doc/net.example: Add warnings that changing MAC on bonds can break things.

In most cases, changing the MAC on a bond manually is wrong. The bonding
module will do it as needed to failover between interfaces, or to get
multiple interfaces to correctly have the same MAC.

We cannot however enforce it, as there are some corner cases where it is
actually valid (hardware that requires specific MAC configuration, like
some quad-port NICs).

Suggested-by: Martin Mokrejs <mmokrejs@fold.natur.cuni.cz>
Signed-off-by: Robin H. Johnson <robbat2@gentoo.org>

1 files changed, 8 insertions, 0 deletions

diff --git a/doc/net.example.Linux.in b/doc/net.example.Linux.in
index 51df8a9..ac63715 100644
--- a/doc/net.example.Linux.in
+++ b/doc/net.example.Linux.in
@@ -616,6 +616,12 @@
 #slaves_bond0="eth0 eth1 eth2"
 #config_bond0="null" # You may not want to assign an IP the the bond
 
+# Please note, that you should generally NOT try to change the MAC addresses of
+# a bond interface yourself. If you do so, the kernel and your network switches
+# may not work quite right. It is permissible to set the MAC addresses of bond
+# slaves BEFORE the bond comes up, but not after the bond is up (it will change
+# MAC addresses of the slaves on it's own).
+
 # You can also configure the parameters of the bond here, which must be done
 # via sysfs on 2.6 kernels or newer. The description of all the options can be
 # found in the kernel: /usr/src/linux-*/Documentation/networking/bonding.txt
@@ -787,6 +793,8 @@
 
 #-----------------------------------------------------------------------------
 # MAC changer
+# Warning: Do NOT use this on bonding interfaces! Bonding changes MACs itself.
+#
 # To set a specific MAC address
 #mac_eth0="00:11:22:33:44:55"