I have been experiencing multicast subscription when subscribing to more that 20 IP’s via smcroute and python socket module. After vigorous googling I finally found a fix.
Linux OS, limit the number of multicast group memberships that a machine can belong to simultaneously. (A “multicast group membership” indicates that a machine is listening to messages for a specific multicast IP address. In other words, there is a limit on how many multicast IP addresses you can listen to.)
On Linux, in particular, the default limit is relatively small (only 20 on many standard kernels). However, this limit can be configured dynamically.
If you try to subscribe to too many multicast addresses at once, you may run into the error message below:
daemon error: Warn: ADD MEMBERSHIP failed; Errno(105): No buffer space available 22 daemon error: Warn: ADD MEMBERSHIP failed; Errno(105): No buffer space available 23 daemon error: Warn: ADD MEMBERSHIP failed; Errno(105): No buffer space available
The “Errno 105” in this message indicates that the errno value returned by the Linux network stack is 105, or ENOBUFS. This return value while adding a multicast address indicates that your machine is trying to be a member of too many multicast groups at the same time.
Solution is to tune your kernel, backup your current sysclt.conf and replace contents with the ones below.
sudo vim /etc/sysctl.conf
# Bigger buffers (to make 40Gb more practical). These are maximums, but # the default is unaffected. net.core.wmem_max=268435456 net.core.rmem_max=268435456 net.core.netdev_max_backlog=10000 # Avoids problems with multicast traffic arriving on non-default interfaces net.ipv4.conf.default.rp_filter=0 net.ipv4.conf.all.rp_filter=0 # Force IGMP v2 (required by CBF switch) net.ipv4.conf.all.force_igmp_version=2 net.ipv4.conf.default.force_igmp_version=2 # Increase the ARP cache table net.ipv4.neigh.default.gc_thresh3 = 4096 net.ipv4.neigh.default.gc_thresh2 = 2048 net.ipv4.neigh.default.gc_thresh1 = 1024 # Increase number of multicast groups permitted net.ipv4.igmp_max_memberships = 1024
You can reload the configuration file by executing,
sudo sysctl -p or by rebooting your system.