dhcpcd-discuss

Hi Mike

On 17/01/2014 7:23, Mike Kazantsev wrote:
> I'm trying to setup dhcpcd 6.2.0 to get delegated IPv6 range from local
> ISP via DHCPv6 IA_PD mechanism.
>
> ISP explicitly claims to support getting IA_NA (address), IA_PD (prefix
> delegation) after IA_NA, and IA_PD without (preceding?) IA_NA request.
>
> And with dhcpcd it seem to be almost working, but with three quirks I
> can't seem to figure out.
>
>
> 1. vendorclassid configuration parameter seem to be completely
>   ignored for DHCPv6, yet applied for IPv4 DHCP.
>
> With configuration file like this:
>
>   duid
>   persistent
>   option rapid_commit, classless_static_routes
>   require dhcp_server_identifier
>   nohook lookup-hostname
>   noipv4ll
>   vendorclassid dhcpcd:Linux-3.X.X:x86_64
>
>   debug
>
> And starting dhcpcd as "dhcpcd -f /etc/dhcpcd.myisp.conf ext1" (ext1 is
> an interface name), it can be clearly seen in tcpdump that for IPv4,
> sepcified vendor string gets sent, but for IPv6 it's:
>
>   dhcpcd-6.2.0:Linux-3.10.19-fg.mf_master:x86_64:GenuineIntel
>
> Which corresponds to this machine ID, which I'd prefer to override, and
> expected that aforementioned option will do that, same as for IPv4 
> DHCP.

In DHCPv6, VendorClass ID does exist, but it requires an IANA assigned 
enterprise number and thus has a different option.
From dhcpcd.conf(5):

     vendclass en data
             Add the Vendor Indetifying Vendor Class with the IANA 
assigned
             Enterprise Number en with the data.  This option can be set 
more
             than once to add more data, but the behaviour, as per 
RFC(3925)
             is undefined if the Enterprise Number differs.

What could do with some improving is indicating in the man page which 
are DHCPv4 only and DHCPv6 only options as that is non clear and the doc 
assumes you know a little of either spec.


> 2. "waitip 4, 6" seem to wait for IPv4 only.
>
> I've tried firewalling IPv6 UDP (so DHCPv6 would timeout) and that
> option seem to not wait for it.
>
> Just "wait 6" works (hangs until timeout), but I'd like for dhcpcd to
> wait for both IP addresses.
>
> Manpage suggests that it should be possible (without explaining how),
> but using "wait 4" followed by "wait 6" on separate lines seem a bit
> counter-intuitive - will the last line just override the first one or
> will they merge?

waitip 46
is equivalent to
waitip 4
waitip 6

I have deliberately not documented that behavior though because one day 
protocol 46 or 64 might exist!
I have no idea if DHCP would still be relevant then though ....

> 3. "ia_pd" seem to get more than one range, even though it doesn't
>   seem to correspond to captured traffic.
>
> With configuration like this:
>
>   duid
>   persistent
>   option rapid_commit, classless_static_routes
>   require dhcp_server_identifier
>   nohook lookup-hostname
>   noipv4ll
>   vendorclassid dhcpcd:Linux-3.X.X:x86_64
>
>   noipv6rs
>   iaid b9:86:f4:39
>   ia_pd b9:86:f4:39 ext1/0/56
>   ipv6ra_own_default
>
>   debug

This configuration is invalid. dhcpcd.conf(5) needs to explicitly state 
that ia_pd should fall inside an interface scope option
AND not to assign the delegated prefix to itself.

> Since ia_na and ia_pd can't seem to be used together (resulting in
> "dhcpcd[4030]:  cannot specify a different IA type" error), is there
> any other way to pass ia_pd parameters from DHCPv6 to hook script on
> address assignment?

So basically dhcpcd is designed to work with either PD or NA/TA.
I don't see a good reason for allowing PD and NA/TA on the same 
interface.

> There seem to be ROUTERADVERT events a bit later, but they come a bit
> too late, and clearly dhcpcd has that address/range way before them.
>
> Also, dhcpcd output shows two "delegated prefix" lines, for some 
> reason:
>
>   dhcpcd[5044]: ext1: delegated prefix 2a02:17d0:3b0:a500::/56
>   dhcpcd[5044]: ext1: delegated prefix 
> 2a02:17d0:3b0:a500:1ebd:b9ff:fe86:f439/56
>   dhcpcd[5044]: ext1: adding address 
> 2a02:17d0:3b0:a500:1ebd:b9ff:fe86:f439/56
>
> But looking at actual traffic, I can't seem to find that second prefix
> anywhere, and it clearly corresponds to MAC, so I assume generated by
> dhcpcd and not a bug?

A lack of scope :)

Let me draw you a picture

ext1 == connected to ISP
int1 == internal LAN

Your config, based on above should look like so:

   duid
   persistent
   option rapid_commit, classless_static_routes
   require dhcp_server_identifier
   nohook lookup-hostname
   noipv4ll
   vendorclassid dhcpcd:Linux-3.X.X:x86_64
   # Replace 1234 with your enterprise number
   vendclass 1234 dhcpcd:Linux-3.X.X:x86_64

   noipv6rs
   ipv6ra_own_default

   debug

   interface ext1
   ia_pd b9:86:f4:39 int1/0/56


So the last block says "the below config is for ext1 only. We will use 
an IAID of b9:86:fe:39 to request a PD and then assign the result to 
interface int1 with a /56 prefix length"

Thanks

Roy