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Category: VXLAN

Why Would You Need an Overlay Network?

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.

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Using EVPN/VXLAN with MLAG Clusters

There’s no better way to start this blog post than with a widespread myth: we don’t need MLAG now that most vendors have implemented EVPN multihoming.

TL&DR: This myth is close to the not even wrong category.

As we discussed in the MLAG System Overview blog post, every MLAG implementation needs at least three functional components:

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Worth Reading: VXLAN Drops Large Packets

Ian Nightingale published an interesting story of connectivity problems he had in a VXLAN-based campus network. TL&DR: it’s always the MTU (unless it’s DNS or BGP).

The really fun part: even though large L2 segments might have magical properties (according to vendor fluff), there’s no host-to-network communication in transparent bridging, so there’s absolutely no way that the ingress VTEP could tell the host that the packet is too big. In a layer-3 network you have at least a fighting chance…

For more details, watch the Switching, Routing and Bridging part of How Networks Really Work webinar (most of it available with Free Subscription).

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Worth Reading: EVPN/VXLAN with FRR on Linux Hosts

Jeroen Van Bemmel created another interesting netlab topology: EVPN/VXLAN between SR Linux fabric and FRR on Linux hosts based on his work implementing VRFs, VXLAN, and EVPN on FRR in netlab release 1.3.1.

Bonus point: he also described how to do multi-vendor interoperability testing with netlab.

If only he wouldn’t be publishing his articles on a platform that’s almost as user-data-craving as Google.

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Combining MLAG Clusters with VXLAN Fabric

In the previous MLAG Deep Dive blog posts we discussed the innards of a standalone MLAG cluster. Now let’s see what happens when we connect such a cluster to a VXLAN fabric – we’ll use our standard MLAG topology and add a VXLAN transport underlay to it with another switch connected to the other end of the underlay network.

MLAG cluster connected to a VXLAN fabric

MLAG cluster connected to a VXLAN fabric

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Repost: On the Viability of EVPN

Jordi left an interesting comment to my EVPN/VXLAN or Bridged Data Center Fabrics blog post discussing the viability of using VXLAN and EVPN in times when the equipment lead times can exceed 12 months. Here it is:


Interesting article Ivan. Another major problem I see for EPVN, is the incompatibility between vendors, even though it is an open standard. With today’s crazy switch delivery times, we want a multi-vendor solution like BGP or LACP, but EVPN (due to vendors) isn’t ready for a multi-vendor production network fabric.

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VXLAN-to-VXLAN Bridging in DCI Environments

Almost exactly a decade ago I wrote that VXLAN isn’t a data center interconnect technology. That’s still true, but you can make it a bit better with EVPN – at the very minimum you’ll get an ARP proxy and anycast gateway. Even this combo does not address the other requirements I listed a decade ago, but maybe I’m too demanding and good enough works well enough.

However, there is one other bit that was missing from most VXLAN implementations: LAN-to-WAN VXLAN-to-VXLAN bridging. Sounds weird? Supposedly a picture is worth a thousand words, so here we go.

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VXLAN-Focused Design Clinic in June 2022

ipSpace.net subscribers are probably already familiar with the Design Clinic: a monthly Zoom call in which we discuss real-life design- and technology challenges. I started it in September 2021 and it quickly became reasonably successful; we covered almost two dozen topics so far.

Most of the challenges contributed for the June 2022 session were focused on VXLAN use cases (quite fitting considering I just updated the VXLAN Technical Deep Dive webinar), including:

  • Can we implement Data Center Interconnect (DCI) with VXLAN? (Yes, but…)
  • Can we run VXLAN over SD-WAN (and does it make sense)? (Yes/No)
  • What happened to traditional MPLS/VPN Enterprise core and can we use VXLAN/EVPN instead? (Still there/Maybe)
  • Should we use routers or switches as data center WAN edge devices, and how do we integrate them with VXLAN/EVPN data center fabric? (Yes 😊)

For more details, join us on June 6th. There’s just a minor gotcha: you have to be an active ipSpace.net subscriber to do it.

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Overlay Virtual Networking Examples

One of ipSpace.net subscribers wanted to see a real-life examples in the Overlay Virtual Networking webinar:

I would be nice to have real world examples. The webinar lacks of contents about how to obtain a fully working L3 fabric overlay network, including gateways, vrfs, security zones, etc… I know there is not only one “design for all” but a few complete architectures from L2 to L7 will be appreciated over deep-dives about specific protocols or technologies.

Most ipSpace.net webinars are bits of a larger puzzle. In this particular case:

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EVPN/VXLAN Complexity

We have school holidays this week, so I’m reposting wonderful comments that would otherwise be lost somewhere in the page margins. Today: Minh Ha on complexity of emulating layer-2 networks with VXLAN and EVPN.


Dmytro Shypovalov is a master networker who has a sophisticated grasp of some of the most advanced topics in networking. He doesn’t write often, but when he does, he writes exceptional content, both deep and broad. Have to say I agree with him 300% on “If an L2 network doesn’t scale, design a proper L3 network. But if people want to step on rakes, why discourage them.

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Why Would You Need VXLAN Transport?

It’s amazing how sometimes people fond of sharing their opinions and buzzwords on various social media can’t answer simple questions. Today’s blog post is based on a true story… a “senior network architect” fully engaged in a recent hype cycle couldn’t answer a simple question:

Why exactly would you need VXLAN and EVPN?

We could spend a day (or a week) discussing the nuances of that simple question, but all I have at the moment is a single web page, so here we go…

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