Network Working Group Dan Li
Internet Draft Jianhua Gao
Huawei
Arun Satyanarayana
Cisco
Intended Status: Informational
Expires: December 2007 June, 2007
Description of the RSVP-TE Graceful Restart Procedures
draft-li-ccamp-gr-description-00.txt
Status of this Memo
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Abstract
The Hello message for the Resource Reservation Protocol (RSVP) has
been defined to establish and maintain basic signaling node
adjacencies for Label Switching Routers (LSRs) participating in a
Multiprotocol Label Switching (MPLS) traffic engineered (TE)
network. The Hello message has been extended for use in Generalized
MPLS (GMPLS) network for state recovery of control channel or nodal
faults.
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GMPLS protocol definitions for RSVP also allow a restarting node to
learn the label that it previously allocated for use on a Label
Switching Path (LSP).
Further RSVP protocol extensions have been defined to enable a
restarting node to recover full control plane state by exchanging
RSVP messages with its upstream and downstream neighbors.
This document provides an informational clarification of the
control plane procedures for a GMPLS network when there are
multiple node failures, and describes how full control plane state
can be recovered in different scenarios where the order in which
the nodes restart is different.
This document does not define any new processes or procedures. All
protocol mechanisms are already defined in the referenced documents.
Table of Contents
1. Introduction................................................3
2. Existing Procedures for Single Node Restart..................4
2.1. Procedures defined in [RFC3473]............................4
2.2. Procedures defined in [GR-EXT].............................5
3. Multiple Node Restart Scenarios..............................5
4. RSVP State..................................................6
5. Procedures for Multiple Node Restart.........................7
5.1. Procedures for the Normal Node.............................7
5.2. Procedures for the Restarting Node.........................7
5.2.1. Procedures for Scenario 1...............................7
5.2.2. Procedures for Scenario 2...............................9
5.2.3. Procedures for scenario 3..............................10
5.2.4. Procedures for scenario 4..............................11
5.2.5. Procedures for scenario 5..............................11
5.3. Consideration of Re-Use of Data Plane Resources...........12
5.4. Consideration of Management Plane Intervention............12
6. Security Considerations....................................12
7. IANA Considerations........................................13
8. Acknowledgments............................................13
9. References.................................................13
9.1. Normative References.....................................13
10. Authors' Addresses........................................14
11. Full Copyright Statement..................................14
12. Intellectual Property Statement............................15
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1. Introduction
The Hello message for the Resource Reservation Protocol (RSVP) has
been defined to establish and maintain basic signaling node
adjacencies for Label Switching Routers (LSRs) participating in a
Multiprotocol Label Switching (MPLS) traffic engineered (TE)
network [RFC3209]. The Hello message has been extended for use in
Generalized MPLS (GMPLS) network for state recovery of control
channel or nodal faults through the exchange of the Restart
Capabilities object [RFC3473].
GMPLS protocol definitions for RSVP [RFC3473] also allow a
restarting node to learn the label that it previously allocated for
use on a Label Switching Path (LSP) through the Recovery Label
object carried on a Path message sent to a restarting node from its
upstream neighbor.
Further RSVP protocol extensions have been defined [GR-EXT] to
perform graceful restart and to enable a restarting node to recover
full control plane state by exchanging RSVP messages with its
upstream and downstream neighbors. State previously transmitted to
the upstream neighbor (principally the downstream label) is
recovered from the upstream neighbor on a Path message (using the
Recovery Label object as described in [RFC3473]). State previously
transmitted to the downstream neighbor (including the upstream
label, interface identifiers, and the explicit route) is recovered
from the downstream neighbor using a RecoveryPath message.
[GR-EXT] also extends the Hello message to exchange information
about the ability to support the RecoveryPath message.
The examples and procedures in [RFC3473] and [GR-EXT] focus on the
description of a single node restart when adjacent network nodes
are operative. Although the procedures are equally applicable to
multi-node restarts, no detailed explanation is provided.
This document provides and informational clarification of the
control plane procedures for a GMPLS network when there are
multiple node failures, and describes how full control plane state
can be recovered in different scenarios where the order in which
the nodes restart is different.
This document does not define any new processes or procedures. All
protocol mechanisms already defined in [RFC3473] and [GR-EXT] are
definitive.
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2. Existing Procedures for Single Node Restart
This section documents for information the existing procedures
defined in [RFC3473] and [GR-EXT]. Those documents are definitive,
and the description here is non-normative. It is provided for
informational clarification only.
2.1. Procedures defined in [RFC3473]
In the case of nodal faults, the procedures for the restarting node
and the procedures for the neighbor of a restarting node are
applied to the corresponding nodes. These procedures described in
[RFC3473] are summarized as follows:
For the Restarting Node:
1) Tells its neighbors that state recovery is supported using the
Hello message;
2) Recovers its RSVP state with the help of a Path message received
from its upstream neighbor carrying the RECOVERY_LABEL object;
3) For bidirectional LSPs, the UPSTREAM_LABEL object on the received
Path message is used to recover the corresponding RSVP state;
4) If the corresponding forwarding state in data plane is not existed,
the node treats this as a setup for a new LSP. If the forwarding
state in data plane is existed, the forwarding state is bound to the
LSP associated with the message, and related forwarding state should
be considered as valid and refreshed. In addition, if the node is not
the tail-end of the LSP, the corresponding outgoing Path messages is
sent with the incoming label from that entry carried in the
UPSTREAM_LABEL object.
For the Neighbor of a restarting node:
1) Sends the Path message with RECOVERY_LABEL object containing a
label value corresponding to the label value received in the most
recently received corresponding Resv message;
2) Resumes refreshing Path state with the restarting node;
3) Resumes refreshing Resv state with the restarting node.
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2.2. Procedures defined in [GR-EXT]
A new message is introduced in [GR-EXT] which is called the
RecoveryPath message. The message is sent by the downstream
neighbor of a restarting node to convey the contents of the last
received Path message back to the restarting node.
The restarting node will receive the Path message with the
RECOVERY_LABEL object from its upstream neighbor, and/or the
RecoveryPath message from its downstream neighbor. The full RSVP
state of the restarting node can be recovered from these two
messages.
From the received Path message the following state can be recovered:
o Upstream data interface (from RSVP_HOP object)
o Label on the upstream data interface (from RECOVERY_LABEL object)
o Upstream label for bidirectional LSP (from UPSTREAM_LABEL object)
From the received RecoveryPath message the following state can be
recovered:
o Downstream data interface (from RSVP_HOP object)
o Label on the downstream data interface (from RECOVERY_LABEL object)
o Upstream direction label for bidirectional LSP (from
UPSTREAM_LABEL object)
The other objects also can be recovered either by regular Path
message or RecoveryPath message, and Resv message.
3. Multiple Node Restart Scenarios
We define the following terms for the different node types:
Restarting - The node has restarted; communication with its
neighbor nodes is restored, its RSVP state is under recovery.
Delayed Restarting - The node has restarted, but the communication
with a neighbor node is interrupted (for example, the neighbor node
needs to restart).
Normal - The normal node is the fully operational neighbor of a
restarting or delayed restarting node.
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There are five scenarios for multi-node restart. We will focus on
the different positions of a restarting node. As shown in Figure 1,
an LSP starts from Node A, traverses Nodes B and C, and ends at
Node D.
+-----+ Path +-----+ Path +-----+ Path +-----+
| PSB |------->| PSB |------->| PSB |------->| PSB |
| | | | | | | |
| RSB |<-------| RSB |<-------| RSB |<-------| RSB |
+-----+ Resv +-----+ Resv +-----+ Resv +-----+
Node A Node B Node C Node D
Figure 1 Two neighbor nodes restart
1) A Restarting node with downstream Delayed Restarting node. For
example, in Figure 1, Nodes A and D are Normal nodes, Node B is a
Restarting node, and Node C is a Delayed Restarting node.
2) A Restarting node with upstream Delayed Restarting node. For
example, in Figure 1, Nodes A and D are Normal nodes, Node B is a
Delayed Restarting node, and Node C is a Restarting node.
3) A Restarting node with downstream and upstream Delayed Restarting
nodes. For example, in Figure 1, Node A is a Normal node, Nodes B and
D are Delayed Restarting nodes, and Node C is a Restarting node.
4) A Restarting Ingress node with downstream Delayed Restarting node.
For example, in Figure 1, Node A is a Restarting node, and Node B is
a Delayed Restarting node. Nodes C and D are Normal nodes.
5) A Restarting Egress node with upstream Delayed Restarting node.
For example, in Figure 1, Nodes A and B are Normal nodes, Node C is a
Delayed Restarting node, and Node D is a Restarting node.
If the communication between two nodes is interrupted, the upstream
node may think the downstream node is a Delayed Restarting node, or
vice versa.
4. RSVP State
For each scenario, the RSVP state needs to be recovered at the
restarting nodes are Path State Block (PSB) and Resv State Block
(RSB), which are created when the node receives the corresponding
Path message and Resv message.
According to [RFC2209], how to construct the PSB and RSB is really
an implementation issue. In fact, there is no requirement to
maintain separate PSB and RSB data structures. And in GMPLS, there
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is a much closer tie between Path and Resv state so it is possible
to combine the information into a single state block (the LSP state
block). On the other hand, if P2MP is supported, it may be
convenient to maintain separate upstream and downstream state. Note
that the PSB and RSB are not upstream and downstream state since
the PSB is responsible for receiving a Path from upstream and
sending a Path to downstream.
Regardless of how the RSVP state is implemented, on recovery there
are two logical pieces of state to be recovered and these
correspond to the PSB and RSB.
5. Procedures for Multiple Node Restart
In this document, all the nodes are assumed to have the graceful
restart capabilities which are described in [RFC3473] and [GR-EXT].
5.1. Procedures for the Normal Node
When the downstream Normal node detects its neighbor restarting, it
must send a RecoveryPath message for each LSP associated with the
restarting node for which it has previously sent a Resv message and
which has not been torn down.
When the upstream Normal node detects its neighbor restarting, it
must send a Path message with RECOVERY_LABEL object containing a
label value corresponding to the label value received in the most
recently received corresponding Resv message.
This document does not modify the procedures for the Normal node
which are described in [RFC3473] and [GR-EXT].
5.2. Procedures for the Restarting Node
This document does not modify the procedures for the Restarting
node which are described in [RFC3473] and [GR-EXT].
5.2.1. Procedures for Scenario 1
After the Restarting node restarts, it starts a Recovery Timer. Any
RSVP state that has not been resynchronized when the Recovery Timer
expires, should be cleared.
At the Restarting node (Node B in the example), full
resynchronization with the upstream neighbor (Node A) is possible
because Node A is a Normal node. The upstream Path information is
recovered from the Path message received from Node A. Node B also
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recovers the upstream Resv information (that it had previously sent
to Node A) from the RECOVERY_LABEL object carried in the Path
message received from Node A, but, obviously, some information
(like the Recorded Route Object) will be missing from the new Resv
message generated by Node B, and can not be supplied until the
downstream Delayed Restarting node (Node C) restarts and sends a
Resv.
After the upstream Path information and upstream Resv information
has been recovered by Node B, the normal refresh procedure with the
upstream Node A should be started.
As per [GR-EXT], the Restarting node (Node B) would normally expect
to receive a RecoveryPath message from its downstream neighbor
(Node C). It would use this to recover the downstream Path
information, and would subsequently send a Path message to its
downstream neighbor and receive a Resv message. But in this
scenario, because the downstream neighbor has not restarted yet,
Node B detects the communication with Node C is interrupted and
must wait before resynchronizing with its downstream neighbor.
In this case, the Restarting node (Node B) follows the procedures
in section 9.3 of [RFC3473] and may run a Restart Timer to wait for
the downstream neighbor (Node C) to restart. If its downstream
neighbor (Node C) has not restarted before the timer expires the
corresponding LSPs may be torn down according to local policy
[RFC3473]. Note, however, that the Restart Time value suggested in
[RFC3473] is based on the previous Hello message exchanged with the
node that has not restarted yet (Node C). Since this time value is
unlikely to be available to the restarting node (Node B), a
configured time value must be used if the timer is operated.
The RSVP state must be reconciled with the retained data plane
state if the cross-connect information can be retrieved from the
data plane. In the event of any mismatches, local policy will
dictate the action that must be taken which could include:
- reprogramming the data plane
- sending an alert to the management plane
- tearing down the control plane state for the LSP.
In the case that the Delayed Restarting node never comes back, and
where a Restart Timer is not used to automatically tear down LSPs,
the LSPs can be tidied up through the control plane using a
PathTear from the upstream node (Node A). Note that if Node C
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restarts after this operation, the RecoveryPath message that it
sends to Node B will not be matched with any state on Node B and
will receive a PathTear as its response resulting in the teardown
of the LSP at all downstream nodes.
5.2.2. Procedures for Scenario 2
In this case, the Restarting node (Node C) can recover full
downstream state from its downstream neighbor (Node D) which is a
Normal node. The downstream Path state can be recovered from the
RecoveryPath message which is sent by Node D. This allows Node C to
send a Path refresh message to Node D, and Node D will respond with
a Resv message from which Node C can reconstruct the downstream
Resv state.
After the downstream Path information and downstream Resv
information has been recovered in Node C, the normal refresh
procedure with downstream Node D should be started.
The Restarting node would normally expect to resynchronize with its
upstream neighbor to re-learn the upstream Path and Resv state, but
in this scenario, because the upstream neighbor (Node B) has not
restarted yet, the Restarting node (Node C) detects that the
communication with upstream neighbor (Node B) is interrupted. The
Restarting node (Node C) follows the procedures in section 9.3 of
[RFC3473] and may run a Restart Timer to wait the upstream neighbor
(Node B) to restart. If its upstream neighbor (Node B) has not
restarted before the Restart Timer expires, the corresponding LSPs
may be torn down according to local policy [RFC3473]. Note, however,
that the Restart Time value suggested in [RFC3473] is based on the
previous Hello message exchanged with the node that has not
restarted yet (Node B). Since this time value is unlikely to be
available to the restarting node (Node C), a configured time value
must be used if the timer is operated.
Note that no Resv message is sent to the upstream neighbor (Node B)
because it has not restarted.
The RSVP state must be reconciled with the retained data plane
state if the cross-connect information can be retrieved from the
data plane.
In the event of any mismatches, local policy will dictate the
action that must be taken which could include:
- reprogramming the data plane
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- sending an alert to the management plane
- tearing down the control plane state for the LSP.
In the case that the Delayed Restarting node never comes back, and
where a Restart Timer is not used to automatically tear down LSPs,
the LSPs cannot be tidied up through the control plane using a
PathTear from the upstream node(Node A), because there is no
control plane connectivity to Node C from the upstream direction.
There are two possibilities in [RFC3473]:
- Management action may be taken at the Restarting node to tear the
LSP. This will result in the LSP being removed from Node C, and a
PathTear being sent downstream to Node D.
- Management action may be taken at any downstream node (for
example, Node D) resulting in a PathErr message with the
Path_State_Reomved flag set being sent to Node C to tear the LSP
state.
Note that if Node B restarts after this operation, the Path message
that it sends to Node C will not be matched with any state on Node
C and will be treated as a new Path message resulting in LSP setup.
Node C should use the labels carried in the Path message (in the
UPSTREAM_LABEL object and in the RECOVERY_LABEL object) to drive
its label allocation, but may use other labels according to normal
LSP setup rules.
5.2.3. Procedures for scenario 3
In this example, the Restarting node (Node C) is isolated. It's
upstream and downstream neighbors have not restarted.
The Restarting node (Node C) follows the procedures in section 9.3
of [RFC3473] and may run a Restart Timer for each of its neighbors
(Nodes B and D). If a neighbor has not restarted before its Restart
Timer expires, the corresponding LSPs may be torn down according to
local policy [RFC3473]. Note, however, that the Restart Time values
suggested in [RFC3473] are based on the previous Hello message
exchanged with the nodes that have not restarted yet. Since these
time values are unlikely to be available to the restarting node
(Node C), a configured time value must be used if the timer is
operated.
During the Recovery Time, if the upstream Delayed Restarting node
has restarted, the procedure for scenario 1 can be applied.
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During the Recovery Time, if the downstream Delayed Restarting node
has restarted, the procedure for scenario 2 can be applied.
In the case that neither Delayed Restarting node ever comes back,
and where a Restart Timer is not used to automatically tear down
LSPs, management intervention is required to tidy up the control
plane and the data plane on the nodes that are waiting for the
failed device to restart.
If the downstream Delayed Restarting node restarts after the
cleanup of LSPs at Node C, the RecoveryPath message from Node D
will be responded with a PathTear message. If the upstream Delayed
Restarting node restarts after the cleanup of LSPs at Node C, the
Path message from Node B will be treated as a new LSP setup request,
but the setup will fail because Node D cannot be reached - Node C
will respond with a PathErr message. Since this happens to Node B
during its restart processing, it should follow the rules of [GR-
EXT] and tear down the LSP.
5.2.4. Procedures for scenario 4
When the Ingress node (Node A) restarts, it does not know which
LSPs it caused to be created. Usually, however, this information is
retrieved from the management plane or from the configuration
requests stored in non-volatile form in the node in order to
recover the LSP state.
Furthermore, if the downstream node (Node B) is a Normal node,
according to the procedures in [GR-EXT], the ingress will receive a
RecoveryPath message and will understand that it was the ingress of
the LSP.
However, in this scenario, the downstream node is a Delayed
Restarting node, so Node A must rely on the information from the
management plane or stored configuration, or it must wait for Node
B to restart.
In the event that Node B never restarts, management plane
intervention may be used at Node A to clean up any LSP state
restored from the management plane or from local configuration.
5.2.5. Procedures for scenario 5
In this scenario the Egress node (Node D) restarts, and its
upstream neighbor (Node C) has not restarted. In this case, the
Egress node is completely unaware of the LSPs. It has no downstream
neighbor to help it, and no management plane or configuration
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information. The Egress node must simply wait until its upstream
neighbor restarts and gives it the information as Path messages
carrying RECOVERY_LABEL objects.
5.3. Consideration of Re-Use of Data Plane Resources
Fundamental to the processes described above is an understanding
that data plane resources may remain in use (allocated and cross-
connected) when control plane state has not been fully
resynchronized because some control plane nodes have not restarted.
It is assumed that these data plane resources might be carrying
traffic and should not be reconfigured except through application
of operator-configured policy, or as a direct result of operator
action.
In particular, new LSP setup requests from the control plane or the
management plane should not be allowed to use data plane resources
that are still in use. Specific action must first be taken to
release the resources.
5.4. Consideration of Management Plane Intervention
The management plane must always retain the ability to control data
plane resources and to over-ride the control plane. In this context,
the management plane must always be able to release data plane
resources that were previously in place for use by control-plane
established LSPs. Further, the management plane must always be able
to instruct any control plane node to tear down any LSP.
Operators should be aware of the risks of misconnection that could
be caused by careless manipulation from the management plane of in-
use data plane resources.
6. Security Considerations
This document clarifies the procedures to be performed on RSVP
agents that neighbor one or more restarting RSVP agents. In the
case of the control plane in general, and the RSVP agent in
particular, where one or more nodes carrying one or more LSPs are
restarted due to external attacks, the procedures defined in [GR-
EXT] and described in this document provide the ability for the
restarting RSVP agents to recover the RSVP state in each restarting
node corresponding to the LSPs, with the least possible
perturbation to the rest of the network. Ideally, only the
neighboring RSVP agents should notice the restart and hence need to
perform additional processing. This allows for a network with
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active LSPs to recover LSP state gracefully from an external attack,
without perturbing the data/forwarding plane state.
7. IANA Considerations
This document defines no new protocols or extensions and makes no
requests to IANA for registry management.
8. Acknowledgments
We would like to thank Adrian Farrel, Dimitri Papadimitriou, and
Lou Berger for their useful comments.
9. References
9.1. Normative References
[RFC2209] R. Braden, L. Zhang, "Resource ReSerVation Protocol
(RSVP) -- Version 1 Message Processing Rules", RFC 2209,
September 1997.
[RFC3209] 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.
[RFC3473] Berger, L., "Generalized Multi-Protocol Label Switching
(GMPLS) Signaling Resource ReserVation Protocol-Traffic
Engineering (RSVP-TE) Extensions", RFC 3473, January
2003.
[GR-EXT] A. Satyanarayana, R. Rahman, "Extensions to GMPLS RSVP
Graceful Restart", Internet Draft, work in progress,
draft-ietf-ccamp-rsvp-restart-ext-08.txt, January 2007.
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10. Authors' Addresses
Dan Li
Huawei Technologies Co., Ltd.
F3-5-B R&D Center, Huawei Base,
Bantian, Longgang District
Shenzhen 518129 P.R.China
Phone: +86-755-28972910
Email: danli@huawei.com
Jianhua Gao
Huawei Technologies Co., Ltd.
F3-5-B R&D Center, Huawei Base,
Bantian, Longgang District
Shenzhen 518129 P.R.China
Phone: +86-755-28972902
Email: gjhhit@huawei.com
Arun Satyanarayana
Cisco Systems, Inc.
170 West Tasman Dr.
San Jose, CA 95134, USA
Phone: +1 408 853-3206
Email: asatyana@cisco.com
11. Full Copyright Statement
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FOR A PARTICULAR PURPOSE.
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