kern/71474: route lookup does not skip interfaces marked down
ru at FreeBSD.ORG
Wed Sep 8 06:50:36 PDT 2004
The following reply was made to PR kern/71474; it has been noted by GNATS.
From: Ruslan Ermilov <ru at FreeBSD.ORG>
To: Thomas Quinot <thomas at FreeBSD.ORG>
Cc: bug-followup at FreeBSD.ORG
Subject: Re: kern/71474: route lookup does not skip interfaces marked down
Date: Wed, 8 Sep 2004 16:49:27 +0300
On Wed, Sep 08, 2004 at 03:06:48PM +0200, Thomas Quinot wrote:
> * Ruslan Ermilov, 2004-09-08 :
> > > ifconfig I1 192.168.0.1 netmask 255.255.255.0
> > > ifconfig I1 down
> > > ifconfig I2 192.168.0.2 netmask 255.255.255.0
> > > route add default 192.168.0.254
> > >
> > > The default route will be set to 192.168.0.254 on I1, not on I2 as
> > > expected.
> > >
> > It's still a misconfiguration -- if you do not bring the I1 interface
> > down, the "interface" route for I2 will not be installed, and the
> > ifconfig(8) command will be aborted. Anyway...
> I am not sure I get what you mean. The point of this PR is that I *do*
> bring I1 down, that the kernel has an unambiguous indication of how to
> reach the specified gateway ('ping 192.168.0.254' works in the example
> described above), and in spite of that the wrong interface is selected
> when creating a route.
This is a misconfiguration because you cannot expect two broadcast
interfaces configured with the same IP network to work. The fact
that it works at all, in a scenario you shown, is probably a bug.
> > I reproduced this with two ng_eiface(4) nodes. There's still a useful
> > option in the route(8) utility -- you can supply an explicit reference
> > to the interface, like this:
> > : route add default 192.168.0.254 -ifp I1
> Right, I was not aware of that option.
> > This is also vaguely documented in the route(8) manpage, FWIW:
> *Vaguely* is the right term I think. :-)
> Having browsed through the code, I think the interface lookup for route
> additions should use a modified version of ifa_ifwithaddr ignoring
> non-up interfaces.
If we change ifa_ifwith*() to ignore !IFF_UP interfaces, I suspect this
will break too many things. I think the correct change here would be
to set the interface of the route to the interface of its gateway (if
route is through the gateway (RTF_GATEWAY)). This should be easy to
fix, but I don't have a time for this now.
ru at FreeBSD.org
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