netdev - Re: mac addresses of local interfaces do not obey setageing 0

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Date:	Tue, 15 Feb 2011 10:25:38 -0800
From:	Stephen Hemminger <shemminger@...tta.com>
To:	Veaceslav Falico <vfalico@...hat.com>
Cc:	netdev@...r.kernel.org, bridge@...ts.linux-foundation.org
Subject: Re: mac addresses of local interfaces do not obey setageing 0

On Wed, 9 Feb 2011 19:17:52 +0100
Veaceslav Falico <vfalico@...hat.com> wrote:

> Hello,
> 
> I have a host and a VM inside this host bridged. I've set ageing_time and
> forward_delay to 0 and trying to capture all the traffic that goes through that
> bridge from my VM, but it fails to capture the traffic that has dst ether
> address the same as the hosts address (i.e. I can't capture the traffic to the
> host).
> 
> From the code, I see that br->ageing_time doesn't really work with local mac
> addresses - has_expired() function never says that a local interface mac address
> is expired, because it verifies if fdb->is_static is set and returns right away.
> 
> Is this the desired behaviour? If so, is there a way to capture packets with
> destination to a local interface from another interface?
> 
> I've also done a small patch and it seems to fix the situation, but I am not
> sure if it's the right way to do it.
> 
> 
> Regards,
> Veaceslav
> 
> ---
>  net/bridge/br_fdb.c |    4 ++--
>  1 files changed, 2 insertions(+), 2 deletions(-)
> 
> diff --git a/net/bridge/br_fdb.c b/net/bridge/br_fdb.c
> index 88485cc..3d380c2 100644
> --- a/net/bridge/br_fdb.c
> +++ b/net/bridge/br_fdb.c
> @@ -61,8 +61,8 @@ static inline unsigned long hold_time(const struct net_bridge *br)
>  static inline int has_expired(const struct net_bridge *br,
>  				  const struct net_bridge_fdb_entry *fdb)
>  {
> -	return !fdb->is_static &&
> -		time_before_eq(fdb->ageing_timer + hold_time(br), jiffies);
> +	return (br->ageing_time == 0) || (!fdb->is_static &&
> +		time_before_eq(fdb->ageing_timer + hold_time(br), jiffies));
>  }
>  

No.
Local addresses should never age.

The proper way to capture packet is to us AF_PACKET or tc actions.
-- 
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