Strange ICMP bursts at firewall
I am experiencing strange ICMP bursts from different IP addresses. They come every day and common thing is that 177 packets are received every time. Packets come 6 - 10 in one second. Only thing which changes is TTL which is always from 1 to 59. TTL starts from low numbers and gradually increases. Could this be a fingerprint of some tool which hackers are using?
I am attaching a sample of one burst(with my firewall ID and IP addresses removed).