LSP-Ping extensions for MPLS-TP
draft-nitinb-mpls-tp-lsp-ping-extensions-00

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Abstract

LSP-Ping is an existing and widely deployment OAM mechanism for MPLS LSPs. This document describes extensions to LSP-Ping so that LSP-Ping can be used to perform OAM on MPLS-TP LSPs. It also clarifies the procedures to be used for processing the OAM packets. Further, it describes how LSP-Ping can be used to perform Connectivity Verification, Route Tracing and Adjacency functions in MPLS-TP networks.

Table of Contents

1.  Introduction
    1.1.  Conventions used in this document
    1.2.  LSP-Ping for MPLS-TP LSPs using IP encapsulation
    1.3.  LSP-Ping for MPLS-TP LSPs using non-IP encapsulation
2.  LSP-Ping extensions
    2.1.  New address type for Downstream Mapping TLV
    2.2.  Source Address TLV
    2.3.  Destination Address TLV
    2.4.  MEP and MIP Identifier
    2.5.  Specifications for statically provisioned LSPs
3.  Performing LSP-Ping over MPLS-TP LSPs
    3.1.  LSP-Ping with IP encapsulation
    3.2.  Non-IP based LSP-Ping
    3.3.  P2MP Considerations
4.  Performing LSP Traceroute over MPLS-TP LSPs
    4.1.  LSP Traceroute with IP encapsulation
    4.2.  Non-IP based LSP Traceroute
        4.2.1.  Ingress node procedure for sending echo request packets
        4.2.2.  Ingress node procedure for receiving echo response packets
        4.2.3.  Transit and egress node procedure
    4.3.  P2MP Considerations
    4.4.  ECMP Considerations
5.  Applicability
6.  Security Considerations
7.  IANA Considerations
8.  Contributing Authors
9.  References
    9.1.  Normative References
    9.2.  Informative References
§  Authors' Addresses

1.  Introduction

LSP-Ping [RFC4379] (Kompella, K. and G. Swallow, “Detecting Multi-Protocol Label Switched (MPLS) Data Plane Failures,” February 2006.)is an OAM mechanism for MPLS LSPs. This document describes extensions to LSP-Ping so that LSP-Ping can be used to perform OAM on MPLS-TP LSPs. It also clarifies the procedures to be used for processing the OAM packets. Further, it describes how LSP-Ping can be used to perform Connectivity Verification, Route Tracing and Adjacency functions specified in [I‑D.ietf‑mpls‑tp‑oam‑requirements] (Vigoureux, M. and D. Ward, “Requirements for OAM in MPLS Transport Networks,” March 2010.).

1.1.  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 [RFC2119] (Bradner, S., “Key words for use in RFCs to Indicate Requirement Levels,” March 1997.).

1.2.  LSP-Ping for MPLS-TP LSPs using IP encapsulation

LSP-Ping requires IP addressing on the egress and transit LSRs for performing OAM on MPLS signaled LSPs and pseudowires. In particular, in these cases the LSP-Ping packets generated by an ingress LSR are encapsulated in an IP/UDP header with the destination address from the 127/8 range and then encapsulated in the MPLS label stack ([RFC4379] (Kompella, K. and G. Swallow, “Detecting Multi-Protocol Label Switched (MPLS) Data Plane Failures,” February 2006.) , [I‑D.ietf‑bfd‑mpls] (Aggarwal, R., Kompella, K., Nadeau, T., and G. Swallow, “BFD For MPLS LSPs,” June 2008.)). Egress LSRs use the presence of the 127/8 destination address to identify the OAM packets and rely further on the UDP port number to determine whether the packet is a LSP-Ping packet. It is to be noted that this determination does not require IP forwarding capabilities. It requires the presence of an IP host stack which enables egress LSRs to process packets with a destination address from the 127/8 range. [RFC1122] (Braden, R., “Requirements for Internet Hosts - Communication Layers,” October 1989.) allocates the 127/8 range as "Internal host loopback address" and [RFC1812] (Baker, F., “Requirements for IP Version 4 Routers,” June 1995.) states that "a router SHOULD NOT forward, except over a loopback interface, any packet that has a destination address on network 127".

1.3.  LSP-Ping for MPLS-TP LSPs using non-IP encapsulation

In certain MPLS-TP deployment scenarios IP addressing might not be available or it may be preferred to use non-IP encapsulation for LSP-Ping and BFD packets. In such scenarios, LSP-Ping must be run without IP addressing, using the ACH channel type specified in [I‑D.nitinb‑mpls‑tp‑lsp‑ping‑bfd‑procedures] (Bahadur, N., Aggarwal, R., Ward, D., Nadeau, T., Sprecher, N., and Y. Weingarten, “LSP-Ping and BFD encapsulation over ACH,” February 2010.).

Sections Section 3.2 (Non-IP based LSP-Ping) and Section 4.2 (Non-IP based LSP Traceroute) describe the theory of operation for performing LSP-Ping over MPLS-TP LSPs with a non-IP encapsulation.

2.  LSP-Ping extensions

2.1.  New address type for Downstream Mapping TLV

[RFC4379] (Kompella, K. and G. Swallow, “Detecting Multi-Protocol Label Switched (MPLS) Data Plane Failures,” February 2006.) defines the Downstream Mapping TLV. This document defines the following new Address type which is added to the Downstream Mapping TLV:

      Type #        Address Type           K Octets
      ------        --------------         --------
          0         Not Applicable                8

The new address type indicates that no address is present in the Downstream Mapping TLV. Multipath type MAY be set to 0 (no multipath) when using this address type.

When this address type is used, on receipt of a LSP-Ping echo request, interface verification MUST be bypassed. Thus the receiving node SHOULD only perform mpls label control-plane/data-plane consistency checks.

The new address type is also applicable to the Detailed Downstream Mapping TLV defined in [I‑D.ietf‑mpls‑lsp‑ping‑enhanced‑dsmap] (Bahadur, N., Kompella, K., and G. Swallow, “Mechanism for performing LSP-Ping over MPLS tunnels,” October 2009.).

2.2.  Source Address TLV

When sending LSP-Ping packets using ACH, without IP encapsulation, there MAY be a need to identify the source address of the packet. This source address will be specified via the Source Address TLV, being defined in [I‑D.ietf‑mpls‑tp‑ach‑tlv] (Boutros, S., Bryant, S., Sivabalan, S., Swallow, G., Ward, D., and V. Manral, “Definition of ACH TLV Structure,” March 2010.). Only 1 source address TLV MUST be present in a LSP-Ping packet. The source address MUST specify the address of the originator of the packet. If more than 1 such TLV is present in a LSP-Ping request packet, then an error of "Malformed echo request received" SHOULD be returned. If more than 1 source address TLV is present, then the packet SHOULD be dropped without further processing.

2.3.  Destination Address TLV

When sending LSP-Ping packets using ACH, without IP encapsulation, there MAY be a need to identify the destination address of the packet. This destination address will be specified via the Destination Address TLV, being defined in [I‑D.ietf‑mpls‑tp‑ach‑tlv] (Boutros, S., Bryant, S., Sivabalan, S., Swallow, G., Ward, D., and V. Manral, “Definition of ACH TLV Structure,” March 2010.). One or more of this TLVs MAY be included. The destination address MUST specify the intended receipient(s) of the packet. If the destination address specified in any of the Destination Address TLVs does not match any address associated with the node which receives the LSP-Ping packet, then the LSP-Ping packet SHOULD be dropped without further processing.

2.4.  MEP and MIP Identifier

When sending LSP-Ping packets using ACH, there MAY be a need to identify the maintenance end point (MEP) and/or the maintenance intermediate point (MIP) being monitored. The MEP/MIP identifiers defined in [I‑D.swallow‑mpls‑tp‑identifiers] (Bocci, M. and G. Swallow, “MPLS-TP Identifiers,” October 2009.) MAY be carried in the ACH TLVs [I‑D.ietf‑mpls‑tp‑ach‑tlv] (Boutros, S., Bryant, S., Sivabalan, S., Swallow, G., Ward, D., and V. Manral, “Definition of ACH TLV Structure,” March 2010.) for identification. Only one identifier (MEP or MIP) may be present in a packet. The MEP/MIP identifiers associated with the packet MUST be checked for the MPLS-TP LSP path/section that is being monitored. If the identifier does not match the LSP path/section, then the packet MUST be dropped.

2.5.  Specifications for statically provisioned LSPs

Details of LSP-Ping for statically provisioned LSPs will be specified in a future revision of this document.

3.  Performing LSP-Ping over MPLS-TP LSPs

This section specifies how LSP-Ping ping can be used in the context of MPLS-TP LSPs. The LSP-Ping ping function meets the Connectivity Verification requirement specified in [I‑D.ietf‑mpls‑tp‑oam‑requirements] (Vigoureux, M. and D. Ward, “Requirements for OAM in MPLS Transport Networks,” March 2010.). This function SHOULD be performed on-demand. This function SHOULD be performed between End Points (MEPs) and Intermediate Points (MIPs) of PWs and LSPs, and between End Points of PWs, LSPs and Sections. In order for the LSP-Ping packet to be processed at the desired MIP, the TTL of the MPLS label should be set such that it expires at the MIP to be probed.

3.1.  LSP-Ping with IP encapsulation

LSP-Ping packets as specified in [RFC4379] (Kompella, K. and G. Swallow, “Detecting Multi-Protocol Label Switched (MPLS) Data Plane Failures,” February 2006.) are sent over the MPLS LSP for which OAM is being performed and contain an IP/UDP packet within them. The IP header is not used for forwarding (since the LSP is forward using MPLS label switching). The IP header is used mainly for addressing and can be used in the context of MPLS-TP LSPs. This form of LSP-Ping OAM MUST be supported for MPLS-TP LSPs when IP addressing is in use. The LSP-Ping Reply mode [RFC4379] (Kompella, K. and G. Swallow, “Detecting Multi-Protocol Label Switched (MPLS) Data Plane Failures,” February 2006.) in the LSP-Ping echo request MUST be set to 4 (Reply via application level control channel).

The LSP-Ping echo response message MUST be sent on the reverse path of the LSP. The reply MUST contain IP/UDP headers followed by the LSP-Ping payload. The destination address in the IP header MUST be set to that of the sender of the echo request message. The source address in the IP address MUST be set to a valid address of the replying node.

3.2.  Non-IP based LSP-Ping

The OAM procedures defined in [RFC4379] (Kompella, K. and G. Swallow, “Detecting Multi-Protocol Label Switched (MPLS) Data Plane Failures,” February 2006.) require the use of IP addressing and in some cases IP routing to perform OAM functions. When the ACH header is used, IP addressing and routing is not needed. This section describes procedures for performing lsp-ping without a dependency on IP addressing and routing.

When using LSP-Ping over the ACH header, the LSP-Ping Reply mode [RFC4379] (Kompella, K. and G. Swallow, “Detecting Multi-Protocol Label Switched (MPLS) Data Plane Failures,” February 2006.) in the LSP-Ping echo request MUST be set to 4 (Reply via application level control channel).

The ingress node MAY attach a Source Address TLV (Section 2.2 (Source Address TLV)) to identify the node originating the request.

The LSP-Ping reply message MUST be sent on the reverse path of the LSP using ACH. The LSP-Ping payload MUST directly follow the ACH header (and any ACH TLVs) and no IP and/or UDP headers MUST be attached. If the request message contained the Source Address TLV and a response is being sent to the originator, then a Destination Address TLV (Section 2.3 (Destination Address TLV)) SHOULD be added to the reply message. The contents of the LSP-Ping request Source Address TLV should be copied into the LSP-Ping response Destination Address TLV. The responding node MAY attach a Source Address TLV to identify the node sending the response.

If a node receives an MPLS echo request packet over ACH, without IP/UDP headers and if that node does not have a return MPLS LSP path to the echo request source, then the node MUST drop the echo request packet and not attempt to send a response.

3.3.  P2MP Considerations

[I‑D.ietf‑mpls‑p2mp‑lsp‑ping] (Yasukawa, S., Farrel, A., Ali, Z., Swallow, G., Nadeau, T., and S. Saxena, “Detecting Data Plane Failures in Point-to-Multipoint Multiprotocol Label Switching (MPLS) - Extensions to LSP Ping,” March 2010.) describes how LSP-Ping can be used for OAM on P2MP LSPs with IP encapsulation. This MUST be supported for MPLS-TP P2MP LSPs when IP addressing is used. When IP addressing is not used, then the procedures described in Section 3.2 (Non-IP based LSP-Ping) can be applied to P2MP MPLS-TP LSPs as well.

4.  Performing LSP Traceroute over MPLS-TP LSPs

This section specifies how LSP-Ping traceroute can be used in the context of MPLS-TP LSPs. The LSP-Ping traceroute function meets the Adjancency and Route Tracing requirement specified in [I‑D.ietf‑mpls‑tp‑oam‑requirements] (Vigoureux, M. and D. Ward, “Requirements for OAM in MPLS Transport Networks,” March 2010.). This function SHOULD be performed on-demand. This function SHOULD be performed between End Points and Intermediate Points of PWs and LSPs, and between End Points of PWs, LSPs and Sections.

When performing lsp-ping traceroute, the ingress node inserts a Downstream Mapping TLV to get the downstream node information and to enable LSP verification along the transit nodes. The Downstream Mapping TLV can be used as is for performing the traceroute. If IP addressing is not in use, then the Address Type field in the Downstream Mapping TLV can be set to "Not applicable" (Section 2.1 (New address type for Downstream Mapping TLV)). The Downstream Mapping TLV address type field can be extended to include other address types as need be.

4.1.  LSP Traceroute with IP encapsulation

The mechanics of LSP-Ping traceroute are similar to that described for ping in Section 3.1 (LSP-Ping with IP encapsulation). Traceroute packets sent by the LSP ingress MUST follow procedures described in [RFC4379] (Kompella, K. and G. Swallow, “Detecting Multi-Protocol Label Switched (MPLS) Data Plane Failures,” February 2006.). This form of LSP-Ping OAM MUST be supported for MPLS-TP LSPs, when IP addressing is used.

4.2.  Non-IP based LSP Traceroute

This section describes the procedures for performing LSP traceroute when using the ACH header and without any dependency on IP addressing. The procedures specified in Section 3.2 (Non-IP based LSP-Ping) with regards to Source Address TLV, Destination Address TLV and MEP/MIP identifiers apply to LSP traceroute as well.

4.2.1.  Ingress node procedure for sending echo request packets

Traceroute packets sent by the LSP ingress MUST adhere to the format described in Section 3.2 (Non-IP based LSP-Ping). MPLS-TTL expiry (as described in [RFC4379] (Kompella, K. and G. Swallow, “Detecting Multi-Protocol Label Switched (MPLS) Data Plane Failures,” February 2006.)) will be used to direct the packets to specific nodes along the LSP path.

4.2.2.  Ingress node procedure for receiving echo response packets

The LSP-Ping traceroute responses will be received on the LSP itself and the presence of an ACH header with channel type of LSP-Ping is an indicator that the packet contains LSP-ping payload.

4.2.3.  Transit and egress node procedure

When a echo request reaches the transit or egress, the presence of the ACH channel type of LSP-Ping will indicate that the packet contains LSP-Ping data. The LSP-Ping data, the label stack and the MEP/MIP identifier should be able to identify the LSP associated with the echo request packet. In case if there is an error and the node is unable to idenfity the LSP on which the echo response should to be sent, the node MUST drop the echo request packet and not send any response back. All responses MUST always be sent on a LSP path using the ACH header and ACH channel type of LSP-Ping.

4.3.  P2MP Considerations

[I‑D.ietf‑mpls‑p2mp‑lsp‑ping] (Yasukawa, S., Farrel, A., Ali, Z., Swallow, G., Nadeau, T., and S. Saxena, “Detecting Data Plane Failures in Point-to-Multipoint Multiprotocol Label Switching (MPLS) - Extensions to LSP Ping,” March 2010.) describes how LSP-Ping can be used for OAM on P2MP LSPs. This MUST be supported for MPLS-TP P2MP LSPs when IP addressing is used. When IP addressing is not used, then the procedures described in Section 4.2 (Non-IP based LSP Traceroute) can be applied to P2MP MPLS-TP LSPs as well.

4.4.  ECMP Considerations

LSP-Ping using ACH SHOULD NOT be used when there is ECMP (equal cost multiple paths) for a given LSP. The addition of the additional ACH header may modify the hashing behavior for OAM packets which may result in incorrect monitoring of path taken by data traffic.

5.  Applicability

The non-IP addressing based procedures specified in this document apply only to MPLS-TP LSPs. They also apply to PWs when IP encapsulation is not desired. However, when IP addressing is used, as in non MPLS-TP LSPs, procedures specified in [RFC4379] (Kompella, K. and G. Swallow, “Detecting Multi-Protocol Label Switched (MPLS) Data Plane Failures,” February 2006.) MUST be used.

6.  Security Considerations

The draft does not introduce any new security considerations. Those discussed in [RFC4379] (Kompella, K. and G. Swallow, “Detecting Multi-Protocol Label Switched (MPLS) Data Plane Failures,” February 2006.) are also applicable to this document.

7.  IANA Considerations

This document has no actions for IANA.

8.  Contributing Authors

The following individuals also contributed to this document:

• Thomas D. Nadeau, BT
• Nurit Sprecher, Nokia Siemens Networks
• Yaacov Weingarten, Nokia Siemens Networks

9.  References

9.1. Normative References

9.2. Informative References

Authors' Addresses