Hello, I have been directed to this list by IANA when I asked the
following question:
I am researching ways of device/machine discovery on the
network. This
is similar to the Discovery phase of UPnP devices, which uses the SSDP
protocol.
I have researched far enough to know that my best bet for UDP
multicast address group is the Site-Local Scope address range of
239.255.000.000-239.255.255.255
SSDP and UPnP protocols use the address 239.255.255.250
My question is this:
How do I pick a group address within this range and not have a
chance of colliding with some other application on the network already
using the group address I just picked?
Do I just randomly pick an address in that range and hope for
the best? I am running on Windows and cannot assume that there is a
MADCAP server available.
Thanks in advance!
Dave Raskin
Rimage Corporation
Hello, I have been directed to this list by IANA when I asked the
following question:
An even better set of lists might be:
<https://www1.ietf.org/mailman/listinfo/mboned>
<https://mail.internet2.edu/wws/info/wg-multicast>
There is some overlap between the two, but the former is probably
the best place to start. Both are good lists that may be relevant
for you to hang out in as they often cover the protocol and
operational aspects you may want to follow. Both are low volume.
My question is this:
First, let me say... THANK YOU! Presuming you are a multicast app
developer, you actually asked, terrific! Most don't and what ends
up happening is growth in the "multicast swamp", where site local
apps like the one you're presuming working with end up leaking all
over the place taking up valuable mcast router memory space and cpu
time.
Now, the bad news.
How do I pick a group address within this range and not have a
chance of colliding with some other application on the network already
using the group address I just picked?
Do I just randomly pick an address in that range and hope for
the best? I am running on Windows and cannot assume that there is a
MADCAP server available.
You can probably never expect to find a MADCAP server. I don't think
I've even ever heard of anyone deploying one, though I'm sure a handful
have tried, I don't think it ever got much deployment outside a select
few environments or the lab.
IP multicast addressing has been a bit of a problem to say the least.
A couple of documents to read might be:
<http://www.watersprings.org/pub/id/draft-ietf-mboned-addrarch-05.txt>
<http://www.watersprings.org/pub/id/draft-ietf-mboned-addrdisc-problems-02.txt>
Then perhaps follow up on mboned if you still have questions. Some
of the people that hang out there hang out here and may have more to
say since I haven't been following closely what's going on for the
past year. I don't think you're going to find the satisfying answer
you were looking for, but that's IP multicast for you.
John
Hello;
I think that pretty much everything John Kristoff said was spot on, especially to thank you for asking.
Unfortunately, there is no general method for doing this except to use your GLOP address, if you have one, and that is not really appropriate for site-local work. Madcap and MZAP were implemented into Windows, but I have never heard of them being used.
If you look at
http://www.iana.org/assignments/multicast-addresses
it says that
239.255.000.000-239.255.255.255 Site-Local Scope [Meyer,RFC2365]
should be used for site local scope, but I know that that is not really followed much either.
So, my advice is
- pick something at random from 239.255/16
- let us know what it is
- give the user a config file or some other means to change it if they have too.
I would be glad to collect and maintain a list of site-local multicast addresses, but I have no illusions that
such a list would be complete. It would be worth doing, however.
If you really feel that this is something where there will be millions deployed, contact me offlist and we
can discuss getting an address from IANA.
Hope this helped, and, again, thank you for asking.
Regards
Marshall Eubanks