SSH Dictionary Attack and DNS Reverse Resolution Traffic in Campus Network

We performed statistical analysis on the total PTR resource record (RR) based DNS query packet traffic from a university campus network to the top domain DNS server through March 14th, 2009, when the network servers in the campus network were under inbound SSH dictionary attack. The interesting results are obtained, as follows: (1) the network servers, especially, they have a function of SSH services, generated the significant PTR RR based DNS query request packet traffic through 07:30-08:30 in March 14th, 2009, (2) we calculated sample variance for the DNS query request packet traffic, and (3) the variance can change in a sharp manner through 07:30-08:30. From these results, it is clearly concluded that we can detect the inbound SSH dictionary attack to the network server by only observing the variance of the total PTR RR based DNS query request packet traffic from the network servers in the campus network.