dhcpcd-discuss

On 06/06/2014 17:09, David Hauck wrote:
> Can you say more about how dhcpcd manages this? Our system has very
> diverse network configurations (including up to 6+ network interfaces
> - all wired) and we need fairly explicit control of these. One
> configuration that I'm currently pondering is the "all interfaces
> configured for DHCP" scenario and it is this scenario that I'm curious
> about. Unless I understand exactly how dhcpcd controls this case (in
> any/all circumstances) I would like to be able to control its
> operation on an interface by interface basis (for e.g., I know about
> the lowest metric wins, multi-default gateway scenario, but I need to
> prevent this configuration from occurring - i.e., enforce a single
> gateway on a specific interface only).

You could add -DHAVE_ROUTE_METRIC=0 to CPPFLAGS and recompile dhcpcd.
This would effectively manage your routing like BSD where there are no 
route metrics and enforce your one gateway policy.
To ensure that your specific interface "wins" just give it the lowest 
metric number in dhcpcd.conf

But Beware!
IF this interface is not configured (ie, link down) and another is then 
dhcpcd will install a default interface for that interface and gateway.
When the interface is configured (ie, link up) then dhcpcd will change 
the default route to the preferred interface and gateway.

> As far as I know (under my Debian-like sysvinit system) the network is
> brought up during init via an RC script  with 'ifup -a'. I'm not
> exactly sure how ifup/down iterates interfaces, but my understanding
> is that it invokes dhcpcd "an interface at a time". If so, I wonder if
> these invocations can be parameterized in any particular way (e.g.,
> the reference I saw somewhere to /etc/default/dhcpcd), or whether the
> recommendation is to do this via the dhcpdh-hooks mechanism instead
> (which would be somewhat intricate).

Ah yes.
You're probably thinking of the dhcpcd package in Debian. That is 
ancient, the package you want is dhcpcd5 (really dhcpcd6) and also old, 
I should update it.
Of course, hopefully you're compiling from source ;)

The dhcpcd5 package has a script that pops into /etc/init.d (yes, I need 
to supply a systemd script as Debian recently changed)

So basically it's one daemon that controls all interfaces, and 
realistically the only way it can work in a BSD way which you want.
I would NOT use the per interface invocation, which is a positively 
ancient way of managing this kind of stuff!

> > As to information duplication, well all of the hook scripts take this
> > into account.
> > So for resolv.conf and ntp{d}.conf it's all managed.
> > You may want to look into using resolvconf (I personally recommend
> > openresolv ;) ) as that can handle it better than dhcpcd.
>
> Interesting. So multiple identical incoming nameserver parameters are
> merged/normalized across interfaces (resulting in a single
> recolve.conf file with the merged nameserver list - including removed
> duplicates)?
>
> If I wanted to do the same for hostname and gateway across interfaces
> I would need to do something similar? This would be instead of doing
> some other kind of interface-specific invocation of dhcpcd from ifup
> that just informed this interface negotiation to ignore/not negotiate
> (for e.g.) gateway and/or hostname? Personally, I'd prefer the former
> if it was available since it seems easier ;).

hostname, no.
hostname has specific rules of when it's configured, please read the 
hook script for exact details
Basically it will update it IF unset or localhost or the the OLD name 
provided by the DHCP server.
That may or may not fit your goal.

gateway, well dhcpcd handles this internally. We've already discussed 
the possible options above.

Thanks

Roy