Definition of a Record Route Object (RRO) Node-Id Sub-Object
draft-ietf-mpls-nodeid-subobject-07

Network Working Group                             J.-P Vasseur (Editor) 
IETF Internet Draft                                           Zafar Ali 
                                                         Siva Sivabalan 
                                                    Cisco Systems, Inc. 
                                                                         
Proposed Status: Standard 
Expires: May 2006                                                
                                                          November 2005 
 
 
                                     
                draft-ietf-mpls-nodeid-subobject-07.txt 
 
 
                 Definition of an RRO node-id subobject 
 
 
 
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draft-ietf-mpls-nodeid-subobject-07.txt                   November 2005 
 
 
Abstract 
 
In the context of MPLS TE Fast Reroute, the Merge Point (MP) address is 
required at the Point of Local Repair (PLR) in order to select a backup 
tunnel intersecting a fast reroutable Traffic Engineering Label 
Switched Path (TE LSP) on a downstream Label Switching Router (LSR).  
However, existing protocol mechanisms are not sufficient to find an MP 
address in multi-domain routing networks where a domain is defined as 
an IGP area or an Autonomous System. Hence, the current MPLS Fast 
Reroute mechanism cannot be used in order to protect inter-domain TE 
LSPs from a failure of an ABR (Area Border Router) or ASBR (Autonomous 
System Border Router) respectively. This document specifies the use of 
existing Route Record Object (RRO) IPv4 and IPv6 sub-objects (with a 
new flag defined) thus defining the node-id subobject in order to solve 
this issue. The MPLS Fast reroute mechanism mentioned in this document 
refers to the "Facility backup" MPLS TE Fast Reroute method. 
 
Table of content 

1. Terminology...............................2
2. Introduction..............................3
3. Signaling node-ids in RROs................5
4. Finding Merge Points......................6
5. Security Considerations...................6
6. IANA Considerations.......................6
7. Intellectual Property Considerations......6
8. Acknowlegments............................7
9. References................................7
9.1 Normative References.....................7
9.2 Informative References...................7
10. Authors' addresses.......................8

Conventions used in this document 
 
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 RFC-2119 [i]. 
 
 
1.      Terminology 
  
ABR Routers: border routers used to connect two IGP areas (areas in 
OSPF or levels in IS-IS) 
 
ASBR Routers: border routers used to connect to another AS of a 
different or the same Service Provider via one or more links inter-
connecting between ASs. 
 
Backup Tunnel: the LSP that is used to backup up one of the many LSPs 
in many-to-one backup. 
 
Inter-AS TE LSP: A TE LSP that crosses an AS boundary. 
 
Inter-area TE LSP: A TE LSP that crosses an IGP area. 
 
LSR: Label Switching Router 
 
LSP: Label Switched Path 
 
Local Repair: techniques used to repair LSP tunnels quickly when a node 
or link along the LSPs path fails. 
 
PCE: Path Computation Element: an entity (component, application or 
 
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draft-ietf-mpls-nodeid-subobject-07.txt                   November 2005 
 
 
network node) that is capable of computing a network path or route 
based on a network graph and applying computational constraints. 
 
MP: Merge Point. The LSR where one or more backup tunnels rejoin the 
path of the protected LSP downstream of the potential failure.  
 
Protected LSP: an LSP is said to be protected at a given hop if it has 
one or multiple associated backup tunnels originating at that hop. 
 
PLR: Point of Local Repair. The head-end of a backup tunnel. 
 
Reroutable LSP: Any LSP for with the "Local protection desired" bit is 
set in the Flag field of the SESSION_ATTRIBUTE object of its Path 
messages. 
 
TE LSP: Traffic Engineering Label Switched Path 
 
2.      Introduction 
 
MPLS Fast Reroute (FRR) ([FAST-REROUTE]) is a fast recovery local 
protection technique used to protect Traffic Engineering LSPs from 
link/SRLG/node failure.  One or more backup tunnels are pre-established 
to protect against the failure of a link/node/SRLG. In case of failure, 
every protected TE LSP traversing the failed resource is rerouted onto 
the appropriate backup tunnels. 
 
There are several requirements on the backup tunnel path that must be 
satisfied. First, the backup tunnel must not traverse the element that 
it protects. Additionally, a primary tunnel and its associated backup 
tunnel should intersect at least at two points (nodes): Point of Local 
Repair (PLR) and Merge Point (MP). The former is the Head-end LSR of 
the backup tunnel and the latter is the Tail-end LSR of the backup 
tunnel. The PLR is where FRR is triggered when link/node/SRLG failure 
happens.  
 
There are different methods for computing paths for backup tunnels at a 
given PLR. Specifically, a user can statically configure one or more 
backup tunnels at the PLR with an explicitly configured path or the PLR 
can be configured to automatically compute a backup path or to send a 
path computation request to a PCE (see [PCE-ARCH]). 
 
Consider the following scenario (figure 1) 
 
Assumptions: 
- A multi-area network made of three areas: 0, 1 and 2, 
- A fast reroutable TE LSP T1 (TE LSP signaled with the "local 
Protection desired" bit set in the SESSION-ATTRIBUTE object or the 
FAST-REROUTE object) from R0 to R3, 
- A backup tunnel B1 from R1 to R2, not traversing ABR1, and following 
the R1-ABR3-R2 path.  

 
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draft-ietf-mpls-nodeid-subobject-07.txt                   November 2005 
 
 
- The PLR R1 reroutes any protected TE LSP traversing ABR1 onto the 
backup tunnel B1 in case of ABR1's failure. 
 
           <--- area 1 --><---area 0---><---area 2---> 
              R0-----R1-ABR1--R2------ABR2--------R3 
                     \        / 
                      \      / 
                        ABR3 
 
Figure 1: Use of Fast Reroute to protect a TE LSP against an ABR 
failure with MPLS Traffic Engineering Fast Reroute 
 
When T1 is first signaled, the PLR R1 needs to dynamically select an 
appropriate backup tunnel intersecting T1 on a downstream LSR. However, 
existing protocol mechanisms are not sufficient to unambiguously find 
the MP address in a network with inter-domain TE LSP. This document 
addresses these limitations.  
 
R1 needs to select an existing backup tunnel with the following 
properties: 
 
   1. The backup tunnel intersects with the primary tunnel at the MP. 
      For the sake of illustration, in Figure 1, R1 needs to determine 
      that T1 and B1 intersect at the node R2. 
 
   2. The backup tunnel satisfies the primary LSP's request with 
      respect to the bandwidth protection request (i.e., bandwidth 
      guaranteed for the primary tunnel during failure), and the type 
      of protection (link or node failure), as specified in [FAST-
      REROUTE]. 
 
One technique for the PLR to ensure that condition (1) is met consists 
of examining the Record Route Object (RRO) of the primary tunnel to see 
if any of the addresses specified in the RRO corresponds to the MP. 
That said, as per [RSVP-TE], the addresses specified in the RRO IPv4 or 
IPv6 sub-objects sent in Resv messages can be node-ids and/or interface 
addresses. Hence, in Figure 1, router R2 may specify interface 
addresses in the RROs for T1 and B1. Note that these interface 
addresses are different in this example.  
 
The problem of finding the MP using the interface addresses or node-ids 
can be easily solved in the case of a single IGP area. Specifically, in 
the case of a single IGP area, the PLR has the knowledge of all the 
interfaces attached to the tail-end of the backup tunnel. This 
information is available in PLR's IGP topology database. Thus, the PLR 
can unambiguously determine whether a backup tunnel intersecting a 
protected TE LSP on a downstream node exists and can also find the MP 
address regardless of how the addresses carried in the RRO IPv4 or IPv6 
sub-objects are specified (i.e., whether using the interface addresses 
or the node-ids). However, such routing information is not available in 
the case of inter-domain environments. Hence, unambiguously making sure 
 
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draft-ietf-mpls-nodeid-subobject-07.txt                   November 2005 
 
 
that condition (1) above is met in the case of inter-domain TE LSPs is 
not possible with existing mechanisms. 
 
In this document, we define extensions to and describe the use of RSVP 
[RSVP, RSVP-TE] to solve the above-mentioned problem. Note that the 
requirement for the support of the fast recovery technique specified in 
[FAST-REROUTE] to inter-domain TE LSPs has been specified in [INTER-
AREA-TE-REQS] and [INTER-AREA-TE-REQS]. 
 
3.      Signaling node-ids in RROs 
 
As mentioned above, the limitation that we need to address is the 
generality of the contents of the RRO IPv4 and IPv6 sub-objects, as 
defined in [RSVP-TE]. [RSVP-TE] defines the IPv4 and IPv6 RRO sub-
objects. Moreover, two additional flags are defined in [FAST-REROUTE]: 
the "Local Protection Available" and "Local protection in use" bits. 
 
In this document, we define the following new flag: 
 
Node-id: 0x20 
 
        When set, this indicates that the address specified in the 
        RRO's IPv4 or IPv6 subobject is a node-id address, which refers 
        to the "Router Address" as defined in [OSPF-TE], or "Traffic 
        Engineering Router ID" as defined in [ISIS-TE]. A node MUST use 
        the same address consistently. Once an address is used in RRO's 
        IPv4 or IPv6 subobject, it SHOULD always be used for the 
        lifetime of the LSP. 
 
An IPv4 or IPv6 RRO subobject with the node-id flag set is also called 
a node-id subobject. The problem of finding a MP address in a network 
with inter-domain TE LSP is solved by inserting a node-id subobject (an 
RRO "IPv4" and "IPv6" sub-object with the 0x20 flag set) in the RRO 
object carried in the RSVP Resv message. 
         
An implementation may either decide to:  
 
1) Add the node-id subobject in the RRO carried in an RSVP Resv message 
and, when required, also add another IPv4/IPv6 subobject to record 
interface address. 
 
Example: an inter-domain fast reroutable TE LSP would have in the RRO 
carried in Resv message two sub-objects: a node-id subobject and a 
label sub-object. If recording the interface address is required, then 
an additional IPv4/IPv6 subobject is added.  
 
2) Add an IPv4/IPv6 sub-object recording the interface address and, 
when required, add a node-id subobject in the RRO. 
 
Example: an inter-domain fast reroutable TE LSP would have in the RRO  
carried in Resv message three sub-objects: an IPv4/IPv6 sub-object 
 
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draft-ietf-mpls-nodeid-subobject-07.txt                   November 2005 
 
 
recording interface address, a label sub-object and a node-id sub-
object. 
 
Note also that the node-id sub-object may have other application than 
Fast Reroute backup tunnel selection. Moreover, it is RECOMMENDED that 
an LSR recording a node-id address in an IPv4/IPv6 RRO sub-object also 
set the Node-id flag. 
 
4.      Finding Merge Point  
 
Two cases should be considered: 
 
- Case 1: the backup tunnel destination is the MP's node-id. Then a PLR 
can find the MP and suitable backup tunnel by simply comparing the 
backup tunnel's destination address with the node-id included in the 
RRO of the primary tunnel.  
- Case 2: the backup tunnel terminates at an address different than the 
MP's node-id. Then a node-id subobject MUST also be included in the RRO 
object of the backup tunnel. A PLR can find the MP and suitable backup 
tunnel by simply comparing the node-ids present in the RRO objects of 
both the primary and backup tunnels. 
 
It must be noted that although the technique described in this document 
for selecting an appropriate backup tunnel using the node-id sub-object 
applies to the case of Inter-area and Inter-AS, in the case of Inter-
AS, the assumption is made that the MP's node-id (of the downstream 
domain) does not overlap with any LSR's node-id present in the PLR's 
AS. 
 
When both IPv4 node-id and IPv6 node-id sub-objects are present, a PLR 
may use any or both of them in finding the MP address.  
 
5.      Security Considerations 
 
This document does not introduce new security issues. The security 
considerations pertaining to [RSVP] and [RSVP-TE] remain relevant. 
 
6.      IANA considerations 
 
This document does not make any request for IANA action.  
 
7.      Intellectual Property Considerations 
 
The IETF takes no position regarding the validity or scope of any 
Intellectual Property Rights or other rights that might be claimed to 
pertain to the implementation or use of the technology described in 
this document or the extent to which any license under such rights 
might or might not be available; nor does it represent that it has made 
any independent effort to identify any such rights. Information on the 
procedures with respect to rights in RFC documents can be found in BCP 
78 and BCP 79. 
 
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draft-ietf-mpls-nodeid-subobject-07.txt                   November 2005 
 
 
 
Copies of IPR disclosures made to the IETF Secretariat and any 
assurances of licenses to be made available, or the result of an 
attempt made to obtain a general license or permission for the use of 
such proprietary rights by implementers or users of this specification 
can be obtained from the IETF on-line IPR repository at 
http://www.ietf.org/ipr. 
 
The IETF invites any interested party to bring to its attention any 
copyrights, patents or patent applications, or other proprietary rights 
that may cover technology that may be required to implement this 
standard. Please address the information to the IETF at ietf-   
ipr@ietf.org. 
 
8.      Acknowledgments 
 
We would like to acknowledge input and helpful comments from Carol 
Iturralde, Anca Zamfir, Reshad Rahman, Rob Goguen, Philip Matthews. A 
special thank to Adrian Farrel for his thorough review of this 
document. 
 
9.      References 
 
9.1 Normative References 
 
[RFC2119]Bradner, S., "Key words for use in RFCs to Indicate 
Requirement Levels", BCP 14, RFC 2119, March 1997. 
 
[RSVP] Braden, et al, "Resource ReSerVation Protocol (RSVP) - Version 
1, Functional Specification", RFC 2205, September 1997. 
 
[RSVP-TE] Awduche, et al, "Extensions to RSVP for LSP Tunnels", RFC 
3209, December 2001. 
 
[FAST-REROUTE] Ping Pan, et al, "Fast Reroute Extensions to RSVP-TE for 
LSP Tunnels", draft-ietf-mpls-rsvp-lsp-fastreroute-07.txt. RFC 4090, 
May 2005. 
 
[OSPF-TE] Katz et al., "Traffic Engineering (TE) Extensions to OSPF  
Version 2", RFC3630.  
    
[ISIS-TE] Smit et al., "Intermediate System to Intermediate System (IS-
IS) - Extensions for Traffic Engineering (TE)IS-IS extensions for 
Traffic Engineering", RFC3784.  
 
9.2 Informative references 
 
[INTER-AREA-TE-REQS] Le Roux, Vasseur, Boyle et al., "Requirements for 
Inter-Area MPLS Traffic Engineering", RFC 4105, June 2005. 
 

 
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draft-ietf-mpls-nodeid-subobject-07.txt                   November 2005 
 
 
[INTER-AS-TE-REQS] Zhang, Vasseur et al, "MPLS Inter-AS Traffic 
Engineering requirements", RFC 4216, November 2005. 
 
[PCE-ARCH] Farrel, A., Vasseur JP., Ash J., "Path Computation Element 
(PCE) Architecture", draft-ietf-pce-architecture, work in progress. 
 
 
10.     Authors' Addresses 
 
J.-P Vasseur (Editor) 
Cisco Systems, Inc. 
1414 Massachusetts Avenue 
Boxborough , MA - 01719 
USA 
Email: jpv@cisco.com 
 
Zafar Ali 
Cisco Systems, Inc. 
100 South Main St. #200 
Ann Arbor, MI 48104 
USA 
zali@cisco.com 
 
Siva Sivabalan  
Cisco Systems, Inc.  
2000 Innovation Drive  
Kanata, Ontario, K2K 3E8  
Canada  
msiva@cisco.com  
                     
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