On Mon, Feb 15, 2010 at 11:52:08AM -0800, Jen Chitty wrote: > You can use the "--force-bind" option to force avahi-autoipd to ignore > other interface configuration (for example, configuration by DHCP client) > and go ahead and assign a link-local address no matter what. > > Hopefully your network admin is a bit more on-the-ball than to allow a > bunch of uncoordinated DHCP servers on the network. But, if you're > building consumer electronics products, it's probably a good idea to be > ready for such a thing, if possible. Of course, there's only so much we > can do to deal with a network mis-configuration like that, and we must be > very careful not to make the problem worse with our workarounds. Yes, sure. You guys probably know a lot better about the side-effects of a hacky "fix" :). But thanks for the "--force-bind", looks interesting. Hmm, well, I think our setup looks a bit more "chaotic" - if that might be the right word for the setup here - than a well-coordinated network maintained by one admin :D.
Cheers, Linus > > Cheers. > > --Jen > > > > > > Linus Lüssing <[email protected]> > Sent by: [email protected] > 02/12/2010 06:54 PM > Please respond to Avahi ML > > To: Avahi ML <[email protected]> > cc: (bcc: Jen Chitty/ENG/VTNCAN/VTECH) > Subject: Re: [avahi] General Avahi usage questions > > > Moin moin, Lennart, > Hi Jen, > > thanks a lot for your detailed explanations so far. > > On Wed, Feb 10, 2010 at 11:26:36PM +0100, Lennart Poettering wrote: > > On Sat, 06.02.10 18:46, Linus Lüssing ([email protected]) wrote: > > > > > hi guys. I was looking for a way to get pidgin/libpurple working > > > with avahi+ipv6. but then I realised, that I'm lacking some basic > > > knowledge about avahi :) > > > > > > first question: I think I remember having the avahi-daemon running > > > which assigned an ipv4 address on a new alias interface. when does > > > this happen, when not? > > > > avahi-autoipd is usually used as a fallback for dhcp. > I see. In the beginning I more had the impression that avahi would utilise > dedicated subnets only. But sounds plausible as at least for IPv4 > IP collisions are a lot less when using dhcp. Hmm, but also... if > I intend to use a network without a dhcp server and all clients > rely on just using the link local ones, then one host that left its dhcp > server on by mistake could cause quite a lot of trouble couldn't > it? Or even if there were two dhcp serves on by mistake with two > different subnets... hell, that would split everything in two to > three clouds! I couldn't find an option to enforce link-local > addresses for avahi anywhere, is there something like this? > > > > > I also found this avahi-ipauto thingy, but it does not seem to be > > > running for this avahi-ip4ll stuff to assign a 169.254.0.0/16 > > > adress > > > -169.254.0.0/24 and 169.254.254.0/24 (if I remember right) > > > > uh? avahi-autoipd will assign one of those addresses if no other > > address is configured via dhcp or so. > Ah, okay. I had to play a little with dhcp client and avahi to > see when and how avahi-autoipd is actually determening this state. > On my Debian system it also looks like, that additionally I have > to set the according interface to static, dhcp or NetworkManager > in /etc/network/interfaces, right? (according to > /etc/avahi/avahi-autoipd.action) > > > > 2nd question: how can I look up the ip addresses that are assigned > > > to mylaptop.local (mylaptop should just be the local host name in > > > /etc/hosts on 127.0.1.1 on a debian system, right?) > > > > getent hosts mylaptop.local > Hmm, that did not seem to work, I'm just getting the local ip > addresses specified in /etc/hosts. But hey, the mdns-scan did at > least find the other machine in my network. > > > > (you need nss-mdns installed for that) > Ehm, and there's only the libnss-mdns available in Debian > unstable (and it is installed here). > > > > > Avahi will always announce the "best" address it can find on each > > interface. Meaning that global addresses are generally preferred over > > link-local ones. > So like global -> organisation -> site -> link -> host? (Is the > ipv6 multicast scopes list the one that can be used as a > reference? Or is there something more complete?) > Another question that comes in my mind here: What happens, if two > computers have two different subnets configured which can't reach > each other over this one but could reach each other over their > ipv6 link local address as being on the same ethernet link. > Shouldn't avahi announce this link local address as well so that > those two hosts could communicate with each other anyway? > Is there a reason why avahi is not announcing all ip addresses > available on an interface (with adding its prefered priorities so > that the another host could choose the interface with the highest > priority stated and reachable as well)? > > And I guess, avahi is announcing both the "best" ipv6 and ipv4 > address letting the other hosts decide which type they are > capable connecting to, right? > > > > > 3rd question: when exactly is avahi-dnsconfd needed and why? Is my > > > assupmtion right, that I need this thing, if I want to use > > > applications that are not utilising avahi (for instance a normal > > > ping tool) and I want to reach mylaptop.local with that? > > > > It's useful when unicast-DNS server adresses are stored in multicast > > DNS. it could be used to configure unicast DNS servers in a non-dhcp > > environment. It is a more exotic feature and hence not installed by > > default on most distros. > > > > > 4th question: so an application that uses the libavahi can tell > > > the avahi-daemon to announce a certain service with the specified > > > port. which ip addresses would/should the avahi-daemon be > > > announcing then? > > > > as mentioned above avahi uses the "best" ip adress of each respective > > iface, and treat every iface seperately. > > > > > 5th question: what has to be kept in mind when using avahi with > > > ipv4+ipv6 or ipv6 only? read this article in the german linux > > > maganzine 03/06. at the end it is saying that for ipv6 stateless > > > autoconfiguration, avahi-dnsconfd is necessary. sounds plausible > > > because of the lack of a dhcp server. but why is this not the case > > > for avahi with ipv4? > > > > Some awesome dude wrote that article. He is really brainy and smart. I > > am a great admirer of his ;-) > > That said, I cannot remember I wrote "necessary" in that > > article. useful, yes. But necessary, no. In IPv4 if you do automatic > > configuration of routable IP adresses you use DHCP. And DHCP allows > > configuration of unicast DNS servers anyway. That's why the > > avahi-dnsconfd stuff is not really that useful there. > > > > Lennart > > > Okay, and then I'd have some more questions about how applications > that utilise the libavahi stuff should react. Sorry in advance, > didn't find the time to look at it yet, but will definitely do > that in two weeks the latest. > Should applications only allow connections from other hosts that > had previously announced themselves via avahi or should they accept > any connection (which might be a security issue?). But the first > thing could cause some trouble if the kernel would decide to use > source address differing from the one announced by avahi... > And again for IPv6, generally an application should try connecting > to the host's announced IPv6 address first and retry the IPv4 one > after a timeout? > > Cheers, Linus > _______________________________________________ > avahi mailing list > [email protected] > http://lists.freedesktop.org/mailman/listinfo/avahi > > _______________________________________________ > avahi mailing list > [email protected] > http://lists.freedesktop.org/mailman/listinfo/avahi _______________________________________________ avahi mailing list [email protected] http://lists.freedesktop.org/mailman/listinfo/avahi
