Re: [libvirt] dhcp6, radvd, ip6tables, etc. (update)

On 10/30/2012 11:58 AM, Gene Czarcinski wrote: > > Well, ff02::1:2 does have some meaning in dhcp6. > > From what I have seen by "well behaved" clients is that the client > always uses port 546 and the server always uses port 547. But, > dnsmasq have some comments/code which indicates that not all clients > are "well behaved." > > In dhcp6, a little four dhcpv6 dance is performed to establish the > clients address: > > 1. dhcpv6 solicit: from=fe80::client:546 to=ff02::1:2:547 > 2. dhcpv6 advertise: from=fe80::server:547 to=fe80::client:546 > 3. dhcpv6 request: from=fe80::client:546 to=ff02::1:2:547 > 4. dhcpv6 reply: from=fe80::server:547 to=fe80::client:546 > > Or, in other words: (1) need dhcpv6, (2) I serve it, (3) OK, give me > one, and (4) here it is. Ah, so that address has a special meaning/function.

> Since dnsmasq does its own packet filtering and with bind-interfaces > having a real meaning, it all works (assuming that radvd has the right > configuration). >> >>> This works With the radvd configuration and a dhcp-range specified for >>> a ipv6 subnet, a guest will get a dhcp6 address and RA default route. >> Interesting - so both radvd and dnsmasq are involved, correct? > Yes, why not? No reason. Just curious. > Sometime in the future this should be reconsidered and either > everything is done by dnsmasq or it is at least an option. Yeah, it couldn't be mandatory, at least not now, since there are still lots of people using dnsmasq versions that don't have all the required capabilities.

> I must say that having dnsmasq do everything does have appeal ... > one less dependency. >>>> 4. After getting all of this working to my satisfaction, my next >>>> mountain to climb is VM ... it really does not like network xml >>>> definitions which include a dhcp-range for an ipv6 definition. >>>> >>>> Comments? >>>> >>>> NOTE: I am implementing all of this assuming that my previous >>>> patches have been accepted ... the ones for creating a dnsmasq >>>> conf-file for parameters rather than using the dnsmasq command-line. >> I have no problem with the "convert from long commandline to conf file" >> patch except for the bit that points to a "conf directory" where user >> supplied conf files can be added. Aside from that part needing to be in >> a spearate patch, if we're going to add that kind of configurability, we >> need to do it in a way that will allow us to easily see that the user is >> playing outside the fence (otherwise we spend a lot of time chasing >> "bugs" that end up being caused by user-supplied options). > Originally, I wanted the conf-dir so that I could pop in/out some > configuration changes that would happen when dnsmasq re-read the > configuration. Well, it does not work that way and dnsmasq has to be > restarted for some of the more interesting changes. Given this, I > believe that conf-dir serves no useful purpose and should be removed > and I will remove it and resubmit the patch. >> Because we're in freeze right now I haven't spent a lot of time >> discussing that, but planned to send a message about it when I get a >> minute. > Right now I am working on getting dhcpv6 functional and, while what I > have works, there is still more to do. >>>> I am sure that someone could spend the time refitting the dhcp6 >>>> patches to the old code but why get aggravated? If you folks do not >>>> want to do things that way, fine, please say so. But if it is going >>>> to be accepted, then I would like some indication of this. >>> 5. As far as I can tell (or at least this is for dnsmasq), >>> "dhcp-no-override", "enable-tftp", "tftp-root=", and "dhcp-boot=" are >>> all IPv4 only and thus ignored for IPv6 in bridge_driver. I have not >>> looked to see what network_conf.c does. >> "what network_conf.c does"? Well, it of course doesn't deal directly >> with those options, but the config that feeds into some of those options >> is parsed in virNetworkIPParseXML(), and is only done if the <ip> >> element is ipv4. But then you've already seen that code if you have dhcp >> working for ipv6 - the <dhcp> element is also only parsed for ipv6. The >> format-side code doesn't have that extra check; I guess I figured that >> if there was no way to configure ipv6 with dhcp or tftp, it was safe to >> assume any ip element with dhcp or tftp info was ipv4 anyway. > I have now dived into network_conf.c and a little into dnsmasq.c. Yet > again I was surprised because most of what was needed for dhcpv6 was a > little tweaking here and there. I'd like to think that's because we've tried to do things in a manner that anticipates future expansions, but some of it may be pure luck :-)

> To support dhcp-host for IPv6, I did assumed that for IPv6 no MAC > address would be specified since it does not have a defined meaning in > DHCPv6. Therefore, in dnsmasq.c/hostsfileAdd(), if the mac==NULL, I > use the IPv6 format of <hostname>,[<ipv6-addr>] whereas for IPv4 it > is either MAC,<ipv4-addr>,<hostname. or MAC,<ipv4-addr>. > > This way most of the code works as is. Dnsmasq has lots of options > and different ways that dhcp-host= can be specified, but this is > simple and I know it works. >>> 6. Handling of the info for addn-hosts file and the dhcp-hostsfile. >>> This currently works because things are forced so that one and only >>> one IPv4 dhcp definition will be handled. With the addition of IPv6 >>> dhcp, things fall apart. >>> >>> 6a. addn-hosts: The addn-hosts file is similar to the /etc/hosts file >>> in both form and function. The <dns>-<host> specification is done on >>> an interface bases and, thus, the processing of the data and creation >>> of the file should only be done once. >>> >>> 6b. dhcp-hostsfile (dhcp-host=): This needs to be done at least for >>> every ip definition that is processed for dhcp. Initially, this will >>> be for dhcp4 only until I can figure out how to do it for dhcp6. >>> >>> 6c. Thus, networkBuildDnsmasqHostsfile() needs to be split into two >>> functions [one for addn-hosts and one for dhcp-hosts]. Additionally, >>> all the functions which call dnsmasqSave() need to be reworked >>> appropriately. >> I've actually never liked the "dnsmasqContext" concept, as it seems like >> overkill and has conceptual problems such as what you've described. I >> would be just as happy with replacements that were simpler and easier to >> deal with. I think part of what complicates dnsmasq.[hc] is that it's in >> the util directory, so it isn't allowed to understand the contents of >> virNetworkDef, and must instead be sent the list of hosts in a simpler >> format. If, instead, there was a file src/network/bridge_dnsmasq.[hc], >> that could have functions that took virNetworkDef as an arg, and just >> immediately return a string (or, in a separate function, write to a >> file). That should simplify calling, and writing tests. And existing >> dnsmasq-related functions in bridge_driver.c could be moved there as >> well, reducing clutter in bridge_driver.c. (Of course I'm saying all >> this without ever seriously considering it, just talking off the cuff, >> so I may be completely wrong :-) > Right now I have fixed things up so they work. I would like to leave > this as an exercise for someone else [or at least a later time]. > > Besides, isn't bridge_driver.c pretty much for dnsmasq only? Right now, yes. It's always possible that an alternative could come along, of course...

>>> 7. So far, the only things I have done involving the xml specification >>> is to enable <dhcp> for IPv6. However, the xml to specify a dns >>> addn-hosts appears, IMHO, to be overly verbose and complicated. >> It is made that way because a single IP address may have multiple >> hostnames associated with it, and we want to avoid having multiple >> methods of describing the same thing. What you propose in the next >> couple sentences was already proposed, tried, and rejected when dns host >> support was originally added. > OK. >>> So, while allowing the current xml to be valid, I suggest adding an >>> alternate form for which is similar to that used for dhcp-host. An >>> example is "<host ip='1.2.3.4' name='one' />" >>> >> There are a few places in libvirt's XML where the same thing can be >> expressed in two different ways, but that is only done when necessary >> because the existing XML is unable to completely describe the new >> functionality but backward compatibility is required. It creates all >> sorts of problems when formatting the config back into XML though (which >> of the two do you choose? Or do you do both? Either of these is a bad >> answer), therefore we definitely don't want to do that except in cases >> where it is absolutely necessary; this isn't one of those cases. > This is why I have tried to tweak and bend things so it works (and > because it mostly worked before). > > And now, as the saying goes, one more thing. > > I now realize that I am going to need to get into virsh net-update > since I am adding things to the xml specification and net-update will > need to differentiate between dhcp4 and dhcp6 changes. > > Another thought that occurs to me is whether there has any > consideration been given having a "virsh net-restart" which would just > restart dnsmasq and radvd. Typing stuff in for the command line of > net-update is a little prone to typos. You can always put them in (temporary) files :-)