From 12f9d75e7b63b1121848b45da9a10a15852ed951 Mon Sep 17 00:00:00 2001
From: Iustin Pop <iustin@google.com>
Date: Tue, 8 May 2012 13:06:10 +0200
Subject: [PATCH] Add note to the install doc about bridge MAC issues
Thanks to Faidon Liambotis for explaining this on the external IRC
channel.
Signed-off-by: Iustin Pop <iustin@google.com>
Reviewed-by: Faidon Liambotis <paravoid@gmail.com>
Reviewed-by: Guido Trotter <ultrotter@google.com>
---
doc/install.rst | 22 ++++++++++++++++++++++
1 file changed, 22 insertions(+)
diff --git a/doc/install.rst b/doc/install.rst
index d899abda4..54a76ab98 100644
--- a/doc/install.rst
+++ b/doc/install.rst
@@ -341,6 +341,26 @@ outside of ganeti. The vif scripts will only add /32 routes to your
instances, through their interface, in the table you specified (under
KVM, and in the main table under Xen).
+.. admonition:: Bridging issues with certain kernels
+
+ Some kernel versions (e.g. 2.6.32) have an issue where the bridge
+ will automatically change its ``MAC`` address to the lower-numbered
+ slave on port addition and removal. This means that, depending on
+ the ``MAC`` address of the actual NIC on the node and the addresses
+ of the instances, it could be that starting, stopping or migrating
+ instances will lead to timeouts due to the address of the bridge
+ (and thus node itself) changing.
+
+ To prevent this, it's enough to set the bridge manually to a
+ specific ``MAC`` address, which will disable this automatic address
+ change. In Debian, this can be done as follows in the bridge
+ configuration snippet::
+
+ up ip link set addr $(cat /sys/class/net/$IFACE/address) dev $IFACE
+
+ which will "set" the bridge address to the initial one, disallowing
+ changes.
+
.. admonition:: Bridging under Debian
The recommended way to configure the Xen bridge is to edit your
@@ -357,6 +377,8 @@ KVM, and in the main table under Xen).
bridge_ports eth0
bridge_stp off
bridge_fd 0
+ # example for setting manually the bridge address to the eth0 NIC
+ up ip link set addr $(cat /sys/class/net/eth0/address) dev $IFACE
The following commands need to be executed on the local console:
--
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