| Network Working Group | F. Zhang, Ed. |
| Internet-Draft | D. Li |
| Intended status: Standards Track | Huawei |
| Expires: October 13, 2013 | O. Gonzalez de Dios, Ed. |
| Telefonica I+D | |
| C. Margaria | |
| Nokia Siemens Networks | |
| M. Hartley | |
| Cisco | |
| April 11, 2013 |
RSVP-TE Extensions for Collecting SRLG Information
draft-ietf-ccamp-rsvp-te-srlg-collect-02
This document provides extensions for the Resource ReserVation Protocol-Traffic Engineering (RSVP-TE) to support automatic collection of Shared Risk Link Group (SRLG) Information for the TE link formed by a LSP.
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It is important to understand which TE links in the network might be at risk from the same failures. In this sense, a set of links may constitute a 'shared risk link group' (SRLG) if they share a resource whose failure may affect all links in the set [RFC4202].
On the other hand, as described in [RFC4206] and [RFC6107], H-LSP (Hierarchical LSP) or S-LSP (stitched LSP) can be used for carrying one or more other LSPs. Both of the H-LSP and S-LSP can be formed as a TE link. In such cases, it is important to know the SRLG information of the LSPs that will be used to carry further LSPs.
This document provides an automatic mechanism to collect the SRLG for the TE link formed by a LSP. Note that how to use the collected SRLG information is out of scope of this document
The head nodes of the LSP must be capable of indicating whether the SRLG information of the LSP should be collected during the signaling procedure of setting up an LSP. SRLG information should not be collected without an explicit request for it being made by the head node.
If requested, the SRLG information should be collected during the setup of an LSP. The endpoints of the LSP may use the collected SRLG information and use it for routing, sharing and TE link configuration purposes.
When the SRLG information of an existing LSP for which SRLG information was collected during signaling changes, the relevant nodes of the LSP must be capable of updating the SRLG information of the LSP. This means that that the signaling procedure must be capable of updating the new SRLG information.
In order to indicate nodes that SRLG collection is desired, this document defines a new flag in the Attribute Flags TLV, which is carried in an LSP_REQUIRED_ATTRIBUTES or LSP_ATTRIBUTE Object:
The SRLG Collection flag is meaningful on a Path message. If the SRLG Collection flag is set to 1, it means that the SRLG information should be reported to the head and tail node along the setup of the LSP.
The rules of the processing of the Attribute Flags TLV are not changed.
This document defines a new RRO sub-object (ROUTE_RECORD sub-object) to record the SRLG information of the LSP. Its format is modeled on the RRO sub-objects defined in RFC 3209 [RFC3209].
0 1 2 3
0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Type | Length | Reserved | Flags |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| SRLG ID 1 (4 bytes) |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
~ ...... ~
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| SRLG ID n (4 bytes) |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
Type
The type of the sub-object, to be assigned by IANA, which is recommended 34.
Length
The Length contains the total length of the sub-object in bytes, including the Type and Length fields. The Length depends on the number of SRLG IDs.
Flags
The Flags are used to indicate properties of the SRLG-list contained in the sub-object.
SRLG Id
The 32-bit identifier of the SRLG.
Reserved
This field is reserved. It SHOULD be set to zero on transmission and MUST be ignored on receipt.
The rules of the processing of the LSP_REQUIRED_ATTRIBUTES, LSP_ATTRIBUTE and ROUTE_RECORD Objects are not changed.
Typically, the head node gets the route information of an LSP by adding a RRO which contains the sender’s IP addresses in the Path message. If a head node also desires SRLG recording, it sets the SRLG Collection Flag in the Attribute Flags TLV which can be carried either in an LSP_REQUIRED_ATTRIBUTES Object if the collection is mandatory, or in an LSP_ATTRIBUTES Object if the collection is desired, but not mandatory
When a node receives a Path message which carries an LSP_REQUIRED_ATTRIBUTES Object and the SRLG Collection Flag is set, if local policy determines that the SRLG information should not be provided to the endpoints, it MUST return a PathErr message with Error Code 2 (policy) and Error subcode "SRLG Recording Rejected" (value to be assigned by IANA, suggest value 108) to reject the Path message.
When a node receives a Path message which carries an LSP_ATTRIBUTES Object and the SRLG Collection Flag is set, if local policy determines that the SRLG information should not be provided to the endpoints, the Path message SHOULD NOT be rejected due to SRLG recording restriction and the Path message SHOULD be forwarded without the SRLG sub-object(s) in the Path RRO.
If local policy permits the recording of the SRLG information, the processing node SHOULD add an SRLG sub-object to the RRO to carry the local SRLG information. It then forwards the Path message to the next node in the downstream direction.
Following the steps described above, the intermediate nodes of the LSP can collect the SRLG information in the RRO during the forwarding of the Path message hop by hop. When the Path message arrives at the tail node, the tail node can get the SRLG information from the RRO.
Before the Resv message is sent to the upstream node, the tail node adds the SRLG subobject with the SRLG value(s) associated with the local hop to the Resv RRO in a similar manner to that specified above for the addition of Path RRO sub-objects by midpoint nodes.
When a node receives a Resv message for an LSP for which SRLG Collection is specified, if local policy determines that the SRLG information should not be provided to the endpoints, if the SRLG-recording request was in a LSP_REQUIRED_ATTRIBUTES object, then a ResvErr with Error code 2 (policy) and Error subcode "SRLG Recording Rejected" (value to be assigned by IANA, suggest value 108) MUST be sent. If the request was in a LSP_ATTRIBUTES object, then a ResvErr SHOULD NOT be generated, but SRLG information must not be added in the RRO. Otherwise, if local policy allows to provide the SRLG informatin, it MUST add an SRLG sub-object to the RRO to carry the SRLG information in the upstream direction. When the Resv message arrives at the head node, the head node can get the SRLG information from the RRO in the same way as the tail node.
Note that a link’s SRLG information for the upstream direction cannot be assumed to be the same as that in the downstream.
Based on the above procedure, the endpoints can get the SRLG information automatically. Then the endpoints can for instance advertise it as a TE link to the routing instance based on the procedure described in [RFC6107] and configure the SRLG information of the FA automatically.
It is noted that a node (e.g. the edge node of a domain) may edit the RRO to remove the route information (e.g. node, interface identifier information) before forwarding it due to some reasons (e.g.confidentiality or reduce the size of RRO). A node MAY edit SRLG information within the RRO of a Path or Resv message if dictated by its local policy. If a node makes such an alteration to an existing RRO object, it SHOULD set the "SRLG-list edited" flag in the edited RRO sub-object to indicate to other nodes that this has been done.
When the SRLG information of a link is changed, the LSPs using that link should be aware of the changes. The procedures defined in Section 4.4.3 of RFC 3209 [RFC3209] MUST be used to refresh the SRLG information if the SRLG change is to be communicated to other nodes according to the local node's policy. If local policy is that the SRLG change should be suppressed or would result in no change to the previously signaled SRLG-list, the node need not send an update
In a border node of inter-domain or inter-layer network, the following SRLG processing policy should be capable of being configured:
In a multi-layer multi-domain scenario, SRLG ids may be configured by different management entities in each layer/domain. In such scenarios, maintaining a coherent set of SRLG IDs is a key requirement in order to be able to use the SRLG information properly. Thus, SRLG IDs must be unique. Note that current procedure is targeted towards a scenario where the different layers and domains belong to the same operator, or to several coordinated administrative groups. Ensuring the aforementioned coherence of SRLG IDs is beyond the scope of this documen
Further scenarios, where coherence in the SRLG IDs cannot be guaranteed are out of the scope of the present document and are left for further study.
This document does not introduce any additional security issues above those identified in [RFC5920][RFC3209][RFC3473]
IANA has created a registry and manages the space of attributes bit flags of Attribute Flags TLV as described in section 11.3 of [RFC5420]. It is requested that IANA makes assignments from the Attribute Bit Flags.
This document introduces a new Attribute Bit Flag:
IANA has made the following assignments in the "Class Names, Class Numbers, and Class Types" section of the "RSVP PARAMETERS" registry located at http://www.iana.org/assignments/rsvp-parameters. We request that IANA make assignments from the ROUTE_RECORD RFC 3209 [RFC3209] portions of this registry.
This document introduces a new RRO sub-object:
Type Name Reference
--------- ---------------------- ---------
TBD (34) SRLG sub-object This I-D
It is requested that the IANA ceates a registry to manage the space of bit flags of the SRLG sub-object defined in this document. It is requested that IANA makes assignments from the SRLG sub-object Flags.
This document introduces two new SRLG sub-object Flags.
| Bit Number | Name | Reference |
|---|---|---|
| 1 | SRLG-list edited | This document |
| 2 | Partial SRLG-list | This document |
IANA has made the following assignments in the "Error Codes and Globally-Defined Error Value Sub-Codes" section of the "RSVP PARAMETERS" registry located at http://www.iana.org/assignments/rsvp-parameters. We request that IANA make assignments from the Policy Control Failure Sub-Codes registry.
This document introduces a new Policy Control Failure Error sub-code:
The authors would like to thank Igor Bryskin, Ramon Casellas, Lou Berger and Alan Davey for their useful comments and improvements to the document.