draft-ietf-mpls-crlsp-modify-02.txt   draft-ietf-mpls-crlsp-modify-03.txt 
MPLS WG J. Ash A new Request for Comments is now available in online RFC libraries.
Internet Draft Y. Lee
Document: draft-ietf-mpls-crlsp-modify-02.txt AT&T
P. Ashwood-Smith
B. Jamoussi
D. Fedyk
D. Skalecki
Nortel Networks
L. Li
SS8 Networks
October, 2000
Expires: April 2001
LSP Modification Using CR-LDP
Status of this Memo
This document is an Internet-Draft and is in full conformance with
all provisions of Section 10 of RFC2026 [1].
Internet-Drafts are working documents of the Internet Engineering
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1. Abstract
After a CR-LSP is set up, its bandwidth reservation may need to be
changed by the network operator, due to the new requirements for the
traffic carried on that CR-LSP [2]. This contribution presents an
approach to modify the bandwidth and possibly other parameters of an
established CR-LSP using CR-LDP [3] without service interruption.
The LSP modification feature can be supported by CR-LDP by use of
the _modify_ value for the _action indicator flag_ in the LSPID TLV
[3]. This feature has application in dynamic network resources
management where traffic of different priorities and service classes
is involved.
Table of Contents
1. Abstract . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1
2. Conventions Used in This Document . . . . . . . . . . . . . . . . 3
3. Introduction . . . . . . . . . . . . . . . . . . . . . . . . . . . 3
4. LSP Modification Using CR-LDP. . . . . . . . . . . . . . . . . . . 3
4.1 Basic Procedure for Resource Modification . . . . . . . . . . . . 3
4.2 Rerouting LSPs . . . . . . . . . . . . . . . . . . . . . . . . . . 5
4.3 Priority Handling . . . . . . . . . . . . . . . . . . . . . . . . 6
4.4 Modification Failure Case Handling . . . . . . . . . . . . . . . . 6
5. Application of LSP Bandwidth Modification in Dynamic Resource
Management . . . . . . . . . . . . . . . . . . . . . . . . . . . . 7
6. Acknowledgments . . . . . . . . . . . . . . . . . . . . . . . . . 8
7. Intellectual Property Considerations . . . . . . . . . . . . . . . 8
8. Security Considerations . . . . . . . . . . . . . . . . . . . . . 8
9. References . . . . . . . . . . . . . . . . . . . . . . . . . . . . 8
10. Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . . 9
2. Conventions Used in This Document
L: LSP (Label Switched Path)
L-id: LSPID (LSP Identifier)
T: Traffic Parameters
R: LSR (Label Switching Router)
FEC: Forwarding Equivalence Class
NHLFE: Next Hop Label Forwarding Entity
FTN: FEC To NHLFE
TLV: Type Length Value
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 [4].
3. Introduction
Consider an LSP L1 that has been established with its set of traffic
parameters T0. A certain amount of bandwidth is reserved along the
path of L1. Consider then that some changes are required on L1. For
example, the bandwidth of L1 needs to be increased to accommodate
the increased traffic on L1. Or the SLA associated with L1 needs to
be modified because a different service class is desired. The
network operator, in these cases, would like to modify the
characteristics of L1, for example, to change its traffic parameter
set from T0 to T1, without releasing the LSP L1 to interrupt the
service. In some other cases, network operators may want to reroute
a CR-LSP to a different path for either improved performance or
better network resource utilization. In all these cases, LSP
modification is required. In section 4 below, a method to modify an
active LSP using CR-LDP is presented. The concept of LSPID in CR-LDP
is used to achieve the LSP modification, without releasing the LSP
and interrupting the service and, without double booking the
bandwidth. In Section 5, an example is described to demonstrate an
application of the presented method in dynamically managing network
bandwidth requirements without interrupting service. In CR-LDP, an
action indicator flag of _modify_ is used in order to explicitly
specify the behavior, and allow the existing LSPID to support other
networking capabilities in the future. Reference [3],
<draft-ietf-mpls-cr-ldp-03.txt>, specifies the action indicator flag
of _modify_ for CR-LDP.
4. LSP Modification Using CR-LDP
4.1 Basic Procedure for Resource Modification
LSP modification can only be allowed when the LSP is already set up
and active. That is, modification is not defined nor allowed during
the LSP establishment or label release/withdraw phases. Only
modification requested by the ingress LSR of the LSP is considered
in this draft for CR-LSP. The Ingress LSR cannot modify an LSP before
a previous modification procedure is completed.
Assume that CR-LSP L1 is set up with LSPID L-id1, which is unique in
the MPLS network. The ingress LSR R1 of L1 has in its FTN (FEC To
NHLFE) table FEC1 -> Label A mapping where A is the outgoing label
for LSP L1. To modify the characteristics of L1, R1 sends a Label
Request Message. In the message, the TLVs will have the new
requested values, and the LSPID TLV is included which indicates the
value of L-id1. The Traffic Parameters TLV, the ER-TLV, the Resource
Class (color) TLV and the Preemption TLV can have values different
from those in the original Label Request Message, which has been
used to set up L1 earlier. Thus, L1 can be changed in its bandwidth
request (traffic parameter TLV), its traffic service class (traffic
parameter TLV), the route it traverses (ER TLV) and its setup and
holding (Preemption TLV) priorities. The ingress LSR R1 now still
has the entry in its FTN as FEC1 -> Label A. R1 is waiting to
establish another entry for FEC1.
When an LSR Ri along the path of L1 receives the Label Request
message, its behavior is the same as that of receiving any Label
request message. The only extension is that Ri examines the LSPID
carried in the Label Request Message, L-id1, and identifies if it
already has L-id1. If Ri does not have L-id1, Ri behaves the same as
receiving a new Label Request message. If Ri already has L-id1, Ri
takes the newly received Traffic Parameter TLV and computes the new
bandwidth required and derives the new service class. Compared with
the already reserved bandwidth for L-id1, Ri now reserves only the
difference of the bandwidth requirements. This prevents Ri from
doing bandwidth double booking. If a new service class is requested,
Ri also prepares to receive the traffic on L1 in just the same way as
handling it for a Label Request Message, perhaps using a different
type of queue. Ri assigns a new label for the Label Request Message.
When the Label Mapping message is received, two sets of labels exist
for the same LSPID. Then the ingress LSR R1 will have two outgoing
labels, A and B, associated with the same FEC, where B is the new
outgoing label received for LSP L1. The ingress LSR R1 can now
activate the new entry in its FTN, FEC1 - > Label B. This means that
R1 swaps traffic on L1 to the new label _B_ (_new_ path) for L1. The
packets can now be sent with the new label B, with the new set of
traffic parameters if any, on a new path, that is, if a new path is
requested in the Label Request Message for the modification. All the
other LSRs along the path will start to receive the incoming packets
with the new label. For the incoming new label, the LSR has already
established its mapping to the new outgoing label. Thus, the packets
will be sent out with the new outgoing label. The LSRs do not have
to implement new procedures to track the new and old characteristics
of the LSP.
The ingress LSR R1 then starts to release the original label A for
LSP L1. The Label Release Message is sent by R1 towards the down
stream LSRs. The Release message carries the LSPID of L-id1 and the
Label TLV to indicate which label is to be released. The Release
Message is propagated to the egress LSR to release the original
labels previously used for L1. Upon receiving the Label Release
Message, LSR Ri examines the LSPID, L-id1, and finds out that the
L-id1 has still another set of labels (incoming/outgoing) under it.
Thus, the old label is released without releasing the resource in
use. That is, if the bandwidth has been decreased for L1, the delta
bandwidth is released. Otherwise, no bandwidth is released. This
modification procedure can not only be applied to modify the traffic
parameters and/or service class of an active LSP, but also to
reroute an existing LSP (as described in Section 4.2 below), and/or
change its setup/holding priority if desired. After the release
procedure, the modification of the LSP is completed.
The method described above follows the normal behavior of Label
Request / Mapping / Notification / Release / Withdraw procedure of a
CR-LDP operated LSR with a specific action taken on an LSPID. If a
Label Withdraw Message is used to withdraw a label associated with an
LSPID, the Label TLV should be included to specify which label to
withdraw. Since the LSPID can also be used for other feature
support, an action indication flag of _modify_ assigned to the LSPID
would explicitly explain the action/semantics that should be
associated with the messaging procedure. The details of this flag
are addressed in the CR-LDP draft, Reference [3].
4.2 Rerouting LSPs
LSP modification can also be used to reroute an existing LSP. Only
modification requested by the ingress LSR of the LSP is considered
in this draft for CR-LSP. The Ingress LSR cannot modify an LSP before
a previous modification procedure is completed.
As in the previous section, consider a CR-LSP L1 with LSPID L-id1.
To modify the route of the LSP, the ingress LSR R1 sends a Label
Request Message. In the message, the LSPID TLV indicates L-id1 and
the Explicit Route TLV is specified with some different hops from
the explicit route specified in the original Label Request Message.
The action indication flag has the value _modify_.
At this point, the ingress LSR R1 still has an entry in FTN as
FEC1 -> Label A. R1 is waiting to establish another entry for FEC1.
When an LSR Ri along the path of L1 receives the Label Request
message, its behavior is the same as that of receiving a Label
Request Message that modifies some other parameters of the LSP.
Ri assigns a new label for the Label Request Message and forwards
the message along the explicit route. It does not allocate any
more resources except as described in section 4.1.
At another LSR Rj further along the path, the explicit route
diverges from the previous route. Rj acts as Ri, but forwards the
Label Request message along the new route. From this point onwards
the Label Request Message is treated as setting up a new LSP by
each LSR until the paths converge at later LSR Rk. The _modify_
value of the action indication flag is ignored.
At Rk and subsequent LSRs, the Label Request Message is handled as
at Ri.
On the return path, when the Label Mapping message is received, two
sets of labels for the LSPID exist where the new route coincide
with the old. Only one set of labels will exist at LSRs where the
routes diverge.
When the Label Mapping message is received at the ingress LSR R1 it
has two outgoing labels, A and B, associated with the same
FEC, where B is the new outgoing label received for LSP L1. R1 can
now activate the new entry in the FTN, FEC1 - > Label B and
de-activate the old entry FEC1 - > Label A. This means that R1
swaps traffic on L1 to the new label B. The packets are now sent
with the new label B, on the new path.
The ingress LSR R1 then starts to release the original label A for
LSP L1. The Label Release Message is sent by R1 towards the down
stream LSRs following the original route. The Release message
carries the LSPID of L-id1 and the Label TLV to indicate which
label is to be released. At each LSR the old label is released - no
further action is required to change the path of the data packets
which are already following the new route programmed by the Label
Mapping message.
At some LSRs, where the routes diverged, there is only one label
for the LSPID. For example, between Rj and Rk, the Label Release
Message will follow the old route. At LSRs between Rj and Rk only
the labels from the original route will exist for LSPID L-id1. At
these LSRs the LSPID TLV does not need to be examined to release the
correct label, but it must still be updated and passed on to the
next LSR as the Label Release message is propagated. In this way, at
Rk where the routes converge, the downstream LSR will know which
label to release and can continue to forward the Label Release
Message along the old route.
4.3 Priority Handling
When sending a Label Request Message for an active LSP L1 to request
changes, the setup priority used in the label Request Message can be
different from the one used in the previous Label Request Message,
effectively indicating the priority of this _modification_ request.
Network operators can use this feature to decide what priority is to
be assigned to a modification request, based on their
policies/algorithms and other traffic situations in the network. For
example, the priority for modification can be determined by the
priority of the customer/LSP. If a customer has exceeded the
reserved bandwidth of its VPN LSP tunnel by too much, the
modification request's priority may be given as a higher value.
The Label Request message for the modification of an active LSP can
also be sent with a holding priority different from its previous
one. This effectively changes the holding priority of the LSP.
Upon receiving a Label Request Message that requests a new holding
priority, the LSR assigns the new holding priority to the bandwidth.
That is, the new holding priority is assigned to both the existing
incoming / outgoing labels and the new labels to be established for
the LSPID in question. In this way self-bumping is prevented.
4.4 Modification Failure Case Handling
A modification attempt may fail due to insufficient resource or
other situations. A Notification message is sent back to the ingress
LSR R1 to indicate the failure of Label Request Message that
intended to modify the LSP. A retry may be attempted if desired by
the network operator. If the LSP on the original path failed when a
modification attempt is in progress, the attempt should be aborted by
using the Label Abort Request message as specified in the LDP draft
[5].
In the event of a modification failure, all modifications to the LSP
including the holding priority must be restored to their original
values.
5. Application of LSP Bandwidth Modification in Dynamic Resource
Management
In this section, we gave an example of dynamic network resource
management using the LSP bandwidth modification capability. The
details of this example can be found in a previous Internet draft
[2]. Assume that customers or services are assigned with given
CR-LSPs. These customers/services are assigned with one of three
priorities: key, normal or best effort. The network operator does
not want to bump any LSPs during an LSP setup, so after these
CR-LSPs are set up, their holding priorities are all assigned as
the highest value.
The network operator wants to control the resource on the links of
the LSRs, so each LSR keeps the usage status of its links. Based
on the usage history, each link is assigned a current threshold
priority Pi, which means that the link has no bandwidth available
for a Label Request with a setup priority lower than Pi. When an
LSP's bandwidth needs to be modified, the operator uses a
policy-based algorithm to assign a priority for its modification
request, say Mp for LSP L2. The ingress LSR then sends a Label
Request message with Setup Priority = Mp. If there is sufficient
bandwidth on the link for the modification, and the Setup priority
in the Label Request Message is higher in priority (Mp numerically
smaller) than the Pi threshold of the link, the Label Request
Message will be accepted by the LSR. Otherwise, the Label Request
message will be rejected with a Notification message which
indicates that there are insufficient resources. It should also be
noted that when OSPF (or IS-IS) floods the available-link-bandwidth
information, the available bandwidth associated with a priority
lower than Pi (numerical value bigger) should be interpreted as _0_.
This example based on a priority threshold Pi is implementation
specific, and illustrates the flexibility of the modification
procedure to prioritize and control network resources.
The calculation of Mp can be network and service dependent, and is
based on the operator's routing policy. For example, the operator
may assign a higher priority (lower Mp value) to L2 bandwidth
modification if L2 belongs to a customer or service with _Key_
priority. The operator may also collect the actual usage of each
LSP and assign a lower priority (higher Mp) to L2
bandwidth-increase modification if, for example, in the past week
L2 has exceeded its reserved bandwidth by 2 times on the average.
In addition, an operator may try to increase the bandwidth of L2
on its existing path unsuccessfully if there is insufficient
bandwidth available on L2. In that case, the operator is willing
to increase the bandwidth of another LSP, L3, with the same
ingress/egress LSRs as L2, in order to increase the overall
ingress/egress bandwidth allocation. However, in this case the
L3 bandwidth modification is performed with a lower priority
(higher Mp value) since L3 is routed on a secondary path, which
results in the higher bandwidth allocation priority being given
to the LSPs that are on their primary paths [2].
6. Acknowledgments
The authors would like to acknowledge the careful review and
comments of Adrian Farrel.
7. Intellectual Property Considerations
Nortel Networks may seek patent or other intellectual property
protection for some or all of the technologies disclosed in this
document. If any standards arising from this document are or become
protected by one or more patents assigned to Nortel Networks, Nortel
Networks is prepared to make a license available to any qualified
applicant upon reasonable and non-discriminatory terms and
conditions. Any such licenses will be subject to negotiations
outside of the IETF.
8. Security Considerations
Protection against modification to LSPs by malign agents has to be
controlled by the MPLS domain.
9. References
1 Bradner, S., "The Internet Standards Process -- Revision 3", BCP RFC 3214
9, RFC 2026, October 1996.
2 Ash, J., et. al., QoS Resource Management in MPLS-Based Networks, Title: LSP Modification Using CR-LDP
draft-ash-qos-routing-00.txt, (work in progress). Author(s): J. Ash, Y. Lee, P. Ashwood-Smith, B. Jamoussi,
D. Fedyk, D. Skalecki, L. Li
Status: Standards Track
Date: January 2002
Mailbox: gash@att.com, jamoussi@NortelNetworks.com,
petera@NortelNetworks.com,
dareks@nortelnetworks.com,
ylee@ceterusnetworks.com,
lili@ss8networks.com, dwfedyk@nortelnetworks.com
Pages: 11
Characters: 25453
Updates/Obsoletes/SeeAlso: NONE
3 Jamoussi, B., et. al., Constraint-Based LSP Setup using LDP, I-D Tag: draft-ietf-mpls-crlsp-modify-03.txt
draft-ietf-mpls-cr-ldp-03.txt, September 1999, (work in progress).
4 Bradner, S., "Key words for use in RFCs to Indicate Requirement URL: ftp://ftp.rfc-editor.org/in-notes/rfc3214.txt
Levels", BCP 14, RFC 2119, March 1997.
5 Andersson, L., et. al., LDP Specification, draft-ietf-mpls-ldp- This document presents an approach to modify the bandwidth and
05.txt, (work in progress). possibly other parameters of an established CR-LSP (Constraint-based
Routed Label Switched Paths) using CR-LDP (Constraint-based Routed
Label Distribution Protocol) without service interruption. After a
CR-LSP is set up, its bandwidth reservation may need to be changed by
the network operator, due to the new requirements for the traffic
carried on that CR-LSP. The LSP modification feature can be supported
by CR-LDP by use of the _modify_value for the _action indicator flag_
in the LSPID TLV. This feature has application in dynamic network
resources management where traffic of different priorities and service
classes is involved.
10. Authors' Addresses This document is a product of the Multiprotocol Label Switching
Working Group of the IETF.
Gerald R. Ash Young Lee This is now a Proposed Standard Protocol.
AT&T AT&T
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Email: gash@att.com Email: younglee@att.com
Bilel Jamoussi This document specifies an Internet standards track protocol for
Nortel Networks Corp. the Internet community, and requests discussion and suggestions
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Peter Ashwood-Smith Li Li This announcement is sent to the IETF list and the RFC-DIST list.
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