Network Working Group N. Bahadur
Internet-Draft K. Kompella
Updates: RFC4379 Juniper Networks, Inc.
(if approved) G. Swallow
Intended status: Standards Track Cisco Systems
Expires: August 5, 2009 February 1, 2009
Mechanism for performing LSP-Ping over MPLS tunnels
draft-ietf-mpls-lsp-ping-enhanced-dsmap-02
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Abstract
This document describes methods for performing lsp-ping traceroute
over mpls tunnels and for traceroute of stitched mpls LSPs. The
techniques outlined in RFC 4379 are insufficient to perform
traceroute FEC validation and path discovery for a LSP that goes over
other mpls tunnels or for a stitched LSP. This document describes
enhancements to the downstream-mapping TLV (defined in RFC 4379).
These enhancements along with other procedures outlined in this
document can be used to trace such LSPs.
Table of Contents
1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . . 3
1.1. Conventions used in this document . . . . . . . . . . . . 3
2. Motivation . . . . . . . . . . . . . . . . . . . . . . . . . . 3
3. Packet format . . . . . . . . . . . . . . . . . . . . . . . . 4
3.1. Introduction . . . . . . . . . . . . . . . . . . . . . . . 4
3.2. New Return Codes . . . . . . . . . . . . . . . . . . . . . 5
3.2.1. Return code per downstream . . . . . . . . . . . . . . 5
3.2.2. Return code for stitched LSPs . . . . . . . . . . . . 5
3.3. Downstream Detailed Mapping TLV . . . . . . . . . . . . . 5
3.3.1. Multipath data sub-TLV . . . . . . . . . . . . . . . . 7
3.3.2. Label stack sub-TLV . . . . . . . . . . . . . . . . . 8
3.3.3. FEC Stack change sub-TLV . . . . . . . . . . . . . . . 8
3.4. Deprecation of Downstream Mapping TLV . . . . . . . . . . 10
4. Performing lsp-ping traceroute on tunnels . . . . . . . . . . 11
4.1. Transit node procedure . . . . . . . . . . . . . . . . . . 11
4.1.1. Addition of a new tunnel . . . . . . . . . . . . . . . 11
4.1.2. Transition between tunnels . . . . . . . . . . . . . . 11
4.2. Ingress node procedure . . . . . . . . . . . . . . . . . . 13
4.2.1. Processing Downstream Detailed Mapping TLV . . . . . . 13
4.2.1.1. Stack Change sub-TLV not present . . . . . . . . . 14
4.2.1.2. Stack Change sub-TLV(s) present . . . . . . . . . 14
4.2.3. Handling of new return codes . . . . . . . . . . . . . 16
4.3. Handling deprecated Downstream Mapping TLV . . . . . . . . 16
5. Security Considerations . . . . . . . . . . . . . . . . . . . 17
6. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 18
7. Acknowledgements . . . . . . . . . . . . . . . . . . . . . . . 19
8. References . . . . . . . . . . . . . . . . . . . . . . . . . . 19
8.1. Normative References . . . . . . . . . . . . . . . . . . . 19
8.2. Informative References . . . . . . . . . . . . . . . . . . 19
Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . . 19
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1. Introduction
This documents describes methods for performing lsp-ping traceroute
over mpls tunnels. The techniques outlined in [RFC4379] outline a
traceroute mechanism that includes FEC validation and ECMP path
discovery. Those mechanisms are insufficient and do not provide
details in case the FEC being traced traverses one or more mpls
tunnels and in case where LSP stitching is in use. This document
defines enhancements to the downstream-mapping TLV [RFC4379] to make
it more extensible and to enable retrieval of detailed information.
Using the enhanced TLV format along with the existing definitions of
[RFC4379], this document describes procedures by which a traceroute
request can correctly traverse mpls tunnels with proper FEC and label
validations.
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].
2. Motivation
A LSP-Ping traceroute may cross multiple mpls tunnels en-route the
destination. Let us consider a simple case.
A B C D E
o -------- o -------- o --------- o --------- o
\_____/ | \______/ \______/ | \______/
LDP | RSVP RSVP | LDP
| |
\____________________/
LDP
Figure 1: LDP over RSVP tunnel
When a traceroute is initiated from router A, router B returns
downstream mapping information for node C in the echo-response. The
next echo request reaches router C with a LDP FEC. Node C is a pure
RSVP node and does not run LDP. Node C will receive the packet with
2 labels but only 1 FEC in the Target FEC stack. Consequently, node
C will be unable to perform FEC complete validation. It will let the
trace continue by just providing next-hop information based on
incoming label, and by looking up the forwarding state associated
with that label. However, ignoring FEC validation defeats the
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purpose of control plane validatations. The echo request should
contain sufficient information to allow node C to perform FEC
validations to catch any misrouted echo-requests.
The above problem can be extended for a generic case of tunnel over
tunnel or multiple tunnels (e.g. B-C can be a separate RSVP tunnel
and C-D can be a separate RSVP tunnel). The problem of FEC
validation for tunnels can be solved if the transit routers (router B
in the above example) provide some hint or information to the ingress
regarding the start of a new tunnel.
Stitched LSPs involve 2 or more LSP segments stitched together. The
LSP segments can be signaled using the same or different signaling
protocols. In order to perform an end-to-end trace of a stitched
LSP, the ingress needs to know FEC information regarding each of the
stitched LSP segments. For example, conside the figure below.
A B C D E F
o -------- o -------- o --------- o -------- o ------- o
\_____/ \______/ \______/ \______/ \_______/
LDP LDP BGP RSVP RSVP
Figure 2: Stitched LSP
Consider ingress (A) tracing end-to-end LSP A--F. When an echo
request reaches router C, there is a FEC stack change happening at
router C. With current lsp-ping mechanisms, there is no way to convey
this information to A. Consequently, when the next echo request
reaches router D, router D will know nothing about the LDP FEC that A
is trying to trace.
Thus, the procedures outlined [RFC4379] do not make it possible for
the ingress node to:
1. Know that tunneling has occured
2. Trace the path of the tunnel
3. Trace the path of stitched LSPs
3. Packet format
3.1. Introduction
In many cases there has been a need to associate additional data in
the lsping echo response. In most cases, the additional data needs
to be associated on a per downstream neighbor basis. Currently, the
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echo response contains 1 downstream map TLV (DSMAP) per downstream
neighbor. But the DSMAP format is not extensible and hence it's not
possible to associate more information with a downstream neighbor.
This draft defines a new extensible format for the DSMAP and provides
mechanisms for solving the tunneled lsp-ping problem using the new
format. In summary, the draft makes the following TLV changes:
o Addition of new Downstream Detailed Mapping TLV (DDMAP).
o Deprecation of existing Downstream Mapping TLV.
o Addition of Downstream FEC Stack Change Sub-TLV to DDMAP.
3.2. New Return Codes
3.2.1. Return code per downstream
A new return code is being defined "See DDM TLV for Return Code and
Return SubCode" (Section 6.3) to indicate that the return code is per
Detailed Downstream Mapping TLV (Section 3.3). This return code MUST
be used only in the message header and MUST be set only in the echo
response message. If the return code is set in the echo request
message, then it SHOULD be ignored. When this return code is set,
each Detailed Downstream Mapping TLV MUST have an appropriate return
code and return subcode. This return code is to be used when there
are multiple downstreams for a given node (such as P2MP or ECMP), and
the node wants to return a different return code/return subcode for
each downstream.
3.2.2. Return code for stitched LSPs
When a traceroute is being performed on stitched LSPs Figure 10, the
stitching point SHOULD indicate the stitching action to the node
performing the trace. This is done by setting the return code to
"Label switched with FEC change" (Section 6.3). If a node is
performing FEC hiding, then it MAY choose to set the return code to a
value other than "Label switched with FEC change". This return code
MUST NOT be used if no Label Stack sub-TLVs (Section 3.3.3) are
present in the Detailed Downstream Mapping TLV(s). This new return
code MAY be used for hierarchical LSPs (for indicating start or end
of an outer LSP).
3.3. Downstream Detailed Mapping TLV
A new TLV has been added to the mandatory range of TLVs. The TLV
type is pending IANA allocation.
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Type # Value Field
------ ------------
TBD Downstream detailed mapping
Figure 3
The Downstream Detailed Mapping object is a TLV that MAY be included
in an echo request message. Only one Downstream Detailed Mapping
object may appear in an echo request. The presence of a Downstream
Mapping object is a request that Downstream Detailed Mapping objects
be included in the echo reply. If the replying router is the
destination of the FEC, then a Downstream Detailed Mapping TLV SHOULD
NOT be included in the echo reply. Otherwise the replying router
SHOULD include a Downstream Detailed Mapping object for each
interface over which this FEC could be forwarded.
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 2
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| MTU | Address Type | DS Flags |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Downstream IP Address (4 or 16 octets) |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Downstream Interface Address (4 or 16 octets) |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Return Code | Return SubCode| Sub-tlv length |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
. .
. List of Sub TLVs .
. .
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
Figure 4: Downstream Detailed Mapping TLV
The Downstream Detailed Mapping TLV format is derived from the
Downstream Mapping TLV format. The key change is that variable
length and optional fields have been coverted into sub-TLVs. The
fields have the same use and meaning as in [RFC4379]. The newly
added sub-TLVs and their fields are as described below.
Return code
The Return Code and Return SubCode are set to zero by the sender.
The receiver can set it to one of the values specified in the
"Multi-Protocol Label Switching (MPLS) Label Switched Paths (LSPs)
Parameters" registry, "Return Codes" sub-registry. The notation
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<RSC> refers to the Return Subcode. This field is filled in with
the stack-depth for those codes that specify that. For all other
codes, the Return Subcode MUST be set to zero.
If the receiver sets the value of Return Code and Return SubCode
in the Downstream Detailed Mapping TLV, then the receiver MUST set
the Return Code in the echo response header to "See DDM TLV for
Return Code and Return SubCode" Section 6.3).
If the Return Code of the echo response message is not set to "See
DDM TLV for Return Code and Return SubCode" Section 6.3, then the
Return Code and Return SubCode specified in the Downstream
Detailed Mapping TLV SHOULD be ignored.
Sub-tlv length
Total length in bytes of the sub-TLVs associated with this TLV.
Sub-Type Value Field
--------- ------------
TBD Multipath data
TBD Label stack
TBD FEC Stack change
Figure 5: Downstream Detailed Mapping Sub-TLV List
3.3.1. Multipath data sub-TLV
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 2
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
|Multipath Type | Multipath Length |Reserved (MBZ) |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| |
| (Multipath Information) |
| |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
Figure 6: Multipath Sub-TLV
The multipath data sub-TLV includes information multipath
information. The TLV fields and their usage is as defined in
[RFC4379].
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3.3.2. Label stack sub-TLV
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 2
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Downstream Label | Protocol |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
. .
. .
. .
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Downstream Label | Protocol |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
Figure 7: Label Stack Sub-TLV
The Label stack sub-TLV contains the set of labels in the label stack
as it would have appeared if this router were forwarding the packet
through this interface. Any Implicit Null labels are explicitly
included. The number of labels present in the sub-TLV is determined
based on the sub-TLV data length. Labels are treated as numbers,
i.e., they are right justified in the field. The label format and
protocol type are as defined in [RFC4379]. When the Detailed
Downstream Mapping TLV in sent in the echo response, this sub-TLV
MUST be included.
3.3.3. FEC Stack change sub-TLV
A router SHOULD include the the FEC Stack change sub-TLV when the
downstream node in the echo response has a different FEC stack than
the FEC stack received in the echo request. One or more FEC Stack
change sub-TLVs MAY be present in the Downstream Detailed Mapping
TLV. The format is as below.
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 2
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
|Operation Type | Address type | FEC-tlv length| Reserved |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Remote Peer Address (0, 4 or 16 octets) |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
. .
. FEC TLV .
. .
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
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Figure 8: FEC Stack Change Sub-TLV
Operation Type
The operation type specifies the action associated with the FEC
stack change. The following operation types are defined.
Type # Operation
------ ---------
1 Push
2 Pop
3 Swap
Operation Type Values
A FEC Stack change sub-TLV containing a PUSH operation MUST NOT be
followed by a FEC Stack change sub-TLV containing a POP operation.
One or more POP operations MAY be followed by one or more PUSH
operations. One FEC Stack change sub-TLV MUST be included per FEC
stack change. For example, if 2 labels are going to be pushed,
then 1 FEC Stack change sub-TLV MUST be included for each FEC. A
FEC splice operation (an operation where 1 FEC ends and another
FEC starts, see Figure 10) SHOULD be performed by including a POP
type FEC Stack change sub-TLV followed by a PUSH type FEC Stack
change sub-TLV.
A Downstream detailed mapping TLV containing only 1 FEC change
sub-TLV with Pop operation is equivalent to EGRESS_OK for the
outermost FEC in the FEC stack. The ingress router performing the
lsp trace MUST treat such a case as an EGRESS_OK for the outermost
FEC.
The Downstream Detailed Mapping TLV MUST contain at most 1 FEC
Stack change sub-TLV of type Swap. In a FEC Stack change sub-TLV
with Swap operation, the address-type MAY be set to Unspecified
and the FEC-tlv length MAY be set to 0.
FEC tlv Length
Length in bytes of the FEC TLV.
Address Type
The Address Type indicates the remote peer's address type. The
Address Type is set to one of the following values. The peer
address length is determined based on the address type. The
address type MAY be different from the address type included in
the Downstream Detailed Mapping TLV. This can happen in case the
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LSP goes over a tunnel of a different address family. The address
type MAY be set to Unspecified if the peer-address is either
unavailable or the transit router does not wish it provide it for
security or administrative reasons.
Type # Address Type Address length
------ ------------ --------------
0 Unspecified 0
1 IPv4 4
2 IPv6 16
Figure 9: Remote peer address type
Remote peer address
The remote peer address specifies the remote peer which is the
next-hop for the FEC being currently traced. E.g. In the LDP
over RSVP case Figure 1, router B would respond back with the
address of router D as the remote peer address for the LDP FEC
being traced. This allows the ingress node to provide helpful
information regarding FEC peers. If the operation type is PUSH,
the remote peer address is the address of the peer from which the
FEC was learned. If the operation type is POP, the remote peer
address MAY be set to Unspecified. For upstream assigned labels
[RFC5331], an operation type of POP will have a remote peer
address (the upstream node that assigned the label) and this
SHOULD be included in the FEC Stack change sub-TLV.
FEC TLV
The FEC TLV is present only when FEC-tlv length field is non-zero.
The FEC TLV specifies the FEC associated with the FEC stack change
operation. This TLV MAY be included when the operation type is
POP. It SHOULD be included when the operation type is PUSH. The
FEC TLV contains exactly 1 FEC from the list of FECs specified in
[RFC4379]. A NIL FEC MAY be associated with a PUSH operation if
the responding router wishes to hide the details of the FEC being
pushed.
3.4. Deprecation of Downstream Mapping TLV
The Downstream Mapping TLV has been deprecated. LSP-ping procedures
should now use the Downstream Detailed Mapping TLV. Detailed
procedures regarding interoperability between the deprecated TLV and
the new tlv are specified in Section 4.3.
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4. Performing lsp-ping traceroute on tunnels
This section describes the procedures to be followed by an ingress
node and transit nodes when performing lsp-ping traceroute over mpls
tunnels.
4.1. Transit node procedure
4.1.1. Addition of a new tunnel
A transit node (Figure 1) knows when the FEC being traced is going to
enter a tunnel at that node. Thus, it knows about the new outer FEC.
All transit nodes that are the origination point of a new tunnel
SHOULD add the a FEC Stack change sub-TLV (Section 3.3.3) to the
Downstream Detailed Mapping TLV (Figure 4) in the echo-response. The
transit node SHOULD add 1 FEC Stack change sub-TLV of operation type
PUSH, per new tunnel being originated at the transit node.
A transit node that sends a Downstream FEC Stack change sub-TLV in
the echo response SHOULD fill the address of the remote peer; which
is the peer of the current LSP being traced. If the transit node
does not know the address of the remote peer, it MAY leave it as
unspecified.
If the transit node wishes to hide the nature of the tunnel from the
ingress of the echo-request, then it MAY not want to send details
about the new tunnel FEC to the ingress. In such a case, the transit
node SHOULD use the NIL FEC. The echo response would then contain a
FEC Stack change sub-TLV with operation type PUSH and a NIL FEC. The
value of the label in the NIL FEC MUST be set to zero. The remote
peer address length MUST be set to 0 and the remote peer address type
MUST be set to Unspecified. The transit node SHOULD add 1 FEC Stack
change sub-TLV of operation type PUSH, per new tunnel being
originated at the transit node.
4.1.2. Transition between tunnels
A B C D E F
o -------- o -------- o --------- o -------- o ------- o
\_____/ \______/ \______/ \______/ \_______/
LDP LDP BGP RSVP RSVP
Figure 10: Stitched LSPs
In the above figure, we have 3 seperate LSP segments stitched at C
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and D. Node C SHOULD include 2 FEC Stack change sub-TLVs. One with a
POP operation for the LDP FEC and one with the PUSH operation for the
BGP FEC. Similarly, node D SHOULD include 2 FEC Stack change sub-
TLVs, one with a POP operation for the BGP FEC and one with a PUSH
operation for the RSVP FEC. Nodes C and D SHOULD set the return code
to "Label switched with FEC change" (Section 6.3) to indicate change
in FEC being traced.
If node C wishes to perform FEC hiding, it SHOULD respond back with 2
FEC Stack change sub-TLVs. One POP followed by 1 PUSH. The POP
operation MAY either exclude the FEC TLV (by setting FEC TLV length
to 0) or set the FEC TLV to contain the LDP FEC. The PUSH operation
SHOULD have the FEC TLV containing the NIL FEC. The return code
SHOULD be set to "Label switched with FEC change".
If node C performs FEC hiding and node D also performs FEC hiding,
then node D MAY choose to not send any FEC Stack change sub-TLVs in
the echo response since the number of labels has not changed (for the
downstream of node D) and the FEC type also has not changed (NIL
FEC). In such a case, node D MUST NOT set the return code to "Label
switched with FEC change". If node D performs FEC hiding, then node
F will respond as EGRESS_OK for the NIL FEC. The ingress (node A)
will know that EGRESS_OK corresponds to the end-to-end LSP.
A B C D E F
o -------- o -------- o --------- o --------- o --------- o
\_____/ |\____________________/ |\_______/
LDP |\ RSVP-A | LDP
| \_______________________________/|
| RSVP-B |
\________________________________/
LDP
Figure 11: Hierarchical LSPs
In the above figure, the following sequence of FEC Stack change sub-
TLVs will be performed
Node B:
Respond with 2 FEC Stack change sub-TLVs: PUSH RSVP-B, PUSH RSVP-A.
Node D:
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Respond with a return code of EGRESS_OK when RSVP-A is top of FEC
stack. Downstream information for node E when echo request contains
RSVP-B as top of FEC stack and an appropriate return code.
If node B is performing tunnel hiding, then:
Node B:
Respond with 2 FEC Stack change sub-TLVs: PUSH NIL-FEC, PUSH NIL-FEC.
Node D:
Respond with either return code of EGRESS_OK (if D can co-relate that
the NIL-FEC corresponds to RSVP-A which is terminating at D) or
respond with FEC Stack change sub-TLV: POP (since D knows that number
of labels towards next-hop is decreasing).
A B C D E F G
o -------- o -------- o ------ o ------ o ----- o ----- o
LDP LDP BGP \ RSVP RSVP / LDP
\_____________/
LDP
Figure 12: Stitched hierarchical LSPs
In the above case, node D will send 3 FEC Stack change sub-TLVs. One
POP (for the BGP FEC) followed by 2 PUSHes (one for LDP and one for
RSVP). Nodes C and D SHOULD set the return code to "Label switched
with FEC change" (Section 6.3) to indicate change in FEC being
traced.
4.2. Ingress node procedure
It is the responsibility of an ingress node to understand tunnel
within tunnel semantics and lsp stitching semantics when performing a
lsp traceroute. This section describes the ingress node procedure
based on the kind of response an ingress node receives from a transit
node.
4.2.1. Processing Downstream Detailed Mapping TLV
Downstream Detailed Mapping TLV should be processed in procedures
similar to those of Downstream Mapping TLV, defined in Section 4.4 of
[RFC4379]
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4.2.1.1. Stack Change sub-TLV not present
This would be the default behavior as described in [RFC4379]. The
ingress node MUST perform echo response processing as per the
procedures in [RFC4379].
4.2.1.2. Stack Change sub-TLV(s) present
If one or more FEC Stack change sub-TLVs (Section 3.3.3) are received
in the echo response, the ingress node SHOULD process them and
perform some validation.
The FEC stack changes are associated with a downstream neighbor and
along a particular path of the LSP. Consequently, the ingress will
need to maintain a FEC-stack per path being traced (in case of
multipath). All changes to the FEC stack resulting from the
processing of FEC Stack change sub-TLV(s) should be applied only for
the path along a given downstream neighbor. The following algorithm
should be followed for processing FEC Stack change sub-TLVs.
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push_seen = FALSE
fec_stack_depth = current-depth-of-fec-stack-being-traced
saved_fec_stack = current_fec_stack
while (sub-tlv = get_next_sub_tlv(downstream_detailed_map_tlv))
if (sub-tlv == NULL) break
if (sub-tlv.type == FEC-Stack-Change) {
if (sub-tlv.operation == POP) {
if (push_seen) {
Drop the echo response
current_fec_stack = saved_fec_stack
return
}
if (fec_stack_depth == 0) {
Drop the echo response
current_fec_stack = saved_fec_stack
return
}
Pop FEC from FEC stack being traced
fec_stack_depth--;
}
if (sub-tlv.operation == PUSH) {
push_seen = 1
Push FEC on FEC stack being traced
fec_stack_depth++;
}
}
}
if (fec_stack_depth == 0) {
Drop the echo response
current_fec_stack = saved_fec_stack
return
}
Figure 13: FEC Stack Change Sub-TLV Processing Guideline
The next echo request along the same path should use the modified FEC
stack obtained after processing the FEC Stack change sub-TLVs. A
non-NIL FEC guarantees that the next echo request along the same path
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will have the Downstream Detailed Mapping TLV validated for IP
address, Interface address and label stack mismatches.
If the top of the FEC stack is a NIL FEC and the echo response does
not contain any FEC Stack change sub-TLV, then it does not
necessarily mean that the LSP has not started traversing a different
tunnel. It could be that the LSP associated with the NIL FEC
terminated at a transit node and at the same time a new LSP started
at the same transit node. The NIL FEC would now be associated with
the new LSP (and the ingress has no way of knowing this). Thus, it
is not possible to build an accurate hierarchical LSP topology if a
traceroute contains NIL FECs.
4.2.2. Modifications to handling to EGRESS_OK responses.
The procedures above allow the addition of new FECs to the original
FEC being traced. Consequently, the EGRESS_OK response from a
downstream node may not necessarily be for the FEC being traced. It
could be for one of the new FECs that was added. On receipt of an
EGRESS_OK response, the ingress should check if the depth of Target
FEC sent to the node that just responded, was the same as the depth
of the FEC that was being traced. If it was not, then it should pop
the an entry from the Target FEC stack and resend the request with
the same TTL (as previously sent). The process of popping a FEC is
to be repeated until either the ingress receives a non-EGRESS_OK
response or until all the additional FECs added to the FEC stack have
already been popped. Using EGRESS_OK responses, an ingress can build
a map of the hierarchical LSP structure traversed by a given FEC.
4.2.3. Handling of new return codes
When the echo response return code is "Label switched with FEC
change" (Section 3.2.2), the ingress node SHOULD manipulate the FEC
stack as per the FEC Stack change sub-TLVs contained in the detailed
downstream mapping TLV. A transit node can use this return code for
stitched LSPs and for hierarchical LSPs. In case of ECMP or P2MP,
there could be multiple paths and detailed downstream mapping TLVs
with different return codes (Section 3.2.1). The ingress node should
build the topology based off the return code per ECMP path/P2MP
branch.
4.3. Handling deprecated Downstream Mapping TLV
The Downstream Mapping TLV has been deprecated. Applications should
now use the Downstream Detailed Mapping TLV. The following
procedures SHOULD be used for backward compatibility with routers
that do not support the Downstream Detailed Mapping TLV.
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o The Downstream Mapping TLV and the Downstream Detailed Mapping TLV
MUST never be sent together in the same echo request or in the
same echo response.
o If the echo request contains a Downstream Detailed Mapping TLV and
the corresponding echo response contains an error code of 2 (one
or more of the TLVs was not understood), then the sender of the
echo request MAY resend the echo request with the Downstream
Mapping TLV (instead of the Downstream Detailed Mapping TLV). In
cases where a detailed response is needed, the sender can choose
to ignore the router that does not support the Downstream Detailed
Mapping TLV.
o If the echo request contains a Downstream Mapping TLV, then a
Downstream Detailed Mapping TLV MUST NOT be sent in the echo
response. This is to handle the case that the sender of the echo
request does not support the new TLV.
o If echo request forwarding is in use; such that the echo request
is processed at an intermediate router and then forwarded on; then
the intermediate router is responsible for making sure that the
TLVs being used among the ingress, intermediate and destination
are consistent. The intermediate router MUST NOT forward an echo
request or an echo response containing a Downstream Detailed
Mapping TLV if it itself does not support that TLV.
5. Security Considerations
Tracing inside a tunnel might have some security implications. There
are different ways to prevent tracing tunnel details.
1. If one wants to prevent tracing inside a tunnel, one can hide the
outer MPLS tunnel by not propagating the MPLS TTL into the outer
tunnel (at the start of the outer tunnel). By doing this, lsp-
ping packets will not expire in the outer tunnel and the outer
tunnel will not get traced. TTL hiding can be imposed on a per
LSP basis, as need be.
2. If one doesn't wish to expose the details of the new outer LSP,
then the NIL FEC can be used to hide those details. Using the
NIL FEC ensures that the trace progresses without false negatives
and all transit nodes (of the new outer tunnel) perform some
minimal validations on the received echo requests.
In inter-AS (autonomous system) scenarios, information regarding the
LSP FEC change(s) SHOULD NOT be passed across domains. A NIL FEC MAY
be used to make the trace go through without false positives. An
ASBR (autonomous system border router) may choose to intercept all
echo requests and echo responses and change them to hide FEC
information from other domains. Detailed operation regarding the
same is outside the scope of this document. Passing of FEC stack
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change information between domains MAY be done if the two AS domains
belong to the same provider/organization.
Other security considerations, as discussed in [RFC4379] are also
applicable to this document.
6. IANA Considerations
6.1. New TLV
IANA is requested to assign TLV type value to the following TLV from
the "Multiprotocol Label Switching Architecture (MPLS) Label Switched
Paths (LSPs) Parameters - TLVs" registry, "TLVs and sub-TLVs" sub-
registry.
Downstream Detailed Mapping TLV (See Section 3.3). Suggested value:
20.
6.2. New Sub-TLV types and associated registry
IANA is requested to create a new registry for the Sub-Type field of
Downstream Detailed Mapping TLV. The valid range for this is
0-65535. Assignments in the range 0-16383 and 32768-49161 are made
via Standards Action as defined in [RFC3692]; assignments in the
range 16384-31743 and 49162-64511 are made via Specification Required
([RFC4379]); values in the range 31744-32767 and 64512-65535 are for
Vendor Private Use, and MUST NOT be allocated. If a sub-TLV has a
Type that falls in the range for Vendor Private Use, the Length MUST
be at least 4, and the first four octets MUST be that vendor's SMI
Enterprise Code, in network octet order. The rest of the Value field
is private to the vendor.
It is requested that IANA assign sub-TLV types from this new registry
to the following sub-TLVs (See Figure 5).
Multipath data sub-TLV: Suggested value: 1
Label stack sub-TLV: Suggested value: 2
FEC Stack change sub-TLV: Suggested value: 3
6.3. New Return Codes
IANA is requested to assign new Return Code values from the "Multi-
Protocol Label Switching (MPLS) Label Switched Paths (LSPs)
Parameters" registry, "Return Codes" sub-registry as follows using a
Standards Action value.
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Value Meaning
----- -------
TBD See DDM TLV for Return Code and Return SubCode
TBD Label switched with FEC change
Suggested values: 14 and 15 respectively
7. Acknowledgements
The authors would like to thank Yakov Rekhter and Adrian Farrel for
their suggestions on the draft.
8. References
8.1. Normative References
[RFC2119] Bradner, S., "Key words for use in RFCs to Indicate
Requirement Levels", BCP 14, RFC 2119, March 1997.
[RFC3692] Narten, T., "Assigning Experimental and Testing Numbers
Considered Useful", BCP 82, RFC 3692, January 2004.
[RFC4379] Kompella, K. and G. Swallow, "Detecting Multi-Protocol
Label Switched (MPLS) Data Plane Failures", RFC 4379,
February 2006.
8.2. Informative References
[RFC5331] Aggarwal, R., Rekhter, Y., and E. Rosen, "MPLS Upstream
Label Assignment and Context-Specific Label Space",
RFC 5331, August 2008.
Authors' Addresses
Nitin Bahadur
Juniper Networks, Inc.
1194 N. Mathilda Avenue
Sunnyvale, CA 94089
US
Phone: +1 408 745 2000
Email: nitinb@juniper.net
URI: www.juniper.net
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Kireeti Kompella
Juniper Networks, Inc.
1194 N. Mathilda Avenue
Sunnyvale, CA 94089
US
Phone: +1 408 745 2000
Email: kireeti@juniper.net
URI: www.juniper.net
George Swallow
Cisco Systems
1414 Massachusetts Ave
Boxborough, MA 01719
US
Email: swallow@cisco.com
URI: www.cisco.com
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