Hi again,
Just to make sure I've got all of this ok...
autoipd gets its chance to run and set an ipv4ll address when
dhclient fails for some reason to set a routable address, and with
the default script it can then get killed when dhclient obtains an ip
address lease. On top of this, by default autoipd can remove the
ipv4ll address when a routable address has somehow been set (by
monitoring Netlink events?). If a user/admin wants to ensure tcp
transmission doesn't get cut during a switch from ipv4ll to routable,
they can use --force-bind so the Netlink events have no effect, and
also alter the dhclient hook script so autoipd is not killed.
Does that sound right?
A couple of other things...
Apple has this page on mixed routable and ip4ll addresses:
http://developer.apple.com/qa/qa2004/qa1357.html
I have no idea of the default routing settings of most of the linux
distributions, but it seems debian at least doesn't have the settings
for responding to a host with an ipv4ll address when a routable
address is set. Do you have any plans for providing defaults/
guidance for these?
In the current avahi-autoipd.action script, a label is set when using
the ip tool, but no alias is defined when setting the address with
ifconfig. Was there a reason for that? (sorry... I don't know a lot
about interface labels/aliases)
Sorry for all the questions,
Chris
On 2006/09/04, at 1:30, Lennart Poettering wrote:
avahi-autoipd supports two different modes: the default mode is to
assign an IPv4LL address only if no other routable address is
configured. That means that IPv4ll is deactivated as soon as a
routable address is added to the iface and activated again soon as a
it is removed again.
This mode is of course "vulnerable" to the problems you mentioned
above. However this mode is probably the mode that will confuse people
the least and causes the least routing problems. That's why I chose to
make it the default.
Alternatively you can pass "--force-bind" to avahi-autoipd. If you do
this IPv4LL will be activated even when a routable address is already
assigned to the interface. This will fix the problems you mentioned
above, however might be confusing to people (see Debian bug #302684)
and makes routing non-trivial. (multicast routing that is, such as
what is needed for mDNS)
The actual interface configuration is done by an action script which
is called whenever an IPv4LL address needs to be added or removed from
the network interface. This is similar to the way ISC's dhclient
works.
The default action script uses Linux' iproute tool for adding the
address to the the network interface. The address is added with link
local scope and is labeled "eth0:avahi". For the legacy IP
configuration tools such as "ifconfig" such an address will show up as
alias interface "eth0:avahi".
With minor changes on the action script you could create a mode where
zeroconf is only activated when no other address is configured, but
the zeroconf address is left on the interface, even after a routable
address is configured later in time. This however I would consider
"configuration" and is as such left to the user/administrator.
Lennart
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