ИСТИНА

Designing of network update algorithms is urgent for development of SDN control software. A particular case of Network Update Problem is that of adding a set of forwarding rules into flow-tables of SDN switches (say, to install new paths in the network) or restoring seamlessly a given network configuration after some packet forwarding rules have been disabled (say, at the expiry of their time-outs). Some algorithms provide solutions to these problems but only with the help of tagging techniques. But is it possible to perform a consistent network update without tagging? We study this problem in the framework of a formal model of SDN, develop correct and safe network updating algorithms, and show that in some cases it is impossible to update consistently network configurations without resorting either to tagging or to priorities of packet forwarding rules.