RFC 2746 (rfc2746) - Page 2 of 25

RSVP Operation Over IP Tunnels

RFC 2746             RSVP Operation Over IP Tunnels         January 2000


   datagrams through IPv4 networks.  [RFC 1701] describes a generic
   routing encapsulation, while [RFC 1702] applies this encapsulation to
   IPv4.  Finally, [ESP] describes a mechanism that can be used to
   tunnel an encrypted IP datagram.

   From the perspective of traditional best-effort IP packet delivery, a
   tunnel behaves as any other link. Packets enter one end of the
   tunnel, and are delivered to the other end unless resource overload
   or error causes them to be lost.

   The RSVP setup protocol [RFC 2205] is one component of a framework
   designed to extend IP to support multiple, controlled classes of
   service over a wide variety of link-level technologies. To deploy
   this technology with maximum flexibility, it is desirable for tunnels
   to act as RSVP-controllable links within the network.

   A tunnel, and in fact any sort of link, may participate in an RSVP-
   aware network in one of three ways, depending on the capabilities of
   the equipment from which the tunnel is constructed and the desires of
   the operator.

      1. The (logical) link may not support resource reservation or QoS
         control at all. This is a best-effort link. We refer to this as
         a best-effort or type 1 tunnel in this note.
      2. The (logical) link may be able to promise that some overall
         level of resources is available to carry traffic, but not to
         allocate resources specifically to individual data flows.  A
         configured resource allocation over a tunnel is an example of
         this.  We refer to this case as a type 2 tunnel in this note.
      3. The (logical) link may be able to make reservations for
         individual end-to-end data flows.  We refer to this case as a
         type 3 tunnel. Note that the key feature that distinguishes
         type 3 tunnels from type 2 tunnels is that in the type 3 tunnel
         new tunnel reservations are created and torn down dynamically
         as end-to-end reservations come and go.

   Type 1 tunnels exist when at least one of the routers comprising the
   tunnel endpoints does not support the scheme we describe here. In
   this case, the tunnel acts as a best-effort link. Our goal is simply
   to make sure that RSVP messages traverse the link correctly, and the
   presence of the non-controlled link is detected, as required by the
   integrated services framework.

   When the two end points of the tunnel are capable of supporting RSVP
   over tunnels, we would like to have proper resources reserved along
   the tunnel.  Depending on the requirements of the situation, this
   might mean that  one client's data flow is placed into a larger
   aggregate reservation  (type 2 tunnels) or that possibly a new,



Terzis, et al.              Standards Track