CCAMP S. Balls, Ed. Internet-Draft J. Hardwick Updates: 3209 (if approved) Metaswitch Intended status: Informational C. Margaria Expires: November 24, 2012 Nokia Siemens Networks May 23, 2012 Relaxing RSVP Loop Checking draft-balls-ccamp-relax-loop-check-01 Abstract This specification relaxes the rules governing loop checking within RSVP. These were originally defined in [RFC3209] and are too strict for the requirements of today's data planes. Status of this Memo This Internet-Draft is submitted in full conformance with the provisions of BCP 78 and BCP 79. Internet-Drafts are working documents of the Internet Engineering Task Force (IETF). Note that other groups may also distribute working documents as Internet-Drafts. The list of current Internet- Drafts is at http://datatracker.ietf.org/drafts/current/. 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." This Internet-Draft will expire on November 24, 2012. Copyright Notice Copyright (c) 2012 IETF Trust and the persons identified as the document authors. All rights reserved. This document is subject to BCP 78 and the IETF Trust's Legal Provisions Relating to IETF Documents (http://trustee.ietf.org/license-info) in effect on the date of publication of this document. Please review these documents carefully, as they describe your rights and restrictions with respect to this document. Code Components extracted from this document must include Simplified BSD License text as described in Section 4.e of the Trust Legal Provisions and are provided without warranty as described in the Simplified BSD License. Balls, et al. Expires November 24, 2012 [Page 1] Internet-Draft Relaxing RSVP Loop Checking May 2012 1. Introduction Generalized MPLS (GMPLS) Traffic Engineering (TE) Label Switched Paths (LSPs) are prohibited from passing through a single node more than once. Today's data planes are such that allowing certain loops is required for some LSPs to be possible. 1.1. Requirements Language The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT", "SHOULD", "SHOULD NOT", "RECOMMENDED", "MAY", and "OPTIONAL" in this document are to be interpreted as described in [RFC2119]. 2. General Overview With today's data planes it is acceptable for a single data flow (LSP) to pass through a single control plane node on more than one occasion on the path from source to destination. Currently control plane protocols will prevent such a path being managed in the control plane as they explicitly prevent routing loops. It is desirable for such LSPs to be able to be managed in the same way as non-looping LSPs. 2.1. Example in WDM networks In WDM networks it can be necessary to route the data via an additional box in order to fulfil regeneration or wavelength conversion requirements. For example, consider the following simple example. Balls, et al. Expires November 24, 2012 [Page 2] Internet-Draft Relaxing RSVP Loop Checking May 2012 +-----+ +-----+ +-----+ | | Link 1 | | Link 2 | | | A |----------| B |----------| C | | | | | | | +-----+ +-----+ +-----+ | | | | Link 3 | | Link 4 | | | | +-----+ | | | D | | | +-----+ Figure 1 If node B cannot perform wavelength conversion but Link 1 and Link 2 do not have a common free wavelength then the only way to set up a path from node A to node C will be via node D. This requires two passes through node B which to RSVP looks like a loop. 2.2. Example using Connectivity Matrices In any type of network a specific node may have connectivity restrictions that limit the output ports available given the input ports. For example, given the above network, where node B has the following connectivity restrictions. +-------+ | | 1 | B | 2 ----|-\ /-|---- | | | | | | | | +-------+ | | 3 | | 4 | | Figure 2 As in the above example, the only way to set up a path from node A to Balls, et al. Expires November 24, 2012 [Page 3] Internet-Draft Relaxing RSVP Loop Checking May 2012 node C will be via node D. This requires two passes through node B which to RSVP looks like a loop. 2.3. Example with additional label restrictions Connections between ports on a node may be restricted based on labels. Consider the following network. +-----+ +-----+ +-----+ | | Link 1 | | Link 2 | | | A |----------| B |----------| C | | | | | | | +-----+ +-----+ +-----+ \ | \ | \ Link 3 | \ | \ +-----+ \ | | Link 4 +-------| D | | | +-----+ Figure 3 This network has the following properties. o Node A is electro-optical outputting Lambda 1 and can switch Lambda 2. o Node D can convert between Lambda 1 and Lambda 2. o Link 1 and Link 3 have Lambda 1 available. o All links have Lambda 2 available. To setup a path from A to C in this network, the LSP must pass through Link 1 twice: once using Lambda 1 and once using Lambda 2. This results in the path A-B-D-A-B-C being taken which requires two passes through node A. 3. Existing workaround In current networks it is possible to support such paths either Balls, et al. Expires November 24, 2012 [Page 4] Internet-Draft Relaxing RSVP Loop Checking May 2012 through management configuration at each node, or splitting the path into two or more signalling sessions. In the above examples this can be achieved with one session from A to D, and a second session from D to C. It would also require management on node D to join the data paths together. It is desirable that a single signalling session can be used to set up such paths, thus only requiring management input at the ingress. 4. Solution 4.1. Overview To support such networks, the rules governing RSVP loop checking are relaxed. No changes to protocol messages are made. 4.2. Assumptions and limitations These changes are only applicable to GMPLS out of band signalling when using point to point data links. 4.3. General Rules The following rules govern the changes in behaviour that allow RSVP loop checking to be relaxed while still setting up non-looping data paths in RSVP. o For each pass through the node, the pair of inbound and outbound data interfaces and labels must be different. Are there any further rules when are loops OK and when not OK? 4.4. RRO handling Section 4.4.4 of [RFC3209] states that RSVP must reject a Path message if the receiving router is already in the RRO. This is now relaxed to allow such a condition provided a different interface- label pair is used in each case. If the router has existing session state for a received Path message, and it MUST verify that the newly requested data path (input and output interface and label) is different from the existing data path(s) for that session, and the existing data path(s) is (are) present earlier in the RRO. If this is not the case, the router MUST return a "Routing problem" PathErr message with the error value "loop detected". In order to carry out this checking correctly, specific interfaces and labels SHOULD be recorded in the RRO. If this is not the case, each node can only verify the path is acceptable against local state Balls, et al. Expires November 24, 2012 [Page 5] Internet-Draft Relaxing RSVP Loop Checking May 2012 and should not reject the RRO if the local state is valid. It is allowable for local policy to exist to limit the number of different paths through a router in a single LSP instance. If this limit is exceeded the router SHOULD return a "Routing problem" PathErr message with the error value "loop detected". This local policy is not intended to be advertised in routing. It is present as a backstop to protect against malicious Path messages consuming all resources on the router. 4.5. ERO handling Sections 4.3.4.1 and 4.3.5 of [RFC3209] also state that RSVP must detect and avoid loops. This checking is also relaxed to allow loops in the cases stated above. Again, local policy can limit the number of different paths through a router in a single LSP instance. A router may "look ahead" in the ERO to determine such local policy will be exceeded in advance of it happening and SHOULD return a "Routing problem" PathErr message with the error value "loop detected" in such a case. When calculating or expanding an ERO a router may include multiple entries through a single router. If the ERO contains loose hops that form a loop, and a node determines a non-looping route is available, it MAY remove the loop from the ERO. 4.6. Interface handling As stated in the general rules, an implementation supporting multiple passes through a node must ensure that for each pass the input and output interfaces and labels are different. Internally, this means that if a Path message is received using a different input interface this may no longer mean the LSP has been rerouted upstream. Implementations must check the RRO to determine the correct behaviour when processing such a Path message. Care must be taken to handle valid cases where the incoming label can change. 4.7. Signalling For the avoidance of doubt, no new signalling is being defined in this draft. The behaviour of refresh or error messages is unchanged and should therefore be sent along the looped path (if present). Nodes SHOULD NOT shortcut the loop. Balls, et al. Expires November 24, 2012 [Page 6] Internet-Draft Relaxing RSVP Loop Checking May 2012 4.8. Error Handling How to behave when receiving a PathErr with error value "loop detected" is out of scope of this draft and is a local implementation decision. For example, it may choose to try and recalculate the path mandating that the error node is avoided, or does not support looping. 5. IANA Considerations This memo includes no request to IANA. 6. Security Considerations In principle these changes to RSVP pose no security exposures over and above [RFC3209]. However, by allowing loops a single LSP can now consume multiple resources. As suggested local policy can limit the number of paths and thus the resource a single LSP can consume. 7. Normative References [RFC2119] Bradner, S., "Key words for use in RFCs to Indicate Requirement Levels", BCP 14, RFC 2119, March 1997. [RFC3209] Awduche, D., Berger, L., Gan, D., Li, T., Srinivasan, V., and G. Swallow, "RSVP-TE: Extensions to RSVP for LSP Tunnels", RFC 3209, December 2001. Authors' Addresses Steve Balls (editor) Metaswitch 100 Church Street Enfield, EN2 6BQ UK Phone: +44 208 366 1177 Email: steve.balls@metaswitch.com Balls, et al. Expires November 24, 2012 [Page 7] Internet-Draft Relaxing RSVP Loop Checking May 2012 Jonathan Hardwick Metaswitch 100 Church Street Enfield, EN2 6BQ UK Phone: +44 208 366 1177 Email: jonathan.hardwick@metaswitch.com Cyril Margaria Nokia Siemens Networks St Martin Strasse 76 Munich, 81541 Germany Phone: +49 89 5159 16934 Email: cyril.margaria@nsn.com Balls, et al. Expires November 24, 2012 [Page 8]