topic SEQ #, SYN, SYN-ACK, ACK numbers transversing the PIX in Network Security https://community.cisco.com/t5/network-security/seq-syn-syn-ack-ack-numbers-transversing-the-pix/m-p/183698#M607946 <P>When an IP packet tranverses a PIX from the inside to the outside, with NAT or STATIC configured, the source IP address is changed and the sequence number is randomized. What other IP field's change...Do the Seq, SYN, SYN-ACK and ACK number change also. </P><P></P> Fri, 21 Feb 2020 06:38:11 GMT a-alao 2020-02-21T06:38:11Z SEQ #, SYN, SYN-ACK, ACK numbers transversing the PIX https://community.cisco.com/t5/network-security/seq-syn-syn-ack-ack-numbers-transversing-the-pix/m-p/183698#M607946 <P>When an IP packet tranverses a PIX from the inside to the outside, with NAT or STATIC configured, the source IP address is changed and the sequence number is randomized. What other IP field's change...Do the Seq, SYN, SYN-ACK and ACK number change also. </P><P></P> Fri, 21 Feb 2020 06:38:11 GMT https://community.cisco.com/t5/network-security/seq-syn-syn-ack-ack-numbers-transversing-the-pix/m-p/183698#M607946 a-alao 2020-02-21T06:38:11Z Re: SEQ #, SYN, SYN-ACK, ACK numbers transversing the PIX https://community.cisco.com/t5/network-security/seq-syn-syn-ack-ack-numbers-transversing-the-pix/m-p/183699#M607947 <HTML><HEAD></HEAD><BODY><P>In addition to modifying the IP address, NAT must modify the IP checksum and the TCP checksum. Remember, TCP's checksum also covers a pseudo header which contains the source and destination address.</P><P></P><P>Other then this I don't think it changes anything. For certain protocols like FTP which carry the IP address in the Data Part, NAT changes the IP address where ever it appears.</P></BODY></HTML> Thu, 27 Mar 2003 14:22:30 GMT https://community.cisco.com/t5/network-security/seq-syn-syn-ack-ack-numbers-transversing-the-pix/m-p/183699#M607947 mchin345 2003-03-27T14:22:30Z