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[Xen-users] Jumbo frame support for Xen


I had to use bridge interfaces with mtu other than 9000, so I started to
google for a solution. Then I found this thread:

But, It didn't work, as the original author says.
I tried to find an easier way, to setup this, so as I found out: If you
configure a vif's mtu, the logical solution is to use the same mtu as the
bridge interface -> So I wrote a smaller, nicer, and... a working patch.

The "trick" is that, I don't use the xen's bridge creation scripts, I
preconfigure my bridge interfaces from my Debian configuration, far before
the xen things would start.
bridge entry from my /etc/network/interfaces:
auto br201
iface br201 inet static
        mtu 9000
        bridge_ports bond0.201
        bridge_fd 0
        bridge_maxwait 0

This iface config pre-creates the vlan if on my bonding if, creates the
bridge, add the bond.vlan into my bridge interface, and every mtu is OK,
until xen starts...
Then, with my patched xen scripts,... work again, still, whatever you want:
It's just work! ;-)

Use it wise, and for your own risk!

The patch:

diff -urN /etc/xen/scripts.orig/vif-bridge /etc/xen/scripts/vif-bridge
--- /etc/xen/scripts.orig/vif-bridge    2011-04-14 15:24:51.000000000 +0200
+++ /etc/xen/scripts/vif-bridge 2011-10-12 18:13:13.873102049 +0200
@@ -82,6 +82,7 @@
 case "$command" in
        setup_bridge_port "$vif"
+       set_vif_mtu "$vif" "$(get_if_mtu $bridge)"
        add_to_bridge "$bridge" "$vif"
diff -urN /etc/xen/scripts.orig/xen-network-common.sh 
--- /etc/xen/scripts.orig/xen-network-common.sh 2010-06-21 15:46:02.000000000 
+++ /etc/xen/scripts/xen-network-common.sh      2011-10-12 18:07:00.456909410 
@@ -116,3 +116,19 @@
     ip link set ${dev} up
+get_if_mtu () {
+    local dev=$1
+    local line
+    ip link show $dev | \
+       ( read line
+       line="${line##*mtu }"
+       line="${line%% *}"
+       echo $line
+       cat >/dev/null )
+set_vif_mtu () {
+    local vif=$1
+    local mtu=$2
+    ip link set "$vif" mtu "$mtu"


Attachment: xen-bridge-fix-mtu.patch.gz
Description: Binary data

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