Can several clients on my local network use IPsec simultaneously?
Yes, though there may occasionally be minor problems. The IPsec protocols define a method for identifying the traffic streams called the Security Parameters Index (“SPI”). Unfortunately the SPI used by outbound traffic is different from the SPI used by inbound traffic, and there is no other identifying information available that is not encrypted, so association of the inbound and outbound data streams is difficult and not perfectly reliable. IPsec Masquerade attempts to associate inbound and outbound ESP traffic by serializing new connections. While this has worked well in testing, it cannot be guaranteed to be perfectly reliable, and the serialization of new traffic may result in some timeouts if the link is saturated or if many local IPsec hosts attempt to initiate communications or rekey with the same remote IPsec host simultaneously. It is also assumed that should this association scheme fail to associate the traffic streams correctly, the IPsec hosts themselves will discard the in
