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 Task Force (IETF), its areas, and its working groups. Note that other groups may also distribute working documents as Internet- Drafts. Internet-Drafts are draft documents valid for a maximum of six months and may be updated, replaced, or obsoleted by other documents at any time. It is inappropriate to use Internet-Drafts as reference material or to cite them other than as "work in progress." The list of current Internet-Drafts can be accessed at http://www.ietf.org/ietf/1id-abstracts.txt The list of Internet-Draft Shadow Directories can be accessed at http://www.ietf.org/shadow.html. 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: firstname.lastname@example.org Kireeti Kompella Juniper Networks, Inc. 1194 N. Mathilda Ave. Sunnyvale, California 94089 Email: email@example.com Dave Myers Email: firstname.lastname@example.org 9. Full Copyright Statement Copyright (C) The Internet Society (2003). All Rights Reserved. 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