docker-dhcpd and macvlan interfaces

[rostchri]

The following information is useful for everybody who is using macvlan-interfaces and dhcpd ...

To get network-boot/docker-dhcpd working with macvlan-interfaces in a setup like this:

    version: "3"
    networks:
       macvlan-network1:
         external:
             name: macvlan-network1
       macvlan-network2:
         external:
             name: macvlan-network2
       macvlan-network3:
         external:
             name: macvlan-network3
    services:
      dhcpd:
        cap_add:
        - NET_ADMIN
        container_name: dhcpd
        hostname: dhcpd
        image: networkboot/dhcpd:latest
        networks:
            macvlan-network1:
                aliases:
                - dhcpd_network1
                ipv4_address: 10.0.0.7
            macvlan-network2:
                aliases:
                - dhcpd_network2
                ipv4_address: 10.1.0.7
            macvlan-network3:
                aliases:
                - dhcpd_network3
                ipv4_address: 192.168.132.7

the entrypoint.sh script should be extended by:

for i in /sys/class/net/eth*
do 
  echo "### Enabling promiscous mode for network-interface $${i##*/net/}"
  ip link set $${i##*/net/} promisc on || ifconfig $${i##*/net/} promisc
done

I don't know exactly why this is needed for macvlan, but with promiscuous-mode enabled interfaces, the dhcpd works fine in the above setup. Without promisc-mode, the dhcpd is not answering to broadcast-requests at all. To get the interfaces in the promisc-mode NET_ADMIN-capability is needed and the docker-image should be extended by iproute2 (ip-command) or net-tools (ifconfig-command). Maybe together with an environment-variable which signalize
entrypoint.sh to put the interfaces in promiscuous mode ...

At least this case should be mentioned in the documentation ...

[robinsmidsrod]

@rostchri This is not a bad idea, but I think it would be beneficial if this is an optional feature to enable, possibly with an environment variable. I'm thinking maybe setting PROMISC=1 would be a decent way of turning it on. Alternatively, the network interface glob to enable promiscious mode for should be in the environment variable, e.g. PROMISC=eth*.

Could you try to supply a PR with these things in mind?