30-nsupdate

### /etc/hotplug.d/iface/30-nsupdate
###
### Update the WAN interface's IPv4 address (A) record in the DNS
### using the DNS UPDATE protocol.
###
### Author:       Simon Leinen  <simon.leinen@gmail.com>
### Date Created: 10-Apr-2014
###
### based on instructions by Justin Foell found on
### http://www.foell.org/justin/diy-dynamic-dns-with-openwrt-bind/
###
### I had to update Justin's script a little:
###
### 1) My WAN interface is called "ge00", not "wan".
### 2) scan_interfaces fails to put the WAN interface's IPv4 address
###    in a CONFIG_ variable.  Therefore, we use a fallback method to
###    get it using "ip -4 addr show"
###
### Note that this needs the "bind-client" package installed.
###
### Tested on a WNDR3700v2 under CeroWrt Vancouver 3.10.18-1

exec >>/tmp/foo.log 2>&1

## The name of the "WAN" interface
wan=ge00

## Tag and facility under which messages are logged
facility=daemon
tag="30-nsupdate[$$]"

## Authoritative name server to update
nameserver=AUTH.NAMESERVER.EXAMPLE

## Zone to update
zonename=MYZONE.EXAMPLE

## Hostname to update
hostname=ROUTER.${zonename}

## Desired TTL (time-to-live), in seconds
ttl=600

## Key file
key=/root/K${zonename}.key

[ "$INTERFACE" != "${wan}" ] && exit 0
[ "$ACTION" != "ifup" ] && [ "$ACTION" != "update" ] && exit 0

## This doesn't seem very necessary, because we run an NTP client.
## But maybe it is useful when booting the router after some time.
## NTP may take a while to converge.
##
rdate -s time.nist.gov

## ## scan_interfaces puts a bunch of information in CONFIG_ variables.
## ## But on my router, it fails to get the IP address of the WAN interface
## ## (ge00).  Maybe this is because it isn't configured, but assigned
## ## via DHCP? Anyway, we have to use a fallback method to get the address.
## ##
## include /lib/network
## scan_interfaces
## config_get ipaddr ${wan} ipaddr
## if [ -z "${ipaddr}" ]
## then
##   : logger -t ${tag} -p ${facility}.warn "config_get did not find ipaddr, trying ip -4 addr show"
  ipaddr=`ip -4 addr show dev ${wan} | grep inet | sed -e 's/.*inet \([.0-9]*\).*/\1/'`
## fi

## Now we construct a DNS UPDATE packet and send it to the
## authoritative server.  We need to provide key material to authenticate.
##
echo "server $nameserver
zone ${zonename}
update delete ${hostname}. IN A
update add ${hostname}. ${ttl} IN A $ipaddr
send" | nsupdate -k ${key} -v || logger -t ${tag} -p ${facility}.error "Update $hostname IN A $ipaddr failed"
logger -t ${tag} -p ${facility}.info "Updated $hostname IN A $ipaddr"