Tagged: ospf
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OSPF on Linux Part 1: A Brief History of Routing on Linux
The first post in a companion series to OSPF Deep Dive: how Linux went from a kernel that could route packets but not speak a routing protocol, through GNU Zebra and Quagga, to FRRouting. History first, because the config in Part 3 makes more sense once you know why it looks the way it does.
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OSPF on Linux Part 2: Why FRRouting Is the Defacto Choice
The zebra/protocol-daemon/vtysh architecture from the inside, FRR against its one real remaining competitor, BIRD, and why FRR's Cisco-shaped CLI is a genuine advantage for this specific series rather than a cosmetic one.
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OSPF on Linux Part 3: Installing and Configuring OSPF with FRR
Getting FRR onto a Linux box for real: the package, the users it creates without asking, the daemon on/off switch in /etc/frr/daemons, and the first router ospf block in vtysh. Verified against a real install, not written from memory.
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OSPF on Linux Part 4: Wiring LAB-LNX into the OSPF Deep Dive Lab
Adding a fourth router to CORE-CSR, BRANCH-FGT, and EDGE-MX: a Linux box running the FRR config from Part 3, walked from Down to Full against the neighbor state machine from OSPF Deep Dive Part 1, with an LSDB parity check across all four platforms.
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OSPF on Linux Part 5: Troubleshooting OSPF on Linux
The closing post: OSPF Deep Dive Part 11's three-vendor show-command table extended to four with FRR's vtysh, then the failure modes that only exist on Linux, ip_forward, a firewall dropping protocol 89, multicast group membership, the wrong network namespace, veth MTU, and tcpdump on the wire.
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OSPF Deep Dive Part 1: Neighbor States, DR/BDR Election, and Network Types
The first post in a full OSPF series covering Cisco, FortiOS, and Junos: the hello protocol, the neighbor state machine, why DR/BDR election exists, and the network types that decide whether an election happens at all.
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OSPF Deep Dive Part 10: A Vendor-Neutral Troubleshooting Methodology
A structured way to diagnose OSPF problems that works on any vendor, because it's built on the neighbor state machine from Part 1, not on any platform's specific commands: what state is it stuck at, and what does that state rule in or out.
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OSPF Deep Dive Part 11: Show Commands and the LSDB, Side by Side
The same neighbor table, interface state, and LSDB, read through three different command sets: Cisco IOS/IOS-XE, FortiOS, and Junos, mapped side by side against the CORE-CSR/BRANCH-FGT/EDGE-MX lab from this series.
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OSPF Deep Dive Part 12: A Multi-Vendor Outage, Start to Finish
A closing walkthrough on the CORE-CSR/BRANCH-FGT/EDGE-MX lab: a complaint with no down interfaces and no failed adjacencies anywhere, a red herring that turns out to be real but irrelevant, and a root cause that traces straight back to Part 3's reference-bandwidth warning.
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OSPF Deep Dive Part 2: LSA Types and the Area Type Hierarchy
What actually travels in the LSDB: the seven LSA types that matter in practice, and how stub, totally stubby, NSSA, and totally NSSA areas each filter a different subset of them.
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OSPF Deep Dive Part 3: The SPF Algorithm, Cost, and Route Selection
How a full LSDB actually becomes a routing table: Dijkstra's algorithm, the reference-bandwidth cost trap every vendor shares, and why intra-area, inter-area, and external routes are preferred in that exact order regardless of cost.
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OSPF Deep Dive Part 4: Virtual Links, Summarization, and Redistribution
Fixing the lab's missing backbone connection with a virtual link, then summarizing at the ABR and redistributing a static route at the NSSA's ASBR, with working syntax on Cisco, FortiOS, and Junos for each.
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OSPF Deep Dive Part 5: OSPFv3 and Running OSPF Over IPv6
OSPFv3 isn't OSPFv2 with bigger addresses. It separates topology from addressing, drops built-in authentication in favor of IPsec, and runs over link-local addresses by default, plus the per-vendor syntax to bring it up on Cisco, FortiOS, and Junos.
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OSPF Deep Dive Part 6: Authentication and Security Hardening
What an unauthenticated OSPF segment actually exposes, why plaintext and MD5 authentication are both weaker than they look, and how to configure HMAC-SHA key chains on Cisco, FortiOS, and Junos.
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OSPF Deep Dive Part 7: Cisco IOS/IOS-XE Implementation and Gotchas
CORE-CSR's actual configuration: process ID scope, the network-statement vs interface-based config split, the passive-interface-default trap, and why raising reference-bandwidth only ever warns once, locally, at configuration time.
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OSPF Deep Dive Part 8: FortiOS Implementation and Gotchas
BRANCH-FGT's configuration: why FortiOS has no passive-interface-default equivalent, how OSPF scopes to a VDOM, the router-id selection rule that actually differs from Cisco's, and how OSPF interacts with SD-WAN policy routes.
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OSPF Deep Dive Part 9: Junos Implementation and Gotchas
EDGE-MX's configuration: why Junos never adds an interface to OSPF by accident, the policy-based redistribution model, and the one default that catches Cisco and FortiOS engineers off guard, OSPF outranking eBGP by default.
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SDWAN Resilience Part 3: DC to DCE Routing — Static, OSPF, and BGP
The hub FortiGate has to glue the spoke overlay to the data-centre environment that hosts the services. Static, OSPF, and eBGP each work — but only two of them fail correctly when the DCE peering goes down on one DC and not the other.
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Designing an Arista SDWAN Spoke with Enhanced HA, Dual DIA, and OSPF
Building a resilient Arista (formerly VeloCloud) SDWAN spoke: two Edges in Enhanced HA, two DIA circuits wired the optimal way, a multi-VLAN LAN, OSPF for route exchange, and the caveats that bite in practice.
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Linux Networking from the Ground Up: Network Namespaces, veth Pairs, and Building a Multi-Router Lab on One Host
Build a real multi-router BGP and OSPF lab on a single Linux box using network namespaces, veth pairs, and FRRouting — no VMs, no containers, no GNS3. A practical walk-through of the primitives that GNS3, Docker, and Kubernetes are quietly using under the hood.