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SubjectRe: [PATCH] l2tp: Add protocol field decompression
From: Sam Protsenko <>
Date: Fri, 14 Dec 2018 19:59:21 +0200

> When Protocol Field Compression (PFC) is enabled, the "Protocol" field
> in PPP packet will be received without leading 0x00. See section 6.5 in
> RFC 1661 for details. So let's decompress protocol field if needed, the
> same way it's done in drivers/net/ppp/pptp.c.
> In case when "nopcomp" pppd option is not enabled, PFC (pcomp) can be
> negotiated during LCP handshake, and L2TP driver in kernel will receive
> PPP packets with compressed Protocol field, which in turn leads to next
> error:
> Protocol Rejected (unsupported protocol 0x2145)
> because instead of Protocol=0x0021 in PPP packet there will be
> Protocol=0x21. This patch unwraps it back to 0x0021, which fixes the
> issue.
> Sending the compressed Protocol field will be implemented in subsequent
> patch, this one is self-sufficient.
> Signed-off-by: Sam Protsenko <>

Applied, thanks.

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