IP Protocol Reference
Reference 为 IPv4 和 IPv6: addressing, fragmentation, 头结构, 和 routing.
IPv4 and IPv6
IPv4 uses 32-bit addresses (dotted-decimal), IPv6 uses 128-bit addresses (hex with colons). IPv6 eliminates NAT, simplifies header structure, and removes broadcast (uses multicast instead). IPv4 headers are variable-length (options); IPv6 headers are fixed 40 bytes with extension headers. IPv6 addresses have scope (link-local, global) and can be autoconfigured via SLAAC. Dual-stack and tunneling (6to4, 6rd) aid transition.
- IPv4
- 32-bit, dotted-decimal
- IPv6
- 128-bit, hex:colons
- NAT
- IPv4 only, IPv6 eliminates
192.0.2.12001:db8::1end-to-endFragmentation and Routing
IPv4 fragmentation splits packets exceeding MTU, reassembled at the destination. IPv6 fragmentation is end-host only via Fragment extension header; routers drop oversized packets with ICMP6 Packet Too Big. The TTL/Hop Limit field prevents routing loops. DSCP/ECN fields support QoS and congestion signaling. Routing uses longest-prefix match on the forwarding table. PMTUD discovers the path MTU to avoid fragmentation.
- fragmentation
- IPv4: routers, IPv6: hosts
- TTL/Hop Limit
- Loop prevention
- PMTUD
- Discover path MTU
MTU exceededdecrement per hopavoid fragmentation