Questions[mdns](server)

I have a FreeBSD 9 router (a Soekris net6501) connected to the internet via a dsl modem (bridged), doing NAT for two internal subnets, 10.0.1.0/24 (LAN) and 10.0.2.0/24 (wifi net).

There are routes between the subnets and things like ssh host-A.wifi from host-B.lan works.

But, wireless clients (like iPads and iPhones) on the 10.0.2.0/24 net can't seem to find stuff on the LAN (for example, airplay to an Apple-TV on the LAN).

I'm not totally sure, but I think this is because Apple uses Bonjour and Bonjour uses Multicast to find things and Multicast is not routed across subnets.

According to the FreeBSD handbook, to route multicast, I need to compile the kernel with options MROUTING and create a /etc/mrouted.conf, but I can't find any good examples of the configuration file.

1. Is my problem related to multicasting across subnets?
2. Is mrouted the preferred solution in FreeBSD to enable routing?
3. How do I create a /etc/mrouted.conf that routes between 10.0.1.0/24 and 10.0.2.0/24?

I have the following very peculiar issue with using Avahi on the DreamPlug (which is a plug computer running Ubuntu Jaunty).

After spending days on this, I think I've managed to narrow down the issue.

The DreamPlug acts as the WiFi access point, and has the hostname plug and IP address 192.168.1.1 (which is set in both /etc/hosts and /etc/hostname) and runs lighttpd.

Now my Mac works straight away with accessing http://plug.local in Chrome, however if I try and load http://plug.local on the iPad, it doesn't work. That is, it doesn't work until I load the page on the desktop.

For some reason, the iPads are never able to resolve the hostname, until the hostname is first resolved on the Mac... which is weird because there is no connection between the iPads and the Mac other than the fact that they are connected to the same access point (the DreamPlug).

So just to clarify again: Safari on the iPad will hang (until it reports that browsing failed) when accessing http://plug.local unless I access http://plug.local on the Mac, run ping plug.local, do ssh [email protected] or basically do anything else that resolves the hostname, at which point the iPad instantly resolves the hostname and it starts working properly.

If my understanding is correct, when the iPads connect they broadcast a resolution request for plug.local. For whatever reason, this request is ignored by the DreamPlug (or it never gets received). However, the Mac does manage to broadcast its request. It broadcasts a resolution request and the DreamPlug brodcasts back the result plug.local -> 192.168.1.1. The iPads then receive this result (which was really destined for the Mac) and are then able to resolve successfully.

I'd be happy to supply my avahi-daemon.conf or other config files on request.

Update: I've now managed to use Wireshark and found that the iPads do indeed broadcast a request to the network.

I've captured both a packet that DID result in a response from Avahi, as well as one that did NOT.

They both appear completely identical, the only difference is that the one that failed specified an additional RR of type OPT... I have no idea what an OPT record is. Could it be that Avahi doesn't like DNS queries with OPT RRs attached for some reason?

Here are two screenshots taken from Wireshark. The first one shows a "good" mDNS request which is sent from the desktop computer (in this case, the device is called runway.local). This query works fine and the server (at 192.168.1.1) responds straight away:

Here is an example of the response that is returned from runway.local:

Meanwhile, here is a second DNS query which has been sent from the iPad for the same hostname, runway.local. In this case, the request seems to be simply ignored (in any event, no response is ever received for this DNS query):

Trying to track down what it is in the iPad request that causes the issue, it appears that the two packets are almost identical, the only difference between mDNS queries sent from the desktop (running OS X) and the iPad, is that the iPad appends an OPT resource record to the bottom of the DNS request.

The question is: what is the significance of the resource record -- and is it this -- or is it something else -- that is responsible for this DNS request being ignored by Avahi.

UPDATE This could be the breakthrough I've been looking for:

I've been running avahi-daemon with --debug flag and I've noticed a lot of "Invalid query packet." messages. This led me to this page: http://avahi.org/ticket/284 which seems that this is a known issue (albeit one that's supposed to be resolved).

Specifically:

A tcpdump makes me believe that this is due to Mac OS 10.6 using RFC2671 to add information in the additional data section of DNS queries. Specifically, it is supplying the 'UDP payload size' (in my case, 1440) as hint for the max size of response packets. [...] Avahi considers queries with non-empty additional data sections invalid, where it checks that AVAHI_DNS_FIELD_ARCOUNT != 0 just before generating the Invalid query packet message.

First, some background: We've got a lab containing a handful of dedicated Linux servers that run on an isolated LAN. All the servers run the same OS (Debian Linux) and the same proprietary server software, and the server processes communicate with each other to keep their data in sync. That means that as far as any clients are concerned, it doesn't matter which server the client connects to -- any server will return the same data as any other.

These Linux servers all run avahi-daemon to publish mDNS hostnames for themselves, which means that a client can enter e.g. "http://linux-server-1.local." into his web browser and connect to Linux server #1, and so on.

This is all well and good, except it means that a user sitting at the client machine (typically a Mac or Windows laptop with Bonjour installed) has to know (or figure out) which of the Linux servers are currently online, and he has to make sure he connects to one of those. For example, if server #2 is offline today, and the client enters "http://linux-server-2.local." into his URL bar, he's not going to get a response. That isn't the end of the world, of course, but it is annoying for newbie users who expect everything to "just work", and also it makes the development of robust client-side scripting more complicated (since the client-side script would need to know how to deal with offline servers explicitly).

With that in mind, my question is this: is it possible to configure Avahi to publish an anycast-style mDNS hostname alias as well? The goal is that anyone could sit down with his laptop, enter "http://any-linux-server.local." (or similar), and get connected to one of the servers that is currently on line (again, it doesn't matter which one).

Note that this needs to work without any special configuration of client laptops, as we have no control over them (other than the requirement that they have Bonjour installed).

Also note that we can't rely on the presence of a separate nameserver or proxy box, or on the presence of any particular Linux server, since that would introduce a single point of failure, which we're trying to avoid.

I have a list of IP addresses on a network, and most of them support multicast DNS. I'd like to be able to resolve the server name instead of just having the IP address.

ping computer.local
64 bytes from 192.168.0.52: icmp_seq=1 ttl=64 time=5.510 ms
64 bytes from 192.168.0.52: icmp_seq=2 ttl=64 time=5.396 ms
64 bytes from 192.168.0.52: icmp_seq=3 ttl=64 time=5.273 ms

Works, but I'd like to be able to determine that name from the IP. Also the devices don't necessarily broadcast any services, but definitely do support mDNS broadcast. So looking through services won't work.

1. First, what exactly Bonjour does (pleas read my guesses written bellow)?
   Here I found out that Bonjour enables automatic discovery of computers, devices, and services on IP networks. But I thought that it not only "discovers devices on IP network" it also creates an IP network by assigning IP addresses to devices where Bonjour is running. Am I right?

2. And I still miss the essence. Does it work in the following way? First I connect devices (for example laptops) physically so that they potentially can communicate with each other. Then, let say, on some laptops I have Bonjour running and then, as a consequence, these laptops assign IP addresses to them self in automatic way. So, laptops (where Bonjour is running) build an IP network. Does it work in this way?

3. Or may be a computer running Bonjour is not considered as a service and it does not broadcast itself just because Bonjour is running on this computer. I mean that the applications running on the computers need to use Bonjour to broadcast themself. So, it is applications that broadcast themself (not computers) and it is not done automatically (application needs to broadcast themself explicitly). Is it right?

4. How exactly my application can broadcast itself? Can I use command line to register an service (so that all applications using Bonjour knows that a new service appeared)?

5. Further, I would like to have an application which use the IP network created by Bonjour. For that my application needs to know which devices/services are present in the network. In more details, my application needs to have a list of services. Each service in the list should have a name, the IP address where it is running and the port which is used by the application. Can Bonjour provide this information in some way? If it is the case, how exactly it works. How my program can get this information from Bonjour? Can my program read some file created by Bonjour and containing the above mentioned information? Can I use some commands in command line to retrieve this information?

6. I have a special interest in accessing the information about services from files, environment variables or commands in command line. These options seems to me to be the simplest! Since in these case I do not need to use any additional libraries to communicate with Bonjour from a particular programming language.

P.S. Pleas ask questions if something is not clear in my question. I will try to formulate my question in a more clear way.

P.P.S. I use Windows 7.

ADDED: I plan to write my applications in PHP. Every computer should run a Apache web server. And I want to use Bonjour to help computer discover each other (computers are working in a local network).