9 / 14 IP & Addressing

Both Behind A Box

Two home users, on different ISPs, each behind a NAPT with a single public IPv4 address, want their laptops to open a direct connection to each other. Neither is running a server.

Which statement identifies the architectural problem, in the terms RFC 2993 uses?

A

A NAPT can hold at most 65535 simultaneous mappings, and typical household traffic exhausts the table before a peer-to-peer connection can be created.

B

Neither host owns a globally reachable address, and a packet arriving at a NAT's public address has no mapping to a private host until that host has sent something outbound first; a globally routable address per host is the property IPv6 restores.

C

The NAT rewrites the IP header but not the TCP checksum, so the peer discards every segment as corrupt.

D

RFC 1918 private ranges are filtered by ISPs, and IPv6 fixes this by encrypting addresses so intermediate routers cannot inspect them.