IPv6: Instructions for Use

Retirement obviously does not sit well with my friend Tiziano Tofoni; the English version of his IPv6 book just came out.

It is a bit sad, though, that we still need “how to use IPv6” books when the protocol is old enough to enjoy a nice glass of whiskey (in the US) trying to drown its sorrow at its slow adoption.

Repost: Building Layer-3-Only EVPN Lab

In early August, I published step-by-step instructions for a lab you can use to explore how to implement pure L3VPN with an EVPN control plane.

Custom netlab Reports

A previous blog post described how you can use the netlab report functionality to generate addressing, wiring, BGP, and OSPF reports from a running lab. But what could you do if you need a report that doesn’t exist yet? It’s straightforward to define one (what else did you expect?).

Let’s create the report I used in the EVPN Hub-and-Spoke Layer-3 VPN blog post to create the VRF table.

EVPN Hub-and-Spoke Layer-3 VPN

Now that we figured out how to implement a hub-and-spoke VPN design on a single PE-router, let’s do the same thing with EVPN. It turns out to be trivial:

• We’ll split the single PE router into three PE devices (pe_a, pe_b, and pe_h)
• We’ll add a core router (p) and connect it with all three PE devices.

As we want to use EVPN and have a larger core network, we’ll also have to enable VLANs, VXLAN, BGP, and OSPF on the PE devices.

This is the topology of our expanded lab:

Hub-and-Spoke VPN on a Single PE-Router

Yesterday’s blog post discussed the traffic flow and the routing information flow in a hub-and-spoke VPN design (a design in which all traffic between spokes flows through the hub site). It’s time to implement and test it, starting with the simplest possible scenario: a single PE router using inter-VRF route leaking to connect the VRFs.

Hub-and-Spoke VPN Topology

Hub-and-spoke topology is by far the most complex topology I’ve ever encountered in the MPLS/VPN (and now EVPN) world. It’s used when you want to push all the traffic between sites attached to a VPN (spokes) through a central site (hub), for example, when using a central firewall.

You get the following diagram when you model the traffic flow requirements with VRFs. The forward traffic uses light yellow arrows, and the return traffic uses dark orange ones.

Repost: Using netlab Reports

A quick reminder in case you were on vacation in late July: I published a short guide to creating netlab reports. Hope you’ll find it useful.

New Project: IS-IS Hands-On Labs

A year after I started the open-source BGP configuration labs project, I was persuaded to do something similar for IS-IS. The first labs are already online (with plenty of additional ideas already in the queue), and you can run them on any device for which we implemented IS-IS support in netlab.

Want an easy start? Use GitHub Codespaces. Have a laptop with Apple Silicon? We have you covered ;)

Live: BGP Labs and Netlab Testing @ SINOG 8

I’ll talk about the BGP labs and the magic behind the scenes that ensures the lab configurations are correct at the SINOG 8 meeting later today (selecting the English version of the website is counter-intuitive; choose English from the drop-down field on the right-hand side of the page).

The SINOG 8 presentations will be live-streamed; I should start around 13:15 Central European Time (11:15 GMT; figuring out the local time is left as an exercise for the reader).

Public Videos: Network Connectivity and Graph Theory

In May 2024, I made public the first half of the Network Connectivity and Graph Theory videos by Rachel Traylor.

Now, you can also enjoy the second part of the webinar without a valid ipSpace.net account; it describes trees, spanning trees, and the Spanning Tree Protocol. Enjoy!

Repost: BGP, EVPN, VXLAN, or SRv6?

Did you know that some vendors use the ancient MPLS/VPN (RFC 4364) control plane when implementing L3VPN with SRv6?

That’s just one of the unexpected tidbits I discovered when explaining why you can’t compare BGP, EVPN, and SRv6.

EVPN Designs: Scaling IBGP with Route Reflectors

In the previous blog posts, we explored the simplest possible IBGP-based EVPN design and tried to figure out whether BGP route reflectors do more harm than good. Ignoring that tiny detail for the moment, let’s see how we could add route reflectors to our leaf-and-spine fabric.

As before, this is the fabric we’re working with:

Routing Table and BGP RIB on SR Linux

Ages ago, I described how “traditional” network operating systems used the BGP Routing Information Base (BGP RIB), the system routing table (RIB), and the forwarding table (FIB). Here’s the TL&DR:

1. Routes received from BGP neighbors are stored in BGP RIB.
2. Routes redistributed into BGP from other protocols are (re)created in the BGP RIB.
3. BGP selects the best routes in BGP RIB using its convoluted set of rules.
4. Best routes from the BGP RIB are advertised to BGP neighbors
5. Best routes from the BGP RIB compete (based on their administrative distance) against routes from other routing protocols to enter the IP routing table (system RIB)
6. Routes from the system RIB are copied into FIB after their next hops are fully evaluated (a process that might involve multiple recursive lookups).

Repost: Why Are Layer-2 VPNs So Popular?

Béla Várkonyi wrote a succinct comment explaining why so many customers prefer layer-2 VPNs over layer-3 VPNs:

The reason of L2VPN is becoming more popular by service providers and customers is about provisioning complexity.

Worth Exploring: Free, OpenSource IPv6 Textbook

Nick Buraglio and Brian E. Carpenter published a free, open-source IPv6 textbook.

The book seems to be in an early (ever-evolving) stage, but it’s well worth exploring if you’re new to the IPv6 world, and you might consider contributing if you’re a seasoned old-timer.

It would also be nice to have a few online labs to go with it ;)

Worth Exploring: Open-Source Network Automation Labs

Urs Baumann loves hands-on teaching and created tons of lab exercises to support his Infrastructure-as-Code automation course.

During the summer, he published some of them in a collection of GitHub repositories and made them work in GitHub Codespaces. An amazing idea well worth exploring!

Common Services VRF with EVPN Control Plane

After discovering that some EVPN implementations support multiple transit VNI values in a single VRF, I had to check whether I could implement a common services L3VPN with EVPN.

TL&DR: It works (on Arista cEOS)¹.

Here are the relevant parts of a netlab lab topology I used in my test (you can find the complete lab topology in netlab-examples GitHub repository):

Multivendor EVPN Just Works

Shipping netlab release 1.9.0 included running 36 hours of integration tests, including fifteen VXLAN/EVPN tests covering:

• Bridging multiple VLANs
• Asymmetric IRB, symmetric IRB, central routing, and running OSPF within an IRB VRF.
• Layer-3 only VPN, including routing protocols (OSPF and BGP) between PE-router and CE-routers
• All designs evangelized by the vendors: IBGP+OSPF, EBGP-only (including reusing BGP AS number on leaves), EBGP over the interface (unnumbered) BGP sessions, IBGP-over-EBGP, and EBGP-over-EBGP.

All tests included one or two devices under test and one or more FRR containers¹ running EVPN/VXLAN with the devices under test. The results were phenomenal; apart from a few exceptions, everything Just Worked™️.

Repost: The Benefits of SRv6

I love bashing SRv6, so it’s only fair to post a (technical) counterview, this time coming as a comment from Henk Smit.

There are several benefits of SRv6 that I’ve heard of.

Using No-Export Community to Filter Transit Routes

The very first BGP Communities RFC included an interesting idea: let’s tag paths we don’t want to propagate to other autonomous systems. For example, the prefixes received from one upstream ISP should not be propagated to another upstream ISP (sadly, things don’t work that way in reality).

Want to try out that concept? Start the Using No-Export Community to Filter Transit Routes lab in GitHub Codespaces.