[lwip-users] multicast group membership not working for tap device

[Stefan P. Galanos]

I am running lwip version 1.41 on a Linux server(red hat release 6.4).  I am using the socket API and attempting to listen to multicast packets that a test client running on the same linux server is sending.  I have successfully send unicast packets using this setup on the tap0 device.   However, when my listener tries to join a multicast group, I see the IGMP v2 report packets going out and the igmp_joingroup call returns without an error code but I don’t join the multicast group(I have confirmed this with a netstat –g).  It appears that I have done all the setup successfully so I am stumped.  Any ideas as to what I might be doing wrong? 

 

As a side question, I was wondering why the system command ifconfig(in file tapif.c) used to configure the tap0 device uses the gateway instead of the IP:

 

netif: IP address of interface  set to 192.168.1.2

netif: netmask of interface  set to 255.255.255.0

netif: GW address of interface  set to 192.168.1.1

tapif_init: system("/sbin/ifconfig tap0 inet 192.168.1.1")

 

tap0      Link encap:Ethernet  HWaddr 12:48:BE:27:92:1E 

          inet addr:192.168.1.1  Bcast:192.168.1.255  Mask:255.255.255.0

          UP BROADCAST RUNNING MULTICAST  MTU:1500  Metric:1

          RX packets:0 errors:0 dropped:0 overruns:0 frame:0

          TX packets:0 errors:0 dropped:0 overruns:0 carrier:0

          collisions:0 txqueuelen:500

          RX bytes:0 (0.0 b)  TX bytes:0 (0.0 b)

 

Thanks in advance for any help,

Stefan