From d1dd6bb746a0aad19549b4fc364e4106b688de72 Mon Sep 17 00:00:00 2001 From: Seewer Philippe Date: Tue, 6 Oct 2009 15:09:34 +0200 Subject: [PATCH] Be a bit more optimistic when setting mtus The usual approach to setting mtus is to set the interface down, set the mtu then set the interface back up again. Modern hardware and/or drivers may support setting this on the fly, so we try this and fall back to the old behaviour it it doesn't work. In addition this patch only allows mtus greater than 576, this is taken from debian/ubuntu dhclient-script. --- modules.d/40network/dhclient-script | 16 ++++++++++++---- 1 file changed, 12 insertions(+), 4 deletions(-) diff --git a/modules.d/40network/dhclient-script b/modules.d/40network/dhclient-script index afe2799c..f739d8d8 100755 --- a/modules.d/40network/dhclient-script +++ b/modules.d/40network/dhclient-script @@ -13,11 +13,19 @@ setup_interface() { [ -f /tmp/net.$netif.override ] && . /tmp/net.$netif.override - if [ -n "$mtu" ] ; then - echo ip link set $netif down - echo ip link set $netif mtu $mtu - echo ip link set $netif up + # Taken from debian dhclient-script: + # The 576 MTU is only used for X.25 and dialup connections + # where the admin wants low latency. Such a low MTU can cause + # problems with UDP traffic, among other things. As such, + # disallow MTUs from 576 and below by default, so that broken + # MTUs are ignored, but higher stuff is allowed (1492, 1500, etc). + if [ -n "$mtu" ] && [ $mtu -gt 576 ] ; then + echo "if ! ip link set $netif mtu $mtu ; then" + echo "ip link set $netif down" + echo "ip link set $netif mtu $mtu" + echo "ip link set $netif up" echo wait_for_if_up $netif + echo "fi" fi > /tmp/net.$netif.up echo ip addr add $ip${mask:+/$mask} ${bcast:+broadcast $bcast} dev $netif >> /tmp/net.$netif.up