RFC7110: Return Path Specified Label Switched Path (LSP) Ping
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Related keywords:
(Reply TC)
(Tunnel Stack)
Internet Engineering Task Force (IETF) M. Chen
Request for Comments: 7110 W. Cao
Category: Standards Track Huawei Technologies Co., Ltd
ISSN: 2070-1721 S. Ning
Tata Communications
F. Jounay
Orange CH
S. Delord
January 2014
Return Path Specified Label Switched Path (LSP) Ping
Abstract
This document defines extensions to the data-plane failure-detection
protocol for Multiprotocol Label Switching (MPLS) Label Switched
Paths (LSPs) known as "LSP ping". These extensions allow a selection
of the LSP to be used for the echo reply return path. Enforcing a
specific return path can be used to verify bidirectional connectivity
and also increase LSP ping robustness.
Status of This Memo
This is an Internet Standards Track document.
This document is a product of the Internet Engineering Task Force
(IETF). It represents the consensus of the IETF community. It has
received public review and has been approved for publication by the
Internet Engineering Steering Group (IESG). Further information on
Internet Standards is available in Section 2 of RFC 5741.
Information about the current status of this document, any errata,
and how to provide feedback on it may be obtained at
http://www.rfc-editor.org/info/rfc7110.
Chen, et al. Standards Track [Page 1]
RFC 7110 Return Path Specified LSP Ping January 2014
Copyright Notice
Copyright (c) 2014 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.
Table of Contents
1. Introduction ....................................................3
2. Requirements Language ...........................................3
3. Problem Statements and Solution Overview ........................3
3.1. Limitations of Existing Mechanisms for Bidirectional LSPs ..4
3.2. Limitations of Existing Mechanisms for Handling
Unreliable Return Paths ....................................4
4. Extensions ......................................................5
4.1. Reply via Specified Path Mode ..............................6
4.2. Reply Path (RP) TLV ........................................6
4.3. Tunnel Sub-TLVs ............................................8
4.3.1. IPv4 RSVP Tunnel Sub-TLV ...........................10
4.3.2. IPv6 RSVP Tunnel Sub-TLV ...........................11
4.3.3. Static Tunnel Sub-TLV ..............................12
4.4. Reply TC TLV ..............................................12
5. Theory of Operation ............................................13
5.1. Sending an Echo Request ...................................14
5.2. Receiving an Echo Request .................................14
5.3. Sending an Echo Reply .....................................15
5.4. Receiving an Echo Reply ...................................16
5.5. Non-IP Encapsulation for MPLS-TP LSPs .....................16
6. Security Considerations ........................................16
7. IANA Considerations ............................................17
7.1. TLVs ......................................................17
7.2. New Target FEC Stack Sub-TLVs .............................17
7.3. New Reply Mode ............................................17
7.4. Reply Path Return Code ....................................18
8. Contributors ...................................................19
9. Acknowledgements ...............................................19
10. References ....................................................19
10.1. Normative References .....................................19
10.2. Informative References ...................................20
Chen, et al. Standards Track [Page 2]
RFC 7110 Return Path Specified LSP Ping January 2014
1. Introduction
This document defines extensions to the data-plane failure-detection
protocol for Multiprotocol Label Switching (MPLS) Label Switched
Paths (LSPs) known as "LSP ping" [RFC4379] that can be used to
specify the return paths for the echo reply message, increasing the
robustness of LSP ping, reducing the opportunity for error, and
improving the reliability of the echo reply message. A new Reply
Mode, which is referred to as "Reply via Specified Path", is added
and a new Type-Length-Value (TLV), which is referred to as "Reply
Path (RP) TLV", is defined in this memo. The procedures defined in
this document currently only apply to "ping" mode. The "traceroute"
mode is out of scope for this document.
In this document, the term bidirectional LSP includes the co-routed
bidirectional LSP defined in [RFC3945] and the associated
bidirectional LSP that is constructed from a pair of unidirectional
LSPs (one for each direction) that are associated with one another at
the LSP's ingress/egress points [RFC5654]. The mechanisms defined in
this document can apply to both IP/MPLS and MPLS Transport Profile
(MPLS-TP) scenarios.
2. 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].
3. Problem Statements and Solution Overview
MPLS LSP ping is defined in [RFC4379]. It can be used to detect
data-path failures in all MPLS LSPs.
LSPs are increasingly being deployed to provide bidirectional
services. The co-routed bidirectional LSP is defined in [RFC3945],
and the associated bidirectional LSP is defined in [RFC5654]. With
the deployment of such services, operators have a desire to test both
directions of a bidirectional LSP in a single operation.
Additionally, when testing a single direction of an LSP (either a
unidirectional LSP or a single direction of a bidirectional LSP)
using LSP ping, the validity of the result may be affected by the
success of delivering the echo reply message. Failure to exchange
these messages between the egress Label Switching Router (LSR) and
the ingress LSR can lead to false negatives where the LSP under test
is reported as "down" even though it is functioning correctly.
Chen, et al. Standards Track [Page 3]
RFC 7110 Return Path Specified LSP Ping January 2014
3.1. Limitations of Existing Mechanisms for Bidirectional LSPs
With the existing LSP ping mechanisms, as defined in [RFC4379],
operators have to enable LSP detection on each of the two ends of a
bidirectional LSP independently. This not only doubles the workload
for the operators but may also bring additional difficulties when
checking the backward direction of the LSP under the following
condition:
The LSR that the operator logged on to perform the checking
operations might not have out-of-band connectivity to the LSR at
the far end of the LSP. That can mean it is not possible to check
the return direction of a bidirectional LSP in a single operation
-- the operator must log on to the LSR at the other end of the LSP
to test the return direction.
Associated bidirectional LSPs have the same issues as those listed
for co-routed bidirectional LSPs.
This document defines a mechanism to allow the operator to request
that both directions of a bidirectional LSP be tested by a single LSP
ping message exchange.
3.2. Limitations of Existing Mechanisms for Handling Unreliable Return
Paths
[RFC4379] defines four Reply Modes:
1. Do not reply
2. Reply via an IPv4/IPv6 UDP packet
3. Reply via an IPv4/IPv6 UDP packet with Router Alert
4. Reply via application level control channel
Obviously, the issue of the reliability of the return path for an
echo reply message does not apply in the first of these cases.
[RFC4379] states that the third mode may be used when the IP return
path is deemed unreliable. This mode of operation requires that all
intermediate nodes support the Router Alert option and understand how
to forward MPLS echo replies. This is a rigorous requirement in
deployed IP/MPLS networks, especially since the return path may be
through legacy IP-only routers.
Chen, et al. Standards Track [Page 4]
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In any case, the use of Reply Modes 2 or 3 cannot guarantee the
delivery of echo responses through an IP network that is
fundamentally unreliable. The failure to deliver echo response
messages can lead to false negatives, making it appear that the LSP
has failed.
Allowing the ingress LSR to control the path used for echo reply
messages enables an operator to apply an extra level of deterministic
process to the LSP ping test. For example, when testing an LSP,
Reply Mode 2 is used at the beginning but no echo reply is received.
When failure of the return path is suspected, the operator can
initiate another LSP ping with the Reply Mode defined in this
document and specify a different return path that is deemed workable
to complete the test.
This document defines extensions to LSP ping that can be used to
specify the return paths of the echo reply message in an echo request
message.
4. Extensions
LSP ping, defined in [RFC4379], is carried out by sending an echo
request message. It carries the Forwarding Equivalence Class (FEC)
information of the LSP being tested. The FEC information indicates
which MPLS path is being verified along the same data path as other
normal data packets belonging to the FEC.
LSP ping [RFC4379] defines four Reply Modes that are used to direct
the egress LSR in how to send back an echo reply. This document
defines a new Reply Mode, the "Reply via Specified Path" mode. This
new mode is used to direct the egress LSR of the tested LSP to send
the echo reply message back along the path specified in the echo
request message.
In addition, two new TLVs, the "Reply Path (RP) TLV" and "Reply
Traffic Class (TC) TLV" [RFC5462], are defined in this document. The
Reply Path TLV contains one or more nested sub-TLVs that can be used
to carry the specified return path information to be used by the echo
reply message.
Chen, et al. Standards Track [Page 5]
RFC 7110 Return Path Specified LSP Ping January 2014
4.1. Reply via Specified Path Mode
A new Reply Mode is defined to be carried in the Reply Mode field of
the echo request message.
The value of the Reply via Specified Path mode is 5 (This has been
allocated by IANA using early allocation and is to be confirmed by
IANA).
Value Meaning
----- -------
5 Reply via Specified Path
The Reply via Specified Path mode is used to request that the remote
LSR receiving the echo request message sends back the echo reply
message along the specified paths carried in the Reply Path TLV.
4.2. Reply Path (RP) TLV
The Reply Path (RP) TLV is an optional TLV within the LSP ping
protocol. However, if the Reply via Specified Path mode requested,
as described in Section 4.1, the Reply Path (RP) TLV MUST be included
in an echo request message, and its absence is treated as a malformed
echo request, as described in [RFC4379]. Furthermore, if a Reply
Path (RP) TLV is included in an echo request message, a Reply Path
(RP) TLV MUST be included in the corresponding echo reply message
sent by an implementation that is conformant to this specification.
The Reply Path (RP) TLV carries the specified return path that the
echo reply message is required to follow. The format of Reply Path
TLV is as follows:
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
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Reply Path TLV Type | Length |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Reply Path return code | Flags |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Reply Path |
~ ~
| |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
Figure 1: Reply Path TLV
Chen, et al. Standards Track [Page 6]
RFC 7110 Return Path Specified LSP Ping January 2014
Reply Path TLV Type: It is 2 octets in length, and the type value is
21.
Length: It is 2 octets in length. It defines the length in octets
of the Reply Path return code, Flags, and Reply Path fields.
Reply Path return code: The Reply Path return code field is 2 octets
in length. It is defined for the egress LSR of the forward LSP to
report the results of Reply Path TLV processing and return path
selection. This field MUST be set to zero in a Reply Path TLV
carried on an echo request message and MUST be ignored on receipt.
This document defines the following Reply Path return codes for
inclusion in a Reply Path TLV carried on an echo reply:
Value Meaning
------ ----------------------
0x0000 Reserved, MUST NOT be used
0x0001 Malformed Reply Path TLV was received
0x0002 One or more of the sub-TLVs in the Reply Path TLV
were not understood
0x0003 The echo reply was sent successfully using the
specified Reply Path
0x0004 The specified Reply Path was not found, the echo
reply was sent via another LSP
0x0005 The specified Reply Path was not found, the echo
reply was sent via pure IP forwarding (non-MPLS)
path
0x0006-0xfffb Unassigned
0xfffc-0xffff Experimental Use
Chen, et al. Standards Track [Page 7]
RFC 7110 Return Path Specified LSP Ping January 2014
Flags: It is also 2 octets in length, it is used to notify the
egress how to process the Reply Paths field when performing return
path selection. The Flags field is a bit vector and has following
format:
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| MUST be zero |A|B|
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
Figure 2: Flags
A (Alternative path): the egress LSR MUST select a non-default
path as the return path. This is very useful when reverse
default path problems are suspected that can be confirmed when
the echo reply is forced to follow a non-default return path.
Here, the default path refers to the path that the egress LSR
will use to send the echo reply when Reply Mode 2 or 3 is used.
If A bit is set, there is no need to carry any specific reply
path sub-TLVs, and when received, the sub-TLVs SHOULD be
ignored.
B (Bidirectional): the return path is required to follow the
reverse direction of the tested bidirectional LSP. If B bit is
set, there is no need to carry any specific reply path sub-
TLVs, and when received, the sub-TLVs SHOULD be ignored.
The A flag and B flag MUST NOT both be set, otherwise, an echo
reply with the RP return code set to "Malformed Reply Path TLV
was received" MUST be returned.
Reply Path: It is used to describe the return path that an echo
reply will be send along. It is variable in length and can
contain zero, one or more Target FEC sub-TLVs [RFC4379]. In an
echo request, it carries sub-TLVs that describe the specified path
that the echo reply message is required to follow. In an echo
reply, the sub-TLVs describe the FEC Stack information of the
return path (when the return path is an MPLS path) that the echo
reply will be sent along.
4.3. Tunnel Sub-TLVs
[RFC4379] has already defined several Target FEC sub-TLVs, the Target
FEC sub-TLVs provide a good way to identify a specific return path.
The Reply Path TLV can carry any (existing and future defined) sub-
TLV defined for use in the Target FEC Stack TLV to specify the return
path.
Chen, et al. Standards Track [Page 8]
RFC 7110 Return Path Specified LSP Ping January 2014
This document defines three new Target FEC sub-TLVs: IPv4 RSVP Tunnel
sub-TLV, IPv6 RSVP Tunnel sub-TLV, and Static Tunnel sub-TLV. One
usage of these generic RSVP Tunnel sub-TLVs is when LSP ping is used
to periodically verify the control plane against the data plane
[RFC5884], using a Tunnel other than a particular LSP can avoid the
impact of an LSP identifier changing when Make-Before-Break (MBB) is
deployed. These sub-TLVs also can be used in the Reply Path TLV to
allow the operator to specify a more generic tunnel FEC other than a
particular LSP as the return path.
No assignments of sub-TLVs are made directly for TLV Type 21, the
sub-TLV space and assignments for TLV Type 21 will be the same as
that for TLV Type 1. Sub-types for TLV Type 1 and TLV Type 21 MUST
be kept the same. Any new sub-type added to TLV Type 1 MUST apply to
the TLV Type 21 as well.
With the Return Path TLV flags and the sub-TLVs defined for the
Target FEC Stack TLV and in this document, it could provide the
following options for return paths specifying:
1. a particular LSP as return path
- use those sub-TLVs defined for the Target FEC Stack TLV
2. a more generic tunnel FEC as return path
- use the IPv4/IPv6 RSVP and Static Tunnel sub-TLVs defined in
Sections Section 4.3.1, Section 4.3.2, and Section 4.3.3 of
this document
3. the reverse path of the bidirectional LSP as return path
- use B bit defined in Section 4.2 of this document.
4. Force return path to non-default path
- use A bit defined in Section 4.2 of this document.
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4.3.1. IPv4 RSVP Tunnel Sub-TLV
The format of the IPv4 RSVP Tunnel sub-TLV is as follows:
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
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| IPv4 RSVP Tunnel sub-TLV Type | Length |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| IPv4 tunnel end point address |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Flags | Tunnel ID |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Extended Tunnel ID |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| IPv4 tunnel sender address |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
Figure 3: IPv4 RSVP Tunnel Sub-TLV
The IPv4 RSVP Tunnel sub-TLV is derived from the RSVP IPv4 FEC TLV
that is defined in Section 3.2.3 of [RFC4379]. All fields have the
same semantics as defined in [RFC4379] except that the LSP-ID field
is omitted and a new Flags field is defined.
The IPv4 RSVP Tunnel sub-TLV Type field is 2 octets in length, and
the recommended type value is 26.
The Flags field is 2 octets in length, it is used to notify the
egress LSR how to choose the return path. The Flags field is a bit
vector and has following format:
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| MUST be zero |S|P|
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
Figure 4: Tunnel Flags
P (Primary): the return path MUST be chosen from the LSPs that belong
to the specified Tunnel and the LSP MUST be the primary LSP.
S (Secondary): the return path MUST be chosen from the LSPs that
belong to the specified Tunnel and the LSP MUST be the secondary LSP.
Primary and secondary LSPs are defined in [RFC4872].
Chen, et al. Standards Track [Page 10]
RFC 7110 Return Path Specified LSP Ping January 2014
P bit and S bit MUST NOT both be set, otherwise, an echo reply with
the RP return code set to "Malformed Reply Path TLV was received"
SHOULD be returned. If P bit and S bit are both not set, the return
path could be any one of the LSPs from the same Tunnel.
4.3.2. IPv6 RSVP Tunnel Sub-TLV
The format of the IPv6 RSVP Tunnel sub-TLV is as follows:
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
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| IPv6 RSVP Tunnel sub-TLV Type | Length |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| IPv6 tunnel end point address |
| |
| |
| |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Flags | Tunnel ID |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Extended Tunnel ID |
| |
| |
| |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| IPv6 tunnel sender address |
| |
| |
| |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
Figure 5: IPv6 RSVP Tunnel Sub-TLV
The IPv6 RSVP Tunnel sub-TLV is derived from the RSVP IPv6 FEC TLV
that is defined in Section 3.2.4 of [RFC4379]. All fields have the
same semantics as defined in [RFC4379] except that the LSP-ID field
is omitted and a new Flags field is defined.
The IPv6 RSVP Tunnel sub-TLV Type field is 2 octets in length, and
the type value is 27.
The Flags field is 2 octets in length and is identical to that
described in Section 4.3.1.
Chen, et al. Standards Track [Page 11]
RFC 7110 Return Path Specified LSP Ping January 2014
4.3.3. Static Tunnel Sub-TLV
The format of the Static RSVP Tunnel sub-TLV is as follows. The
value fields are taken from the definitions in [RFC6370].
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
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Static Tunnel sub-TLV Type | Length |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Source Global ID |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Source Node ID |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Destination Global ID |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Destination Node ID |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Source Tunnel Num | Destination Tunnel Num |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Flags | Must Be Zero |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
Figure 6: Static Tunnel Sub-TLV
The Flags field is 2 octets in length and is identical to that
described in Section 4.3.1.
The sub-TLV type value is 28.
4.4. Reply TC TLV
Reply TOS Byte TLV [RFC4379] is used by the originator of the echo
request to request that an echo reply be sent with the IP header TOS
byte set to the value specified in the TLV. Similarly, in this
document, a new TLV, Reply TC TLV, is defined and MAY be used by the
originator of the echo request to request that an echo reply be sent
with the TC bits of the return path LSP set to the value specified in
this TLV. The Reply TC TLV is not limited to the Reply Mode
specified in this document (Reply via Specified Path) but may be used
in all the other Reply Modes as well. The format of Reply TC TLV is
as follows:
Chen, et al. Standards Track [Page 12]
RFC 7110 Return Path Specified LSP Ping January 2014
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
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Reply TC TLV type | Length |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| TC | MUST be zero |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
Figure 7: Reply TC TLV
The Reply TC TLV Type field is 2 octets in length, and the type value
is 22.
The Length field is 2 octets in length, the value of length field is
fixed 4 octets.
5. Theory of Operation
The procedures defined in this document currently only apply to
"ping" mode. The "traceroute" mode is out of scope for this
document.
In [RFC4379], the echo reply is used to report the LSP checking
result to the LSP ping initiator. This document defines a new Reply
Mode and a new TLV (Reply Path TLV) that enable the LSP ping
initiator to specify or constrain the return path of the echo reply.
Similarly, the behavior of echo reply is extended to detect the
requested return path by looking at a specified path FEC TLV. This
enables LSP ping to detect failures in both directions of a path with
a single operation; of course, this cuts in half the operational
steps required to verify the end-to-end bidirectional connectivity
and integrity of an LSP.
When the return path is an MPLS path, the echo reply MUST carry the
FEC Stack information in a Reply Path TLV to test the return MPLS LSP
path. The destination IP address of the echo reply message MUST
never be used in a forwarding decision. To avoid this possibility
the destination IP address of the echo reply message that is
transmitted along the specified return path MUST be set to numbers
from the range 127/8 for IPv4 or 0:0:0:0:0:FFFF:127.0.0.0/104 for
IPv6, and the IP Time to Live (TTL) MUST be set 1, and the TTL in the
outermost label MUST be set to 255.
When the return path is a pure IP forwarding path, the procedures
defined in [RFC4379] (the destination IP address is copied from the
source IP address) apply unchanged.
Chen, et al. Standards Track [Page 13]
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5.1. Sending an Echo Request
When sending an echo request, in addition to the rules and procedures
defined in Section 4.3 of [RFC4379], the Reply Mode of the echo
request MUST be set to "Reply via Specified Path", and a Reply Path
TLV MUST be carried in the echo request message correspondingly. The
Reply Path TLV includes one or several reply path sub-TLV(s) to
identify the return path(s) the egress LSR should use for its reply.
For a bidirectional LSP, since the ingress LSR and egress LSR of a
bidirectional LSP are aware of the relationship between the forward
and backward direction LSPs, only the B bit SHOULD be set in the
Reply Path TLV. If the operator wants the echo reply to be sent
along a path other than the reverse direction of the bidirectional
LSP, the A bit SHOULD be set or another FEC sub-TLV SHOULD be carried
in the Reply Path TLV instead, and the B bit MUST be clear.
In some cases, operators may want to treat two unidirectional LSPs
(one for each direction) as a pair. There may not be any binding
relationship between the two LSPs. Using the mechanism defined in
this document, operators can run LSP ping one time from one end to
complete the failure detection on both unidirectional LSPs. To
accomplish this, the echo request message MUST carry (in the Reply
Path TLV) a FEC sub-TLV that belongs to the backward LSP.
5.2. Receiving an Echo Request
"Ping" mode processing, as defined in Section 4.4 of [RFC4379],
applies in this document. In addition, when an echo request is
received, if the egress LSR does not know the Reply Mode defined in
this document, an echo reply with the return code set to "Malformed
echo request received" and the Subcode set to zero will be send back
to the ingress LSR according to the rules of [RFC4379]. If the
egress LSR knows the Reply Mode, according to the Reply Path TLV, it
SHOULD find and select the desired return path. If there is a
matched path, an echo reply with a Reply Path TLV that identifies the
return path SHOULD be sent back to the ingress LSR, the Reply Path
return code SHOULD be set to "The echo reply was sent successfully
using the specified Reply Path". If there is no such path, an echo
reply with the Reply Path TLV SHOULD be sent back to the ingress LSR,
the Reply Path return code SHOULD be set to the relevant code
(defined in Section 4.2) for the real situation to reflect the result
of Reply Path TLV processing and return path selection. For example,
if the specified LSP is not found, the egress then chooses another
LSP as the return path to send the echo reply, the Reply Path return
code SHOULD be set to "The specified reply path was not found, the
echo reply was sent via another LSP", and if the egress chooses an IP
path to send the echo reply, the Reply Path return code SHOULD be set
Chen, et al. Standards Track [Page 14]
RFC 7110 Return Path Specified LSP Ping January 2014
to "The specified Reply Path was not found, the echo reply was sent
via pure IP forwarding (non-MPLS) path". If there is an unknown sub-
TLV in the received Reply Path TLV, the Reply Path return code SHOULD
be set to "One or more of the sub-TLVs in the Reply Path TLV were not
understood".
If the A bit of the Reply Path TLV in a received echo request message
is set, the egress LSR SHOULD send the echo reply along a non-default
return path.
If the B bit of the Reply Path TLV in a received echo request message
is set, the egress LSR SHOULD send the echo reply along the reverse
direction of the bidirectional LSP.
In addition, the FEC validate results of the forward path LSP SHOULD
NOT affect the egress LSR continue to test return path LSP.
5.3. Sending an Echo Reply
As described in [RFC4379], the echo reply message is a UDP packet,
and it MUST be sent only in response to an MPLS echo request. The
source IP address is a valid IP address of the replier, the source
UDP port is the well-know UDP port for LSP ping.
When the return path is an MPLS LSP, the destination IP address of
the echo reply message is copied from the destination IP address of
the echo request, and the destination UDP port is copied from the
source UDP port of the echo request. The IP TTL MUST be set to 1,
the TTL in the outermost label MUST be set to 255.
When the return path is a pure IP forwarding path, the same as
defined in [RFC4379], the destination IP address and UDP port are
copied from the source IP address and source UDP port of the echo
request.
When sending the echo reply, a Reply Path TLV that identifies the
return path MUST be carried, the Reply Path return code SHOULD be set
to relevant code that reflects results about how the egress processes
the Reply Path TLV in a previous received echo request message and
return path selection. By carrying the Reply Path TLV in an echo
reply, it gives the ingress LSR enough information about the reverse
direction of the tested path to verify the consistency of the data
plane against control plane. Thus, a single LSP ping could achieve
both directions of a path test. If the return path is pure IP path,
no sub-TLVs are carried in the Reply Path TLV.
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5.4. Receiving an Echo Reply
The rules and process defined in Section 4.6 of [RFC4379] apply here.
When an echo reply is received, if the Reply Mode is "Reply via
Specified Path" and the Reply Path return code is "The echo reply was
sent successfully using the specified Reply Path", and if the return
path is an MPLS LSP. The ingress LSR MUST perform FEC validation
(based on the FEC Stack information of the return path carried in the
Reply Path TLV) as an egress LSR does when receiving an echo request,
the FEC validation process (relevant to "ping" mode) defined in
Section 4.4.1 of [RFC4379] applies here.
When an echo reply is received with return code set to "Malformed
echo request received" and the Subcode set to zero. It is possible
that the egress LSR may not know the "Reply via Specified Path" Reply
Mode, the operator may choose to re-perform another LSP ping by using
one of the four Reply Modes defined [RFC4379].
On receipt of an echo reply with Reply Path return code in the Reply
Path TLV set to "The specified reply path was not found, ...", it
means that the egress LSR could not find a matched return path as
specified. Operators may choose to specify another LSP as the return
path or use other methods to detect the path further.
5.5. Non-IP Encapsulation for MPLS-TP LSPs
In some MPLS-TP deployment scenarios, IP addressing might not be
available or the use of some form of non-IP encapsulation might be
preferred. In such scenarios, the Non-IP encapsulation defined in
[RFC6426] applies here. The LSP Ping Reply Mode in the echo request
and echo reply is set to 5. The return path of the echo reply is as
specified in the Reply Path TLV.
6. Security Considerations
Security considerations discussed in [RFC4379] apply to this
document.
In addition, the extensions defined in this document may be used for
potential "proxying" attacks. For example, an echo request initiator
may specify a return path that has a destination different from that
of the initiator. But normally, such attacks will not happen in an
MPLS domain where the initiators and receivers belong to the same
domain. Even this, in order to prevent using the extension defined
in this document for proxying any possible attacks, the return path
LSP should have destination to the same node where the forward path
is from. The receiver may drop the echo request when it cannot
determine whether the return path LSP has the destination to the
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initiator. That means, when sending echo request, the initiator
should choose a proper source address according the specified return
path LSP to help the receiver to make the decision.
7. IANA Considerations
7.1. TLVs
IANA has assigned the value 21 for the Reply Path TLV and assigned
the value 22 for Reply TC TLV from the "Multiprotocol Label Switching
Architecture (MPLS) Label Switched Paths (LSPs) Ping Parameters"
registry, "TLVs" subregistry.
Value Meaning Reference
----- ------- ---------
21 Reply Path TLV this document (Section 4.2)
22 Reply TC TLV this document (Section 4.4)
The sub-TLV space and assignments for the Reply Path TLV will be the
same as that for the Target FEC Stack TLV. Sub-types for the Target
FEC Stack TLV and the Reply Path TLV MUST be kept the same. Any new
sub-type added to the Target FEC Stack TLV MUST apply to the Reply
Path TLV as well.
7.2. New Target FEC Stack Sub-TLVs
IANA has assigned three new sub-TLV types from the "Multiprotocol
Label Switching Architecture (MPLS) Label Switched Paths (LSPs) Ping
Parameters - TLVs" registry, "Sub-TLVs for TLV Types 1, 16, and 21"
subregistry.
Sub-Type Sub-TLV Name Reference
------- ----------- ---------
26 IPv4 RSVP Tunnel this document (Section 4.3.1)
27 IPv6 RSVP Tunnel this document (Section 4.3.2)
28 Static Tunnel this document (Section 4.3.3)
7.3. New Reply Mode
IANA has allocated (5 - Reply via Specified Path) from the "Multi-
Protocol Label Switching (MPLS) Label Switched Paths (LSPs) Ping
Parameters" registry, the "Reply Modes" subregistry.
Value Meaning Reference
----- ------- ----------
5 Reply via Specified Path this document (Section 4.1)
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7.4. Reply Path Return Code
IANA has created a new subregistry for the "Multi-Protocol Label
Switching (MPLS) Label Switched Paths (LSPs) Ping Parameters" for
Reply Path return codes.
This document (Section 4.2) defines the following return codes:
Value Meaning
------ ----------------------
0x0000 No return code
0x0001 Malformed Reply Path TLV was received
0x0002 One or more of the sub-TLVs in the Reply Path TLV
were not understood
0x0003 The echo reply was sent successfully using the
specified Reply Path
0x0004 The specified Reply Path was not found, the echo
reply was sent via another LSP
0x0005 The specified Reply Path was not found, the echo
reply was sent via pure IP forwarding (non-MPLS)
path
0x0006-0xfffb Unassigned
0xfffc-0xffff Reserved for Experimental Use
The range of 0x0006-0xfffb is not allocated and reserved for future
extensions and is allocated via Standard Action; the range of 0xfffc-
0xffff is for Experimental Use.
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8. Contributors
The following individuals also contributed to this document:
Ehud Doron
Orckit-Corrigent
EMail: ehudd@orckit.com
Ronen Solomon
Orckit-Corrigent
EMail: RonenS@orckit.com
Ville Hallivuori
Tellabs
Sinimaentie 6 C
FI-02630 Espoo, Finland
EMail: ville.hallivuori@tellabs.com
Xinchun Guo
EMail: guoxinchun@huawei.com
9. Acknowledgements
The authors would like to thank Adrian Farrel, Peter Ashwood-Smith,
Sriganesh Kini, Gregory Mirsky, Eric Gray, Loa Andersson, Carlos
Pignataro, and Tom Petch for their reviews, suggestions, and
comments.
10. References
10.1. Normative References
[RFC2119] Bradner, S., "Key words for use in RFCs to Indicate
Requirement Levels", BCP 14, RFC 2119, March 1997.
[RFC4379] Kompella, K. and G. Swallow, "Detecting Multi-Protocol
Label Switched (MPLS) Data Plane Failures", RFC 4379,
February 2006.
[RFC6370] Bocci, M., Swallow, G., and E. Gray, "MPLS Transport
Profile (MPLS-TP) Identifiers", RFC 6370, September 2011.
Chen, et al. Standards Track [Page 19]
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10.2. Informative References
[RFC3945] Mannie, E., "Generalized Multi-Protocol Label Switching
(GMPLS) Architecture", RFC 3945, October 2004.
[RFC4872] Lang, J., Rekhter, Y., and D. Papadimitriou, "RSVP-TE
Extensions in Support of End-to-End Generalized Multi-
Protocol Label Switching (GMPLS) Recovery", RFC 4872, May
2007.
[RFC5462] Andersson, L. and R. Asati, "Multiprotocol Label Switching
(MPLS) Label Stack Entry: "EXP" Field Renamed to "Traffic
Class" Field", RFC 5462, February 2009.
[RFC5654] Niven-Jenkins, B., Brungard, D., Betts, M., Sprecher, N.,
and S. Ueno, "Requirements of an MPLS Transport Profile",
RFC 5654, September 2009.
[RFC5884] Aggarwal, R., Kompella, K., Nadeau, T., and G. Swallow,
"Bidirectional Forwarding Detection (BFD) for MPLS Label
Switched Paths (LSPs)", RFC 5884, June 2010.
[RFC6426] Gray, E., Bahadur, N., Boutros, S., and R. Aggarwal, "MPLS
On-Demand Connectivity Verification and Route Tracing",
RFC 6426, November 2011.
Chen, et al. Standards Track [Page 20]
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Authors' Addresses
Mach(Guoyi) Chen
Huawei Technologies Co., Ltd
Q14 Huawei Campus, No. 156 Beiqing Road, Hai-dian District
Beijing 100095
China
EMail: mach.chen@huawei.com
Wei Cao
Huawei Technologies Co., Ltd
Q14 Huawei Campus, No. 156 Beiqing Road, Hai-dian District
Beijing 100095
China
EMail: wayne.caowei@huawei.com
So Ning
Tata Communications
EMail: ning.so@tatacommunications.com
Frederic Jounay
Orange CH
4 rue caudray 1020 Renens
Switzerland
EMail: frederic.jounay@orange.ch
Simon Delord
EMail: Simon.delord@team.telstra.com
Chen, et al. Standards Track [Page 21]