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Re: [RFC/PATCH] "strict" ipv4 reassembly

To: Herbert Xu <herbert@xxxxxxxxxxxxxxxxxxx>
Subject: Re: [RFC/PATCH] "strict" ipv4 reassembly
From: David Stevens <dlstevens@xxxxxxxxxx>
Date: Tue, 17 May 2005 16:55:20 -0700
Cc: Arthur Kepner <akepner@xxxxxxx>, netdev@xxxxxxxxxxx, rick.jones2@xxxxxx
In-reply-to: <20050517232556.GA26846@xxxxxxxxxxxxxxxxxxx>
Sender: netdev-bounce@xxxxxxxxxxx
BSD systems, and derivatives, at least 20 years ago, had a single,
global IP ID for all destinations. The requirement was that at least
a single src-dest pair should be unique, which didn't prohibit all IP
ID's generated by the system from being unique. And BSD systems
generated an ID for every IP packet, not just frags, if memory serves.

IP ID wrap wasn't the concern, obviously, since those two pieces make
a wrap on any one destination more likely-- a wrap is for all packets
sent, not just on one interface or to one destination.

Some later systems use randomization of IP ID to make it harder to
inject data into fragments by guessing the ID, which means the entire
IP ID space isn't necessarily consumed before a "wrap" in the
pseudo-random sequence (thus, may happen even sooner than
a simple increment).

I don't know if any recent, common systems use a per-host global
IP ID, but yes, almost every host did 15-20 years ago
(and after RFC 791 :-) ).

                                        +-DLS


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