com:9060/ers/config/authorizationprofile), and the required (Content-Type and Accept) headers.

API Tip: Before we get started I want to highlight that the ERS API returns 20 results by default. This might not seem important but what if you have 27 records? 95 records? 1,200 records?

The API uses pagination and returns groups of results (20 by default) per page of responses. This maximum records response can be adjusted with a maximum of 100 records per response.

This is done by adding ?size=(1 – 100)

Some of my datasets are less than 100 records so I add ?size=100 to my string to get, effectively, all records back.

We will cycle back to how to handle paginated responses later in this post. For now lets just some datasets that come back in a single response to ease into this concept.

Take it to Postman

Next step we build our Cisco ISE Postman Collection (or in my case add to my existing collection) and setup our request

The results are interesting – I have found 27 AuthZ Profiles and I get the basic internal ISE ID, name, and description of each.

Part of the pagination tip includes how ISE handles Get-All responses.

  1. Get-All
  2. List Total
  3. List Each Resource summary
  4. Include the Resource’s detailed href

The href attribute specifies the URL of the page the link goes to.

So we follow this link for a specific AuthZ profile and see what the individual resource details look like:

Ok here we go!

Move it into Ansible URI

Create a new YAML file – the Ansible playbook – and convert the working Postman string, with authentication and headers, and register the JSON response from the Get-All Authorization Profile with up to 100 records.

Now we have the first Postman response back – the list of AuthZ Profiles – registered in AuthorziationProfiles_List which we now can loop-over and go get each profile’s href and get that JSON. Follow the trail.

So here our loop simply loops over the natural JSON list we get back. If you were to recall the resources is a JSON list

So the actual URL we are visiting on each loop is the item.link.href !

Again I like to have this JSON in a file using the copy module and the | to_nice_json filter.

Which looks just like the Postman body:

Which we then move into a Jinja2 template

Which is easy enough

We loop over each result in AuthorizatonProfiles_Details.results which again is the natural JSON list so each key is simply {{ result.json.AuthorizationProfile.xx }}; .name for example.

Which results in the business-ready CSV !

Refactoring working code – rinse and repeatability

One amazing thing about the ERS API suite is how uniform and standard they all seem to be.

Meaning you can copy the playbook above and make the following adjustments to reflect the API you are developing against

  1. Rename the playbook
  2. Update all comments and task names:
  3. Update the URL
  4. Update all registered variable names
  5. Update all output file names

In fact with a few Find / Replace operations you can copy and transform the first API playbook to any other API playbook.

As an example my CiscoISEAuthenticationProfiles.yml file and my CiscoISEdACLList.yml playbooks are both exactly 55 lines of code each! They are exactly the same minus the unique identifiers linking back to the targeted API.

Handling Pagination

So far I’ve avoided the paginated responses but let’s add pagination handling into the playbook.

Here is an example, my Network Device API

https://ise.my.domain.com:9060/ers/config/networkdevice?size=100

Returns over 1,200 items, with 100 items per page.

So how do we deal with this?

So we should have what we need to convert this to Ansible and automatically handle the pagination using some Ansible math filters.

So inside Page_count we have .json.SearchResult.total (1215) which we can use to establish the number of pages we need to loop over.

And speaking of loops Ansible has a with_sequence looping mechanism that almost seems designed to work with paginated URI responses.

Meaning we can set the start of our sequence (1) and end of our sequence (the total number of responses divided by the number of responses per page (100) rounded up to the next whole number.

So here we go

Pay attention to the page={{ item }} which is each sequence number in the with_sequence loop.

We loop starting at 1 and end at the Total pages divided by 100 (make sure to parenthesize this math) then we use the | round filter specifying to round up (ceil) to the largest next whole number (0) then finally set that value as an integer so the sequence can treat it as a number.

This is pretty neat stuff here is the task in Ansible for me I was expecting 13 pages

Now I need a json_query to loop over the results (outer) and results (inner)

So lets set a fact to do just that

Now we should be able to iterate over this list of URIs

This seems to be working

I’m taking a coffee break while this runs – back in a few minutes!

Compiling

If you know me by now – my next step is always to put this output into a .json file

Which looks like this:

Which I then pass to the Jinaj2 template

Which looks like this:

Which then looks like this!

Which I have filted down to a sample – there are all 1,200+ records in this file!

So now I can handle any paginated responses – with only one or two extra steps!

I hope this series on the Cisco ISE REST APIs – both the ERS and MnT – has been valuable to you ! As you can see regardless or XML or JSON; paginated or not; we can easily use Ansible and a few other tools to automate the Cisco ISE REST APIs!

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JSON-Mania with Heavy Networking

I sat down with my good friend Ethan Banks over at Packet Pushers for my second Heavy Networking podcast in hopes of discussing my JSON-MANIA!

Heavy Networking 563: Automating Documentation With Ansible, Genie, And Jinja2 – Packet Pushers

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Automating the Cisco Identity Services Engine Monitoring and Troubleshooting Node (ISE MnT) REST API

In my opinion Network Access Control (NAC) using a mix of 802.1x and MAC Address Bypass (MAB) with dynamic Access Control Lists (dACL) is not just an extremely important foundation of a modern, high secure, enterprise network. It is actually a Software Defined Network (SDN) that completely changes the operationalization and dynamically adjusts the very configuration of your devices.

Cisco Identity Services Engine (ISE) uses Policy Sets to achieve this providing policy for Authentication – validating the identity a device claims to be – and Authorization – what, if anything, that identified device is permitted access to. Using either certificates and the 802.1x protocol or, if certificates are unfeasible, a MAC-based permission that pushes a dynamic ACL to the switch limited the access that MAC address has on the network.

I’ve implemented this at scale – and now I am trying to use automation tools to help operate, monitor, troubleshoot, and generally understand the impact of my ISE policy sets at the Access layer. And while ISE provides some amazing GUI-based tools – the Live Logs, Live Session, Policy Sets, and Context Visibility – if I can avoid using a GUI, sorting, filtering clicking, menu-driven system – I would like to just get right to the data!

Enter: Monitoring and Troubleshooting Nodes

In your ISE deployment options you can deploy Monitoring nodes / personas

These personas come with REST APIs !

But these are not to be confused with the ISE External REST Service (ERS) APIs!

(You can easily tell the difference in the API URL noting the presence of /mnt or the /esr path respectively)

High-Level Goals

In an Ansible Playbook

  1. Get a Total Session count using the ActiveCount REST API
  2. Get an Active Session details list using the ActiveList REST API
  3. Per-Access Layer send all MAC Addresses with an Authentication Session to the Session/MAC REST API
  4. Transform all returned data into business-ready CSV files

The Tools

A lot of different automation and infrastructure as code tools were used to create this solution including:

  • Cisco ISE MnT Node – REST API Source
  • VS Code – used to write the code
  • VS Code Extensions – used to help write the code
  • Git – used to version and source control the code
  • Azure DevOps Git Repository – used to host the Git repository
  • Postman – used to investigate and develop against the REST API
  • Ansible – automation and orchestration engine driving the solution
  • Ansible Vault – used to encrypt API credentials
  • Ansible Module: URI – module used to interface with REST API
  • Ansible Module: XML – module used to work with XML data
  • Ansible Module: Copy – move data from a variable into a file
  • Ansible Module: Template – call a Jinja2 template as a source to template another filetype as the destination output file
  • Ansible Module: ios_command – run a Cisco IOS CLI command
  • Ansible Module: set_fact – create your own variable
  • Cisco pyATS Genie Parser – transform Cisco IOS command output into structured JSON
  • Filter Plugin: parse_genie – a custom Python file used with Genie to parse CLI output
  • Ansible Utilities: CLI_Parse – parse “CLI” commands
  • CLI_Parser: XML – specify XML as the filetype to feed the CLI_Parser
  • Ansible Filter: to_nice_json – create human readable “pretty” JSON files
  • Ansible Filter: dict2items – transform a dictionary to structure items (list)
  • Ansible Filter: json_query – Use SQL-like structured Queries against JSON
  • Ansible Filter: flatten – flatten a nested list
  • Ansible Filter: hwaddr – manipulate MAC address formats
  • Ansible Filter: upper – change a string to UPPER CASE
  • Jinja2 Templates – Use Pythonic code to structure a template of another filetype using the JSON data as a source
  • CSV – The ultimate business-ready output file format

Wait – did you say XML ?

Yes. For some reason ISE MnT Nodes do not return structured JSON at all and you can only receive XML format.

https://twitter.com/densem0de/status/1359688237464367108

Unacceptable indeed!

Raiding the Lost REST API

Now that we’ve identified this limitation we have another step to consider in our automation orchestration – that is to parse and transform – the XML to JSON so we can work with it in Jinja2

Use Case #1 – Active Sessions

ISE MnT API requires some specific permissions under a user account before you get going:

As with any API development I like to start with Postman.

Setup a Postman Collection called Cisco ISE

Add the username and password under Authentication – Basic Auth

Your GET string to get to the Active Sessions API is as follows:

https://ise.domain.com/admin/API/mnt/Session/ActiveCount

With very simple headers:

Resulting in the following data set:

Now we have the components we need – the working credentials, URL string, headers, and expected output – we can migrate the code over to Ansible using the URI module.

First we need to set up some variables we can use to connect to the ISE MnT API. I use a file called Enterprise.yml for this in group_vars

Then I can proceed with my playbook called CiscoISEActiveSessionTotals.yml

The first task is to use the URI module and register the results from the ActiveCount MnT API into a variable ActiveCount_XML

Next, because it is only a single value, we can simply use XML to parse out that field as follows and register the new variable FilteredCount

I like to always capture a .json file of the data as a RAW artifact of the unmanipulated data:

Which looks just like the Postman output:

It should be noted that the above file is the contents of FilteredCount exactly.

Now I can pass this along to the Jinja2 template:

Which looks like this:

And results in this:

Very nice!

Using this as a foundation can we transform the more advanced APIs that return more than a single XML value?

Let’s find out!

Use Case #2 – Active Session Details

Adding the next API as a Request to the Postman Cisco ISE collection

Which returns a data set like this:

We will need another way, beyond XML and xpath, to parse this output. Ideally we could find a pre-made read-to-go XML to JSON conversion utility.

I tried, and failed, several different parsing tools including the Ansible recommended XML filter parse_xml with a spec file – but I just couldn’t figure this out.

Fortunately Ganesh Nalawade, Principal Engineer at Ansible, reached out to me with a great utility

So first we go out to the ActiveList REST API and register the ActiveList_XML

Now, after installing the Utilities from Ansible Galaxy, we simply feed the text ActiveList_XML.content – into the XML parser – and register the parsed data into a new variable ParsedActiveList

So lets copy that over to a .json file and take a look

Which results in:

Alright we have the XML parsed over to JSON! Now we can template it!

Looking at the JSON above we now need to loop over the activeSession under ParsedActiveList.parsed.activeList

In Jinja2 it looks like this:

Where we pick and choose our fields and the order we want to comma separate them. I like to include the | default(“N/A”) filter to add a value of “N/A” to any empty or non-present value.

The resulting CSV looks like this!

Now this is filtered against my user name but I have all 8,000+ authentication sessions, one per row, in this CSV file!

Easy filtered (as seen above) and sorted. Searchable. Simple.

What else can we do with this API?

Use Case #3 – Per-MAC Session Details

Now in my pièce de résistance we are going to add another parsing technology I love – the Cisco Genie Parser – to capture MAC addresses to feed the last Cisco ISE MnT REST API – the MAC Session.

Add this final Request to your Cisco ISE Postman Collection replacing the MAC with either a Postman variable or a MAC that has a session in ISE.

Which returns:

Ok so now that we know we can send any MAC with a session in ISE against the REST API – how can we dynamically find and feed those MAC addresses from the network?

Answer: Genie

In order to get a list of authentication sessions on a Cisco switch we use the show authentication sessions command at the CLI

So the first thing I do is check the Genie Parser library and see if they have an available parser for the command and for what Cisco platforms they support.

Sure enough – there is a parser for the command I need.

So back to the Ansible playbook – first we need to run the ios_command and run the show authentication sessions command registering the results into a variable. This playbook needs to be scoped for the Access layer hosts where the 802.1x / MAB boundary is enforced.

Then we use the Genie Parser to transform the RAW CLI standard output (stdout) to – you guessed it – JSON ! We only set this fact (the variable) when the output does NOT equal “No sessions currently exist” in case there are no authentication sessions present on the device.

Now we don’t need this output in a JSON file but we do need to parse it, or query it, in order to get the MAC addresses from the results in order to send them to the ISE MnT API.

JSON_Query is another extremely potent Ansible filter that works like an SQL query but against the structured JSON. It can take some getting used to (painful laughing) but once you get the hang of the syntax it’s incredible fast and powerful.

I owe a big shout out to my pair-programming partner who eventually figured this out with (for?) me

To break this apart:

We set a variable up jquery to hold the actual query itself.

Then we set a fact which is the pyats_auth.interfaces value, which we:

  • filter from a dictionary to items (a list with keys and values)
  • JSON_Query with our jquery string
  • Flatten down the list (since we just need the nested value.client key)

Now we have another list, MACList, that contains a list of MAC addresses from the JSON_Query, which is querying the JSON we used Genie to convert from the IOS command!

From here it’s a simple matter of feeding the API each MAC in that list in a loop and registering the results:

I want to draw your attention to additional filters I had to use. Primarily because I was stuck on “Why isn’t this working? It should work .. but it doesn’t work” for a long time at this step. Eventually using debug I printed myself the variable MACList when I spotted something – the format of the MAC address!

The Cisco IOS MAC format is different than the Cisco ISE MnT REST API expects!

Meaning I was feeding the API:

ab00.cd11.ef22

Instead of:

AB:00:CD:11:EF:22

So by adding the hwadd(‘linux’) filter it changed the structure of the MAC address.

Then by adding the upper filter it changed the lower case letters to upper case.

Once I figured this out – it all started to work.

So now we have the XML in MACSessionDetails which we again need to parse with the Ansible Utility CLI_parse

Now we need another loop here to loop over each result and we can use the .content key being the {{ item }}

So now we can actually create our.json file from the parsed XML

Which looks like this:

Now Jinaj2 templating JSON lists are a funny thing. Because we get a natural list back, as indicated by the square bracket after results [ we can loop into this “directly”.

Meaning

{% for result in ParsedActiveSessionMACList.results %}

{{ result.parsed.sessionParameters.user_name }}

{% endfor %}

NOT

{% for result in ParsedActiveSessionMACList.results %}

{{ ParsedActiveSessionMACList.results[result].parsed.sessionParameters.user_name }}

{% endfor %}

Which returns:

Success!

What I find neat:

  • Never need to sign into ISE except for deep audits – which I have the ID in the CSV to look up
  • At the L2 Access Layer I am actually, without DNS, getting the hostnames / usernames / IP addresses of the connected devices! Pretty cool!
  • At scale either in batch or on-demand I can get this data in seconds!
  • I wouldn’t classify anything I am doing as complicated – yes there are a lot of little pieces but they all fit together nicely.
  • I no longer fear XML returning from a REST API
  • I’ve fully automated the 3 key ISE 2.x (3.x has even more) MnT REST APIs!

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Network Automation for Dummies, VMWare Special Edition

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Two more positive reviews!

For whatever reason it seems to be difficult to get even just a “Star” review on Amazon – even harder to get actual comments – but today I received two more 4-5 star reviews!

Thanks again for the support! If you enjoyed the book – or if you didn’t enjoy the book – I would love it if you could take the time to add a star (ok 5 star) review or your feedback on Amazon !

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AutomateYourNetwork in the wild

Woke up to see this amazing post out in the wild today

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An Interview With Charles Uneze – Study Tactics

I recently had the chance to be interviewed, via Twitter, by Charles Uneze !

https://twitter.com/network_charles/status/1356727242852868097

I am really inspired by Charles’ own journey into IT and his passionate pursuit of his CCNA ! It reminds me of trying to get my CompTIA A+ / N+ all those years ago starting my own journey!

Anyway I really had a great time and Charles asked some great thought provoking questions !

Check it out and make sure to follow Charles’ journey !

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Career-Changing Automation Giveaway !

My good buddy Zig – who hosted me on Zigbits podcast for a 2-part Network Design (Part One) and Network Automation (Part Two – coming in February) discussion.

As part of Part Two’s discussion – Zig’s first real conversation about Network Automation and Infrastructure as Code – Zig is having the most amazing giveaway I’ve ever seen!

Including a copy of my book!

THERE ARE 11 WAYS – INCLUDING A DAILY BONUS CLICK – TO ENTER TO WIN!

Good luck! This will change the winner’s career and life!