netdev - RE: How to use gretap with bridge?

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Date:	Thu, 29 Oct 2009 17:04:02 -0500
From:	"Neulinger, Nathan" <nneul@....edu>
To:	"Herbert Xu" <herbert@...dor.apana.org.au>,
	"Stephen Hemminger" <shemminger@...tta.com>
Cc:	<netdev@...r.kernel.org>
Subject: RE: How to use gretap with bridge?

Now I see it - Stephen actually had it right on - the problem is that
the gre tunnel is creating a MAC address on the fly based on the tunnel
endpoint ip address, so if the tunnel endpoint address starts with an
odd number, it hits the multicast check in the bridging code. (I'm sure
that's what he meant and I just missed it entirely.)

Simplest option would probably be to just mask off the first octet with
0xFD or using the ip as the last four octets of the mac instead of the
first four.

-- Nathan

------------------------------------------------------------
Nathan Neulinger                       nneul@....edu
Missouri S&T Information Technology    (573) 612-1412
System Administrator - Principal       KD0DMH


> -----Original Message-----
> From: Neulinger, Nathan
> Sent: Thursday, October 29, 2009 3:59 PM
> To: 'Herbert Xu'
> Cc: 'netdev@...r.kernel.org'
> Subject: RE: How to use gretap with bridge?
> 
> As a note - the bridging/tunneling is working perfectly once I force
it
> to use a bogus IP range that starts with an even number, but
> unfortunately, that's not going to work so good given that our primary
> address space is 131.151.x.x.
> 
> Any ideas on what is up with the even/odd error?
> 
> -- Nathan
> 
> ------------------------------------------------------------
> Nathan Neulinger                       nneul@....edu
> Missouri S&T Information Technology    (573) 612-1412
> System Administrator - Principal       KD0DMH
> 
> 
> > -----Original Message-----
> > From: Neulinger, Nathan
> > Sent: Thursday, October 29, 2009 3:22 PM
> > To: 'Stephen Hemminger'
> > Cc: netdev@...r.kernel.org
> > Subject: RE: How to use gretap with bridge?
> >
> > I was referring to the local IP in the "ip link add ... remote
> x.z.z.z
> > local y.z.z.z" command specifying the endpoints of the tunnel. It
> lets
> > it be added to the bridge if y is even, but not if y is odd. Why
> should
> > it care what the IP of the tunnel endpoints are?
> >
> > -- Nathan
> >
> > ------------------------------------------------------------
> > Nathan Neulinger                       nneul@....edu
> > Missouri S&T Information Technology    (573) 612-1412
> > System Administrator - Principal       KD0DMH
> >
> >
> > > -----Original Message-----
> > > From: Stephen Hemminger [mailto:shemminger@...tta.com]
> > > Sent: Thursday, October 29, 2009 3:01 PM
> > > To: Neulinger, Nathan
> > > Cc: netdev@...r.kernel.org
> > > Subject: Re: How to use gretap with bridge?
> > >
> > > On Thu, 29 Oct 2009 14:01:31 -0500
> > > "Neulinger, Nathan" <nneul@....edu> wrote:
> > >
> > > > Further testing - if the leading octet of the 'local' address is
> > > even,
> > > > it allows it to be added to bridge, if it's odd, it won't.
> > > >
> > > > Any ideas?
> > > >
> > >
> > > If leading octet of MAC address is odd, then bridge thinks it
> > > is not a valid ethernet for bridging because it is a multicast
> > > address.
> > >
> > >
> > > --
--
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