[Xen-devel] [LINUX] ipv6: Disable addrconf on Xen bridge device

[Herbert Xu <herbert@xxxxxxxxxxxxxxxxxxx>]

Hi:

Back in June 2006 an attempt was made to disable IPv6 addrconf so that
the Xen bridge device does not compete with eth0 in performing IPv6
address configuration.  Unfortunately it was incomplete which meant that
IPv6 autoconfiguration was still a hit and miss.

For now the easiest way to disable IPv6 addrconf is to lower the MTU
as follows.

[LINUX] ipv6: Disable addrconf on Xen bridge device

The ipv6-no-autoconf patch didn't disable IPv6 addrconf completely.
This means that the Xen bridge device still interfered with normal
IPv6 operation by engaging the IPv6 network with a bogus MAC address.

For details please refer to

        https://bugzilla.redhat.com/bugzilla/show_bug.cgi?id=200360

The following patch completely disables IPv6 on the Xen bridge device
by temporarily setting the MTU to a value less than the minimum allowed
for IPv6.

Upstream will provide a cleaner way to disable IPv6 addrconf in future,
possibly in the form of a proc sysctl.  Of course if the Xen loopback
device is removed it would render this change unnecessary.

Signed-off-by: Herbert Xu <herbert@xxxxxxxxxxxxxxxxxxx>

Cheers,
-- 
Visit Openswan at http://www.openswan.org/
Email: Herbert Xu ~{PmV>HI~} <herbert@xxxxxxxxxxxxxxxxxxx>
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--
diff -r 4fc6ffff2ac5 -r 65fe67290bbc patches/linux-2.6.16.33/series
--- a/patches/linux-2.6.16.33/series    Sun Dec 31 12:26:42 2006 +0000
+++ b/patches/linux-2.6.16.33/series    Tue Jan 02 13:30:59 2007 +1100
@@ -9,7 +9,6 @@ fix-hz-suspend.patch
 fix-hz-suspend.patch
 fix-ide-cd-pio-mode.patch
 i386-mach-io-check-nmi.patch
-ipv6-no-autoconf.patch
 net-csum.patch
 net-gso-0-base.patch
 net-gso-1-check-dodgy.patch
diff -r 4fc6ffff2ac5 -r 65fe67290bbc tools/examples/xen-network-common.sh
--- a/tools/examples/xen-network-common.sh      Sun Dec 31 12:26:42 2006 +0000
+++ b/tools/examples/xen-network-common.sh      Tue Jan 02 13:30:59 2007 +1100
@@ -117,7 +117,12 @@ create_bridge () {
         ip link set ${bridge} arp off
         ip link set ${bridge} multicast off
     fi
+
+    # A small MTU disables IPv6 (and therefore IPv6 addrconf).
+    mtu=$(ip link show ${bridge} | sed -n 's/.* mtu \([0-9]\+\).*/\1/p')
+    ip link set ${bridge} mtu 68
     ip link set ${bridge} up
+    ip link set ${bridge} mtu ${mtu:-1500}
 }
 
 # Usage: add_to_bridge bridge dev
diff -r 4fc6ffff2ac5 -r 65fe67290bbc 
patches/linux-2.6.16.33/ipv6-no-autoconf.patch
--- a/patches/linux-2.6.16.33/ipv6-no-autoconf.patch    Sun Dec 31 12:26:42 
2006 +0000
+++ /dev/null   Thu Jan 01 00:00:00 1970 +0000
@@ -1,19 +0,0 @@
-diff -pruN ../orig-linux-2.6.16.29/net/ipv6/addrconf.c ./net/ipv6/addrconf.c
---- ../orig-linux-2.6.16.29/net/ipv6/addrconf.c        2006-09-12 
19:02:10.000000000 +0100
-+++ ./net/ipv6/addrconf.c      2006-09-19 13:59:11.000000000 +0100
-@@ -2471,6 +2471,7 @@ static void addrconf_dad_start(struct in
-       spin_lock_bh(&ifp->lock);
- 
-       if (dev->flags&(IFF_NOARP|IFF_LOOPBACK) ||
-+          !(dev->flags&IFF_MULTICAST) ||
-           !(ifp->flags&IFA_F_TENTATIVE)) {
-               ifp->flags &= ~IFA_F_TENTATIVE;
-               spin_unlock_bh(&ifp->lock);
-@@ -2555,6 +2556,7 @@ static void addrconf_dad_completed(struc
-       if (ifp->idev->cnf.forwarding == 0 &&
-           ifp->idev->cnf.rtr_solicits > 0 &&
-           (dev->flags&IFF_LOOPBACK) == 0 &&
-+          (dev->flags & IFF_MULTICAST) &&
-           (ipv6_addr_type(&ifp->addr) & IPV6_ADDR_LINKLOCAL)) {
-               struct in6_addr all_routers;
- 

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