Fix and add a workaround on an issue of EtherIP packet with reversed

version field sent via gif(4)+if_bridge(4).  The EtherIP
implementation found on FreeBSD 6.1, 6.2, 6.3, 7.0, 7.1, and 7.2 had
an interoperability issue because it sent the incorrect EtherIP
packets and discarded the correct ones.

This change introduces the following two flags to gif(4):

 accept_rev_ethip_ver: accepts both correct EtherIP packets and ones
    with reversed version field, if enabled.  If disabled, the gif
    accepts the correct packets only.  This flag is enabled by
    default.

 send_rev_ethip_ver: sends EtherIP packets with reversed version field
    intentionally, if enabled.  If disabled, the gif sends the correct
    packets only.  This flag is disabled by default.

These flags are stored in struct gif_softc and can be set by
ifconfig(8) on per-interface basis.

Note that this is an incompatible change of EtherIP with the older
FreeBSD releases.  If you need to interoperate older FreeBSD boxes and
new versions after this commit, setting "send_rev_ethip_ver" is
needed.

Reviewed by:	thompsa and rwatson
Spotted by:	Shunsuke SHINOMIYA
PR:		kern/125003
MFC after:	2 weeks

1 files changed, 30 insertions, 1 deletions

diff --git a/share/man/man4/gif.4 b/share/man/man4/gif.4
index 936898f..a70db08 100644
--- a/share/man/man4/gif.4
+++ b/share/man/man4/gif.4
@@ -29,7 +29,7 @@
 .\"
 .\" $FreeBSD$
 .\"
-.Dd April 10, 1999
+.Dd June 8, 2009
 .Dt GIF 4
 .Os
 .Sh NAME
@@ -256,3 +256,32 @@ had a multi-destination behavior, configurable via
 .Dv IFF_LINK0
 flag.
 The behavior is obsolete and is no longer supported.
+.Pp
+On
+.Fx
+6.1, 6.2, 6.3, 7.0, 7.1, and 7.2
+the
+.Nm
+sends and receives incorrect EtherIP packets with reversed version
+field when
+.Xr if_bridge 4
+is used together.  As a workaround on this interoperability issue, the
+following two
+.Xr ifconfig 8
+flags can be used:
+.Bl -tag -width "accept_rev_ethip_ver" -offset indent
+.It accept_rev_ethip_ver
+accepts both correct EtherIP packets and ones with reversed version
+field, if enabled.  If disabled, the
+.Nm
+accepts the correct packets only.  This flag is enabled by default.
+.It send_rev_ethip_ver
+sends EtherIP packets with reversed version field intentionally, if
+enabled.  If disabled, the
+.Nm
+sends the correct packets only.  This flag is disabled by default.
+.El
+.Pp
+If interoperability with the older
+.Fx
+machines is needed, both of these two flags must be enabled.