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pf: syncookie support

Description

pf: syncookie support

Import OpenBSD's syncookie support for pf. This feature help pf resist
TCP SYN floods by only creating states once the remote host completes
the TCP handshake rather than when the initial SYN packet is received.

This is accomplished by using the initial sequence numbers to encode a
cookie (hence the name) in the SYN+ACK response and verifying this on
receipt of the client ACK.

Reviewed by: kbowling
Obtained from: OpenBSD
MFC after: 1 week
Sponsored by: Modirum MDPay
Differential Revision: https://reviews.freebsd.org/D31138

Details

Provenance
kpAuthored on May 20 2021, 9:54 AM
Reviewer
kbowling
Differential Revision
D31138: pf: syncookie support
Parents
R10:ee9c3d38039e: pf: factor out pf_synproxy()
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