Resolve LAN addresses

[fortuna]

So I want to mount a samba share at reboot on a device running OpenWrt 19.07.7 firmware and the authoritative DHCP server on the LAN.

I don't want to use the IP address of the samba server in /etc/fstab so I need dnsmasq up and running.

Where do I put mount -a? I've tried /etc/hotplug.d/iface but:

mount error: could not resolve address for vuplus: Unknown error

When in the boot process is dnsmasq capable of resolving LAN addresses and is there a hook that can be used e.g. to mount samba shares?

[iplaywithtoys]

Does /etc/rc.local suit your purposes?

[fortuna]

With logread it turns out that some 4 hours after reboot vuplus asks for a new dhcp lease. I suspect that until then the router is unable to resolve vuplus. Is there a way around this so that immediately after reboot vuplus is resolved?

[iplaywithtoys]

You could give vuplus a static IP address and a corresponding entry in /etc/hosts.

[fortuna]

Exactly. That's what I did. Every reboot I recreated a /tmp/lanhosts hosts file with the hosts in /etc/config/dhcp referred to with:

list addnhosts '/tmp/lanhosts'

in /etc/config/dhcp to avoid having to maintain two files. I still think there should be a better method but I can't figure it out.

[vgaetera]

Configure both static leases and hostnames.

[fortuna]

So instead of entries in /etc/config/dhcp like this?

config host
	option name 'vuplus'
	option mac 'xx:xx:xx:xx:xx:xx'
	option ip '192.168.0.6'

[fortuna]

@vgaetera The /etc/config/dhcp is equivalent to a static lease according to your second link.

[vgaetera]

The settings in both host and domain sections should match for each host.
Both sections are required since restarting the router removes the lease file.

[fortuna]

To ensure consistency I created this sed script called joinhosts:

#!/bin/sed -nf
# Join host name and ip address in /etc/config/dhcp host records to /etc/hosts format

/^\toption name/h
/^\toption ip/{G;s/\toption ip '\(.*\)'\n\toption name '\(.*\)'/\1\t\2/;p}

I call it from /etc/rc.local like this:

/root/bin/joinhosts /etc/config/dhcp > /tmp/lanhosts

In /etc/config/dhcp I have:

list addnhosts '/tmp/lanhosts'

So after every reboot lan host names are resolved. But not immediately. A wait is needed and I haven't figured out yet for how long.

[fortuna]

Actually, this line:

/etc/init.d/dnsmasq restart

is the solution to my problem! After this command added host names are resolved. No wait is needed anymore. So thank you for the link.

I find the way they retrieve the host names from uci more elegant than mine because it doesn't depend on the /etc/config/dhcp file syntax e.g. the use of single quotes which is optional.

Therefore I changed my script joinhosts like this:

#!/bin/sed -nf
# Join host name and ip address in uci host records to /etc/hosts format

/^dhcp.@host\[.*\].name=/h
/^dhcp.@host\[.*\].ip=/{G;s/^dhcp.@host\[.*\].ip='\(.*\)'\ndhcp.@host\[.*\].name='\(.*\)'/\1\t\2/;p}

I call it in /etc/rc.local like this:

uci show dhcp | /root/bin/joinhosts > /tmp/lanhosts

[fortuna]

I simplified the sed command a bit and reduced it to one line. Now my /etc/rc.local looks like this:

# Put your custom commands here that should be executed once
# the system init finished. By default this file does nothing.

uci show dhcp | sed -n "/@host.*name=/h;/@host.*ip=/{G;s/.*='\(.*\)'\n.*='\(.*\)'/\1\t\2/;p}" > /tmp/lanhosts
/etc/init.d/dnsmasq restart
mount -a

exit 0

I consider this issue solved. Thanks everybody!

[vgaetera]

There's actually a simpler method:
https://openwrt.org/docs/guide-user/base-system/dhcp?s=dns#static_leases

[fortuna]

@vgaetera

There's actually a simpler method

This is the solution I was looking for. Adding:

	option dns '1'

to a host section in /etc/config/dhcp adds static forward and reverse DNS entries for that host. I did that for all hosts and now they are all available right after boot completes. The only command remaining in /etc/rc.local is now:

mount -a

Only one method can be the simplest and this is the one. Thanks @vgaetera !