Where can I embed proprietary information in a layer 2 or layer 3 packet?

The Citrix Netscaler has an interesting property that embeds information in the TCP packet that gets sent to the host. This property is echoed back to the Netscaler in such a way that the Netscaler can use this to determine which Virtual Server, host, and route this must take.

The ability to echo proprietary information to a host has interesting applications.

• How does the Citrix Netscaler achieve this (where does it stuff the bits), and what other locations in the packet can the Netscaler (or similar device) theoretically stuff data?

• What devices will (or will not) allow this custom data to pass through untouched?

Solution 1:

Most likely they are using the ToS header (DSCP). It will allow for six bits of information to be stored in the header and most often devices wont take any action based on what's stored there [especially end-users].

All devices allow ToS through as it is part of the standard IPv4 header.