
120 Part Two • IPv6 Protocols
link software. In other words, this approach implements security
through a piece of software that intercepts datagrams being passed
from the existing IP stack to the local link layer interface. This soft-
ware then does the necessary security processing for those datagrams
and hands them off to the link layer. This approach can be used to
upgrade systems to IPsec support without requiring that their IP stack
software be rewritten.
“Bump-in-the-wire” (BITW) Implement IPsec in a hardware crypto-
graphic processor. The crypto processor gets its own IP address;
when used for individual hosts, the bump-in-the-wire acts much