[LEDE-DEV] RFC [PATCH] odhcpd: don't enable server mode on dhcp lan

[Eric Luehrsen]

On Thu, Aug 31, 2017 at 11:35 PM, Karl Palsson <karlp at tweak.net.au> wrote:
> >
> > Daniel Golle <daniel at makrotopia.org> wrote:
> >> Hi Karl,
> >>
> >> On Thu, Aug 31, 2017 at 05:17:38PM +0000, Karl Palsson wrote:
> >> > Instead of blindly enabling the odhcpd v6 server and RA server on the
> >> > lan port, only do that if the lan port isn't set to DHCP.
> >> >
> >> > This prevents the unhelpful case of a device being a dhcpv4 
> client and
> >> > v6 server on the same ethernet port.
> >>
> >> Generating UCI from presumingly already generated UCI has
> >> proven to be a bad practise in the past. See inline for an
> >> alternative approach.
> >
> > Cool with me, the json_load approach is..... kinda opaque still
> > at the moment, but if that's the future and meant to be magically
> > more stable, awesome. (This file was _already_ looking at "uci -q
> > get dhcp.odhcpd" not using any json loading, so... I just
> > followed the course)
> >
> > But the general concept? Is that ok? That's more interesting to
> > me :)
> I like the idea
> I wonder if enabling DHCPv6 and RA as server on interfaces having a
> non static protocol is usefull; so can we just check for the protocol
> being static to enable DHCPv6 and RA as server ?
>
> Hans
> >
> > Sincerely,
> > Karl Palsson
> >
> >> >  uci -q get dhcp.odhcpd && exit 0
> >> >  touch /etc/config/dhcp
> >> >
> >> > +LANPROTO=$(uci -q get network.lan.proto)
> >>
> >> Imho it'd be nicer to read this via
> >> ```
> >> . /usr/share/libubox/jshn.sh
> >>
> >> json_load "$(cat /etc/board.json)"
> >> json_select network
> >> json_select lan
> >> json_get_vars protocol
> >> json_select ..
> >> json_select ..
> >> ```
> >>
> >>
> >> > +MODE=server
> >> > +
> >> > +case "$LANPROTO" in
> >> > +"dhcp")
> >> > +   echo "odhcpd: Not enabling server mode on a dhcp lan!" > 
> /dev/kmsg
> >> > +   MODE=disabled
> >> > +   ;;
> >> > +esac
> >> > +
> >> >  uci batch <<EOF
> >> >  set dhcp.odhcpd=odhcpd
> >> >  set dhcp.odhcpd.maindhcp=0
> >> >  set dhcp.odhcpd.leasefile=/tmp/hosts/odhcpd
> >> >  set dhcp.odhcpd.leasetrigger=/usr/sbin/odhcpd-update
> >> >  set dhcp.odhcpd.loglevel=4
> >> > -set dhcp.lan.dhcpv6=server
> >> > -set dhcp.lan.ra=server
> >> > +set dhcp.lan.dhcpv6=$MODE
> >> > +set dhcp.lan.ra=$MODE
> >> >  commit dhcp
> >> >  EOF
> >> > --
> >> > 2.4.11

This is just a consideration, not a complete thought. odhcpd is a light 
weight server so it doesnt participate with fail over controls (without  
scripting). But fail-over DHCP severs can configure from the 
master/acting DHCP sever; then remain on standby until needed. An 
dynamic LAN protocol could then re-serve on the same interface.

- Eric