Am 19.12.2013 um 16:14 schrieb Stephan Eggermont <stephan@stack.nl>:
Norbert wrote:
To send or receive a broadcast packet you need to put special options on the socket on the native side (setsockopt). You need to >look if the SO_BROADCAST option is mentioned anywhere. If not it wonât work without adding them. And for sending them you >need almost special privileges on the system. This is not a âuser featureâ.
And even though it is "the right thing" for lots of situations, your network is also very likely to not do the right thing with broadcast packets. Etsy decided on using bittorrent protocol to update their production servers indexes, because they found it too difficult to get their network to do the right thing. They found that their switches were basically livelocked while dealing with broadcast packets.
http://codeascraft.com/2012/01/23/solr-bittorrent-index-replication/
If you want the broadcast to travel a little further, the routers need to be configured not to drop the packets.
Stephan
I donât think broadcast is âthe right thingâ in most use cases. It is just a lot less cumbersome to use instead of multicast which is supposed to be the right thing for a broader use. So you can overuse broadcast very easy. In an environment with a lot of cascaded switches broadcast is something that makes the whole thing inoperable. A switch tries to use the smallest number of physical ports to route packets. It decides that based on internal tables recorded from MAC addresses and such. Broadcast is a brute force attempt where every address bit is set to reach every participant in the local hardware segment. So you might see that a switch has basically no other option then to open all ports to send a broadcast packet. So having a prevent-broadcast-packets option is a last ressort option. Norbert