Network Working Group R. Bonica
Request for Comments: 3609 MCI
Category: Informational K. Kompella
Tracing Requirements for Generic Tunnels
Status of this Memo
This memo provides information for the Internet community. It does
not specify an Internet standard of any kind. Distribution of this
memo is unlimited.
Copyright (C) The Internet Society (2003). All Rights Reserved.
This document specifies requirements for a generic route-tracing
application. It also specifies requirements for a protocol that will
support that application. Network operators will use the generic
route-tracing application to verify proper operation of the IP
forwarding plane. They will also use the application to discover
details regarding tunnels that support IP forwarding.
The generic route-tracing application, specified herein, supports a
superset of the functionality that "traceroute" currently offers.
Like traceroute, the generic route-tracing application can discover
the forwarding path between two interfaces that are contained by an
IP network. Unlike traceroute, this application can reveal details
regarding tunnels that support the IP forwarding path.
IP networks utilize several tunneling technologies. Although these
tunneling technologies provide operators with many useful features,
they also present management challenges. Network operators require a
generic route-tracing application that they can use to verify the
correct operation of the IP forwarding plane. The generic
route-tracing application must be capable of detecting tunnels and
revealing tunnel details. The application also must be useful in
diagnosing tunnel faults.
Bonica, et al. Informational [Page 1]RFC 3609 Tracing Requirements for Generic Tunnels September 2003
Implementors also require a new protocol that will support the
generic-route tracing application. This document specifies
requirements for that protocol. It specifies requirements,
primarily, by detailing the desired capabilities of the generic
route-tracing application. A particular version of generic
route-tracing application may implement some subset of the desired
capabilities. It may also implement a superset of those
capabilities. However, protocol designers are not required to
consider the additional capabilities when designing the new protocol.
This document also specifies a few protocol requirements, stated as
such. These requirements are driven by desired characteristics of
the generic route-tracing application. Whenever a protocol
requirement is stated, it is mapped to the desired characteristic of
the route-tracing application.
2. Review of Existing Functionality
Currently, network operators use "traceroute" to trace through the
forwarding path of an IP network. Section 3.4 of [RFC-2151] provides
a thorough description of traceroute. Although traceroute is very
reliable and very widely deployed, it is deficient with regard to
Depending upon tunnel type, traceroute may display an entire tunnel
as a single IP hop, or it may display the tunnel as a collection of
IP hops, without indicating that they are part of a tunnel.
For example, assume that engineers deploy an IP tunnel in an IP
network. Assume also that they configure the tunnel so that the
ingress router does not copy the TTL value from the inner IP header
to outer IP header. Instead, the ingress router always sets the
outer TTL value to its maximum permitted value. When engineers trace
through the network, traceroute will always display the tunnel as a
single IP hop, hiding all components except the egress interface.
Now assume that engineers deploy an MPLS LSP in an IP network.
Assume also that engineers configure the MPLS LSP so that the ingress
router propagates the TTL value from the IP header to the MPLS
header. When engineers trace through the network, traceroute will
display the LSP as a series of IP hops, without indicating that they
are part of a tunnel.
Bonica, et al. Informational [Page 2]RFC 3609 Tracing Requirements for Generic Tunnels September 2003