In the previous BGP load balancing lab exercise, I described the BGP Link Bandwidth attribute and how you can use it on EBGP sessions. This lab moves the unequal-cost load balancing into your network; we’ll use the BGP Link Bandwidth attribute on IBGP sessions.

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.

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.

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:

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 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.

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 ;)

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:

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).

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.

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 ;)

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!

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):

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™️.

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.