Author Archives: Ivan Pepelnjak
Author Archives: Ivan Pepelnjak
I keep getting questions along the lines of “is network automation practical/a reality?” with arguments like:
Many do not see a value and are OK with just a configuration manager such as Arista CVP (CloudVision Portal) and Cisco DNA.
Configuration consistently is a huge win regardless of how you implement it (it’s perfectly fine if the tools your vendor providers work for you). It prevents opportunistic consistency, as Antti Ristimäki succinctly explained:
I got this question from one of ipSpace.net subscribers:
My VP is not a fan of overlays and is determined to move away from our legacy implementation of OTV, VXLAN, and EVPN1. We own and manage our optical network across all sites; however, it’s hard for me to picture a network design without overlays. He keeps asking why we need overlays when we own the optical network.
There are several reasons (apart from RFC 1925 Rule 6a) why you might want to add another layer of abstraction (that’s what overlay networks are in a nutshell) to your network.
It took vendors like Cisco years to start supporting routing protocols between MLAG-attached routers and a pair of switches in the MLAG cluster. That seems like a no-brainer scenario, so there must be some hidden complexities. Let’s figure out what they are.
We’ll use the familiar MLAG diagram, replacing one of the attached hosts with a router running a routing protocol with both members of the MLAG cluster (for example, R, S1, and S2 are OSPF neighbors).
One of the comments I received after publishing the Use VRFs for VXLAN-Enabled VLANs claimed that:
I’m firmly of the belief that VXLAN should be solely an access layer/edge technology and if you are running your routing protocols within the tunnel, you’ve already lost the plot.
That’s a pretty good guideline for typical data center fabric deployments, but VXLAN is just a tool that allows you to build multi-access Ethernet networks on top of IP infrastructure. You can use it to emulate E-LAN service or to build networks similar to what you can get with DMVPN (without any built-in security). Today we’ll use it to build a VRF Lite topology with two tenants (red and blue).
Cloudflare has been using ingress anycast (advertising the same set of prefixes from all data centers) for ages. Now they did a giant leap forward and implemented another “this thing can never work” technology: egress anycast. Servers from multiple data centers use source addresses from the prefix that’s advertised by all data centers.
Not only that, in the long-established tradition they described their implementation in enough details that someone determined enough could go and implement it (as opposed to the typical look how awesome our secret sauce is approach from Google).
Time for another netlab video: after explaining how netlab fits into the virtual lab orchestration picture, let’s answer the next question: what exactly can netlab do?
After VMware launched DPU-based acceleration for VMware NSX, marketing-focused websites frantically started discussing the benefits of DPUs. Although I’ve been writing about SmartNICs and DPUs for years, it’s time for another closer look at the emperor’s clothes.
DPU (Data Processing Unit) is a fancier name for a network adapter formerly known as SmartNIC – a server repackaged into an interface card form factor. We had them for decades (anyone remembers iSCSI offload adapters?)
A while ago, I wrote a blog post explaining why we should (mostly) disable ICMP redirects, triggering a series of comments discussing the root cause of ICMP redirects. A few of those blamed static routes, including:
Put another way, the presence or absence of ICMP Redirects is a red herring, usually pointing to architectural/design issues instead. In this example, using vPC Peer Gateway or, better yet, running a minimal IGP instead of relying on static routes eliminates ICMP Redirects from both the problem and solution spaces simultaneously.
Unfortunately, that’s not the case. You can get suboptimal routing that sometimes triggers ICMP redirects in well-designed networks running more than one routing protocol.
I planned to write a few interesting blog posts last week, but then got sucked into updating Azure Networking webinar. At least I got that completed 😊; the webinar materials now include these new Azure services:
I also added descriptions of numerous new features:
Other new features include:
Upgrading is as easy as ever: execute
pip3 install --upgrade networklab.
Creating a mathematical model of queuing in a distributed system is hard (Queuing Theory was one of the most challenging ipSpace.net webinars so far), and so instead of solutions based on control theory and mathematical models we often get what seems to be promising stuff.
Things that look intuitively promising aren’t always what we expect them to be, at least according to an MIT group that analyzed delay-bounding TCP congestion control algorithms (CCA) and found that most of them result in unfair distribution of bandwidth across parallel flows in scenarios that diverge from spherical cow in vacuum. Even worse, they claim that:
[…] Our paper provides a detailed model and rigorous proof that shows how all delay-bounding, delay-convergent CCAs must suffer from such problems.
It seems QoS will remain spaghetti-throwing black magic for a bit longer…
When trying to decide whether to use EVPN for your next data center fabric, you might want to consider how easy it is to configure and troubleshoot.
You’ll find a few configuration hints in the Multivendor Data Center EVPN part of the EVPN Technical Deep Dive webinar. For the troubleshooting part, check out the phenomenal Troubleshooting EVPN with Arista EOS article by Tony Bourke.
With AWS re:Invent 2022 being just a few days away, it’s time for another cloudy Friday video: using infrastructure-as-code principles to provision public cloud resources by Matthias Luft (part of Introduction to Cloud Computing webinar).
Last week I completed the first part of the annual Azure Networking update. The Azure Firewall section is already online; hope you’ll find it useful. I already have the materials for the Private Link and Gateway Load Balancer services, but haven’t decided whether to schedule another live session to cover them, or just create a short video.
Then there are a half-dozen smaller things I found while processing a year worth of Azure networking News. You’ll find them (and links to documentation) in New Azure Services and Features document.
Imagine you built a layer-2 fabric with tons of VLANs stretched all over the place. Now the users want to exchange traffic between those VLANs, and the obvious question is: which devices should do layer-2 forwarding (bridging) and which ones should do layer-3 forwarding (routing)?
There are four typical designs you can use to solve that challenge:
This blog post is an overview of the design models; we’ll cover each design in a separate blog post.
I really don’t see how a network any larger and more complex than a small and simple enterprise or campus network can be developed and engineered in a consistent manner without full automation. At least routing intensive networks might have very complex configurations related to e.g. routing policies and it would be next to impossible to configure them manually, at least without errors and in a consistent way.
We’ll start with the VLAN trunk lab topology and make the following changes:
After starting the lab you’ll notice the change in node identifiers and interface IP addresses. Without the anycast gateway, netlab assigns node ID 1 (and loopback IP address 10.0.0.1) to S1. Now that the node ID 1 is reserved, S1 gets loopback address 10.0.0.2.
The only other change on the Continue reading
Geoff Huston published a lengthy article (as always) describing talks from recent OARC meeting, including resolver-less DNS and DNSSEC deployment risks.
Definitely worth reading if you’re at least vaguely interested in the technology that supposedly causes all network-related outages (unless it’s BGP, of course)
Bruno Wollmann migrated his blog post to Hugo/GitHub/CloudFlare (the exact toolchain I’m using for one of my personal web sites) and described his choices and improved user- and author experience.
As I keep telling you, always make sure you own your content. There’s absolutely no reason to publish stuff you spent hours researching and creating on legacy platforms like WordPress, third-party walled gardens like LinkedIn, or “free services” obsessed with gathering visitors' personal data like Medium.