IPSec Scenario

[najamssss]

Hi again:

There is a IPSec question. I have faced the following scenario during some experiments during project, kindly help me in this regard:

Two users A and B are communicating using IPSEc. A's TCP acknowledgement gets lost and the user B retransmits the packet for which ACK was lost. Will A's IPSec implementation notice that the packet is duplicated?

If yes then how? If not, why?

[owillins]

What are the devices that you are using for ipsec? If it is a VPN concentrator then I have seen some messages that indicate a Duplicate first packet detected! However it would depend on the hardware that you are using for ipsec. There are also various other features in place to prevent attacks.

[Patrick Iseli]

Do you talk about the IPSec protocol handshake or users communication handshake?

If you talk about Users communication, that is tunneled and encrypted into IPSec/isakmp:

Basicly when the host that send an ACK did not received a SYN ACK in a timely manner it will resend the ACK again. In a packet sniffer you see them as Retransmissions.

This happend often in slow or busy servers or hosts.

If the host receives them twice it will drop the second one. I think this is a normal part of TCP/IP's 3 way handshake implementation.

What is the exactly your problem.

sincerely

Patrick