问题
I'm working on a small, networked game prototype which will be played on LANs using UDP. For the discovery of other computers on the network, I've been investigating broadcasting. However, I'm still unsure about a few details regarding UDP socket setup/usage (networking newbie). I found a good library to use after the game is started, but at first, all computers running the game must be discovered and one has to be chosen as a server. So my questions are the following:
- Can a single UDP socket be used to listen for and send broadcasts? I'm pretty sure the answer to this is yes, but I wanted to verify it.
- When using UDP, do you actually have to use
bind()? As far as I understand,connect()is not required, nor issend()/recv(), since they are for TCP (sendto()/recvfrom()being the replacements).
回答1:
Yes, you can send broadcasts, send unicasts and receive packets (either broadcast or unicast) all from a single socket. This is VERY useful for making "reply to sender" work.
Not every socket needs to use bind. If you don't, a port will be chosen for you automatically. But someone has to bind a pre-shared port number in order for the first packet (possibly a broadcast) to be properly delivered. The first packet contains the source port and IP address; reply packets can just use this.
Binding both ends to fixed port numbers does however make firewall configuration simpler.
setsockopt(SO_BROADCAST), otherwise you'll get errors trying to send broadcast packets.
来源：https://stackoverflow.com/questions/6393123/udp-broadcasting-for-lan-computer-discovery-server-setup