dhcpcd-discuss

First off, I'm glad I found dhcpcd after fighting with ISC dhclient and 
ifup for far too long with the best result being politely described as 
tweaky and fragile.

At least for now, I'm running self-built dhcpcd-7.0.0-rc2 on Ubuntu 17.04.

Seeing that dhcpcd is a solid FreeBSD port means that the transition to 
my strong preference of FreeBSD may not be far off in the future.



I've got a somewhat non-standard application. I'm running a PCEngines 
APU2C4 that has three Intel nics; enp1s0, enp2s0, and enp3s0.

enp1s0:
Connected to a "Motorola" SB8600 DOCSIS 3.1 modem on Comcast.
Comcast will supply both IPv4 and IPv6 address and route information 
over DHCP
Comcast will assign a /64 PD on unqualified request, a /60PD on specific 
request, over DHCP
The modem management interface is on 192.168.1.100.

enp2s0:
Connected to the firewall, no "clients" on the link
Uses manually configured RFC1918 IPv4 and ULA/link-local addressing for 
IPv6.
This is a "private" link with VLANs for segregation of main data flows 
and management channels.

enp3s0:
Generally without link
I mess up badly enough, I want to be able to drag a cable over to it and 
have it get an address and then can access the headless box.


DHCPv4/6 is handled by various relays and kea running on another machine 
behind the firewall.


I've got a Type 4 DUID that I use for client ID so that the 
configuration is hardware independent.


I'd like to be able to configure dhcpcd to help do the following:

enp1s0:
* Immediately gets 192.168.1.n statically assigned so I can access the modem
* Gets a public IPv4 address and IPv6 IA_NA address from Comcast's DHCP 
and configures them on enp1s0
* Routing tables are locally updated with the IPv4 and IPv6 default 
routes via Comcast
* Obtains a /60 PD from Comcast and does nothing with it (outside of the 
scripts that run)
* Comcast gets whatever else they need to route the PD via the IA_NA 
address(likely nothing)

enp2s0:
* Manually configured
* no RA/RS

enp3s0:
* Comes "alive" when I plug in the cable
* Gets an IPv4 and/or IPv6 address from my local DHCP server


Challenge 1 -- clientid/DUID
============================

The first challenge I'm having is that dhcpcd doesn't use the clientid 
given.

In the config below, the actual Type 4 DUID has been redacted. I am 
using the DUID value that is currently working with dhclient and Comcast 
for both IPv4 and IPv6. The logs and wireshark show a Type 1 DUID in use 
by dhcpcd.

I originally had the clientid statement only at the "global" level. 
Adding it to the interface level didn't change the behavior.

(The Type 4 DUID allows me to change hardware without changing the DUID, 
hopefully preserving addressing)


Right now, dhcpcd is being started as a systemd service:

    Wants=network.target
    Before=network.target
    After=network-pre.target

I'm hardly a systemd expert, but I believe it's up and running after the 
interfaces are known and before the network is considered "up" (the logs 
seem to confirm this)

I haven't yet extended this to enp3s0, nor added things like noipv4ll. 
The default IAID is being used for the IA_NA (and its value has been 
confirmed with wireshark). The IAID for the PD was set to "0" as it 
appears that a single IAID can't be used for both the IA_NA and the 
IA_PD by dhcpcd.

The assignment of the static, modem-access IPv4 address is presently 
done through /etc/network/interfaces. It appears properly retained when 
dhcpcd assigns the Comcast-assigned public IP addresses.

auto enp1s0:0
iface enp1s0:0 inet static
  address 192.168.100.101
  netmask 255.255.255.0



dhcpd.conf
----------

controlgroup root

# For now, undo what is done on exit
# persistent

option rapid_commit
option classless_static_routes
option interface_mtu
require dhcp_server_identifier
slaac private

debug

allowinterfaces enp1s0
denyinterfaces  enp2s0

clientid 00:04:00:11:22:33:44:55:66:77:88:99:00:aa:bb:cc:dd:ee

nohook resolv.conf

interface enp1s0
    clientid 00:04:00:11:22:33:44:55:66:77:88:99:00:aa:bb:cc:dd
ia_na
    ia_pd 0
    ipv6rs
    ipv6ra_noautoconf



Challenge 2 -- Obtain, but don't use IA_PD
==========================================

Even after reading the man page from dhcpcd-7.0.0-rc2 I'm at a bit of a 
loss as to how to get a /60 IA_PD, especially without assigning it to 
interfaces.

I'm not adverse to figuring out some of the detailsbut I'm stuck getting 
started with two points related to the ia_pd configuration line

    ia_pd [iaid [/ prefix / prefix_len] [interface [/ sla_id [/ 
prefix_len [/ suffix]]]]]


The first is what to use as a prefix. It seems like something of a 
Catch-22 if I need the prefix I'm about to get to be able to request a 
/60 (Comcast only gives out a /64 unless you request otherwise).


The second is how to *not* do anything with the PD other than pass its 
value to the scripts;"If no interface is given then we will assign a 
prefix to every other interface with a sla_id equivalent to the 
interface index assigned by the OS."


Any suggestions that keep me going on this would be greatly appreciated!

Jeff Kletsky