Patchwork ipv6: address preservation on link down

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Submitter stephen hemminger
Date Jan. 9, 2009, 1:14 a.m.
Message ID <20090108171415.1d282743@extreme>
Download mbox | patch
Permalink /patch/17458/
State RFC
Delegated to: David Miller
Headers show

Comments

stephen hemminger - Jan. 9, 2009, 1:14 a.m.
When an interface goes down, IPV6 deletes all addresses unlike IPV4. This
is a problem since it can break routing protocols and other applications.
It looks like this was done to handle DAD, but is a big stick solution when
other code is possible.

The following patch changes the behaviour to delete link local addresses
but keep all configured addresses and restart DAD when interface comes back up.

See also: https://kerneltrap.org/mailarchive/linux-netdev/2008/3/25/1252064/thread

Signed-off-by: Stephen Hemminger <shemminger@vyatta.com>


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RĂ©mi Denis-Courmont - Jan. 9, 2009, 8:02 a.m.
On Friday 09 January 2009 03:14:15 ext Stephen Hemminger, you wrote:
> When an interface goes down, IPV6 deletes all addresses unlike IPV4. This
> is a problem since it can break routing protocols and other applications.
> It looks like this was done to handle DAD, but is a big stick solution when
> other code is possible.
>
> The following patch changes the behaviour to delete link local addresses
> but keep all configured addresses and restart DAD when interface comes back
> up.

Let alone the backward compatibility problem for a minute. I have two _other_ 
problems with this:

1/ If DAD should fail when the interface is brought back up, wouldn't all the 
EAU-64 autoconfigured address become invalid, rather than just the link-local 
one?

2/ In some case the link-local address is assigned by userland, no different 
from the other ones. At least miredo is behaving this way.

Patch

--- a/net/ipv6/addrconf.c	2009-01-08 16:43:04.921305933 -0800
+++ b/net/ipv6/addrconf.c	2009-01-08 16:47:04.000301344 -0800
@@ -2678,18 +2678,26 @@  static int addrconf_ifdown(struct net_de
 		write_lock_bh(&idev->lock);
 	}
 #endif
-	while ((ifa = idev->addr_list) != NULL) {
-		idev->addr_list = ifa->if_next;
-		ifa->if_next = NULL;
-		ifa->dead = 1;
-		addrconf_del_timer(ifa);
-		write_unlock_bh(&idev->lock);
-
-		__ipv6_ifa_notify(RTM_DELADDR, ifa);
-		atomic_notifier_call_chain(&inet6addr_chain, NETDEV_DOWN, ifa);
-		in6_ifa_put(ifa);
-
-		write_lock_bh(&idev->lock);
+	/* clear regular address list on removal */
+	bifa = &idev->addr_list;
+	while ((ifa = *bifa) != NULL) {
+		if (how || (ipv6_addr_type(&ifa->addr) & IPV6_ADDR_LINKLOCAL)) {
+			*bifa = ifa->if_next;
+			ifa->if_next = NULL;
+			ifa->dead = 1;
+			addrconf_del_timer(ifa);
+			write_unlock_bh(&idev->lock);
+
+			__ipv6_ifa_notify(RTM_DELADDR, ifa);
+			atomic_notifier_call_chain(&inet6addr_chain, NETDEV_DOWN, ifa);
+			in6_ifa_put(ifa);
+
+			write_lock_bh(&idev->lock);
+		} else {
+			/* Force duplicate address detection when link resumes */
+			ifa->flags |= IFA_F_TENTATIVE;
+			bifa = &ifa->if_next;
+		}
 	}
 	write_unlock_bh(&idev->lock);