[PATCH net-2.6] [NEIGH] [resend] Updating affected neighbours when about MAC address change in arp_netdev_event()

[David Shwatrz]

Hello,

This is a resend of the patch according to Yoshifuji comment. I will
send a patch for IPv6 later.

 We know that changes in MAC addresses are not frequent but
we are working on a special, highly advanced networking Linux based project
in our LABs, where we do change MAC addresses of an interface quite frequently.
(We do not go totally wild; the MAC addresses we are changing into are
from a set of given MAC addresses).

Normally, when we change a MAC address of some interface, the
relevant neighbours in the LAN which have entries with the previous MAC
address are not sent any update notification; instead, it is there
regular timers mechanisms which update the MAC address to the new
one in their ARP tables.

I had written a small patch to neigh_changeaddr() in net/ipv4/arp.c
against the 2.6 git net tree, which sends a gratuitous ARP to update
the list of
all the involved neighbours with the change of MAC address.
The patch is for arp_netdev_event() only.

This patch was tested and it does work in my LAB; if such a patch is
not needed,
I wonder why ?
It seems to me that it could not cause any troubles.
BTW, I had noticed that in irlan driver, there is such a mechanism
of sending a gratuitous ARP to update all the
neighbours when a MAC address is changed.

Signed-off-by: David Shwartz <[EMAIL PROTECTED]>

diff --git a/net/ipv4/arp.c b/net/ipv4/arp.c
index 08174a2..7b1162b 100644
--- a/net/ipv4/arp.c
+++ b/net/ipv4/arp.c
@@ -1185,6 +1185,8 @@ out:
 
 static int arp_netdev_event(struct notifier_block *this, unsigned long event, 
void *ptr)
 {
+       struct in_device *in_dev;
+       struct in_ifaddr *ifa;
        struct net_device *dev = ptr;
 
        if (dev->nd_net != &init_net)
@@ -1194,6 +1196,22 @@ static int arp_netdev_event(struct notifier_block *this, 
unsigned long event, vo
        case NETDEV_CHANGEADDR:
                neigh_changeaddr(&arp_tbl, dev);
                rt_cache_flush(0);
+               
+               /* Send gratuitous ARP to the neighbours to update their arp 
tables */
+       
+               rcu_read_lock();
+               in_dev = __in_dev_get_rcu(dev);
+               if (in_dev == NULL)
+                       goto out;
+               for (ifa = in_dev->ifa_list; ifa; ifa = ifa->ifa_next)
+                       arp_send(ARPOP_REQUEST, ETH_P_ARP, 
+                               ifa->ifa_address,
+                               dev, 
+                               ifa->ifa_address,
+                               NULL, dev->dev_addr, NULL);
+out:
+       rcu_read_unlock();
+
                break;
        default:
                break;