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New Member

are packets being spoofed/hijacked?


The following are from syslogs on ASA5510 firewall. Are the following TCP sessions being spoofed in the SYN phase?

07:40:25: %ASA-4-419002: Duplicate TCP SYN from Inside: to outside: with different initial sequence number

(I can not find who has IP Trend Micro shows no one on the LAN .170

The following shows an original udp payload, yet there seems to be a ICMP transmission.

ASA-4-313005 : No matching connection for ICMP error message: icmp src outside: dst inside: 207.105.y.x (type 3, code 1) on outside interface: Original payload: udp src 207.105.y.x/3919 dst


Re: are packets being spoofed/hijacked?

Because connection limits are configured for a good reason, this system log message could indicate a possible DoS attack, in which case the source of the traffic could likely be a spoofed IP address. If the source IP address is not totally random, identifying the source and blocking it using an access-list might help. In other cases, getting sniffer traces and analyzing the source of the traffic would help in isolating unwanted traffic from legitimate traffic.

New Member

Re: are packets being spoofed/hijacked?

Is it best to sniff the traffic on the LAN or in between the perimeter router and the firewall?