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Looking for help troubleshooting my missing UDP Multicasts.

Some background... So I finally got an Amazon Echo and was playing with fauxmo on my PiZero to see if Alexa could find my device, but she couldn't. :(

I fired up Wireshark (on my Windows machine) and watched Alexa send out upnp (239.255.255.250:1900 UDP) multicast packets over my wifi network.

Great! I tried tcpdump on the PiZero (sudo tcpdump -ni wlan0 udp and port 1900 -A) but never saw a thing. Not even the regular broadcasts from my Windows box.

As I also had a Model B Pi kicking around... I tried it instead. Everything works great. It sees the broadcasts just fine. Unfortunately the devices have different versions of OS...

PiZero - Raspbian 8.0 with Linux 4.9.70+ #1068 Mon Dec 18 21:54:13 GMT 2017 armv6l GNU/Linux

Mobel B PI - Raspbian 7.11 with Linux 4.4.38+ #938 Thu Dec 15 15:17:54 GMT 2016 armv6l GNU/Linux

F/W is shut off. I have checked sysctl settings between my two Pi devices, but nothing seems different. There doesn't seem to be anything logged in /var/log/*. Everything I have tried to change/disable does not allow the PiZero to see simple UDP multicasts.

Update: I believe multicast is enabled and getting packets...

> ip -s link
    wlan0: <BROADCAST,MULTICAST,UP,LOWER_UP> mtu 1500 qdisc pfifo_fast state UP mode DORMANT group default qlen 1000
        link/ether b8:27:eb:d5:48:fe brd ff:ff:ff:ff:ff:ff
        RX: bytes  packets  errors  dropped overrun mcast
        5777796    38893    0       0       0       29604

> sudo netstat -g
    IPv6/IPv4 Group Memberships
    Interface       RefCnt Group
    --------------- ------ ---------------------
    lo              1      all-systems.mcast.net
    wlan0           1      224.0.0.251
    wlan0           1      all-systems.mcast.net
    lo              1      ip6-allnodes
    lo              1      ff01::1
    wlan0           1      ff02::fb
    wlan0           1      ff02::1:ff83:6345
    wlan0           1      ip6-allnodes
    wlan0           1      ff01::1

The only difference (between the Pis) I could find in /proc/sys/net/ipv4/conf/wlan0 was that promote_secondaries was set to (1). I tried it at (0) but this made no difference.

Any ideas what I should be checking next?

ctrl-alt-delor
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pedwards
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  • Can you ping the Pi from the machine that is sending the broadcasts? Also, that IP address doesn't look like a broadcast address; it's in the multi-cast address space. – dogoncouch Feb 12 '18 at 18:12
  • Windows besides doing many broadcasts after Windows 7?, started doing a LOT of multicasts. Your problem is that you are not seeing multicasts. Please add the output of `ip addr` to your question. – Rui F Ribeiro Feb 12 '18 at 18:36
  • Also, do you have an AP or are the PIs running `hostapd`? – Rui F Ribeiro Feb 12 '18 at 19:15
  • Sorry, changed broadcast to multicast. Echo uses same SSDP technique as Windows for discovery, so I'd consider this type of traffic (more or less) the same. The PIs are running on my home wifi network (behind a router). All appliances see the multicasts on the wifi network except the PiZero. Won't get to revisit till later tonight... – pedwards Feb 12 '18 at 19:38
  • deleted the cross post as I'm getting more traction here. :) – pedwards Feb 12 '18 at 19:39
  • If other equipments see multicast, then it is not the AP blocking them...(APs can be configured for that) – Rui F Ribeiro Feb 12 '18 at 21:59
  • Which wifi chipset and model are you using in the pizero? – Rui F Ribeiro Feb 13 '18 at 08:35
  • Hmmm. Can't find chipset specs. I have PI Zero W based on the board revision [9000c1](https://www.raspberrypi-spy.co.uk/2012/09/checking-your-raspberry-pi-board-version/) which has "802.11 b/g/n wireless LAN". – pedwards Feb 13 '18 at 21:50
  • Double hmmm. Just booted the model B with my PIZero flash and it works fine. I think the OS is set up ok, but might be the hardware or driver... – pedwards Feb 14 '18 at 03:09
  • You say that `sudo tcpdump -ni wlan0 udp and port 1900 -A` shows nothing. Have you tried lessening the constraints? It may tell you something. – ctrl-alt-delor Aug 28 '19 at 09:16
  • Note1: you can run wireshark on the Pi. Note2: if when installing wireshark (and prabably tcpdump) you select allow other users to run. Then any user in group wireshark, can run these commands. No need to be root. (There is a warning about a security risk, but this is the wrong way around. The only risk is letting people run it, but this is very low compared with running as root.) – ctrl-alt-delor Aug 28 '19 at 09:24

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