From 15b6fc1b646b28a9f7895c88c1ad37dac9f7ed1a Mon Sep 17 00:00:00 2001 From: Darren 'Tadgy' Austin Date: Tue, 21 Aug 2018 16:44:36 +0100 Subject: Mitigate a race condition with Duplicate Address Detection https://www.agwa.name/blog/post/beware_the_ipv6_dad_race_condition This removes the need to sleep for 3 seconds after setting up the interfaces, but does mean we lose detection of address clashes on the inteface - it's a trade off Signed-off-by: Robby Workman --- rc.inet1 | 16 ++++++++++++---- 1 file changed, 12 insertions(+), 4 deletions(-) diff --git a/rc.inet1 b/rc.inet1 index 1e3752a..325ee56 100644 --- a/rc.inet1 +++ b/rc.inet1 @@ -224,6 +224,11 @@ if_up() { fi fi if [ "${USE_DHCP[$i]}" != "yes" ] && [ -n "${IPADDR[$i]}" ]; then # add a fixed v4 IP to the interface + # IPv6's Duplicate Address Detection (DAD) causes a race condition when bringing up interfaces, as + # described here: https://www.agwa.name/blog/post/beware_the_ipv6_dad_race_condition + # Disable DAD while bringing up the interface - but note that this means the loss of detection of a + # duplicate address. It's a trade off, unfortunately. + echo "0" >/proc/sys/net/ipv6/conf/$1/accept_dad if [ -z "${NETMASK[$i]}" ]; then echo "/etc/rc.d/rc.inet1: no NETMASK set for ${1} - assuming 24 (aka, 255.255.255.0)" | $LOGGER NETMASK[$i]="24" @@ -272,6 +277,11 @@ if_up() { done fi if [ -n "${IPALIASES6[$i]}" ]; then + # IPv6's Duplicate Address Detection (DAD) causes a race condition when bringing up interfaces, as + # described here: https://www.agwa.name/blog/post/beware_the_ipv6_dad_race_condition + # Disable DAD while bringing up the interface - but note that this means the loss of detection of a + # duplicate address. It's a trade off, unfortunately. + echo "0" >/proc/sys/net/ipv6/conf/$1/accept_dad for ipalias in ${IPALIASES6[$i]}; do ip="${ipalias%/*}" nm="${ipalias#*/}" @@ -292,10 +302,8 @@ if_up() { echo "/etc/rc.d/rc.inet1: /sbin/ip link set dev ${1} promisc on" | $LOGGER /sbin/ip link set dev ${1} promisc on fi - # Some settings need a small time to come into effect on the interface. - # This mostly affects IPv6, which needs time to make the interfaces available for the - # daemons to bind() - without this delay, they fail to bind() v6 addresses. - sleep 3 + # Reset accept_dad back to default now all the IPs are configured: + cat /proc/sys/net/ipv6/conf/default/accept_dad >/proc/sys/net/ipv6/conf/$1/accept_dad fi else debug_log "${1} is already up, skipping" -- cgit v1.2.3