Category: Switching

Got this question from a networking engineer attending the Building Next-Generation Data Center online course:

Has anyone an advice on LACP fast rate? When and why should you use it instead of normal LACP?

Apart from forming link aggregation groups, you can use LACP to detect link- and node failures (more details). However:

TL&DR: Installing an Ethernet NIC with two uplinks in a server is easy¹. Connecting those uplinks to two edge switches is common sense². Detecting physical link failure is trivial in Gigabit Ethernet world. Deciding between two independent uplinks or a link aggregation group is interesting. Detecting path failure and disabling the useless uplink that causes traffic blackholing is a living hell (more details in this Design Clinic question).

Want to know more? Let’s dive into the gory details.

Sometime last autumn, I was asked to create a short “network security challenges” presentation. Eventually, I turned it into a webinar, resulting in almost four hours of content describing the interesting gotchas I encountered in the past (plus a few recent vulnerabilities like turning WiFi into a thick yellow cable).

Each webinar section started with a short “This is why we have to deal with these stupidities” introduction. You’ll find all of them collected in the Root Causes video starting the Network Security Fallacies part of the How Networks Really Work webinar.

Pete Lumbis concluded his ASICs for Networking Engineers presentation with a brief overview of types of switching ASICs and a wrap-up.

You can watch his entire 90-minute presentation (sliced into shorter videos) with Free ipSpace.net Subscription.

With the widespread deployment of Ethernet-over-something technologies, it became possible to build MLAG clusters without a physical peer link, replacing it with a virtual link across the core fabric. Avaya was one of the first vendors to implement virtual peer links with Provider Backbone Bridging (PBB) transport, and some data center switching vendors (example: Cisco) offer similar functionality with VXLAN transport.

When 400GbE was still an emerging technology, Mark Nowell explained its basics in an update session of the Data Center Fabric Architectures webinar, starting with 400GbE optics.

Pim van Pelt built an x86/Linux-based using Vector Packet Processor that can forwarding IP traffic at 150 Mpps/180 Gbps forwarding rates on a 2-CPU Dell server with E5-2660 (8 core) CPU.

He described the whole thing in a 8-part series of blog posts and a conference talk. Enjoy!

People keep telling me how well large language models like ChatGPT work for them, so now and then, I give it another try, most often resulting in another disappointment¹. It might be that I suck at writing prompts², or it could be that I have a knack for looking in the wrong places³.

This time⁴ I tried to “figure out⁵” why we need iSCSI checksums if we have iSCSI running over Ethernet which already has checksums. Enjoy the (ChatGPT) circular arguments and hallucinations with plenty of platitudes and no clear answer.

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.

Did you know most chassis switches look like leaf-and-spine fabrics¹ from the inside? If you didn’t, you might want to watch the short Chassis Architectures video by Pete Lumbis (author of ASICs for Networking Engineers part of the Data Center Fabric Architectures webinar).