RFC 3609 (rfc3609) - Page 2 of 9

Tracing Requirements for Generic Tunnels

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
   tunnel tracing.

   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