Whenever I compare MPLS-based Segment Routing (SR-MPLS) with it’s distant IPv6-based cousin (SRv6), someone invariably mentions the specter of large label stacks that some hardware cannot handle, for example:

Do you think vendors current supported label max stack might be an issue when trying to route a packet from source using Adj-SIDs on relatively big sized (and meshed) cores? Many seem to be proposing to use SRv6 to overcome this.

I’d dare to guess that more hardware supports MPLS with decent label stacks than SRv6, and if I’ve learned anything from my chats with Laurent Vanbever, it’s that it sometimes takes surprisingly little to push the traffic into the right direction. You do need a controller that can figure out what that little push is and where to apply it though.

In early June 2022 I described a netlab topology using VLAN trunks in netlab. That topology provided pure bridging service for two IP subnets. Now let’s go a step further and add a router-on-a-stick:

• S1 and S2 are layer-2 switches (no IP addresses on red or blue VLANs).
• ROS is a router-on-a-stick routing between red and blue VLANs.
• Hosts on red and blue VLANs should be able to ping each other.

Just FYI: I pushed out netlab release 1.3.3 yesterday. It’s a purely bug fix release, new functionality and a few breaking changes are coming in release 1.4 in a few weeks.

Some of the bugs we fixed weren’t exactly pleasant; if you’re using release 1.3.2 you might want to upgrade with pip3 install --upgrade networklab.

In the EVPN/MPLS Bridging Forwarding Model blog post I mentioned numerous services defined in RFC 7432. That blog post focused on VLAN-Based Service Interface that mirrors the Carrier Ethernet VLAN mode.

RFC 7432 defines two other VLAN services that can be used to implement Carrier Ethernet services:

• Port-based service – whatever is received on the ingress port is sent to the egress port(s)
• VLAN bundle service – multiple VLANs sharing the same bridging table, effectively emulating single outer VLAN in Q-in-Q bridging.

And then there’s the VLAN-Aware Bundle Service, where a bunch of VLANs share the same MPLS pseudowires while having separate bridging tables.

Daniel Dib posted a number of excellent questions on Twitter, including:

While forwarding a received Type-5 LSA to other areas, why does the ABR not change the Advertising Router ID to it’s own IP address? If ABR were able to change the Advertising Router ID in the Type-5 LSA, then there would be no need for Type-4 LSA which meant less OSPF overhead on the network.

TL&DR: The current implementation of external routes in OSPF minimizes topology database size (memory utilization)

Before going to the details, try to imagine the environment in which OSPF was designed, and the problems it was solving.

A few weeks ago I described how Cumulus Linux tried to put lipstick on a pig reduce the Linux data plane configuration pains with Network Command Line Utility. NCLU is a thin shim that takes CLI arguments, translates them into FRR or ifupdown configuration syntax, and updates the configuration files (similar to what Ansible is doing with something_config modules).

Obviously that wasn’t good enough. Cumulus Linux 4.4 introduced NVIDIA User Experience¹ – a full-blown configuration engine with its own data model and REST API².

The star of the netlab release 1.3.2 is Mikrotik RouterOS version 7. Stefano Sasso did a fantastic job adding support for VLANs, VRFs, OSPFv2, OSPFv3, BGP, MPLS, and MPLS/VPN, plus the libvirt box-building recipe.

Jeroen van Bemmel contributed another major PR¹ adding VLANs, VRFs, VXLAN, EVPN, and OSPFv3 to Nokia SR OS.

Other platform improvements include:

Ian Nightingale published an interesting story of connectivity problems he had in a VXLAN-based campus network. TL&DR: it’s always the MTU (unless it’s DNS or BGP).

The really fun part: even though large L2 segments might have magical properties (according to vendor fluff), there’s no host-to-network communication in transparent bridging, so there’s absolutely no way that the ingress VTEP could tell the host that the packet is too big. In a layer-3 network you have at least a fighting chance…

For more details, watch the Switching, Routing and Bridging part of How Networks Really Work webinar (most of it available with Free Subscription).

Christopher Werny covered another interesting IPv6 security topic in the hands-on part of IPv6 security webinar: traffic filtering in the age of dual-stack and IPv6-only networks, including filtering extension headers, filters on Internet uplinks, ICMPv6 filters, and address space filters.

Most BGP implementations I’ve worked with split the neighbor BGP configuration into two parts:

• Global configuration that creates the transport session
• Address family configuration that activates the address family across a configured transport session and changes the parameters that affect BGP updates

AS numbers, source interfaces, peer IPv4/IPv6 addresses, and passwords clearly belong to the global neighbor configuration.

Most networking engineers immediately think about VXLAN and data center switches when they hear about EVPN. While that’s the most hyped use case, EVPN standardization started in 2012 as a layer-2 VPN solution on top of MPLS transport trying to merge the best of VPLS and MPLS/VPN worlds.

If you want to understand how any technology works, and what its quirks are, you have to know how it was designed to be used. In this blog post we’ll start that journey exploring the basics of EVPN used in a simple MLPS network with three PE-routers:

Responding to my Infrastructure as Code Sounds Scary blog post, Deepak Arora posted an interesting (and unfortunately way too accurate) list of challenges you might encounter when trying to introduce network automation in an enterprise environment.

He graciously allowed me to repost his thoughts on my blog.

Why don’t we agree on that :

netlab release 1.3 introduced support for VXLAN transport with static ingress replication and EVPN control plane. Last week we replaced a VLAN trunk with VXLAN transport, now we’ll replace static ingress replication with EVPN control plane.

Bruce Davie makes an excellent point in his QUIC Is Not a TCP Replacement article – QUIC not a next-generation TCP, it’s a reliable RPC transport protocol.

What Bruce forgot to mention is that we had a production-grade RPC transport protocol for years – SCTP (Stream Control Transmission Protocol) – but it had two shortcomings:

• It wasn’t invented by the right people;
• It used a different IP protocol number and thus upset every ossified middlebox in the Internet. QUIC hides on top of UDP (because adding extra headers makes at least as much sense as junk DNA).

Jeroen Van Bemmel created another interesting netlab topology: EVPN/VXLAN between SR Linux fabric and FRR on Linux hosts based on his work implementing VRFs, VXLAN, and EVPN on FRR in netlab release 1.3.1.

Bonus point: he also described how to do multi-vendor interoperability testing with netlab.

If only he wouldn’t be publishing his articles on a platform that’s almost as user-data-craving as Google.