Category: EVPN

VXLAN/EVPN Layer-3 Handoff (L3Out) on Arista EOS

A while ago, I published a blog post describing how to establish a LAN/WAN L3 boundary in VXLAN/EVPN networks using Cisco NX-OS. At that time, I promised similar information for Arista EOS. Here it is, coming straight from Massimo Magnani. The useful part of what follows is his; all errors were introduced during my editing process.


In the cases I have dealt with so far, implementing the LAN-WAN boundary has the main benefit of limiting the churn blast radius to the local domain, trying to impact the remote ones as little as possible. To achieve that, we decided to go for a hierarchical solution where you create two domains, local (default) and remote, and maintain them as separate as possible.

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Worth Reading: Introduction of EVPN at DE-CIX

Numerous Internet Exchange Points (IXP) started using VXLAN years ago to replace tradition layer-2 fabrics with routed networks. Many of them tried to avoid the complexities of EVPN and used VXLAN with statically-configured (and hopefully automated) ingress replication.

A few went a step further and decided to deploy EVPN, primarily to deploy Proxy ARP functionality on EVPN switches and reduce the ARP/ND traffic. Thomas King from DE-CIX described their experience on APNIC blog – well worth reading if you’re interested in layer-2 fabrics.

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Does EVPN/VXLAN over SD-WAN Make Sense?

It looks like we might be seeing VXLAN-over-SDWAN deployments in the wild. Here’s the “why that makes sense” argument I received from a participant of the ipSpace.net Design Clinic in which I wasn’t exactly enthusiastic about the idea.

Also, the EVPN-over-WAN idea is not hypothetical since EVPN+VXLAN is now the easiest way to build L3VPN with data center switches that don’t support MPLS LDP. Folks with no interest in EVPN’s L2 features are still using it for L3VPN.

Let’s unravel this scenario a bit:

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Dataplane MAC Learning with EVPN

Johannes Resch submitted the following comment to the Is Dynamic MAC Learning Better Than EVPN? blog post:

I’ve also recently noticed some vendors claiming that dataplane MAC learning is so much better because it reduces the number of BGP updates in large scale SP EVPN deployments. Apparently, some of them are working on IETF drafts to bring dataplane MAC learning “back” to EVPN. Not sure if this is really a relevant point - we know that BGP scales nicely, and its relatively easy to deploy virtualized RR with sufficient VPU resources.

While he’s absolutely correct that BGP scales nicely, the questions to ask is “what is the optimal way to deliver a Carrier Ethernet service?

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Layer-3 WAN Handoff (L3Out) in VXLAN/EVPN Fabrics

I got a question from a few of my students regarding the best way to implement end-to-end EVPN across multiple locations. Obviously there’s the multi-pod and multi-site architecture for people believing in the magic powers of stretching VLANs across the globe, but I was looking for something that I could recommend to people who understand that you have to have a L3 boundary if you want to have multiple independent failure domains (or availability zones).

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Silent Hosts in EVPN Fabrics

The Dynamic MAC Learning versus EVPN blog post triggered tons of interesting responses describing edge cases and vendor bugs implementation details, including an age-old case of silent hosts described by Nitzan:

Few years ago in EVPN network, I saw drops on the multicast queue (ingress replication goes to that queue). After analyzing it we found that the root cause is vMotion (the hosts in that VLAN are silent) which starts at a very high rate before the source leaf learns the destination MAC.

It turns out that the behavior they experienced was caused by a particularly slow EVPN implementation, so it’s not exactly the case of silent hosts, but let’s dig deeper into what could happen when you do have silent hosts attached to an EVPN fabric.

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Advantages and Drawbacks of EVPN-based Multihoming

Lukas Krattiger wrapped up his EVPN-versus-MLAG presentation (part of EVPN Deep Dive webinar) with an overview of the advantages and drawbacks of EVPN-based multihoming solutions:

  • N-way multihoming
  • Flexible connectivity (no need for a peer link)
  • Fabric-wide scope (MAC multipathing required on ingress node)
You need Free ipSpace.net Subscription to watch the video. To watch the whole webinar, buy Standard or Expert ipSpace.net Subscription.
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Is Dynamic MAC Learning Better Than EVPN?

One of my readers worried about the control-plane-induced MAC learning lag in EVPN-based networks:

In all discussions about the advantages/disadvantages of VXLAN/EVPN, I can’t find any regarding the lag in learning new macs when you use the control plane for mac learning.

EVPN is definitely slower than data plane-based dynamic MAC learning (regardless of whether it’s done in hardware or software), but so is MLAG.

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DHCP Relaying in EVPN VRFs

After figuring out how DHCP relaying works and testing it with VRFs and in VXLAN segments, it seems like a no-brainer to make it work with EVPN.

TL&DR: It works, at least when using Arista vEOS as the relay and Cisco CSR 1000v as the DHCP server.

Lab Topology

We’ll keep using the exact same “physical” topology we used in the VXLAN DHCP relaying lab, add EVPN and BGP to the control-plane cocktail, and put the VXLAN segment into a VRF. We’ll use CSR 1000v as the DHCP server because Cisco IOSv doesn’t support some of the DHCP option-82 sub-options we need.

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Video: vPC Fabric Peering with EVPN Multihoming

After implementing MLAG functionality with EVPN and having a VXLAN-like fabric transport path between MLAG members, it becomes possible to get rid of the MLAG peer link.

Not surprisingly, most implementations of virtual MLAG peer link remain proprietary. Lukas Krattiger described the details of Cisco’s vPC Fabric Peering implementation in the EVPN Deep Dive webinar.

You need Free ipSpace.net Subscription to watch the video. To watch the whole webinar, buy Standard or Expert ipSpace.net Subscription.
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Video: MLAG with EVPN Deep Dive

In November 2022 I described some of the intricacies of using EVPN to implement MLAG control plane. You might have noticed that I didn’t dive deep into EVPN details, and I had a good reason for that – Lukas Krattiger did a wonderful job describing how MLAG works with EVPN in the EVPN Deep Dive webinar.

You need Free ipSpace.net Subscription to watch the video. To watch the whole webinar, buy Standard or Expert ipSpace.net Subscription.
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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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