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</o:shapelayout></xml><![endif]--></head><body lang=EN-US link=blue vlink=purple><div class=WordSection1><p class=MsoNormal>Hello<o:p></o:p></p><p class=MsoNormal><o:p> </o:p></p><p class=MsoNormal>We observed an unusual traffic combining ICMP and UDP packets while running the tcpdump command on the DNS caching server <o:p></o:p></p><p class=MsoNormal>Kindly note that only UDP DNS traffic is allowed on this server (ICMP is not allowed from outside to DNS server)<o:p></o:p></p><p class=MsoNormal>Any help regarding this issue? Why we are getting ICMP and UDP requests? Could it be an attack?<o:p></o:p></p><p class=MsoNormal><o:p> </o:p></p><p class=MsoNormal><o:p> </o:p></p><p class=MsoNormal><b><u>Logs:<o:p></o:p></u></b></p><p class=MsoNormal><o:p> </o:p></p><p class=MsoNormal># tcpdump –n icmp<o:p></o:p></p><p class=MsoNormal><o:p> </o:p></p><p class=MsoNormal>15:41:05.054237 IP 10.151.130.74 > DNSIP: ICMP 10.151.130.74 udp port 52003 unreachable, length 52<o:p></o:p></p><p class=MsoNormal>15:41:05.064449 IP 10.75.6.36 > DNSIP: ICMP 10.75.6.36 udp port 50162 unreachable, length 52<o:p></o:p></p><p class=MsoNormal>15:41:05.067953 IP 10.33.10.155 > DNSIP: ICMP 10.33.10.155 udp port 50233 unreachable, length 52<o:p></o:p></p><p class=MsoNormal>15:41:05.067958 IP 10.75.15.162 > DNSIP: ICMP 10.75.15.162 udp port 53847 unreachable, length 52<o:p></o:p></p><p class=MsoNormal>15:41:05.072727 IP 10.33.12.219 > DNSIP: ICMP 10.33.12.219 udp port 51024 unreachable, length 52<o:p></o:p></p><p class=MsoNormal>….<o:p></o:p></p><p class=MsoNormal>Example: 10.151.130.74 (client source IP)<o:p></o:p></p><p class=MsoNormal>DNSIP: DNSServer IP<o:p></o:p></p><p class=MsoNormal><o:p> </o:p></p><p class=MsoNormal>Regards<o:p></o:p></p><p class=MsoNormal>Daniel<o:p></o:p></p></div></body></html>