RFC 1455 (rfc1455) - Page 2 of 6


Physical Link Security Type of Service



Alternative Format: Original Text Document



RFC 1455                   Link Security TOS                    May 1993


   It is essential that routers have access to header information, so it
   is hard to protect traffic statistics from an adversary with inside
   access to the network.  However, use of more secure physical links
   will make traffic observation by entities outside of the network more
   difficult thus improving protection from traffic analysis.

   No doubt users would like to be able to request a guaranteed level of
   link security, just as they would like to be able to request a
   guaranteed bandwidth or delay through the network.  However, such
   guarantees require a resource reservation and/or policy routing
   scheme and are beyond the scope of the current IP Type of Service
   facility.

   Although the TOS field is provided in all current Internet packets
   and routing based on TOS is provided in routing protocols such as
   OSPF [See 5,6,7], there is no realistic chance that all of the
   Internet will implement this additional TOS any time in the
   foreseeable future.  Nevertheless, users concerned about traffic
   analysis need to be able to request that the physical security of the
   links over which their packets will be pass be maximized in
   preference to other link characteristics.  The proposed TOS provides
   this capability.

1.2 Confidentiality

   Use of physical links with greater physical security provides a layer
   of protection for the confidentiality of the data in the packets as
   well as traffic analysis protection.  If the content of the packets
   are otherwise protected by end-to-end encryption, using secure links
   makes it harder for an external adversary to obtain the encrypted
   data to attack.  If the content of the packets is unencrypted plain
   text, secure links may provide the only protection of data
   confidentiality.

   There are cases where end-to-end encryption can not be used.
   Examples include paths which incorporate links within nations which
   restrict encryption, such as France or Australia, and paths which
   incorporate an amateur radio link, where encryption is prohibited.
   In these cases, link security is generally the only type of
   confidentiality available.  The proposed TOS will provide a way of
   requesting the best that the network can do for the security of such
   unencrypted data.

   This TOS is required for improved confidentiality, especially in
   cases where encryption can not be used, despite the fact that it does
   not provide the guarantees that many users would like.  See
   discussion at the end of the Traffic Analysis section above.




Eastlake