Blog Posts in September 2024
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 ;)
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!
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:
- Routes received from BGP neighbors are stored in BGP RIB.
- Routes redistributed into BGP from other protocols are (re)created in the BGP RIB.
- BGP selects the best routes in BGP RIB using its convoluted set of rules.
- Best routes from the BGP RIB are advertised to BGP neighbors
- 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)
- 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 ;)