netdev - Re: Stale entries in RT_TABLE

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Message-ID: <alpine.LFD.2.00.1103190011430.1678@ja.ssi.bg>
Date:	Sat, 19 Mar 2011 00:57:30 +0200 (EET)
From:	Julian Anastasov <ja@....bg>
To:	Jiri Bohac <jbohac@...e.cz>
cc:	Alex Sidorenko <alexandre.sidorenko@...com>,
	David Miller <davem@...emloft.net>,
	"netdev@...r.kernel.org" <netdev@...r.kernel.org>
Subject: Re: Stale entries in RT_TABLE_LOCAL


 	Hello,

On Thu, 17 Mar 2011, Jiri Bohac wrote:

>>>> IP2: 192.168.142.109/23, primary
>>>> IP3: 192.168.142.109/22, secondary for primary IP1
>>>>
>>>>        It is the route for IP3 that is leaked, with prefsrc=IP1.
>>>> We create local route for secondary IPs with prefsrc=ItsPrimaryIP.
>>>> Both local routes for 109 differ in prefsrc (fa_info)
>
> Is there any reason to set the prefsrc of a local route to the
> primary IP address of the subnet?
>
> I tried the following patch:
>
> diff --git a/net/ipv4/fib_frontend.c b/net/ipv4/fib_frontend.c
> index 1d2cdd4..2046b21 100644
> --- a/net/ipv4/fib_frontend.c
> +++ b/net/ipv4/fib_frontend.c
> @@ -751,7 +751,7 @@ void fib_add_ifaddr(struct in_ifaddr *ifa)
> 		}
> 	}
>
> -	fib_magic(RTM_NEWROUTE, RTN_LOCAL, addr, 32, prim);
> +	fib_magic(RTM_NEWROUTE, RTN_LOCAL, addr, 32, ifa);
>
> 	if (!(dev->flags & IFF_UP))
> 		return;
>
>
> The result with the teststcase mentioned previously is that only
> one local route is created per IP address. The local routes are
> correctly deleted after both identical IP addresses are removed
> from the interface.

 	It is a problem also for the broadcast addresses.

> Furthemore, the testcase uncovers another weirdness with the
> prefsrc of the local routes. When a primary IP address is deleted
> and a secondary IP address is promoted to primary, its prefsrc is
> not updated.

 	Yes, I see the same when the deleted primary is
also in another subnet or device.

> What is the prefrc of a local route good for?

 	To prefer this src when talking to local IP :)
You can always add local IPs with /32 mask but currently
you must add it first, i.e. fib_magic does not remove
the NLM_F_APPEND flag for /32 local routes when dst is
same as ifa->ifa_local. So, the order of IP adding
will determine the order of local routes:

ip addr add 1.2.3.4/24 brd + dev eth1
# secondary
ip addr add 1.2.3.5/24 brd + dev eth1
# primary:
ip addr add 1.2.3.5/32 brd + dev eth1

when talking to 1.2.3.5 you will use 1.2.3.4 because
the secondary is added first.

Regards

--
Julian Anastasov <ja@....bg>
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