RFC 4891:Using IPsec to Secure IPv6-in-IPv4 Tunnel...
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Multihoming


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... in tunnel mode is also more difficult. However, because the Mobility and Multihoming Protocol (MOBIKE) [RFC4555] supports only tunnel mode ...


... Eronen, P., "IKEv2 Mobility and Multihoming Protocol (MOBIKE)", RFC 4555prop, June 2006. ...



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