Linux Ethernet Bridging - Feb 2011 - [Bridge] mac addresses of local interfaces do not obey setageing 0

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).

On Wed, 9 Feb 2011 19:17:52 +0100
Veaceslav Falico <vfalico at redhat.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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