Strictly speaking, packet duplication in IP network is allowed behavior of the network and you have to be able to deal with it in your software even if you will somehow get rid of it this time. If you are just wondering about why this happens in your particular case… at a first glance I … Read more
Here’s the jist of some code I am currently using in a production app that works (we’ve got a bit extra in there to handle the case where the client are server apps are running on a standalone installation). It’s job is to receive udp notifications that messages are ready for processing. As mentioned by … Read more
I have been looking into this for a while after seeing conflicting answers to how SO_BINDTODEVICE is actually used. Some sources claim that the correct usage is to pass in a struct ifreq pointer, which has the device name and index obtained via an ioctl. For example: struct ifreq ifr; memset(&ifr, 0, sizeof(struct ifreq)); snprintf(ifr.ifr_name, … Read more
You do it with the setsockopt() call, by using the IP_DONTFRAG option: int val = 1; setsockopt(sd, IPPROTO_IP, IP_DONTFRAG, &val, sizeof(val)); Here’s a page explaining this in further detail. For Linux, it appears you have to use the IP_MTU_DISCOVER option with the value IP_PMTUDISC_DO (or IP_PMTUDISC_DONT to turn it off): int val = IP_PMTUDISC_DO; setsockopt(sd, … Read more
Overview What is causing the inability to send/receive data locally? Mostly buffer space. Imagine sending a constant 10MB/second while only able to consume 5MB/second. The operating system and network stack can’t keep up, so packets are dropped. (This differs from TCP, which provides flow control and re-transmission to handle such a situation.) Even when data … Read more
TCP: Size of Ethernet frame – 24 Bytes Size of IPv4 Header (without any options) – 20 bytes Size of TCP Header (without any options) – 20 Bytes Total size of an Ethernet Frame carrying an IP Packet with an empty TCP Segment – 24 + 20 + 20 = 64 bytes UDP: Size of … Read more
Does this mean that the send() call will always return immediately if there is room in the kernel send buffer? Yes. As long as immediately means after the memory you provided it has been copied to the kernel’s buffer. Which, in some edge cases, may not be so immediate. For instance if the pointer you … Read more
This is one of my favorite questions. UDP is so misunderstood. In situations where you really want to get a simple answer to another server quickly, UDP works best. In general, you want the answer to be in one response packet, and you are prepared to implement your own protocol for reliability or to resend. … Read more
The receiver must set port of receiver to match port set in sender DatagramPacket. For debugging, try listening on port > 1024 (e.g. 5000 or 9000). Ports < 1024 are normally used by system services and need admin access to bind on such a port. If the receiver sends packet to the hard-coded port it’s … Read more
What you are looking for can’t be done with in Javascript due to security constraints such as Distributed Denial of Service (DDOS) attacks. The closest technology available (that I know of) for client-side JS is WebRTC. With WebRTC you can use DataChannels over SRTP and ICE as a possible solution. See Also: How to send … Read more