RSVP Operation Over IP Tunnels
Network Working Group A. Terzis
Request for Comments: 2746 UCLA
Category: Standards Track J. Krawczyk
RSVP Operation Over IP Tunnels
Status of this Memo
This document specifies an Internet standards track protocol for the
Internet community, and requests discussion and suggestions for
improvements. Please refer to the current edition of the "Internet
Official Protocol Standards" (STD 1) for the standardization state
and status of this protocol. Distribution of this memo is unlimited.
Copyright (C) The Internet Society (2000). All Rights Reserved.
This document describes an approach for providing RSVP protocol
services over IP tunnels. We briefly describe the problem, the
characteristics of possible solutions, and the design goals of our
approach. We then present the details of an implementation which
meets our design goals.
IP-in-IP "tunnels" have become a widespread mechanism to transport
datagrams in the Internet. Typically, a tunnel is used to route
packets through portions of the network which do not directly
implement the desired service (e.g. IPv6), or to augment and modify
the behavior of the deployed routing architecture (e.g. multicast
routing, mobile IP, Virtual Private Net).
Many IP-in-IP tunneling protocols exist today. [IP4INIP4] details a
method of tunneling using an additional IPv4 header. [MINENC]
describes a way to reduce the size of the "inner" IP header used in
[IP4INIP4] when the original datagram is not fragmented. The generic
tunneling method in [IPV6GEN] can be used to tunnel either IPv4 or
IPv6 packets within IPv6. [RFC1933] describes how to tunnel IPv6
Terzis, et al. Standards Track [Page 1]
RFC 2746 RSVP Operation Over IP Tunnels January 2000
datagrams through IPv4 networks. [RFC1701] describes a generic
routing encapsulation, while [RFC1702] 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 [RFC2205] 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
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
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