摘要：We address the issue of a special denial of service (DoS) attack targeting a subcomponent of a Session Initiation Protocol (SIP) based VoIP network. Our focus is fctargeted at attacks that are addressed at the Domain Names Service (DNS). By flooding a SIP element with messages containing difficult-resolvable domain names, it is possible to block the target for a considerable amount of time. We evaluate possibilities to mitigate these effects and show that over-provisioning is not sufficient to handle such attacks. We present results gained from testing with actual SIP providers of a counter solution based on a non-blocking DNS caching solution. Within this cache we evaluate different caching strategies and show that the LeastFrequently-Used caching strategy gives best results to mitigate this kind of attack. (1) LFU policy could help cache to work better than other replacement policies. (2) If there are enough CPU and memory resource, the more parallel processes of SIP proxy, the better performance of SIP proxy. (3) If there are enough CPU and memory resource, the more cache entries, the better performance of SIP proxy. (4) The longer attacking interval, the better performance of SIP proxy
