ANONsec: Anonymous IPsec to Defend Against Spoofing Attacks

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Last updated 2004-05-06
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Recent attacks on core Internet infrastructure indicate an increased vulnerability of TCP connections to spurious resets (RSTs). TCP has always been susceptible to such RST spoof attacks, which were indirectly protected by checking that the RST sequence number was inside the current receive window, as well as via the obfuscation of TCP endpoint and port numbers. For pairs of well-known endpoints often over predictable port pairs, such as BGP, increases in the path bandwidth-delay product of a connection have sufficiently increased the receive window space that off-path third parties can guess a viable RST sequence number. This document addresses this vulnerability, discussing proposed solutions at the transport level and their inherent challenges, as well as existing network level solutions and the feasibility of their deployment. Finally, it proposes an extension to IPsec configuration called ANONsec that intends to efficiently and scalably secure any transport protocol from such off-path third-party spoofing attacks.


Joseph Touch (

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