After identifying some of the challenges every network solution must address (part 1, part 2, part 3) we tried to tackle an interesting question: “how do you implement this whole spaghetti mess in a somewhat-reliable and structured way?”
The Roman Empire had an answer more than 2000 years ago: divide-and-conquer (aka “eating the elephant one bite at a time”). These days we call it layering and abstractions.
In the Need for Network Layers video I listed all the challenges we have to address, and then described how you could group them in meaningful modules (called networking layers).
You need free ipSpace.net subscription to watch the video, or a paid ipSpace.net subscriptions to watch the whole webinar.
I had a fantastic chat with David Bombal a while ago in which we covered tons of network automation topics including “should I use Nornir or NAPALM or Netmiko?”
The only answer one can give would be “it depends… on what you’re trying to do” as these three tools solve completely different challenges.
Paramiko is SSH implementation in Python. It’s used by most Python tools that want to use SSH to connect to other hosts (including networking devices).
Read more ...In Never-Ending Story of IP Fragmentation I described how you could use TCP Maximum Segment Size to minimize the impact of IP fragmentation and PMTUD blackholes (more details on TCP MSS clamping)… but one has to wonder how people use TCP MSS in the wild and what values you might see.
As is often the case, Geoff Houston found a way to measure them, and published the answer: TCP MSS Values
Someone working for a network automation startup desperately tried to persuade me how cool their product is. Here’s what he sent me:
We let network engineers build their own network automation solutions in no time without requiring coding or scripting knowledge. It’s all GUI based, specifically geared towards network engineers - they can simply model services or roll-out networks “as-designed”.
The only problem: I’ve seen that same argument numerous times…
Read more ...Last week we started the Microsoft Azure Networking saga that will eventually mirror the AWS Networking materials.
I recorded the hands-on demos in advance so we had plenty of time to discuss Azure API and CLI, geographies, regions and availability zones, high-availability concepts, and deployments models… and spent the second half of the live session focusing on virtual networks, subnets, interface, and IP addresses. The videos are already online and accessible with Standard ipSpace.net Subscription.
Next step (on September 24th): network security and user-defined routes.
I apologize to my regular readers for a completely off-topic post, but if I manage to save a single traveller the frustrations I experienced a few weeks ago it was well worth it. Also, please help spread the word…
TL&DR: If you travel to Slovenia, DO NOT even consider flying with Adria Airways (and carefully check the code-share flights, they might be hiding under a Lufthansa or Swiss flight number). Their actual flight schedule is resembling a lottery, and while I always had great experience with the friendly, courteous and highly professional cabin crews, it’s totally impossible to reach their customer service.
2019-09-30: The agony ended sooner than I expected. On September 30th Adria Airways declared bankruptcy, ending the frustration and uncertainty of thousands of passengers they left stranded across Europe for almost 10 days. So long Adria, and thanks for all the good flights (we'll eventually forget all the mess you made in the last year)
2019-09-22: Added updates on what happened during last week. The whole thing is becoming a soap opera
In the introductory videos of How Networks Really Work webinar I described the mandatory elements of any networking solution and additional challenges you have to solve when you can’t pull a cable between the adjacent nodes.
It’s time for the next bit of complexity: what if we have more than two nodes connected to the same network segment? Welcome to the world of multi-access networks and data link control.
You need free ipSpace.net subscription to watch the videos in Overview of Networking Challenges section, or a paid ipSpace.net subscriptions to watch the rest of the webinar.
The March 2019 Packet Pushers Virtual Design Clinic had to deal with an interesting question:
Our server team is nervous about full-scale DR testing. So they have asked us to stretch L2 between sites. Is this a good idea?
The design clinic participants were a bit more diplomatic (watch the video) than my TL&DR answer which would be: **** NO!
Let’s step back and try to understand what’s really going on:
Read more ...The last bits of updated Never-Ending Story of IP Fragmentation were published a few days ago: IP fragmentation and tunnels and summary and related blog posts, RFCs and other articles.
Every now and then I stumble upon a blog post saying “OSI 7-layer model sucks” or “OSI 7-layer model is a lie”, most recent one coming from Robert Graham.
Before going into the details, let’s agree on the fundamentals.
Most everyone who ever tried to build a network spanning more than one transmission technology and including intermediate nodes came to the conclusion that layered approach to networking makes sense.
Whether you have three, four, five, or seven layers in your model doesn’t matter. What really matters is that your model contains all the functionality you need to implement host-to-host networking in target environment.
Read more ...Last week we started the Autumn 2019 Building Network Automation Solutions online course with an interesting presentation from Matthias Luft focused on open-source supply chain security
TL&DR: Can I download whatever stuff I found as my first Google hit and use it in my automation solution? ****, NO!
Matthias covered these topics:
Read more ...Imagine you would have a system that would read network device configurations, figure out how those devices might be connected, reverse-engineer the network topology, and be able to answer questions like “what would happen if this link fails” or “do I have fully-redundant network” or even “how will this configuration change impact my network”. Welcome to Batfish.
Interested? You’ll find more in Episode 104 of Software Gone Wild.
As I was preparing the materials for Ansible 2.7 Update webinar sessions I wanted to dive deeper into declarative configuration modules, starting with “I wonder what’s going on behind the scenes”
No problem: configure EEM applet command logging on Cisco IOS and execute an ios_interface module (more about that in another blog post)
Next step: let’s see how multi-platform modules work. Ansible has net_interface module that’s supposed to be used to configure interfaces on many different platforms significantly simplifying Ansible playbooks.
Read more ...After describing MTU basics and drawbacks of IP fragmentation, it’s time for more details: Path MTU Discovery (PMTUD) and network implications of using ICMP for PMTUD.
Interested in similar topics? Check out How Networks Really Work webinar.
This blog post was initially sent to subscribers of my SDN and Network Automation mailing list. Subscribe here.
Have you ever seen a presentation in which a startup is telling you how awesome their product is because it allows you to simulate your whole network in a virtual environment? Not only that, you can use that capability to build a test suite and a full-blown CI/CD pipeline and test whether your network works every time you make a change to any one box in the network.
Sounds awesome, right? It’s also dead wrong. Let me explain why that’s the case.
Read more ...Last year when I was creating the first version of VMware NSX Deep Dive content, NSX-V was mainstream and NSX-T was the new kid on the block. A year later NSX-V is mostly sidelined, and all the development efforts are going into NSX-T. Time to adapt the webinar to new reality… taking the usual staged approach:
After discussing the challenges one encounters even in the simplest networking scenario connecting two computers with a cable we took a short diversion into an interesting complication: what if the two computers are far apart and we can’t pull a cable between them?
Trying to answer that question we entered the wondrous world of transmission technologies. It’s a topic one can spent a whole life exploring and mastering, so we were not able to do more than cover the fundamentals of modulations and multiplexing technologies.
You need free ipSpace.net subscription to watch the video, or a paid ipSpace.net subscriptions to watch the rest of the webinar.
We’re back from the summer break for real - the first autumn 2019 ipSpace.net event takes place today: I’ll talk about the fallacies of distributed computing.
September will be an intensive month:
Of course, we’ll keep going… our event calendar is fully packed till mid-November. More about that in a month.
In mid 2000s I wrote a number of articles describing various TCP/IP features. Most of them are a bit outdated, so I decided to clean up, update and repost the most interesting ones on ipSpace.net, starting with Never-Ending Story of IP Fragmentation.
The first part of that article is already online, covering MTU basics and drawbacks of IP fragmentation.
Andrea Dainese decided to describe a series of mechanisms and protocols you can use in network automation. He started with Zero-Touch Provisioning and continued with screen scraping. Next one on his list: NETCONF and RESTCONF