Bruce Davie continues documenting the tradeoffs we had to make in networking, this time with Was MPLS Traffic Engineering Worthwhile? I found this bit particularly familiar:

It wasn’t hard to make a theoretical argument that MPLS-TE could improve network performance and average link utilization, by moving traffic from congested links to uncongested ones. The hard part was proving that it would actually do a better job in practice than the more traditional methods such as using link weights and multipath routing to achieve the same ends.

After introducing netlab in the Network Automation Tools webinar, I spent a few minutes describing the structure of the netlab lab topology file.

As always, use the video only as a starting point. For more details, read the netlab documentation (overview, reference guide).

I must be a good prompt engineer – every time I ask ChatGPT something really simple it spews out nonsense. This time I asked it to build a small network with four routers:

I have a network with four Cisco routers (A,B,C,D). They are connected as follow: A-B, B-C, A-D, D-C. Each router has a loopback interface. Create router configurations that will result in A being able to reach loopback interfaces of all other routers.

Here’s what I got back¹:

Here’s an example configuration for the four routers that should allow Router A to reach the loopback interfaces of all other routers:

One of my subscribers sent me this question:

I’m being asked to enter a working group on RPKI and route origination. I’m doing research, listening to Jeff Tantsura, who seems optimistic about taking steps to improve BGP security vs Geoff Huston, who isn’t as optimistic. Should I recommend to the group that the application security is the better investment?

You need both. RPKI is slowly becoming the baseline of global routing hygiene (like washing hands, only virtual, and done once every blue moon when you get new IP address space or when the certificates expire). More and more Internet Service Providers (including many tier-1 providers) filter RPKI invalids thus preventing the worst cases of unintentional route leaks.

Previous posts in this series (DHCP relaying principles, inter-VRFs relaying, relaying in VXLAN segments and relaying from EVPN VRF) used a single DHCP server. It’s time to add another layer of complexity: redundant DHCP servers.

Lab Topology

We’ll use a lab topology similar to the VXLAN DHCP relaying lab, add a second DHCP server, and a third switch connecting the two DHCP servers to the rest of the network.

The “beauty” (from an attacker perspective) of the original shared-media Ethernet was the ability to see all traffic sent to other hosts. While it’s trivial to steal someone else’s IPv4 address, the ability to see their traffic allowed you to hijack their TCP sessions without the victim being any wiser (apart from the obvious session timeout). Really smart attackers could go a step further, insert themselves into the forwarding path, and inject extra payload into unencrypted sessions.

A recently-discovered WiFi vulnerability brought us back to that wonderful world.

A friend sent me a video demo of his AI-driven network device configuration proof-of-concept. Before commenting on that idea, I wanted to see how well AI works as an assistant. Once Kristian Larsson mentioned he was using GitHub Copilot, it was obvious what to do next: try it out while working on the next netlab release.

TL&DR:

• It works.
• Some Copilot suggestions are uncannily accurate; others are fishing expeditions.
• It’s bland.

Years ago I loved ranting about the stupidities of building stretched VLANs to run high-availability network services clusters with two nodes (be it firewalls, load balancers, or data center switches with centralized control plane) across multiple sites.

I collected pointers to those blog posts and other ipSpace.net HA cluster resources on the new High Availability Service Clusters page.

netlab release 1.5.1 makes it easier to create topologies with lots of VRF- or VLAN access links, or topologies with numerous similar links. It also includes support for D2 diagram scripting language in case you prefer its diagrams over those generated by Graphviz.

Even if you don’t find those features interesting (more about them later), you might want to upgrade to fix a nasty container-related behavior I discovered in recently-upgraded Ubuntu servers.

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.