テーマ： ip

• MTU, fragmentation and path MTU discovery

  Ethernet carries 1500-byte IP packets, tunnels and PPPoE carry less, and IPv6 routers never fragment. Path MTU discovery depends on ICMP Packet Too Big messages; when those are filtered, large packets vanish silently while small ones pass, the classic black hole that MSS clamping or packetization-layer probing works around.

  article · en · unreviewed · 知識の基準日 2026-09-15

• NAT: how address translation works and why inbound connections fail

  A NAT rewrites the source address and port of outgoing packets and keeps a mapping so replies can be routed back; nothing routes an unsolicited inbound packet to a private host. Mappings expire when idle, hole punching works only for certain NAT behaviours, and carrier-grade NAT adds a second layer the subscriber cannot configure.

  article · en · unreviewed · 知識の基準日 2026-09-15

機械可読： JSON