[avahi] avahi-autoipd

[Lennart Poettering]

On Tue, 05.09.06 22:59, chris mcharg (chris at outtrack.org) wrote:

> -- route add default dev eth0 metric 99 --
> 
> This makes sure that data bound for routable addresses is dumped via  
> eth0 even when we only have a ipv4ll address, as the routable  
> addressed host should be able to respond to us.  As such, it only  
> needs to be set when we have our ipv4ll address set.

Yes, that's how I understood it.

> -- route add -net 169.254.0.0 netmask 255.255.0.0 dev eth0 metric 99 --
> 
> This ensures that we respond to ipv4ll addressed hosts even when we  
> have a routable address set.  Therefore, it should be set by default  
> at boot.

That's mostly right. However this route is not explicitly necessary if
an IPv4LL address is assigned, because a route like this one is
implicitly added by the kernel in that case anyway.

In other words: the first route allows packet flow from a
IPv4LL-only hosts to a host with only a routable address. And the
second route allows the packet flow in the other direction.

The trick is to set the metric to 99 which makes sure that the routes
only take effect if no other routing is configured and allows them to
be set in all cases, with or without IPv4LL configured, without any
drawbacks.

As long as only IPv4LL-only hosts want to communicate, or as long as
only hosts with routable address want to communicate neither of the
routes is required.

Lennart

-- 
Lennart Poettering; lennart [at] poettering [dot] net
ICQ# 11060553; GPG 0x1A015CC4; http://0pointer.net/lennart/