It will be split when it hits a network device with a lower MTU than the packet’s size. Most ethernet devices are 1500, but it can often be smaller, like 1492 if that ethernet is going over PPPoE (DSL) because of the extra routing information, even lower if a second layer is added like Windows … 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
Ok, it was not easy at all but I figured out how to capture packets. Since I am not extremely familiar with networking (but this new job is requesting that I am) I had difficulty with setting everything correctly. Basically after setting the right route in the VpnService.builder I got to receiving packets correctly. So: … Read more
… can’t really grasp how the checksum can be used as an identifier for the start of the package (wouldn’t the checksum change all the time?). Yes, the checksum would change since it is derived from the data. But even a fixed-value start-of-packet nibble would (by itself) not be sufficient to (initially) identify (or verify) … Read more