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Featured posts

Active/Active Firewalls the Routing Way: Palo Alto, BGP, and a 3-Second Hold Timer

Two Palo Altos, both forwarding, no floating IPs: eBGP to the N9K border pair and ECMP does the rest. Then a failover test found 90 seconds of silence, BFD refused to help, and the live re-test revealed that recovery, not failure, is where packets go to die.

10 min read

infiniband verbs banner, hand-drawn excalidraw style: green RNIC chip icon

Skip the Kernel: InfiniBand Verbs in Five Minutes

One Adapter, Many Tenants: InfiniBand Partitions and SR-IOV, From the Firmware to the Wire

Routing Kubernetes into a CLOS fabric with Cilium BGP

Building a Self-Healing OpenShift Platform for AI Inference - and an Agent to Watch It

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Courses

Fabric lab: build a small cloud, end to end

Build a Cloud-Style Fabric Lab

An 11-part, copy-paste-reproducible build of a small cloud: leaf-spine VXLAN/EVPN fabric, Kubernetes with Cilium BGP, and Active/Active firewalls, all virtual, all on one box.

Members only

Mastering BGP

Mastering BGP delves into its architectural strengths: reliability (TCP foundation, keepalives), stability (MAI, dampening, route refresh), scalability (reflection, confederations, selective propagation), and flexibility (policy-driven, path attributes, communities).

Mastering IS-IS

IS-IS, a robust link-state routing protocol, is key for scalable networks. This series demystifies IS-IS from its Layer 2 operations, NSAP addressing, and hierarchical design to advanced traffic engineering with practical Juniper configurations. Master IS-IS for high-performance network designs.

Network Automation with GO

Hello and welcome to "Network Automation with Go," a blog series designed for network engineers and developers. We'll explore how Go's speed, concurrency, and simplicity can help you build powerful, efficient, and scalable network automation solutions. Get ready to level up your skills!

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dual-plane backend networks for b300 gpu clusters

Dual-Plane Backend Networks for B300-Class GPU Clusters

At a few thousand GPUs, the backend network becomes a probability problem: something is always broken and the hash is always unlucky. The fix is two identical fabrics with zero cross-links. A deep dive into dual-plane design, sized for B300 nodes with 800G per GPU.

11 min read

Networks Behind AI, post 2: ECMP's elephant problem

ECMP Has an Elephant Problem

Two elephant flows, six trials, six collisions: one uplink carried everything while its twin sat at zero, and every dashboard stayed green. The measured polarization, the four-witness diagnostic chase, and the birthday math production fabrics live with.

6 min read

Frontend Network vs Backend Network in AI Data Centers

Your AI cluster is two networks wearing one badge. One is judged by whether users notice it. The other is judged by whether GPUs wait on it. Frontend vs backend: the traffic, the rules, and how to design the GPU fabric so compute never waits.

7 min read

Networks Behind AI, post 1: the traffic is different

The Traffic Is Different: Why AI Breaks Your Network

5,412 connections on my Kubernetes cluster versus one RDMA flow moving 59.5 GB a minute. Then three identical transfers, one degraded path, and 32 percent of the workers' time gone. AI traffic measured, not described.

6 min read

InfiniBand for the Ethernet Engineer.

Credit-based flow control, a daemon that runs the whole fabric, adapters that hand out pointers into remote RAM, and switches that do math. Every InfiniBand idea an Ethernet engineer should know, demonstrated live on a real InfiniBand fabric.

10 min read

Build a Cloud-Style Fabric Lab, Part 11: End to End

The finale: one request traced live through all eight hops the series built, the five traps ranked by hours lost, and what I would do differently next time. Plus the honest single point of failure the design still carries.

7 min read

Build a Cloud-Style Fabric Lab, Part 10: The Stack

Longhorn on the workers (the storage leaves finally earn their name), 60Gi of language models surviving node death, a dozen apps behind one login, and the five-object checklist that publishes anything.

5 min read

Build a Cloud-Style Fabric Lab, Part 9: Ingress

One Gateway claims the BGP-advertised VIP, a cert-manager chain makes every app green-padlock HTTPS, sixteen HTTPRoutes share one door, and split-view DNS gives the same names two honest answers.

7 min read

CPU vs GPU vs DPU vs NPU vs TPU vs FPGA: One Job Each

Every chip in the modern data center exists because one bottleneck got expensive enough to deserve its own silicon. The whole zoo in one sitting: real photos, one table, and a memory trick that makes the differences stick.

3 min read

Build a Cloud-Style Fabric Lab, Part 8: Cilium

One helm install, three jobs: the pod network, kube-proxy's whole duty in eBPF, and BGP from every node to its leaf pair's anycast gateway. Plus the consent chain that keeps VIP announcements deliberate, and the anycast peering quirk worth knowing.

11 min read

Build a Cloud-Style Fabric Lab, Part 7: Kubernetes

kubeadm the deliberate way: a load-balanced control-plane endpoint before anything else, stacked etcd split across leaf pairs, no kube-proxy by design, and the NotReady checkpoint that makes Part 8 make sense.

7 min read

Build a Cloud-Style Fabric Lab, Part 6: The Nodes

One golden image, one netplan file per node: LACP bonds into the vPC pairs, out-of-band management, the virtio link-speed trap that silently breaks 802.3ad, and the switch side of every bond.

9 min read

Build a Cloud-Style Fabric Lab, Part 5: The Edge

Wiring Active/Active firewalls into the fabric: four eBGP sessions, thirteen prefixes up and one default down, device-bound NAT, two DNAT pinholes for all inbound traffic, and the vPC SVI timer lesson.

18 min read

Build a Cloud-Style Fabric Lab, Part 4: The Overlay

VXLAN tunnels between loopbacks, EVPN as the directory, anycast gateways everywhere, and the route-target auto trap that silently empties eBGP fabrics. With the complete overlay configs for all twelve switches.

19 min read

Build a Cloud-Style Fabric Lab, Part 3: The Underlay

Twelve switches become a fabric: loopbacks, /31s, jumbo MTU, and eBGP as the only routing protocol. Plus the promised look inside a vPC leaf pair, and the three-command verification that proves the underlay.

18 min read

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