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RE: Minimum IP Compression Algorithm for Interoperability
At 12:44 20.6.2000 -0700, Marc Hasson wrote:
>There are apparently some people who implemented these Alder checksums
>and deflate headers, presumably because of their usage of the ZLIB
>implementation. And these people (several?) interoperated fine at
>bake-offs, with this extra overhead that ZLIB generates in certain
>configurations. Even someone in *that* group stated "...we were all
>(except IRE) wrong.". But, admittedly, properly enforcing the basic
>specs could be a problem for a deployed based depending upon how much
>interoperation is going on out there now. Can anyone comment on
>whether there's significant inter-vendor DEFLATE usage with the extra
>Adler32 checksums and header?
>
>OTOH, someone coding strictly from the specs as I and others did would
>*not* (and don't) have Adler32 checksums nor deflate headers in their
>implementations. Perhaps we need a poll on what vendors have done
>what.
>
Since this:
>"...we were all (except IRE) wrong."
was my own speech, I'd like to announce that I did after that.
Since the RFCs are _perfectly_ clear that the header and checksum
MUST NOT be used, I removed them.
F-Secure VPN+ 4.2 uses them, in 5.0 they are removed.
5.0 also compresses the inner header in tunnel mode.
This will break interoperability, even with our own product.
But such is life. Since the tunnel mode was also broken,
I can just say the 5.0 is the first version to do compression
(correctly).
BTW, just changing the function calls (as suggested by IRE)
does not solve the problem. I needed a short discussion with
Mark Adler (of zlib fame) on the correct use of zlib's undocumented
features, but finally got it right.
And no, we don't support lzs.
I'd be interested what the gateway people have to say. cisco?
J–rn Sierwald, F-Secure Corp.
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