netdev - Re: Why linux keeps connected routes when link goes down

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Date:	Mon, 23 Feb 2009 13:38:15 -0800
From:	Stephen Hemminger <shemminger@...tta.com>
To:	lsorense@...lub.uwaterloo.ca (Lennart Sorensen)
Cc:	???????????? ???????????????????? <homecreate@...t.ru>,
	netdev@...r.kernel.org
Subject: Re: Why linux keeps connected routes when link goes down

On Mon, 23 Feb 2009 16:14:11 -0500
lsorense@...lub.uwaterloo.ca (Lennart Sorensen) wrote:

> On Mon, Feb 23, 2009 at 11:02:55PM +0500, ???????????? ???????????????????? wrote:
> > Can I hope that it will be done some day?
> 
> I don't have much hope that the kernel will ever be changed to behave
> as desired for a router.
> 
> > Linux is used as router in many places, such behavior is a suicide. Of course, 
> > one can use ifplugd (so do I), but it's a crap for network OS, don't you think 
> > so?
> 
> Well you will need some user space support to handle static routes,
> unless you want to make major changes to the kernel route management.
> We use zebra to manage static routes when the link goes up or down, with
> the kernel simply patched to delete the subnet route when an interface
> goes down, and re add it when it comes back up.  All other routes are
> handled by zebra.
> 
> With the current patch I am using all routes assigned to an interface goes
> away when the link goes down, but the kernel only recreates the directly
> connected network's route when it comes up.  Any other static routes
> have to be recreated by user space, hence the user of zebra for that.
> 
> Better and more friendly would be if routes could be marked inactive
> and ignored by the kernel for routing decisions when a link went down.
> That way multiple routes with different metrics could be used with the
> best one who's link is up would be in use.  I find this too much to try
> and put into the kernel though, so I will stick to zebra for that task.
> 
> > Who made linux network subsystem? Can Linus Torvalds say some words about this 
> > problem?
> > 
> > I'm not a developer, but network administrator. So I can't make a patch. I can 
> > only find a solution or make it. So please make my work a bit easier
> 

Like I said already, it is possible to fix Quagga; we have done it the
patches are available. unfortunately quagga is without a real
software maintenance infrastructure at this point.
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