Blog Posts in April 2024

Repost: Campus-Wide Wireless Roaming with EVPN

As a response to my LISP vs EVPN: Mobility in Campus Networks blog post, Route Abel provided interesting real-life details of a large-scale campus wireless testing using EVPN and VXLAN tunnels to a central aggregation point (slightly edited):

I was arguing for VxLAN EVPN with some of my peers, but I had no direct hands-on knowledge of how it would actually perform and very limited ability to lab it on hardware. My client was considering deploying Campus VxLAN, and they have one of the largest campuses in North America.

read more add comment

Unintended Consequences of IPv6 SLAAC

One of my friends is running a large IPv6 network and has already experienced a shortage of IPv6 neighbor cache on some of his switches. Digging deeper into the root causes, he discovered:

In my larger environments, I see significant neighbor table cache entries, especially on network segments with hosts that make many long-term connections. These hosts have 10 to 20 addresses that maintain state over days or weeks to accomplish their processes.

What’s going on? A perfect storm of numerous unrelated annoyances:

read more see 1 comments

Explore: Why No IPv6? (IPv6 SaaS)

Lasse Haugen had enough of the never-ending “we can’t possibly deploy IPv6” excuses and decided to start the IPv6 Shame-as-a-Service website, documenting top websites that still don’t offer IPv6 connectivity.

His list includes well-known entries like,, and plus a few unexpected ones. I find not having an AAAA DNS record truly hilarious. Someone within the company that flawlessly provided my website with IPv6 connectivity for years obviously still has some reservations about their own dogfood ;)

see 2 comments

Stateful Firewall Cluster High Availability Theater

Dmitry Perets wrote an excellent description of how typical firewall cluster solutions implement control-plane high availability, in particular, the routing protocol Graceful Restart feature (slightly edited):

Most of the HA clustering solutions for stateful firewalls that I know implement a single-brain model, where the entire cluster is seen by the outside network as a single node. The node that is currently primary runs the control plane (hence, I call it single-brain). Sessions and the forwarding plane are synchronized between the nodes.

read more see 4 comments

netlab 1.8.1: VRF OSPFv3, Integration Tests

netlab release 1.8.1 added a interesting few features, including:

This time, most of the work was done behind the scenes1.

read more add comment

BGP Challenge: Build BGP-Free MPLS Core Network

Here’s another challenge for BGP aficionados: build an MPLS-based transit network without BGP running on core routers.

That should be an easy task if you configured MPLS in the past, so try to spice it up a bit:

  • Use SR/MPLS instead of LDP
  • Do it on a platform you’re not familiar with (hint: Arista vEOS is a bit different from Cisco IOS)
  • Try to get it running on FRR containers.
see 1 comments

EVPN Designs: VXLAN Leaf-and-Spine Fabric

In this series of blog posts, we’ll explore numerous routing protocol designs that can be used to implement EVPN-with-VXLAN L2VPNs in a leaf-and-spine data center fabric. Every design will come with a companion netlab topology you can use to create a lab and explore the behavior of leaf- and spine switches.

Our leaf-and-spine fabric will have four leaves and two spines (but feel free to adjust the lab topology fabric parameters to build larger fabrics). The fabric will provide layer-2 connectivity to orange and blue VLANs. Two hosts will be connected to each VLAN to check end-to-end connectivity.

read more see 3 comments

Using wemulate with netlab

An RSS hiccup brought an old blog post from Urs Baumann into my RSS reader. I’m always telling networking engineers that it’s essential to set up realistic WAN environments when testing distributed software, and wemulate (a nice tc front-end) seemed like a perfect match. Even better, it runs in a container – an ideal component for a netlab-generated virtual WAN network.

wemulate acts as a bump in the wire; it uses Linux bridges to connect two container interfaces. We’ll use it to introduce jitter into an IP subnet:

┌──┐   ┌────────┐   ┌──┐
└──┘   └────────┘   └──┘                       
read more add comment

Repost: EBGP-Mostly Service Provider Network

Daryll Swer left a long comment describing how he designed a Service Provider network running in numerous private autonomous systems. While I might not agree with everything he wrote, it’s an interesting idea and conceptually pretty similar to what we did 25 years ago (IBGP without IGP, running across physical interfaces, with every router being a route-reflector client of every other router), or how some very large networks were using BGP confederations.

Just remember (as someone from Cisco TAC told me in those days) that “you might be the only one in the world doing it and might hit bugs no one has seen before.”

read more see 1 comments