Network Working Group A. Ayyangar, Ed.
Internet-Draft Juniper Networks
Expires: September 6, 2006 JP. Vasseur
Cisco Systems, Inc.
March 5, 2006
Label Switched Path Stitching with Generalized MPLS Traffic Engineering
draft-ietf-ccamp-lsp-stitching-03.txt
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Abstract
In certain scenarios, there may be a need to combine together
different Generalized Multi-Protocol Label Switching (GMPLS) Label
Switched Paths (LSPs) such that in the data plane, a single end-to-
end (e2e) LSP is realized and all traffic from one LSP is switched
onto the other LSP. We will refer to this as "LSP stitching". This
document covers cases where: a) the node performing the stitching
does not require configuration of every LSP pair to be stitched
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together b) the node performing the stitching is not the egress of
any of the LSPs c) LSP stitching not only results in an end-to-end
LSP in the data plane, but there is also a corresponding end-to-end
LSP (RSVP session) in the control plane.
It may be possible to configure a GMPLS node to switch the traffic
from an LSP for which it is the egress, to another LSP for which it
is the ingress, without requiring any signaling or routing extensions
whatsoever, completely transparent to other nodes. This will also
result in LSP stitching in the data plane. However, this document
does not cover this scenario of LSP stitching.
Table of Contents
1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . . 3
1.1. Conventions used in this document . . . . . . . . . . . . 3
2. Comparison with LSP Hierarchy . . . . . . . . . . . . . . . . 4
3. Usage . . . . . . . . . . . . . . . . . . . . . . . . . . . . 5
3.1. Triggers for LSP segment setup . . . . . . . . . . . . . . 5
3.2. Applications . . . . . . . . . . . . . . . . . . . . . . . 5
4. Routing aspects . . . . . . . . . . . . . . . . . . . . . . . 6
5. Signaling aspects . . . . . . . . . . . . . . . . . . . . . . 7
5.1. RSVP-TE signaling extensions . . . . . . . . . . . . . . . 7
5.1.1. Creating and preparing LSP segment for stitching . . . 7
5.1.2. Stitching the e2e LSP to the LSP segment . . . . . . . 9
5.1.3. RRO Processing for e2e LSP . . . . . . . . . . . . . . 10
5.1.4. Teardown of LSP segment . . . . . . . . . . . . . . . 11
5.1.5. Teardown of e2e LSP . . . . . . . . . . . . . . . . . 11
5.2. Summary of LSP Stitching procedures . . . . . . . . . . . 12
5.2.1. Example topology . . . . . . . . . . . . . . . . . . . 12
5.2.2. LSP segment setup . . . . . . . . . . . . . . . . . . 12
5.2.3. Setup of e2e LSP . . . . . . . . . . . . . . . . . . . 13
5.2.4. Stitching of e2e LSP into an LSP segment . . . . . . . 13
6. Security Considerations . . . . . . . . . . . . . . . . . . . 14
7. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 15
7.1. Attribute Flags for LSP_ATTRIBUTES object . . . . . . . . 15
7.2. New Error Codes . . . . . . . . . . . . . . . . . . . . . 15
8. Acknowledgments . . . . . . . . . . . . . . . . . . . . . . . 16
9. References . . . . . . . . . . . . . . . . . . . . . . . . . . 17
9.1. Normative References . . . . . . . . . . . . . . . . . . . 17
9.2. Informative References . . . . . . . . . . . . . . . . . . 17
Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . . 19
Intellectual Property and Copyright Statements . . . . . . . . . . 20
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1. Introduction
This document describes the mechanisms to accomplish LSP stitching in
the scenarios described above.
LSP hierarchy ([2]) provides signaling and routing procedures so
that:
a. A Hierarchical LSP (H-LSP) can be created. Such an LSP created
in one layer can provide a data link to LSPs in higher layers.
Also one or more LSPs can be nested into this H-LSP.
b. An H-LSP may be managed and advertised (although this is not a
requirement) as a Traffic Engineering (TE) link. Advertising an
H-LSP as a TE link allows other nodes in the TE domain in which
it is advertised to use this H-LSP in path computation. If the
H-LSP TE link is advertised in the same instance of control plane
(TE domain) in which the H-LSP was provisioned, it is then
defined as a forwarding adjacency LSP (FA-LSP) and GMPLS nodes
can form a forwarding adjacency (FA) over this FA-LSP. There is
usually no routing adjacency between end points of an FA. An
H-LSP may also be advertised as a TE link in a different TE
domain. In this case, the end points of the H-LSP are required
have a routing adjacency between them.
c. RSVP signaling for LSP setup can occur between nodes that do not
have a routing adjacency.
A stitched TE LSP comprises of different LSP segments (S-LSPs) that
are connected together in the data plane in such a way that a single
end-to-end LSP is realized in the data plane. In this document, we
define the concept of LSP stitching and detail the control plane
mechanisms and procedures to accomplish this. Where applicable,
similarities and differences between LSP hierarchy and LSP stitching
are highlighted. Signaling extensions required for LSP stitching are
also described here.
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 RFC 2119 [1].
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2. Comparison with LSP Hierarchy
In case of LSP stitching, instead of an H-LSP, an "LSP segment"
(S-LSP) is created between two GMPLS nodes. An S-LSP for stitching
is considered to be the moral equivalent of an H-LSP for nesting. An
S-LSP created in one layer, unlike an H-LSP, provides a data link to
other LSPs in the same layer. Similar to an H-LSP, an S-LSP could be
managed and advertised, although it is not required, as a TE link,
either in the same TE domain as it was provisioned or a different
one. If advertised, other GMPLS nodes could used the corresponding
S-LSP TE link in path computation. While there is a forwarding
adjacency between end points of an H-LSP TE link, there is no
forwarding adjacency between end points of an S-LSP TE link. In this
aspect, an H-LSP TE link more closely resembles a 'basic' TE link as
compared to an S-LSP TE link.
While LSP hierarchy allows more than one LSP to be mapped to an
H-LSP, in case of LSP stitching, at most one LSP may be associated
with an S-LSP. E.g. if LSP-AB is an H-LSP between nodes A and B,
then multiple LSPs, say LSP1, LSP2, LSP3 could potentially be 'nested
into' LSP-AB. This is achieved by exchanging a unique label for each
of LSP1..3 over the LSP-AB hop thereby permitting LSP1..3 to share
the H-LSP LSP-AB. Each of LSP1..3 may reserve some bandwidth on
LSP-AB. On the other hand, if LSP-AB is an S-LSP, then at most one
LSP, say LSP1 may be stitched to the S-LSP LSP-AB. LSP-AB is
dedicated to LSP1 and no other LSPs can be associated with LSP-AB.
The entire bandwith on S-LSP LSP-AB is allocated to LSP1. However,
several S-LSPs MAY be bundled into a TE link ([11]), similar to
H-LSPs.
The LSPs LSP1..3 which are either nested or stitched into another LSP
are termed as end-to-end (e2e) LSPs in the rest of this document.
Routing procedures specific to LSP stitching are detailed in
Section 4.
Targetted (non-adjacent nodes) RSVP signaling defined in [2] is
required for LSP stitching of an e2e LSP to an S-LSP. Specific
extensions for LSP stitching are described later in Section 5.1.
Therefore, in the control plane, there is one RSVP session
corresponding to the e2e LSP as well as one for each S-LSP. The
creation and termination of an S-LSP may be dictated by
administrative control (statically provisioned) or due to another
incoming LSP request (dynamic). Triggers for dynamic creation of an
S-LSP may be different from that of an H-LSP and will be described in
detail later.
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3. Usage
3.1. Triggers for LSP segment setup
An S-LSP may be created either by administrative control
(configuration trigger) or dynamically due to an incoming LSP
request. LSP Hierarchy ([2]) defines one possible trigger for
dynamic creation of FA-LSP by introducing the notion of LSP regions
based on Interface Switching Capabilities. As per [2], dynamic FA-
LSP creation may be triggered on a node when an incoming LSP request
crosses region boundaries. However, this trigger MUST NOT be used
for creation of S-LSP for LSP stitching as described in this
document. In case of LSP stitching, the switching capabilities of
the previous hop and the next hop TE links MUST be the same.
Therefore, local policies configured on the node SHOULD be used for
dynamic creation of LSP segments.
Other possible triggers for dynamic creation of both H-LSPs and
S-LSPs include cases where an e2e LSP may cross domain boundaries or
satisfy locally configured policies on the node as described in [8].
3.2. Applications
LSP stitching procedures described in this document are applicable to
GMPLS nodes that need to associate an e2e LSP with another S-LSP of
the same switching type and LSP hierarchy procedures do not apply.
E.g. if an e2e lambda LSP traverses an LSP segment TE link which is
also lambda switch capable, then in this case LSP hierarchy is not
possible.
LSP stitching procedures could be used for inter-domain TE LSP
signaling to stitch an inter-domain LSP to a local intra-domain TE
S-LSP ([8]).
LSP stitching could also be useful in networks to bypass legacy nodes
which may not have certain new capabilities in the control plane
and/or data plane. E.g. one suggested usage in case of P2MP RSVP
LSPs ([7]) is the use of LSP stitching to stitch a P2MP RSVP LSP to
an LSP segment between P2MP capable LSRs in the network. The LSP
segment would traverse legacy LSRs that may be incapable of acting as
P2MP branch points, thereby shielding them from the P2MP control and
data path. Note, however, that such configuration may limit the
attractiveness of RSVP P2MP and should carefully be examined before
deployment.
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4. Routing aspects
An S-LSP is created between two GMPLS nodes and it may traverse zero
or more GMPLS nodes. There is no forwarding adjacency between the
end points of an S-LSP TE link. So, although in the TE topology, the
end points of an S-LSP TE link are adjacent, in the data plane, these
nodes do not have an adjacency. Hence any data plane resource
identifier between these nodes is also meaningless. The traffic that
arrives at the head end of the S-LSP is switched into the S-LSP
contiguously with a label swap and no label is associated directly
between the end nodes of the S-LSP itself.
An S-LSP MAY be treated and managed as a TE link. This TE link MAY
be numbered or unnumbered. For an unnumbered S-LSP TE link, the
schemes for assignment and handling of the local and remote link
identifiers as specified in [10] SHOULD be used. ISIS/OSPF may flood
the TE information associated with an S-LSP TE link, when
appropriate. Mechanisms similar to that for regular (basic) TE links
SHOULD be used to flood S-LSP TE links. Advertising or flooding the
S-LSP TE link is not a requirement for LSP stitching. Discretion
should be used when advertising an S-LSP TE link in an IGP. If
advertised, this TE information will exist in the TE database (TED)
and can then be used for path computation by other GMPLS nodes in the
TE domain in which it is advertised.
If an S-LSP is advertised as a TE link in the same TE domain in which
it was provisioned, there is no need for a routing adjacency between
end points of this S-LSP TE link. If an S-LSP TE link is advertised
in a different TE domain, the end points of that TE link SHOULD have
a routing adjacency between them.
The TE parameters defined for an FA in [2] SHOULD be used for an
S-LSP TE link as well. The switching capability of an S-LSP TE link
MUST be equal to the switching type of the underlying S-LSP; i.e. an
S-LSP TE link provides a data link to other LSPs in the same layer,
so no hierarchy is possible.
An S-LSP MUST NOT admit more than one e2e LSP into it. However,
multiple S-LSPs between the same pair of nodes MAY be bundled using
the concept of Link Bundling ([11]) into a single TE link. So, while
an S-LSP can have exactly one e2e LSP associated with it, a bundled
TE link comprising of multiple S-LSPs, MAY admit more than one e2e
LSP. When any component S-LSP is allocated for an e2e LSP, the
component's unreserved bandwidth SHOULD be set to zero and the
Minimum and Maximum LSP bandwidth of the TE link SHOULD be
recalculated. This will prevent more than one LSP from being
computed and admitted over an S-LSP.
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5. Signaling aspects
The end nodes of an S-LSP may or may not have a routing adjacency.
However, they SHOULD have a signaling adjacency (RSVP neighbor
relationship) and will exchange RSVP messages with each other. It
may, in fact, be desirable to exchange RSVP Hellos directly between
the LSP segment end points to allow support for state recovery during
Graceful Restart procedures as described in [4].
In order to signal an e2e LSP over an LSP segment, signaling
procedures described in section 8.1.1 of [2] MUST be used.
Additional signaling extensions for stitching are described in the
next section.
5.1. RSVP-TE signaling extensions
The signaling extensions described here MUST be used for stitching an
e2e packet or non-packet GMPLS LSP ([4]), to an S-LSP.
Stitching an e2e LSP to an LSP segment involves the following two
step process:
a. Creating and preparing the S-LSP for stitching by signaling the
desire to stitch between end points of the S-LSP and
b. Stitching the e2e LSP to the S-LSP
5.1.1. Creating and preparing LSP segment for stitching
If a GMPLS node desires to perform LSP stitching, then it MUST
indicate this in the Path message for the S-LSP that it plans to use
for stitching. This signaling explicitly informs the S-LSP egress
node that the ingress node is planning to perform stitching over the
S-LSP. Since an S-LSP is not conceptually different from any other
LSP, explicitly signaling 'LSP stitching desired' helps clarify the
data plane actions to be carried out when the S-LSP is used by some
other e2e LSP. Also, in case of packet LSPs, this is what allows the
egress of the S-LSP to carry out label allocation as explained below.
Also, so that the head-end node can ensure that correct stitching
actions will be carried out at the egress node, the egress node MUST
signal this information back to the head-end node in the Resv, as
explained below.
In order to request LSP stitching on the S-LSP, we define a new bit
in the Attributes Flags TLV of the LSP_ATTRIBUTES object defined in
[3]:
Bit Number 5 (TBD): LSP stitching desired bit - This bit SHOULD be
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set in the Attributes Flags TLV of the LSP_ATTRIBUTES object in the
Path message for the S-LSP by the head-end of the S-LSP, that desires
LSP stitching. This bit MUST NOT be modified by any other nodes in
the network. Nodes other than the egress of the S-LSP SHOULD ignore
this bit.
An LSP segment can be used for stitching only if the egress node of
the S-LSP is also ready to participate in stitching. In order to
indicate this to the head-end node of the S-LSP, the following new
bit is defined in the Flags field of the RRO Attributes subobject:
Bit Number 5 (TBD): LSP segment stitching ready.
If an egress node of the S-LSP receiving the Path message, supports
the LSP_ATTRIBUTES object and the Attributes Flags TLV, and also
recognizes the "LSP stitching desired" bit, but cannot support the
requested stitching behavior, then it MUST send back a PathErr
message with an error code of "Routing Problem" and an error sub-
code="Stitching unsupported" (TBD) to the head-end node of the S-LSP.
If an egress node receiving a Path message with the "LSP stitching
desired" bit set in the Flags field of received LSP_ATTRIBUTES,
recognizes the object, the TLV and the bit and also supports the
desired stitching behavior, then it MUST allocate a non-NULL label
for that S-LSP in the corresponding Resv message. Also, so that the
head-end node can ensure that the correct label (forwarding) actions
will be carried out by the egress node and that the S-LSP can be used
for stitching, the egress node MUST set the "LSP segment stitching
ready" bit defined in the Flags field of the RRO Attribute sub-
object.
Finally, if the egress node for the S-LSP supports the LSP_ATTRIBUTES
object but does not recognize the Attributes Flags TLV, or supports
the TLV as well but does not recognize this particular bit, then it
SHOULD simply ignore the above request.
An ingress node requesting LSP stitching MUST examine the RRO
Attributes sub-object Flags corresponding to the egress node for the
S-LSP, to make sure that stitching actions are carried out at the
egress node. It MUST NOT use the S-LSP for stitching if the "LSP
segment stitching ready" bit is cleared.
5.1.1.1. Steps to support Penultimate Hop Popping
Note that this section is only applicable to packet LSPs that use
Penultimate Hop Popping (PHP) at the last hop, where the egress node
distributes the Implicit NULL Label ([9]) in the Resv Label. These
steps MUST NOT be used for a non-packet LSP and for packet LSPs where
PHP is not desired.
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When the egress node of an S-LSP receives a Path message for an e2e
LSP using this S-LSP and this is a packet LSP, it SHOULD first check
if it is also the egress for the e2e LSP. If the egress node is the
egress for both the S-LSP as well as the e2e TE LSP, and this is a
packet LSP which requires PHP, then the node MUST send back a Resv
trigger message for the S-LSP with a new label corresponding to the
Implicit NULL label. Note that this operation does not cause any
traffic disruption since the S-LSP is not carrying any traffic at
this time, since the e2e LSP has not yet been established.
5.1.2. Stitching the e2e LSP to the LSP segment
When a GMPLS node receives an e2e LSP request, depending on the
applicable trigger, it may either dynamically create an S-LSP based
on procedures described above or it may map an e2e LSP to an existing
S-LSP. The switching type in the Generalized Label Request of the
e2e LSP MUST be equal to the switching type of the S-LSP. Other
constraints like ERO, bandwidth, local TE policies MUST also be used
for S-LSP selection or signaling. In either case, once an S-LSP has
been selected for an e2e LSP, the following procedures MUST be
followed in order to stitch an e2e LSP to an S-LSP.
The GMPLS node receiving the e2e LSP setup Path message MUST use the
signaling procedures described in [2] to send the Path message to the
end point of the S-LSP. In this Path message, the node MUST identify
the S-LSP in the RSVP_HOP. An egress node receiving this RSVP_HOP
should also be able to identify the S-LSP TE link based on the
information signaled in the RSVP_HOP. If the S-LSP TE link is
numbered, then the addressing scheme as proposed in [2] SHOULD be
used to number the S-LSP TE link. If the S-LSP TE link is
unnumbered, then any of the schemes proposed in [10] SHOULD be used
to exchange S-LSP TE link identifiers between the S-LSP end points.
If the TE link is bundled, the RSVP_HOP SHOULD identify the component
link as defined in [11].
In case of a bidirectional e2e TE LSP, an Upstream Label MUST be
signaled in the Path message for the e2e LSP over the S-LSP hop.
However, since there is no forwarding adjacency between the S-LSP end
points, any label exchanged between them has no significance. So the
node MAY chose any label value for the Upstream Label. The label
value chosen and signaled by the node in the Upstream Label is out of
the scope of this document and is specific to the implementation on
that node. The egress node receiving this Path message MUST ignore
the Upstream Label in the Path message over the S-LSP hop.
The egress node receiving this Path message MUST signal a Label in
the Resv message for the e2e TE LSP over the S-LSP hop. Again, since
there is no forwarding adjacency between the egress and ingress S-LSP
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nodes, any label exchanged between them is meaningless. So, the
egress node MAY choose any label value for the Label. The label
value chosen and signaled by the egress node is out of the scope of
this document and is specific to the implementation on the egress
node. The egress S-LSP node SHOULD also carry out data plane
operations so that traffic coming in on the S-LSP is switched over to
the e2e LSP downstream, if the egress of the e2e LSP is some other
node downstream. If the e2e LSP is bidirectional, this means setting
up label switching in both directions. The Resv message from the
egress S-LSP node is IP routed back to the previous hop (ingress of
the S-LSP). The ingress node stitching an e2e TE LSP to an S-LSP
MUST ignore the Label object received in the Resv for the e2e TE LSP
over the S-LSP hop. The S-LSP ingress node SHOULD also carry out
data plane operations so that traffic coming in on the e2e LSP is
switched into the S-LSP. It should also carry out actions to handle
traffic in the opposite direction if the e2e LSP is bidirectional.
Note that the label exchange procedure for LSP stitching on the S-LSP
hop, is similar to that for LSP hierarchy over the H-LSP hop. The
difference is the lack of the significance of this label between the
S-LSP end points in case of stitching. Therefore, in case of
stitching the recepients of the Label/Upstream Label MUST NOT process
these labels. Also, at most one e2e LSP is associated with one
S-LSP. If a node at the head-end of an S-LSP receives a Path Msg for
an e2e LSP that identifies the S-LSP in the ERO and the S-LSP
bandwidth has already been allocated to some other LSP, then regular
rules of RSVP-TE pre-emption apply to resolve contention for S-LSP
bandwidth. If the LSP request over the S-LSP cannot be satisfied,
then the node SHOULD send back a PathErr with the error codes as
described in [5].
5.1.3. RRO Processing for e2e LSP
RRO procedures for the S-LSP specific to LSP stitching are already
described in Section 5.1.1. In this section we will look at the RRO
processing for the e2e LSP over the S-LSP hop.
An e2e LSP traversing an S-LSP, SHOULD record in the RRO for that
hop, an identifier corresponding to the S-LSP TE link. This is
applicable to both Path and Resv messages over the S-LSP hop. If the
S-LSP is numbered, then the IPv4 or IPv6 address subobject ([5])
SHOULD be used to record the S-LSP TE link address. If the S-LSP is
unnumbered, then the Unnumbered Interface ID subobject as described
in [10] SHOULD be used to record the node's Router ID and Interface
ID of the S-LSP TE link. In either case, the RRO subobject SHOULD
identify the S-LSP TE link end point. Intermediate links or nodes
traversed by the S-LSP itself SHOULD NOT be recorded in the RRO for
the e2e LSP over the S-LSP hop.
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5.1.4. Teardown of LSP segment
S-LSP teardown follows the standard procedures defined in [5] and
[4]. This includes procedures without and with setting the
administrative status. Teardown of S-LSP may be initiated by either
the ingress, egress or any other node along the S-LSP path.
Deletion/teardown of the S-LSP SHOULD be treated as a failure event
for the e2e LSP associated with it and corresponding teardown or
recovery procedures SHOULD be triggered for the e2e LSP. In case of
S-LSP teardown for maintenance purpose, the S-LSP ingress node MAY
treat this to be equivalent to administratively shutting down a TE
link along the e2e LSP path and take corresponding actions to notify
the ingress of this event. The actual signaling procedures to handle
this event is out of the scope of this document.
5.1.5. Teardown of e2e LSP
e2e LSP teardown also follows standard procedures defined in [5] and
[4] either without or with the administrative status. Note, however,
that teardown procedures of e2e LSP and of S-LSP are independent of
each other. So, it is possible that while one LSP follows graceful
teardown with adminstrative status, the other LSP is torn down
without administrative status (using PathTear/ResvTear/PathErr with
state removal).
When an e2e LSP teardown is initiated from the head-end, and a
PathTear arrives at the GMPLS stitching node, the PathTear message
like the Path message MUST be IP routed to the LSP segment egress
node with the destination IP address of the Path message set to the
address of the S-LSP end node. Router Alert MUST be off and RSVP TTL
check MUST be disabled on the receiving node. PathTear will result
in deletion of RSVP states corresponding to the e2e LSP and freeing
of label allocations and bandwidth reservations on the S-LSP. The
unreserved bandwidth on the S-LSP TE link SHOULD be re-adjusted.
Similarly, a teardown of the e2e LSP may be initiated from the tail-
end either using a ResvTear or a PathErr with state removal. The
egress of the S-LSP MUST propagate the ResvTear/PathErr upstream, IP
routed to the ingress of the LSP segment.
Graceful LSP teardown using ADMIN_STATUS as described in [4] is also
applicable to stitched LSPs.
If the S-LSP was statically provisioned, tearing down of an e2e LSP
MAY not result in tearing down of the S-LSP. If, however, the S-LSP
was dynamically setup due to the e2e LSP setup request, then
depending on local policy, the S-LSP MAY be torn down if no e2e LSP
is utilizing the S-LSP. Although the S-LSP may be torn down while
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the e2e LSP is being torn down, it is RECOMMENDED that a delay be
introduced in tearing down the S-LSP once the e2e LSP teardown is
complete, in order to reduce the simultaneous generation of RSVP
errors and teardown messages due to multiple events. The delay
interval may be set based on local implementation. The RECOMMENDED
interval is 30 seconds.
5.2. Summary of LSP Stitching procedures
5.2.1. Example topology
The following topology will be used for the purpose of examples
quoted in the following sections.
e2e LSP
++++++++++++++++++++++++++++++++++> (LSP1-2)
LSP segment (S-LSP)
=====================> (LSP-AB)
C --- E --- G
/|\ | / |\
/ | \ | / | \
R1 ---- A \ | \ | / | / B --- R2
\| \ |/ |/
D --- F --- H
PATH
======================> (LSP stitching desired)
RESV
<====================== (LSP segment stitching ready)
PATH (Upstream Label)
+++++++++++++++++++++++
++++++ +++++>
<++++++ ++++++
+++++++++++++++++++++++
RESV (Label)
5.2.2. LSP segment setup
Let us consider an S-LSP LSP-AB being setup between two nodes A and B
which are more than one hop away. Node A sends a Path message for
the LSP-AB with "LSP stitching desired" set in Flags field of
LSP_ATTRIBUTES object. If the egress node B is ready to carry out
stitching procedures, then B will respond with "LSP segment stitching
ready" set in the Flags field of the RRO Attributes subobject, in the
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RRO sent in the Resv for the S-LSP. Once A receives the Resv for
LSP-AB and sees this bit set in the RRO, it can then use LSP-AB for
stitching. A cannot use LSP-AB for stitching if the bit is cleared
in the RRO.
5.2.3. Setup of e2e LSP
Let us consider an e2e LSP LSP1-2 starting one hop before A on R1 and
ending on node R2, as shown above. If the S-LSP has been adevrtised
as a TE link in the TE domain, and R1 and A are in the same domain,
then R1 may compute a path for LSP1-2 over the S-LSP LSP-AB and
identify the LSP-AB hop in the ERO. If not, R1 may compute hops
between A and B and A may use these ERO hops for S-LSP selection or
signaling a new S-LSP. Also, an S-LSP TE link cannot be
distinguished from any basic TE link on R1. If R1 and A are in
different domains, then LSP1-2 is an inter-domain LSP. In this case,
S-LSP LSP-AB, similar to any other basic TE link in the domain will
not be advertised outside the domain. R1 would use either per-domain
path computation ([12]) or PCE based computation ([13]) for LSP1-2.
5.2.4. Stitching of e2e LSP into an LSP segment
When the Path message for the e2e LSP LSP1-2 arrives at node A, A
matches the switching type of LSP1-2 with the S-LSP LSP-AB. If the
switching types are not equal, then LSP-AB cannot be used to stitch
LSP1-2. Once S-LSP LSP-AB to stitch LSP1-2 to has been determined
successfully, the Path message for LSP1-2 is IP routed to node B with
the IF_ID RSVP_HOP identifying the S-LSP LSP-AB. When B receives
this Path message for LSP1-2, if B is also the egress for LSP1-2, and
if this is a packet LSP requiring PHP, then B will send a Resv
refresh for LSP-AB with the NULL Label. In this case, since B is not
the egress, the Path message for LSP1-2 is propagated to R2. The
Resv for LSP1-2 from B is IP routed back to A with a Label value
chosen by B. B also sets up its data plane to swap the Label sent to
either G or H on the S-LSP with the Label received from R2. Node A
ignores the Label on receipt of the Resv message and then propagates
the Resv to R1. A also sets up its data plane to swap the Label sent
to R1 with the Label received on the S-LSP from C or D. This stitches
the e2e LSP LSP1-2 to an S-LSP LSP-AB between nodes A and B. In the
data plane, this yields a series of label swaps from R1 to R2 along
e2e LSP LSP1-2.
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6. Security Considerations
Similar to [2], this document permits that the control interface over
which RSVP messages are sent or received need not be the same as the
data interface which the message identifies for switching traffic.
Also, the 'sending interface' and 'receiving interface' may change as
routing changes. So, these cannot be used to establish security
association between neighbors. Mechanisms described in [6] should be
re-examined and may need to be altered to define new security
associations based on receiver's IP address instead of the sending
and receiving interfaces. Also, this document allows the IP
destination address of Path and PathTear messages to be the IP
address of a nexthop node (receiver's address) instead of the RSVP
session destination address. So, [6] should be revisited to check if
IPSec AH is now a viable means of securing RSVP-TE messages.
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7. IANA Considerations
The following values have to be defined by IANA for this document.
The registry is http://www.iana.org/assignments/rsvp-parameters.
7.1. Attribute Flags for LSP_ATTRIBUTES object
The following new bit is being defined for the Attributes Flags TLV
in the LSP_ATTRIBUTES object. The numeric value should be assigned
by IANA.
LSP stitching desired bit - Bit Number 5 (Suggested value)
This bit is only to be used in the Attributes Flags TLV on a Path
message.
The 'LSP stitching desired bit' has a corresponding 'LSP segment
stitching ready' bit (Bit Number 5) to be used in the RRO Attributes
sub-object.
7.2. New Error Codes
The following new error sub-code is being defined under the RSVP
error-code "Routing Problem" (24). The numeric error sub-code value
should be assigned by IANA.
Stitching unsupported - sub-code 23 (Suggested value)
This error code is to be used only in an RSVP PathErr.
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8. Acknowledgments
The authors would like to thank Adrian Farrel and Kireeti Kompella
for their comments and suggestions. The authors would also like to
thank Dimitri Papadimitriou and Igor Bryskin for their thorough
review of the document and discussions regarding the same.
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9. References
9.1. Normative References
[1] Bradner, S., "Key words for use in RFCs to Indicate Requirement
Levels", BCP 14, RFC 2119, March 1997.
[2] Kompella, K. and Y. Rekhter, "Label Switched Paths (LSP)
Hierarchy with Generalized Multi-Protocol Label Switching
(GMPLS) Traffic Engineering (TE)", RFC 4206, October 2005.
[3] Farrel, A., Papadimitriou, D., Vasseur, J., and A. Ayyangar,
"Encoding of Attributes for Multiprotocol Label Switching (MPLS)
Label Switched Path (LSP) Establishment Using Resource
ReserVation Protocol-Traffic Engineering (RSVP-TE)", RFC 4420,
February 2006.
[4] Berger, L., "Generalized Multi-Protocol Label Switching (GMPLS)
Signaling Resource ReserVation Protocol-Traffic Engineering
(RSVP-TE) Extensions", RFC 3473, January 2003.
[5] Awduche, D., Berger, L., Gan, D., Li, T., Srinivasan, V., and G.
Swallow, "RSVP-TE: Extensions to RSVP for LSP Tunnels",
RFC 3209, December 2001.
[6] Baker, F., Lindell, B., and M. Talwar, "RSVP Cryptographic
Authentication", RFC 2747, January 2000.
9.2. Informative References
[7] Aggarwal, R., "Extensions to RSVP-TE for Point to Multipoint TE
LSPs", draft-ietf-mpls-rsvp-te-p2mp-01 (work in progress),
January 2005.
[8] Ayyangar, A. and J. Vasseur, "Inter domain GMPLS Traffic
Engineering - RSVP-TE extensions",
draft-ietf-ccamp-inter-domain-rsvp-te-00 (work in progress),
February 2005.
[9] Rosen, E., Tappan, D., Fedorkow, G., Rekhter, Y., Farinacci,
D., Li, T., and A. Conta, "MPLS Label Stack Encoding",
RFC 3032, January 2001.
[10] Kompella, K. and Y. Rekhter, "Signalling Unnumbered Links in
Resource ReSerVation Protocol - Traffic Engineering (RSVP-TE)",
RFC 3477, January 2003.
[11] Kompella, K., Rekhter, Y., and L. Berger, "Link Bundling in
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MPLS Traffic Engineering (TE)", RFC 4201, October 2005.
[12] Vasseur, J., "A Per-domain path computation method for
computing Inter-domain Traffic Engineering (TE) Label Switched
Path (LSP)", draft-ietf-ccamp-inter-domain-pd-path-comp-00
(work in progress), April 2005.
[13] Farrel, A., "Path Computation Element (PCE) Architecture",
draft-ietf-pce-architecture-00 (work in progress), March 2005.
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Authors' Addresses
Arthi Ayyangar (editor)
Juniper Networks
1194 N. Mathilda Ave.
Sunnyvale, CA 94089
US
Email: arthi@juniper.net
Jean Philippe Vasseur
Cisco Systems, Inc.
300 Beaver Brook Road
Boxborough, MA 01719
US
Email: jpv@cisco.com
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