Da quello che ho trovato credo che qui si intenda sostanzialmente il supporto dell'incapsulamento (letteralmente l'avvolgimento, a volte si trova anche "wrapping") dello spazio indirizzi con la famiglia di indirizzi VPN-Ipv4, in pratica una sorta di "involucro" virtuale associato con lo spazio indirizzi originale che permette di "lavorare" con la famiglia di indirizzi VPN-Ipv4 delle reti VPN

Hope that helps

Virtual Private Networking Overview

...To emulate a point-to-point link, data is *encapsulated, or wrapped *, with a header that provides routing information that allows packets to traverse a shared or public internetwork. To emulate a private link, the data being sent is encrypted for confidentiality.

http://www.microsoft.com/technet/network/evaluate/technol/tc...

Clearly, a secure VPN requires both authentication and encryption. We know that ESP is the only way to provide encryption, but ESP and AH both can provide authentication: which one do we use?
Packet encapsulation of VPN

The obvious solution of *wrapping* ESP inside of AH is technically possible

http://www.unixwiz.net/techtips/iguide-ipsec.html

In computer networking and telecommunications, MultiProtocol Label Switching (MPLS) is a data-carrying mechanism which emulates some properties of a circuit-switched network over a packet-switched network...
It can be used to carry many different kinds of traffic, including IP packets, as well as native ATM, SONET, and Ethernet frames.

http://en.wikipedia.org/wiki/MPLS

VPN-Ipv4 address family...
VPN-IPV4 Address Family and the address is
defined to be "a 12 byte quantity, beginning with an 8-byte Route
Distinguisher and ending with a 4-byte IPv4 Address".

http://www.ensc.sfu.ca/~ljilja/cnl/presentations/tony/BGP-MP...

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Note added at 2 days1 hr (2007-07-25 09:19:26 GMT)
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>Ho dato un'occhiata ai link che mi hai segnalato. Sembra anche a me che si tratta di questo, dato anche il contenuto della parentesi che segue.
bene, già in pratica una sorta di "impacchettamento" dello spazio indirizzi in modo da supportare la famiglia di indirzzi VPN-Ipv4, un saluto e buon lavoro

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Note added at 3 days2 hrs (2007-07-26 10:21:22 GMT) Post-grading
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>Grazie della consulenza!
grazie mille a te e buon lavoro!