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Expected response on ssdp:discover
29-12-2018, 10:52
Post: #1
Expected response on ssdp:discover
Hi,

My (wireless subnet) control points are (still) struggling detecting my (wired subnet) MinimServers.

I am running 2 MinimServers (basically to support a different approach towards classical music tagging) on a Debian 9 64bit server, having http.port 9710 & 9711 and ohnet.port 9720 & 9721 respectively.

The router/firewall is a Sophos XG. The main switch is a Zyxel GS2210 24 ports. Both are running latest firmware.
The control points are mconnectPlayer (IOS) and BubbleUPnP (Android)

I enabled multicast forwarding for the multicast IP 239.255.255.250
1- from the wired minimserver IP to the wireless subnet
2- from the wireless control point(s) to the wired subnet

For now I disabled IGMP snooping on the switch, but that did not make a difference.

I took some network interface dumps on the server (tcpdump -i eth0 -w <file>).

When I restart a minimserver (MinimWatch) (and rescan in the control point) it becomes visible in the control point, as at that time an alive message is send

NOTIFY * HTTP/1.1
---------------------
HOST: 239.255.255.250:1900
SERVER: Posix/200809.0 UPnP/1.1 ohNet/1.0
CACHE-CONTROL: max-age=1800
LOCATION: http://<ip mediaserver>:9720/<uid>/Upnp/device.xml
NTS: ssdp:alive
...

When I scan from the control points, I see request coming in on the server (below is triggered from mconnectPlayer)

M-SEARCH * HTTP/1.1
--------------------------
HOST: 239.255.255.250:1900
MAN: "ssdp:discover"
MX: 3
ST: urn:schemas-upnp-org:device:MediaServer:1

But I expected a reply from the mediaserver towards this "discovery" request and I don't see them in the dump.

What would have been the expected response ?

Kind regards - Raf
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29-12-2018, 17:35
Post: #2
RE: Expected response on ssdp:discover
See this post for an explanation of why enabling multicast forwarding between the subnets is not sufficient.

The expected response to the M-SEARCH multicast message is a unicast UDP message sent to the source IP address and port that sent the M-SEARCH request to the multicast address. If you haven't set up routing between your subnets for unicast UDP messages, the media server's attempt to send this message will fail.
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29-12-2018, 17:54
Post: #3
RE: Expected response on ssdp:discover
Yes thanks, that was my last years attempt to get it working Smile

I would have expected to see this unicast UDP message popping up in the tcpdump, but I am not too familiar with this.

I will try some other options ... I read that an "IGMP proxy" would be an alternative solution ... which is not supported on Sophos.
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29-12-2018, 21:54
Post: #4
RE: Expected response on ssdp:discover
The problem isn't related to IGMP, so an IGMP proxy won't help. Is there a reason why you can't use the same subnet for wired and wireless?
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29-12-2018, 23:49
Post: #5
RE: Expected response on ssdp:discover
(29-12-2018 21:54)simoncn Wrote:  Is there a reason why you can't use the same subnet for wired and wireless?
True Wink ... when the control point is on the same subnet as the servers and the renderer, all works flawless.
I might decide to go back to one subnet for wireless and wired.

As I have a working alternative this thread is not really urgent, but I have the impression that the server is ignoring the "ssdp:discover". I did a new dump and did not see any response on the network interface (I am looking at the interface of the server, not the control point).
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30-12-2018, 08:44
Post: #6
RE: Expected response on ssdp:discover
The expected response to the M-SEARCH multicast message is a unicast UDP message sent to the source IP address and port that was used to send the M-SEARCH request to the multicast address.

If you haven't set up routing between your subnets for unicast UDP messages, the media server can't open a connection to this IP address and port. This means the response message can't be sent, so you won't see see this message in any log.
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