dhcpcd-discuss

> On Jan 31, 2016, at 2:07 PM, Roy Marples <roy@xxxxxxxxxxxx> wrote:
> 
> On 2016-01-31 15:03, Nick Williams wrote:
>>> On Jan 31, 2016, at 7:48 AM, Roy Marples <roy@xxxxxxxxxxxx> wrote:
>>> Or you can look at the file dhcpcd-definitions.conf in the dhcpcd source tree to find the full definitions and decoding for every RFC DHCP option I know of, along with a short description and RFC number.
>> Excellent! That file was VERY helpful. Using that, I was able to
>> figure the following out (if I’m screwing something up, let me know):
>> We currently send the following options (some of them all the time,
>> some of them just sometimes) with DHCLIENT with DHCPv4:
>> request subnet-mask
>> request broadcast-address
>> requset routers
>> request domain-name-servers
>> request domain-name
>> request interface-mtu
>> And I BELIEVE those are equivalent to the following DHCPCD options:
>> option subnet_mask
>> option broadcast_address
>> option routers
>> option domain_name_servers
>> option domain_search
>> option interface_mtu
> 
> Wrong
> domain_search is a different option from domain_name.
> Normally best to request both options.

Ah. I missed that one. Thanks!

>> Also, we currently send the following DHCPv6 options with DHCLIENT:
>> request domain-name-servers
>> request domain-name
>> And I BELIEVE those are equivalent to the following DHCPCD options:
>> dhcp6_option name_servers
>> dhcp6_option domain_search
> 
> Correct.
> However, if you specify ANY dhcp6_ option then you need to specify ALL dhcp6_ options you want, otherwise dhcpcd will request matching dhcp6_ option from the dhcp4 counterparts.

I don’t quite follow this. Are you saying that if I specify "dhcp6_option name_servers” but don’t specify "option domain_name_servers” then DHPCD will automatically add "option domain_name_servers” to my IPv4 config? It almost reads like one of the “dhcp6_options” in your sentence shouldn’t have been “dhcp6_,” but probably I am just reading it incorrectly.

>> I didn’t find dhcp6_options for subnet mask, broadcast address, or
>> routers, but I’m guessing that’s because those aren’t DHCPv6 options,
>> and it’s all automatic, because I don’t see those in
>> dhclient/WIDE/Google, and we aren’t sending them currently with
>> dhclient.
> 
> :)
> In IPv6, there is no subnet mask. There is a prefix length. In IPv4 this is called CIDR and ranges from 0-32 to match the subnet mask.
> Also a generic broadcast address doesn't exist in IPv6 - broadcast addresses are normally special network addresses such as ALL DHCP Servers

Yep. All like I thought. Thanks!

>> The dhcpcd.conf man page says that the DHCPv6 equivalent of “option”
>> is “dhcp6_option,” but it doesn’t say what the DHCPv6 equivalent of
>> “nooption” is. Is that also just “dhcp6_nooption?”
> 
> Yes

Excellent.

>> Finally, we support IPv6 information-only/parameters-only
>> configuration (where only stateless configuration parameters are
>> requested). This is dhclient command-line option “-S” and WIDE client
>> configuration option “information-only.” By name, I couldn’t find any
>> equivalent option in the man pages or in dhcpcd-definitions.conf, and
>> Googling around for about an hour didn’t turn up which DHCPv6 option
>> dhclient/WIDE send when information-only mode is enabled. Does DHCPCD
>> have an equivalent for this? Does specifying the stateless
>> configuration option “ipv6ra_autoconf" do the equivalent?
> 
> from dhcpcd(8)
>     --inform6
>             Performs a DHCPv6 Information Request.  No address is requested
>             or specified, but all other DHCPv6 options are allowed.  This is
>             normally performed automatically when the IPv6 Router Advertises
>             that the client should perform this operation.  This option is
>             only needed when dhcpcd is not processing IPv6RA messages and the
>             need for DHCPv6 Information Request exists.

Interesting. So it’s a command-line-only option; no config file option. I wonder if we (VyOS) even need to still support this. I’ll ask on the VyOS list what was intended by params-only. I just realized there’s no VyOS config option for auto-configuration, so maybe this was a poorly-named config option meant to enable that.

Nick