Blog Posts in December 2025
netlab 25.12: Cisco IOS/XR Configuration Modules, More VXLAN Goodies
netlab release 25.12 (25.12.02 to be exact – I had a few PEBCAK moments) was published last Friday. Here are the highlights:
- Significantly improved Cisco IOS/XR support. With the netlab release 25.12, you can configure VLANs, VRFs, static routes, route redistribution, OSPF default routes, BGP confederations, and BGP local-as
- VXLAN-over-IPv6 on Arista EOS
- VXLAN with ingress replication on Cisco Catalyst 8000v
- The shutdown link/interface attribute can be used to start labs with interfaces turned off
- Large BGP community lists, implemented on Arista EOS, FRR, and Junos. You can use standard- or large community lists in routing policies
- The netlab validate command will reread validation tests from a modified lab topology file every time you run it. It can also read validation tests from a separate file.
Lab: More Complex VXLAN Deployment Scenario
In the first VXLAN lab, we covered the very basics. Now it’s time for a few essential concepts (before introducing the EVPN control plane or integrated routing and bridging):
- Each VXLAN segment could have a different set of VTEPs (used to build the BUM flooding list)
- While the VXLAN Network Identifier (VNI) must be unique across the participating VTEPs, you could map different VLAN IDs into a single VNI (allowing you to merge two VLAN segments over VXLAN)
- Neither VXLAN VNI nor VLAN ID has to be globally unique (but it helps to make them unique to remain sane)
Technical Writing: Lower Your Expectations
Sean Goedecke published an excellent set of recommendations for good technical writing, including:
- Keep it short
- Try to make your point in the first sentence
- Details matter less than you think.
Based on some emails I received in the past (and the lack of response to the lengthy emails I sent), we should apply the same rules to emails (and all other forms of technical communication).
Worth Watching: AI/ML Data Center Design
What could be better than watching 0x02 Jeffs discuss networking? How about having Petr Lapukhov of the RFC 7938 fame as a guest discussing AI/ML Data Center Design?
Note: Petr disappeared into the information black hole called Facebook over a decade ago, so I wondered how they allowed him to chat on a podcast for hours. It turns out he moved to NVIDIA, which might influence the podcast content a bit, but I’m pretty sure Petr is still Petr ;)
Multi-Pod EVPN Troubleshooting (Part 3)
Last week, we fixed the mismatched route targets in our sample multi-pod EVPN fabric. With that fixed, every PE device should see every other PE device as a remote VTEP for ingress replication purposes. We got that to work on Site-A (AS 65001), but not on Site-B (AS 65002); let’s see what else is broken.
Note: This is the fifth blog post in the Multi-Pod EVPN series. If you stumbled upon it, start with the design overview and troubleshooting overview posts. More importantly, familiarize yourself with the topology we’ll be using; it’s described in the Multi-Pod EVPN Troubleshooting: Fixing Next Hops.
Ready? Let’s go. Here’s our network topology:
netlab as the Universal Configuration Translator
Dan Partelly, a heavy netlab user (and an active contributor), sent me this interesting perspective on how one might want to use netlab without ever building a lab with it. All I added was a bit of AI-assisted editing; my comments are on a grey background.
In all podcasts and interviews I listened to, netlab was referred to as a “lab management solution”. But this is misleading. It’s also a translator, due to its ability to abstract devices, and can easily generate perfectly usable configs for devices or technologies you have never worked on.