Networking · Cluster
IP and Routing
Addressing, forwarding, and route selection.
- 01 The IPv4 Header Fields That Forwarding Rewrites Which of the twenty header bytes a router must read, which it decrements or recomputes in place, and where the header checksum stops protecting anything.
- 02 Longest-Prefix Match and the Structures That Implement It Why a routing table cannot be a hash map, how a binary trie answers the longest-prefix query, and what multibit tries and TCAM buy in exchange for memory.
- 03 CIDR Aggregation and the Reasons It Cannot Fully Summarize How prefix length replaced address classes, which blocks can be merged into one announcement, and why holes and multi-homing leave the table larger than the address plan suggests.
- 04 How a Router Decides a Destination Is On-Link The difference between a route that names a neighbour and one that names a gateway, how the link-layer address is resolved, and what happens when resolution fails.
- 05 Fragmentation, the MTU Floor, and Path MTU Discovery Black Holes How a datagram is split into pieces that a smaller link can carry, why the reassembly rules create ambiguity, and the specific way discovery fails when ICMP is filtered.
- 06 ICMP Errors as the Only Feedback Channel for Forwarding Which errors a router is allowed to generate, what it must quote back, and why rate limiting and filtering turn a diagnostic protocol into a silent failure mode.
- 07 IPv6 Forwarding, Extension Header Chains, and Scoped Addresses How a fixed forty-byte header pushes options into a chain a router must walk, why scopes are part of the address, and which rules a forwarder applies differently than in IPv4.
- 08 Route Preference, Metric, and the Split Between RIB and FIB How competing routes to one prefix are ranked, why administrative distance is not a metric, and what the control plane must do before the forwarding plane can use a table.
- 09 Policy Routing: Keying the Lookup on More Than the Destination How multiple routing tables and a rule list restore source-based and interface-based selection, what the extra lookup costs, and why asymmetric paths become routine.
- 10 The BGP Best-Path Order and Why Its Steps Are Ordered That Way The comparison sequence a router applies to routes for one prefix, which attributes are local to an autonomous system, and how the tiebreak steps create hot-potato routing.