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Date:      Thu, 01 Jan 1998 18:19:50 +0000
From:      Brian Somers <brian@awfulhak.org>
To:        Joerg Wunsch <joerg_wunsch@uriah.heep.sax.de>
Cc:        Brian Somers <brian@awfulhak.org>, John-Mark Gurney <gurney_j@efn.org>, freebsd-bugs@hub.freebsd.org, freebsd-hackers@FreeBSD.ORG
Subject:   Re: kern/5404: slXX slip (tun & ppp) interfaces always point to point 
Message-ID:  <199801011819.SAA19774@awfulhak.demon.co.uk>
In-Reply-To: Your message of "Thu, 01 Jan 1998 18:50:07 %2B0100." <19980101185007.59283@uriah.heep.sax.de> 

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> As Brian Somers wrote:
> 
> > I intended to remove the possibility of netmasks and broadcast 
> > addresses for pointopoint links, but retrospectively, this will break 
> > the ability to attach to a peer that proxy arps for you (well, it's 
> > already broken).
> 
> Why?  Proxyarping is done on the Ethernet interface, and this one
> still has a netmask.

I mean in the sense that the client cannot broadcast on the network 
at the other end of the pointopoint link, or can it ?  I guess you 
could set up a static route for the broadcast address.  That should 
work.  I haven't tried.

> > I would suggest (and I'm willing to do it) adding the ability to use 
> > SIOCSIFPOINTOPOINT and SIOCGIFPOINTOPOINT on sl* ppp* and tun*.  The 
> > default is that these interfaces are pointopoint, but you can change 
> > that by issuing the `S' ioctl.
> 
> Nope, you can't.  `p2p' is an unchangeable attribute of an interface,
> see IFF_CANTCHANGE in /sys/net/if.h.

Perhaps IFF_POINTOPOINT should be settable while the interface is 
down only.

In the `tun' case (I'm not sure about pppX & slX) it could
be done at the ioctl(TUNSIFINFO) stage - the `dummy' part of the 
struct tuninfo could be changed to specify the interface flags.  But 
this would break existing code that never initialises `dummy' 
to zero (which, it really should, although ppp doesn't :-().

OpenBSD already has this requirement.  The `dummy' part is 
replaced by `flags' and those flags must specify IFF_POINTOPOINT if 
you want that.  I'm not actually sure what happens there if you don't 
specify IFF_POINTOPOINT.

> -- 
> cheers, J"org
> 
> joerg_wunsch@uriah.heep.sax.de -- http://www.sax.de/~joerg/ -- NIC: JW11-RIPE
> Never trust an operating system you don't have sources for. ;-)

-- 
Brian <brian@Awfulhak.org>, <brian@FreeBSD.org>, <brian@OpenBSD.org>
      <http://www.Awfulhak.org>;
Don't _EVER_ lose your sense of humour....





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