Issue caused by having iptables rule/s that track connection state. If the number of connections being tracked exceeds the default nf_conntrack table size [65536] then any additional connections will be dropped. Most likely to occur on machines used for NAT and scanning/discovery tools (such as Nessus and Nmap). Symptoms: Once the connection table is full any additional connection attempts will be blackholed.   This issue can be detected using:

Current.. Read More