In particular, some elements of FLEXlm didn't require certain patches, so a 2.4 lmgrd will work successfully with a 2.4b vendor daemon. I've received a new copy of a product from a vendor, and it uses a new version of FLEXlm. Older FLEXlm license files are always valid with newer versions of FLEXlm. As of v3.0, FLEXlm has an optional new format for license files. A server on the internet will serve licenses to anyone else on the internet.
Many firewalls require that port numbers be specified to the firewall.
FLEXlm v5 lmgrd supports this. Yes, unless the client's whole system crashes. Assuming communications is TCP, the license is automatically freed immediately. If communications are UDP, then the license is freed after the UDP timeout, which is set by each vendor, but defaults to 45 minutes. UDP communications is normally only set by the end-user, so TCP should be assumed.