DNS packets were capped at 512 bytes in 1987 when lookups were simple. Now 75% of major websites exceed 738 bytes, forcing TCP fallback that fragments DNSSEC responses. The limit persists because changing it breaks middleboxes everywhere.
TCP guarantees in-order delivery. Sounds reasonable until HTTP/2 multiplexes streams over one connection and a single lost packet stalls everything. At 2% packet loss, six parallel HTTP/1.1 connections actually win. HTTP/3 had to rebuild transport entirely.
BGP assumed cooperative peers in 1989. Routers trust route announcements by default. In 2018, attackers redirected Amazon traffic and stole $150,000 in cryptocurrency. The vulnerability remains because fixing it requires coordinated global adoption that isn't happening.