kern/61215: off-by-one error likely in ip_fragment()

Andre Oppermann andre at
Thu Jan 15 12:44:32 PST 2004

David Gilbert wrote:
> >>>>> "Andre" == Andre Oppermann <andre at> writes:
> >>  I'm not sure what's up.  Your patch wouldn't apply to v1.17 of my
> >> if_gre.c, so something's wrong with the patch.  Regardless, I
> >> applied the patch by hand and things didn't work yet.
> Andre> Didn't it apply because of patch complaining or because it
> Andre> didn't match at all?
> It looked like it was mostly whitespace errors or somesuch.  The patch
> algorythm couldn't find the are to patch.
> ... however, as I said... I was able to patch it by hand.


> >> The kernel didn't crash, but packets routed into the tunnel didn't
> >> show up on the outbound interface.  I my case, the machine has
> >> three ethernet-like interfaces and the gre.
> >>
> >> wi0 and sis0 are internal networks.  dc0 is the external network
> >> interface.  A /32 route for the far end of the tunnel exists (and
> >> works on the new kernel ... it pings), but pings into the tunnel
> >> don't generate traffic on dc0 (at least according to tcpdump).
> Andre> Do you enable "link1" on your GRE interface?
> What does link1 do to gre?  It hasn't been necessary before.
> Andre> What does ifconfig -a show?
> Ifconfig -a output was normal.  I didn't save the new output, but the
> old output is the same ... save the fact that the new output prints
> the tunnel endpoints.
> gre0: flags=9011<UP,POINTOPOINT,LINK0,MULTICAST> mtu 1476
>         inet6 fe80::2d0:9ff:fee4:bbc2%gre0 prefixlen 64 scopeid 0x5
>         inet --> netmask 0xfffffffc

Where are the outer addresses?

It should look like this (at least I was able to get correct packets
out of it this way):

        tunnel inet -->
        inet --> netmask 0xffffff00

I get to this by configuring the following:

ifconfig gre0 create  # create gre0 interface
ifconfig gre0 tunnel  # outer addresses 
ifconfig gre0  # inner addresses
ifconfig gre0 link1  # chose nexthop computation method
ifconfig gre0 up  # enable gre tunnel


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