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Internet Draft                                                R. Bonica
Expiration Date: October 2003                                       MCI
                                                            K. Kompella
                                                       Juniper Networks
                                                               D. Meyer
                                                                 Sprint
                                                             April 2003

                Tracing Requirements for Generic Tunnels
                     draft-ietf-ccamp-tracereq-02

Status of this Memo

   This document is an Internet-Draft and is in full conformance with
   all provisions of Section 10 of RFC-2026.

   Internet-Drafts are working documents of the Internet Engineering
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Abstract

   This document specifies requirements for a generic route-tracing
   application.  It also specifies requirements for a protocol that will
   support the generic route-tracing application. Network operators will
   use the generic route-tracing application to verify proper operation
   of the IP forwarding plane. They also use the application to discover
   details regarding tunnels that support IP forwarding.


1. Introduction

   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. As multiple tunneling
   technologies support 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.

   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 desired characteristic of the route-tracing
   application.


2. Review of Existing Functionality

   Currently, network operators use "traceroute" to identify the path
   toward any destination in 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 a tunnel as a collection of IP
   hops, without indicating that they are part of a tunnel.

   For example, assume that engineers deploy IP tunnels in an IP
   network.  Assume also that they configure a tunnel so that the head-
   end router does not copy the TTL value from the inner IP header to
   outer IP header.  Instead, the head-end router always sets the outer
   TTL value to its maximum permitted value.  When engineers trace
   routes through the network, traceroute will always display the tunnel
   as a single IP hop, hiding all components except the tail-end
   interface.

   Now assume that engineers deploy MPLS in an IP network.  Assume also
   that engineers configure an MPLS LSP so that the ingress router
   propagates the TTL value from the IP header to the MPLS header.  When
   engineers trace routes through the network, traceroute will display
   the LSP as a series of IP hops, without indicating that they are part
   of a tunnel.



3. Application Requirements

   Network operators require a new route-tracing application.  The new
   application must provide all functionality that traceroute currently
   provides. It also must provide enhanced tunnel tracing capabilities.

   The following list provides specific requirements for the new route-
   tracing application:

      1) Support the notion of a security token as part of the tunnel
      trace request.  The security token identifies the tracer's
      privileges in tracing tunnels.  Network elements will use this
      security token to determine whether or not to return the requested
      information to the tracer.  In particular, appropriate privileges
      are required for items (2), (3), (6), (8), (10), (13), and (14).

      Justification: Operators may need to discover network forwarding
      details, while concealing those details from unauthorized parties.

      2) Support in-line traces.  An in-line trace reveals the path
      between the host upon which the route-tracing application executes
      and any interface in an IP network.

      Justification: Operators need to discover how the network would
      forward a datagram between any two IP interfaces.

      3) Support third party traces.  A third party trace reveals the
      path between any two points in an IP network.  The application
      that initiates a third party trace need not execute upon a host or
      router that is part of the traced path. Unlike existing solutions
      [RFC-2151] [RFC-2925], the application will not rely upon IP
      options or require access to the SNMP agent in order to support
      third-party traces.

      Justification: Operators need to discover how the network would
      forward a datagram between any two IP interfaces.

      4) Support partial traces through broken paths or tunnels.

      Justification: Operators need to identify the root cause of
      forwarding plane failures.

      5) When tracing through a tunnel, either as part of an in-line
      trace or a third party trace, display the tunnel either as a
      single IP hop or in detail. The user's request determines how the
      application displays tunnels, subject to the user having
      permission to do this.

      Justification: As they discover IP forwarding details, operators
      may need to reveal or mask tunneling details.

      6) When displaying a tunnel in detail, include the tunnel type
      (e.g., GRE, MPLS), the tunnel name (if applicable), the tunnel
      identifier (if applicable) and tunnel endpoint addresses.  Also,
      include tunnel components and round trip delay across each
      component.

      Justification: As they discover IP forwarding details, operators
      may need to reveal tunneling details.

      7) Support the following tunneling technologies: GRE, MPLS, IPSEC,
      GMPLS, IP-in-IP, L2TP. Be easily extensible to suppport new tunnel
      technologies.

      Justification: Operators will use the generic route-tracing
      application to discover how an IP network forwards datagrams. As
      many tunnel types may support the IP network, the generic route-
      tracing application must detect and reveal details concerning
      multiple tunnel types.

      8) Trace through nested, heterogeneous tunnels (e.g., IP-in-IP
      over MPLS).

      Justification: Operators will use the generic route-tracing
      application to discover how an IP network forwards datagrams. As
      nested, heterogeneous tunnels may support the IP network, the
      generic route-tracing application must detect and reveal details
      concerning nested, heterogeneous tunnels.

      9) At the users request, trace through the forwarding plane, the
      control plane or both.

      Justification: Operators need to identify the root cause of
      forwarding plane failu res. Control plane information is sometimes
      useful in determining the cause of forwarding plane failure.

      10) Support control plane tracing for all tunnel types. When
      tracing through the control plane, the device at the head-end of a
      hop reports hop details.

      Justification: Control plane information is available regarding
      all tunnel types.

      11) Support tracing through forwarding plane for all tunnel types
      that implement TTL decrement (or some similar mechanism). When
      tracing through the forwarding plane, the device at the tail-end
      of a hop reports hop details.

      Justification: Forwarding plane information may not be available
      regarding tunnels that do not support TTL decrement.

      12) Support tracing through the forwarding plane for all tunnel
      types that implement TTL decrement, regardless of whether the
      tunnel engages in TTL propagation. (That is, support tunnel
      tracing regardless of whether the TTL value is copied from an
      inner header to an outer header at tunnel ingress).

      Justification: Forwarding plane information is always available,
      regardless of whether the tunnel engages in TTL propagation.

      13) When tracing through the control plane, display the MTU
      associated with each hop.

      Justification: MTU information is sometimes useful in identifying
      the root cause of forwarding plane failures.

      14) When tracing through the forwarding plane, display the MTU
      associated with each hop in the reverse direction.

      Justification: MTU information is sometimes useful in identifying
      the root cause of forwarding plane failures.



4. Protocol Requirements

   Implementors require a new protocol that supports the generic route-
   tracing application.  This protocol reveals the path between two
   points in an IP network.  When access policy permits, the protocol
   also reveals tunnel details.


4.1. Information Requirements

   The protocol consists of probes and probe responses. Each probe
   elicits exactly one response. Each response represents a hop that
   connects the head-end of the traced path to the tail-end of the
   traced path.  A hop can be either a top-level IP hop or lower-level
   hop that is contained by a tunnel.

   Justification: Because the generic route-tracing application must
   trace through broken paths, the required protocol must use a separate
   response message to deliver details regarding each hop. The protocol
   must use a separate probe to elicit each response because the
   alternative approach, using the single probe with the IP Router Alert
   Option, is unacceptable. Many network forward datagrams that specify
   IP options differently than they would forward datagrams that do not
   specify IP options.


4.2. Transport Layer Requirements

   UDP carries all protocol messages to their destinations.

   Justification: Because the probe/response scheme described above is
   stateless, a stateless transport is required. Candidate transports
   included UDP over IP, IP and ICMP. ICMP was disqualified because
   carrying MPLS information in an ICMP datagram would constitute a
   layer violation. IP was disqualified in order to conserve protocol
   identifiers.


4.3. Stateless Protocol

   The protocol must be stateless. That is, no node should have to
   maintain state between successive traceroute messages.

   Justification: Statelessness is required to support scaling and to
   prevent denial of service attacks.


4.4. Routing Requirements

   The device that hosts the route-tracing application must maintain an
   IP route to the head-end of the traced path. It must also maintain an
   IP route to the head-end of each tunnel for which it is requesting
   tunnel details. The device that hosts the tunnel tracing application
   need not maintain a route to any other device that supports the
   traced path.

   All of the devices to which the route-tracing application must
   maintain a route must maintain a route back to the route-tracing
   application.

   In order for the protocol to provide tunnel details, all devices
   contained by a tunnel must maintain an IP route to the tunnel
   ingress.

   Justification: The protocol must be sufficiently robust to operate
   when tunnel interior devices do not maintain a route back to the
   device that hosts the route tracing application.










5. Security Considerations

   A configurable access control policy determines the degree to which
   features described herein are delivered.  The access control policy
   requires user identification and authorization.

   As stated above, the new protocol must not introduce security holes
   nor consume excessive resources (e.g., CPU, bandwidth).  It also must
   not be exploitable by those launching DoS attacks or replaying
   messages.


6. Informative References

   [RFC-2151], Kessler, G., Shepard, S., A Primer On Internet and TCP/IP
   Tools and Ut ilities, RFC 2151, Hill Associates, Inc., June 1997

   [RFC-2925], White, K., "Definitions of Managed Objects for Remote
   Ping, Traceroute, and Lookup Operations", RFC 2925, September, 2000.


7. Acknowledgements

   Thanks to Randy Bush and Steve Bellovin for their comments.


8. Author's Addresses

      Ronald P. Bonica
      MCI
      22001 Loudoun County Pkwy
      Ashburn, Virginia, 20147
      Phone: 703 886 1681
      Email: rbonica@mci.net

      Kireeti Kompella
      Juniper Networks, Inc.
      1194 N. Mathilda Ave.
      Sunnyvale, California 94089
      Email: kireeti@juniper.net

      Dave Myers
      Email: dmm@sprint.net



9. Full Copyright Statement

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