Internet Draft Ping Pan, Ed (Ciena Corp)
Expires: Dec 2003 Der-Hwa Gan (Juniper Networks)
George Swallow (Cisco Systems)
Jean Philippe Vasseur (Cisco Systems)
Dave Cooper (Global Crossing)
Alia Atlas, Ed (Avici Systems)
Markus Jork (Avici Systems)
Fast Reroute Extensions to RSVP-TE for LSP Tunnels
draft-ietf-mpls-rsvp-lsp-fastreroute-03.txt
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Abstract
This document defines extensions to and describes the use of RSVP to
establish backup label-switched path (LSP) tunnels for local repair
of LSP tunnels. These mechanisms enable the re-direction of traffic
onto backup LSP tunnels in 10s of milliseconds in the event of a
failure.
Two methods are defined here. The one-to-one backup method creates
detour LSPs for each protected LSP at each potential point of local
repair. The facility backup method creates a bypass tunnel to
protect a potential failure point; by taking advantage of MPLS label
stacking, this bypass tunnel can protect a set of protected LSPs that
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have similar backup constraints. Both methods can be used to protect
links and nodes during network failure. The described behavior and
extensions to RSVP allow nodes to implement either or both methods
and to interoperate in a mixed network.
0. Background
Several years before work began on this draft, operational networks
had deployed two independent methods of doing fast reroute, called
herein one-to-one backup and facility backup. Vendors trying to
support both methods were experiencing incompatiblity problems in
attempting to produce a single implementation capable of
interoperating with both. There are technical tradeoffs between
the methods. However these tradeoffs are so topologically
dependent, that the community has not converged on a single
approach.
This draft rationalizes the RSVP signaling for both methods such
that any implementation can recognize all FRR requests and clearly
respond, either positively if they are capable of performing the
method, or with a clear error such that requester is informed and
can seek alternate means of backup. This draft also allows a
single implementation to support both methods, thereby providing a
range of capabilities. Thus the described behavior and extensions
to RSVP allow LERs and LSRs to implement either or both methods.
While the two methods could in principle be used in a single
network, it is expected that operators will continue to choose to
deploy either one or the other. The goal of this draft is to
standardize the RSVP signaling such that either a network with LSRs
that implement both methods or an network composed of some LSRs
that support one method and others that support both, can properly
signal among those LSRs to achieve fast restoration through the
chosen method.
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Contents
1 Introduction ............................................. 4
2 Terminology ............................................... 4
3 Local Repair Techniques ................................... 6
3.1 One-to-one Backup .................................... 6
3.2 Facility Backup ...................................... 7
4 RSVP Extensions ........................................... 8
4.1 FAST_REROUTE Object .................................... 8
4.2 DETOUR Object .......................................... 11
4.3 SESSION_ATTRIBUTE Flags ................................ 12
4.4 RRO IPv4/IPv6 Sub-Object Flags ......................... 13
5 Head-End Behavior ......................................... 14
6 Point of Local Repair Behavior ............................ 15
6.1 Signaling a Backup Path ................................ 16
6.1.1 Backup Path Identification: Sender-Template Specific . 17
6.1.2 Backup Path Identification: Path-Specific ........... 18
6.2 Procedures for Backup Path Computation ................. 18
6.3 Signaling Backups for One-To-One Protection ............ 20
6.3.1 Make-Before-Break with Detour LSPs .................. 21
6.3.2 Message Handling .................................... 21
6.3.3 Local Reroute of Traffic Onto Detour LSP ............ 22
6.4 Signaling for Facility Protection ...................... 23
6.4.1 Discovering Downstream Labels ....................... 23
6.4.2 Procedures for the PLR before Local Repair .......... 23
6.4.3 Procedures for the PLR during Local Repair .......... 23
6.4.4 Processing backup tunnel's ERO ...................... 24
6.5 PLR Procedures During Local Repair ..................... 25
6.5.1 Notification of local repair ........................ 25
6.5.2 Revertive Behavior .................................. 26
7 Merge Node Behavior ....................................... 27
7.1 Handling Backup Path Messages Before Failure ........... 27
7.1.1 Merging Backup Paths using the Sender-Template
Specific Method ..................................... 28
7.1.2 Merging Detours using Path-Specific Method .......... 28
7.1.2.1 An Example on Path Message Merging ............... 29
7.1.3 Message Handling for Merged Detours ................. 30
7.2 Handling Failures ...................................... 30
8 Behavior of all LSRs ...................................... 31
8.1 Merging Detours in Path-Specific Method ................ 31
9 Security Considerations ................................... 32
10 IANA Guidelines ........................................... 32
11 Intellectual Property Considerations ...................... 32
12 Full Copyright Statement .................................. 32
13 Acknowledgments ........................................... 33
14 Normative References ...................................... 33
15 Author Information ........................................ 33
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1. Introduction
This document extends RSVP [RSVP] to establish backup LSP tunnels
for the local repair of LSP tunnels. This technique is presented
to meet the needs of real-time applications, such as voice over IP,
for which it is highly desirable to be able to re-direct user
traffic onto backup LSP tunnels in 10s of milliseconds. This
timing requirement can be satisfied by computing and signaling
backup LSP tunnels in advance of failure and by re-directing
traffic as close to failure point as possible. In this way, the
time for the redirection does not include any path computation or
signaling delays, including delays to propagate failure
notification between LSRs. The speed of repair made possible by
the techniques and extensions described herein is the primary
advantage of this method. We use the term local repair when
referring to techniques which accomplish this, and refer to an
explicitly routed LSP which is provided with such protection as a
protected LSP. These techniques are applicable only to explicitly
routed LSPs; Application of the techniques discussed herein to LSPs
which dynamically change their routes such as those used in unicast
IGP routing is beyond the scope of this document.
Section 2 covers new terminology used in this document. The two
basic strategies for creating backup LSPs are described in Section
3. In Section 4, the protocol extensions to RSVP to support local
protection are described. In Section 5, the behavior of an LER
which wishes to request local protection for an LSP is presented.
The behavior of a potential point of local repair (PLR) is given in
Section 6; this describes how to determine the appropriate strategy
to use for protecting an LSP and how to implement each of the
strategies. The behavior of a merge node, the LSR where a
protected LSP and its backup LSP rejoin, is described in Section 7.
Finally, the required behavior of other nodes in the network is
discussed in Section 8.
For the techniques discussed in this document to function properly,
there are three assumptions which must be made. First, an LSR
which is on the path of a protected LSP SHOULD always assume that
it is a merge point; this is necessary because the facility backup
method does not signal backups through a bypass tunnel before
failure. Second, if the one-to-one backup method is used and a
DETOUR object is included, the LSRs in the traffic-engineered
network should support the DETOUR object; this is necessary so that
the Path message containing the DETOUR object is not rejected.
Third, understanding of the DETOUR object is required to support
the path-specific method which requires that LSRs in the
traffic-engineered network be capable of merging detours.
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2. Terminology
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 [RFC-WORDS].
The reader is assumed to be familiar with the terminology in [RSVP]
and [RSVP-TE].
LSR - Label Switch Router
LSP - An MPLS Label Switched Path. In this document, an LSP
will always refer to an explicitly routed LSP.
Local Repair - Techniques used to repair LSP tunnels quickly
when a node or link along the LSPs path fails.
PLR - Point of Local Repair. The head-end LSR of a backup tunnel
or a detour LSP.
One-to-one Backup - A local repair technique where a backup LSP
is separately created for each protected LSP at a PLR.
Facility Backup - A local repair technique where a bypass tunnel
is used to protect one or more protected LSPs which
traverse the PLR, the resource being protected and the
Merge Point in that order.
Protected LSP - An LSP is said to be protected at a given hop if
it has one or multiple associated backup tunnels originating
at that hop.
Detour LSP - The LSP that is used to re-route traffic around
a failure in one-to-one backup.
Bypass Tunnel - An LSP that is used to protect a set of LSPs
passing over a common facility.
Backup Tunnel - The LSP that is used to backup up one of the many
LSPs in many-to-one backup.
NHOP Bypass Tunnel - Next-Hop Bypass Tunnel. A backup tunnel
which bypasses a single link of the protected LSP.
NNHOP Bypass Tunnel - Next-Next-Hop Bypass Tunnel. A backup
tunnel which bypasses a single node of the protected LSP.
Backup Path - The LSP that is responsible for backing up one
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protection LSP. A backup path refers to either a detour LSP
or a backup tunnel.
MP - Merge Point. The LSR where one or more backup tunnels rejoin
the path of the protected LSP, downstream of the potential
failure. The same LSR may be both an MP and a PLR
simultaneously.
DMP - Detour Merge Point. In the case of one-to-one backup,
this is an LSR where multiple detours converge and only one
detour is signaled beyond that LSR.
Reroutable LSP - Any LSP for which the head-end LSR requests
local protection. See Section 9.1 for more detail.
CSPF - Constraint-based Shortest Path First.
SRLG Disjoint - A path is considered to be SRLG disjoint from a
given link or node if the path does not use any links or
nodes which belong to the same SRLG as that given link or
node.
3. Local Repair Techniques
Two different techniques for local protection are presented here.
The one-to-one backup technique has a PLR compute a separate backup
LSP, called a detour LSP, for each LSP which the PLR protects using
this technique. With the facility backup technique, the PLR creates
a single bypass tunnel which can be used to protect multiple LSPs.
3.1. One-to-one backup
In the one-to-one technique, a label switched path is established
which intersects the original LSP somewhere downstream of the point
of link or node failure. For each LSP which is backed up, a
separate backup LSP is established.
[R1]---[R2]-----[R3]----[R4]---[R5]
\ \ \ / \ /
[R6]---[R7]-------[R8]----[R9]
Protected LSP: [R1->R2->R3->R4->R5]
R1's Backup: [R1->R6->R7->R8->R3]
R2's Backup: [R2->R7->R8->R4]
R3's Backup: [R3->R8->R9->R5]
R4's Backup: [R4->R9->R5]
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Example 1: One-to-One Backup Technique
In the simple topology shown above in Example 1, the protected LSP
runs from R1 to R5. R2 can provide user traffic protection by
creating a partial backup LSP which merges with the protected LSP
at R4. We refer to a partial one-to-one backup LSP
[R2->R7->R8->R4] as a detour.
To fully protect an LSP that traverses N nodes, there could be as
many as (N - 1) detours. The paths for the detours necessary to
fully protect the LSP in Example 1 are given there. To minimize
the number of LSPs in the network, it is desirable to merge a
detour back to its protected LSP when feasible. When a detour LSP
intersects its protected LSP at an LSR with the same outgoing
interface, it will be merged.
When a failure occurs along the protected LSP, the PLR redirects
traffic onto the local detour. For instance, if the link [R2->R3]
fails in Example 1, R2 will switch traffic received from R1 onto
the protected LSP along link [R2->R7] using the label received when
R2 created the detour. When R4 receives traffic with the label
provided for R2's detour, R4 will switch that traffic onto link
[R4-R5] using the label received from R5 for the protected LSP. At
no point does the depth of the label stack increase as a result of
taking the detour. While R2 is using its detour, traffic will take
the path [R1->R2->R7->R8->R4->R5].
3.2. Facility backup
The facility backup technique takes advantage of the MPLS label
stack. Instead of creating a separate LSP for every backed-up LSP, a
single LSP is created which serves to backup up a set of LSPs. We
call such an LSP tunnel a bypass tunnel.
The bypass tunnel must intersect the path of the original LSP(s)
somewhere downstream of the PLR. Naturally, this constrains the
set of LSPs being backed-up via that bypass tunnel to those that
pass through some common downstream node. All LSPs which pass
through the point of local repair and through this common node
which do not also use the facilities involved in the bypass tunnel
are candidates for this set of LSPs.
[R8]
\
[R1]---[R2]----[R3]----[R4]---[R5]
\ / \
[R6]===[R7] [R9]
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Protected LSP 1: [R1->R2->R3->R4->R5]
Protected LSP 2: [R8->R2->R3->R4]
Protected LSP 3: [R2->R3->R4->R9]
Bypass LSP Tunnel: [R2->R6->R7->R4]
Example 2: Facility Backup Technique
In Example 2, R2 has built a bypass tunnel which protects against
the failure of link [R2->R3], link [R3->R4] or node [R3]. The
doubled lines represent this tunnel. The scalability improvement
this technique provides is that the same bypass tunnel can also be
used to protect LSPs from any of R1, R2 or R8 to any of R4, R5 or
R9. Example 2 describes three different protected LSPs which are
using the same bypass tunnel for protection.
As with the one-to-one technique, to fully protect an LSP that
traverses N nodes, there could be as many as (N-1) bypass tunnels.
However, each of those bypass tunnels could protected a set of
LSPs.
When a failure occurs along a protected LSP, the PLR redirects
traffic into the appropriate bypass tunnel. For instance, if link
[R2->R3] fails in Example 2, R2 will switch traffic received from
R1 on the protected LSP onto link [R2->R6]; the label will be
switched for one which will be understood by R4 to indicate the
protected LSP and then the bypass tunnel's label will be pushed
onto the label-stack of the redirected packets. If
penultimate-hop-popping is used, then the merge point in Example 2,
R4, will receive the redirected packet with a label indicating the
protected LSP that the packet is to follow. If
penultimate-hop-popping is not used, then R4 will pop the bypass
tunnel's label and examine the label underneath to determine the
protected LSP that the packet is to follow. When R2 is using the
bypass tunnel for protected LSP 1, the traffic takes the path
[R1->R2->R6->R7->R4->R5]; the bypass tunnel is the connection
between R2 and R4.
4. RSVP Extensions
We propose two additional objects, FAST_REROUTE and DETOUR, to
extend RSVP-TE for fast-reroute signaling. These new objects are
backward compatible with LSRs that do not recognize them (see
section 3.10 in [RSVP]). Both objects can only be carried in RSVP
Path messages.
The SESSION_ATTRIBUTE and RECORD_ROUTE objects are also extended to
support bandwidth and node protection features.
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4.1. FAST_REROUTE Object
The FAST-REROUTE object is used to control the backup used for the
protected LSP. This specifies the setup and hold priorities, the
session attribute filters, and bandwidth to be used for protection.
It also allows a specific local protection technique to be requested.
This object MUST only be inserted into the PATH message by the
head-end LER and MUST NOT be changed by downstream LSRs. The
FAST-REROUTE object has the following format:
Class = TBD (use form 11bbbbbb for compatibility)
C-Type = 1
0 1 2 3
+-------------+-------------+-------------+-------------+
| Length (bytes) | Class-Num | C-Type |
+-------------+-------------+-------------+-------------+
| Setup Prio | Hold Prio | Hop-limit | Flags |
+-------------+-------------+-------------+-------------+
| Bandwidth |
+-------------+-------------+-------------+-------------+
| Include-any |
+-------------+-------------+-------------+-------------+
| Exclude-any |
+-------------+-------------+-------------+-------------+
| Include-all |
+-------------+-------------+-------------+-------------+
Setup Priority
The priority of the backup path with respect to taking
resources, in the range of 0 to 7. The value 0 is the highest
priority. Setup Priority is used in deciding whether
this session can preempt another session. See [RSVP-TE] for
the usage on priority.
Holding Priority
The priority of the backup path with respect to holding
resources, in the range of 0 to 7. The value 0 is the highest
priority. Holding Priority is used in deciding whether this
session can be preempted by another session. See [RSVP-TE] for
the usage on priority.
Hop-limit
The maximum number of extra hops the backup path is allowed
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to take, from current node (a PLR) to a MP, with PLR and MP
excluded in counting. For example, hop-limit of 0 means only
direct links between PLR and MP can be considered.
Flags
0x01 One-to-one Backup Desired
Indicates that protection via the one-to-one backup
technique is desired.
0x02 Facility Backup Desired
Indicates that protection via the facility backup
technique is desired.
Bandwidth
Bandwidth estimate (32-bit IEEE floating point integer) in
bytes-per-second.
Exclude-any
A 32-bit vector representing a set of attribute filters
associated with a backup path any of which renders a link
unacceptable.
Include-any
A 32-bit vector representing a set of attribute filters
associated with a backup path any of which renders a link
acceptable (with respect to this test). A null set (all bits
set to zero) automatically passes.
Include-all
A 32-bit vector representing a set of attribute filters
associated with a backup path all of which must be present for
a link to be acceptable (with respect to this test). A null set
(all bits set to zero) automatically passes.
The two high-order bits of the Class-Num (11) indicate that nodes
that do not understand the object should ignore it and pass if
forward unchanged.
For informational purposes, a different C-type value and format for
the FAST_REROUTE object are specified below. This is used by
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existing implementations. The meaning of the fields is the same as
described for C-Type 1.
C-Type = 7
0 1 2 3
+-------------+-------------+-------------+-------------+
| Length (bytes) | Class-Num | C-Type |
+-------------+-------------+-------------+-------------+
| Setup Prio | Hold Prio | Hop-limit | Reserved |
+-------------+-------------+-------------+-------------+
| Bandwidth |
+-------------+-------------+-------------+-------------+
| Include-any |
+-------------+-------------+-------------+-------------+
| Exclude-any |
+-------------+-------------+-------------+-------------+
4.2. DETOUR Object
The DETOUR object is used in one-to-one backup to identify detour
LSPs. It has the following format:
Class = TBD (to conform 0bbbbbbb format for compatibility)
C-Type = 7
0 1 2 3
+-------------+-------------+-------------+-------------+
| Length (bytes) | Class-Num | C-Type |
+-------------+-------------+-------------+-------------+
| PLR ID 1 |
+-------------+-------------+-------------+-------------+
| Avoid Node ID 1 |
+-------------+-------------+-------------+-------------+
// .... //
+-------------+-------------+-------------+-------------+
| PLR ID n |
+-------------+-------------+-------------+-------------+
| Avoid Node ID n |
+-------------+-------------+-------------+-------------+
PLR ID (1 - n)
IPv4 address identifying the beginning point of detour which
is a PLR. Any local address on the PLR can be used.
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Avoid Node ID (1 - n)
IP address identifying the immediate downstream node that
the PLR is trying to avoid. Router ID of downstream node
is preferred. This field is mandatory, and is used by
the MP for merging rules discussed below.
There can be more than one pair of (PLR_ID, Avoid_Node_ID) entries in
a DETOUR object. If detour merging is desired, after each merging
operation, the Detour Merge Point should combine all the merged
detours in the subsequent Path messages.
The high-order bit of the C-Class is zero; LSRs that do not support
the DETOUR objects MUST reject any Path message containing a DETOUR
object and send a PathErr to notify the PLR. This PathErr SHOULD
be generated as specified in [RSVP] for unknown objects with a
class-num of the form "0bbbbbbb".
4.3. SESSION_ATTRIBUTE Flags
To explicitly request bandwidth and node protection, two new flags
are defined in the SESSION_ATTRIBUTE object.
For both C-Type 1 and 7, the SESSION_ATTRIBUTE object currently has
the following flags defined:
Local protection desired: 0x01
This flag permits transit routers to use a local repair
mechanism which may result in violation of the explicit route
object. When a fault is detected on an adjacent downstream link
or node, a transit node may reroute traffic for fast service
restoration.
Label recording desired: 0x02
This flag indicates that label information should be included
when doing a route record.
SE Style desired: 0x04
This flag indicates that the tunnel ingress node may choose to
reroute this tunnel without tearing it down. A tunnel egress
node SHOULD use the SE Style when responding with a Resv
message. When requesting fast reroute, the head-end LSR
SHOULD set this flag; this is not necessary for the
path-specific method of the one-to-one backup technique.
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The following new flags are defined:
Bandwidth protection desired: 0x08
This flag indicates to the PLRs along the protected LSP path
that a backup path with a bandwidth guarantee is desired.
The bandwidth to be guaranteed is that of the protected
LSP, if no FAST_REROUTE object is included in the PATH message;
if a FAST_REROUTE object is in the PATH message, then the
bandwidth specified therein is that to be guaranteed.
Node protection desired: 0x10
This flag indicates to the PLRs along a protected LSP path
that a backup path which bypasses at least the next node of
the protected LSP is desired.
4.4. RRO IPv4/IPv6 Sub-Object Flags
To report whether bandwidth and/or node protection are provided as
requested, we define two news flags in the RRO IPv4 sub-object.
RRO IPv4 and IPv6 sub-object address:
These two sub-objects currently have the following flags defined:
Local protection available: 0x01
Indicates that the link downstream of this node is protected
via a local repair mechanism, which can be either one-to-one
or facility backup.
Local protection in use: 0x02
Indicates that a local repair mechanism is in use to maintain
this tunnel (usually in the face of an outage of the link it
was previously routed over, or an outage of the neighboring
node).
Two new flags are defined:
Bandwidth protection: 0x04
The PLR will set this when the protected LSP has a backup path
which is guaranteed to provide the desired bandwidth specified
in the FAST_REROUTE object or the bandwidth of the protected
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LSP, if no FAST_REROUTE object was included. The PLR may set
this whenever the desired bandwidth is guaranteed; the PLR
MUST set this flag when the desired bandwidth is guaranteed
and the "bandwidth protection desired" flag was set in the
SESSION_ATTRIBUTE object. If the requested bandwidth is not
guaranteed, the PLR MUST NOT set this flag.
Node protection: 0x08
The PLR will set this when the protected LSP has a backup path
which provides protection against a failure of the next LSR
along the protected LSP. The PLR may set this whenever node
protection is provided by the protected LSP's backup path; the
PLR MUST set this flag when the node protection is provided
and the "node protection desired" flag was set in the
SESSION_ATTRIBUTE object. If node protection is not provided,
the PLR MUST NOT set this flag. Thus, if a PLR could only
setup a link-protection backup path, the "Local protection
available" bit will be set but the "Node protection" bit will
be cleared.
5. Head-End Behavior
The head-end of an LSP determines whether local protection should
be requested for that LSP and which local protection technique is
desired for the protected LSP. The head-end also determines what
constraints should be requested for the backup paths of a protected
LSP.
To indicate that an LSP should be locally protected, the head-end
LSR MUST either set the "Local protection desired" flag in the
SESSION_ATTRIBUTE object or include a FAST_REROUTE object in the
PATH message or both. It is recommended that the "local protection
desired" flag in the SESSION_ATTRIBUTE object always be set. If a
head-end LSR signals a FAST_REROUTE object, it MUST be stored for
Path refreshes.
The head-end LSR of a protected LSP MUST set the "label recording
desired" flag in the SESSION_ATTRIBUTE object. This facilitates
the use of the facility backup technique. If node protection is
desired, the head-end LSR should set the "node protection desired"
flag in the SESSION_ATTRIBUTE object; otherwise this flag should be
cleared. Similarly, if a guarantee of bandwidth protection is
desired, then the "bandwidth protection desired" flag in the
SESSION_ATTRIBUTE object should be set; otherwise, this flag should
be cleared.
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If the head-end LSR determines that control of the backup paths for
the protected LSP is desired, then the LSR should include the
FAST_REROUTE object. The attribute filters, bandwidth, hop-limit
and priorities will be used by the PLRs when determining the backup
paths.
If the head-end LSR desires that the protected LSP be protected via
the one-to-one backup technique, then head-end LSR should include a
FAST_REROUTE object and set the "one-to-one backup desired" flag.
If the head-end LSR desires that the protected LSP be protected via
the facility backup technique, then the head-end LSR should include
a FAST_REROUTE object and set the "facility backup desired" flag.
The lack of a FAST_REROUTE object, or having both these flags
clear should be treated by PLRs as a lack of preference. If
both flags are set a PLR may use either method or both.
The head-end LSR of a protected LSP MUST support the additional
flags defined in Section 4.4 being set or clear in the RRO IPv4 and
IPv6 sub-objects. The head-end LSR of a protected LSP MUST support
the RRO Label sub-object.
If the head-end LSR of an LSP determines that local protection is
newly desired, this should be signaled via make-before-break.
6. Point of Local Repair Behavior
Every LSR along a protected LSP (except the egress) MUST follow the
PLR behavior described in this document.
A PLR SHOULD support the FAST_REROUTE object, the "local protection
desired", "label recording desired", "node protection desired" and
"bandwidth protection desired" flags in the SESSION_ATTRIBUTE
object, and the "local protection available", "local protection in
use", "bandwidth protection", and "node protection" flags in the
RRO IPv4 and IPv6 sub-objects. A PLR MAY support the DETOUR
object.
A PLR MUST consider an LSP as having asked for local protection if
the "local protection desired" flag is set in the SESSION_ATTRIBUTE
object and/or the FAST_REROUTE object is included. If the
FAST_REROUTE object is included, a PLR SHOULD consider providing
one-to-one protection if the "one-to-one desired" is set and SHOULD
consider providing facility backup if the "facility backup desired"
flag is set when determining whether to provide local protection
and which technique to use to provide that local protection. If
the "node protection desired" flag is set, the PLR SHOULD try to
provide node protection; if this is not feasible, the PLR SHOULD
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then try to provide link protection. If the "bandwidth protection
guaranteed" flag is set, the PLR SHOULD try to provide a bandwidth
guarantee; if this is not feasible, the PLR SHOULD then try to
provide a backup without a guarantee of the full bandwidth.
The following treatment for the RRO IPv4 or IPv6 sub-object's flags
must be followed if an RRO is included in the protected LSP's RESV
message. Based on this additional information the head-end may
take appropriate actions.
- Until a PLR has a backup path available, the PLR MUST clear the
relevant four flags in the corresponding RRO IPv4 or IPv6
sub-object.
- Whenever the PLR has a backup path available, the PLR MUST set
the "local protection available" flag. If no established
one-to-one backup LSP or bypass tunnel exists, or the one-to-one
LSP and the bypass tunnel is in "DOWN" state, the PLR MUST clear
the "local protection available" flag in its IPv4 (or IPv6)
address subobject of the RRO and SHOULD send the updated RESV.
- The PLR MUST clear the "local protection in use" flag unless it
is actively redirecting traffic into the backup path instead of
along the protected LSP.
- The PLR SHOULD also set the "node protection" flag if the backup
path protects against the failure of the immediate downstream
node and, if not, the PLR SHOULD clear the "node protection"
flag. This MUST be done if the "node protection desired" flag
was set in the SESSION_ATTRIBUTE object.
- The PLR SHOULD set the "bandwidth protection" if the backup path
offers a bandwidth guarantee and, if not, SHOULD clear the
"bandwidth protection" flag. This MUST be done if the "bandwidth
protection desired" flag was set in the SESSION_ATTRIBUTE
object.
6.1 Signaling a Backup Path
A number of objectives must be met to obtain a satisfactory signaling
solution. These are summarized as follows:
1. Unambiguously and uniquely identify backup paths
2. Unambiguously associate protected LSPs with their backup paths
3. Work with both global and non-global label spaces
4. Allow for merging of backup paths
5. Maintain RSVP state during and after fail-over.
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LSP tunnels are identified by a combination of the SESSION and
SENDER_TEMPLATE objects. The relevant fields are as follows.
IPv4 (or IPv6) tunnel end point address
IPv4 (or IPv6) address of the egress node for the tunnel.
Tunnel ID
A 16-bit identifier used in the SESSION that remains constant
over the life of the tunnel.
Extended Tunnel ID
A 32-bit (IPv4) or 128-bit (IPv6) identifier used in the SESSION
that remains constant over the life of the tunnel. Normally set
to all zeros. Ingress nodes that wish to narrow the scope of a
SESSION to the ingress-egress pair may place their IP address
here as a globally unique identifier.
IPv4 (or IPv6) tunnel sender address
IPv4 (or IPv6) address for a sender node
LSP ID
A 16-bit identifier used in the SENDER_TEMPLATE and the
FILTER_SPEC that can be changed to allow a sender to share
resources with itself.
The first three of these are in the SESSION object and are the basic
identification of the tunnel. Setting the "Extended Tunnel ID" to
an IP address of the head-end LSR allows the scope of the SESSION
to be narrowed to only LSPs sent by that LSR. A backup LSP is
considered to be part of the same session as its protected LSP;
therefore these three cannot be varied.
The last two are in the SENDER_TEMPLATE. Multiple LSPs in the same
SESSION may be protected and take different routes; this is common
when rerouting a tunnel using make-before-break. It is necessary
that a backup path be clearly identified with its protected LSP, so
that correct merging and state treatment can be done. Therefore, a
backup path must inherit its LSP ID from the associated protected
LSP. Thus, the only field in the SESSION and SENDER_TEMPLATE
objects which could be varied between a backup path and a protected
LSP is the "IPv4 (or IPv6) tunnel sender address" in the
SENDER_TEMPLATE.
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There are two different methods to uniquely identify a backup
path. These are described below.
6.1.1. Backup Path Identification: Sender-Template-Specific
In this approach, the SESSION object and the LSP_ID are copied from
the protected LSP. The "IPv4 tunnel sender address" is set to an
address of the PLR. If the head-end of a tunnel is also acting as
the PLR, it MUST choose an IP address different from the one used
in the SENDER_TEMPLATE of the original LSP tunnel.
When using the sender-template-specific approach, the protected
LSPs and the backup paths SHOULD use the Shared Explicit (SE)
style. This allows bandwidth sharing between multiple backup
paths. The backup paths and the protected LSP MAY be merged by the
Detour Merge Points, when the ERO from the MP to the egress is the
same on each LSP to be merged, as specified in [RSVP-TE].
6.1.2. Backup Path Identification: Path-Specific
In this approach, rather than varying the SESSION or
SENDER_TEMPLATE objects, a new object, the DETOUR object, is used
to distinguish between PATH messages for a backup path and the
protected LSP.
Thus, the backup paths use the same SESSION and SENDER_TEMPLATE
objects as the ones used in the protected LSP. The presence of
DETOUR object in Path messages signifies a backup path; the
presence of FAST_REROUTE object and/or the "local protection
requested" flag in the SESSION_ATTRIBUTE object indicates a
protected LSP.
In the path-message-specific approach, when an LSR receives
multiple Path messages which have the same SESSION and
SENDER_TEMPLATE objects and also have the same next-hop, that LSR
MUST merge the Path messages. Without this behavior, the multiple
RESV messages received back would not be distinguishable as to
which backup path each belongs to. This merging behavior does
reduce the total number of RSVP states inside the network at the
expense of merging LSPs with different EROs.
6.2 Procedures for Backup Path Computation
Before a PLR can create a detour or a bypass tunnel, the desired
explicit route must be determined. This can be done using a CSPF.
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Before CSPF computation, the following information should be
collected at a PLR:
- The list of downstream nodes that the protected LSP passes
through. This information is readily available from the
RECORD_ROUTE objects during LSP setup. This information is also
available from the ERO. However, if the ERO contains loose
sub-objects, the ERO may not provide adequate information.
- The downstream links/nodes that we want to protect against. Once
again, this information is learned from the RECORD_ROUTE
objects. Whether node protection is desired is determined by
the "node protection" flag in the SESSION_ATTRIBUTE object and
local policy.
- The upstream uni-directional links that the protected LSP
passes through. This information is learned from the
RECORD_ROUTE objects; it is only needed for setting up
one-to-one protection. In the path-specific method, it is
necessary to avoid the detour and the protected LSP sharing
a common next-hop upstream of the failure. In the
sender-template-specific mode, this same restriction is
necessary to avoid sharing bandwidth between the detour and
its protected LSP, where that bandwidth has only been reserved
once.
- The link attribute filters to be applied. These are derived
from the FAST_REROUTE object, if included in the PATH message,
and the SESSION_ATTRIBUTE object otherwise.
- The bandwidth to be used is found in the FAST_REROUTE object,
if included in the PATH message, and in the SESSION_ATTRIBUTE
object otherwise. Local policy may modify the bandwidth to be
reserved.
- The hop-limit, if a FAST_REROUTE object was included in the
PATH message.
When applying a CSPF algorithm to compute the backup route, the
following constraints should be satisfied:
- For detour LSPs, the destination MUST be the tail-end of the
protected LSP; for bypass tunnels (Section 6), the destination
MUST be the address of the MP.
- When setting up one-to-one protection using the path-specific
method, a detour MUST not traverse the upstream links of the
protected LSP in the same direction. This prevents the
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possibility of early merging of the detour into the protected
LSP. When setting up one-to-one protection using the
sender-template-specific method, a detour should not traverse
the upstream links of the protected LSP in the same direction;
this prevents sharing the bandwidth between a protected LSP
and its backup upstream of the failure where the bandwidth
would be used twice in the event of a failure.
- The backup LSP cannot traverse the downstream node and/or link
whose failure is being protected against. Note that if the
PLR is the penultimate hop, node protection is not possible
and only the downstream link can be avoided. The backup path
may be computed to be SRLG disjoint from the downstream node
and/or link being avoided.
- The backup path must satisfy the resource requirements of the
protected LSP. This includes the link attribute filters,
bandwidth, and hop limits determined from the FAST_REROUTE
object and SESSION_ATTRIBUTE object.
If such computation succeeds, the PLR should attempt to establish a
backup path. The PLR may schedule a re-computation at a later time
to discover better paths that may have emerged. If for any reason,
the PLR is unable to bring up a backup path, it must schedule a
retry at a later time.
6.3 Signaling Backups for One-To-One Protection
Once a PLR has decided to locally protect an LSP with one-to-one
backup, and has identified the desired path, it takes the following
steps to signal the detour.
The following describes the transformation to be performed upon the
protected LSP's PATH message to create the detour LSP's PATH
message.
- If the sender-template specific method is to be used, then the
PLR MUST change the "IPv4 (or IPv6) tunnel sender address" of the
SENDER_TEMPLATE to an address belonging to the PLR that is not
the same as was used for the protected LSP. Additionally, the
DETOUR object MAY be added to the PATH message.
- If the path-specific method is to be used, then the PLR MUST add
a DETOUR object to the PATH message.
- The SESSION_ATTRIBUTE flags "Local protection desired",
"Bandwidth protection desired" and "Node protection desired" MUST
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be cleared. The "Label recording desired" flag MAY be modified.
If the Path Message contained a FAST_REROUTE object, and the ERO
is not completely strict, the Include-any, Exclude-any, and
Include-all fields of the FAST_REROUTE object SHOULD be copied to
the corresponding fields of the SESSION_ATTRIBUTE object.
- If the protected LSP's Path message contained a FAST_REROUTE
object, this MUST be removed from the detour LSP's PATH message.
- The PLR MUST generate an EXPLICIT_ROUTE object toward the egress.
First, the PLR must remove all sub-objects preceding the first
address belonging to the Merge Point. Then the PLR SHOULD add
sub-objects corresponding to the desired backup path between the
PLR and the MP.
- The SENDER_TSPEC object SHOULD contain the bandwidth information
from the received FAST_REROUTE object, if included in the
protected LSP's PATH message.
- The RSVP_HOP object containing one of the PLR's IP address.
- The detour LSPs MUST use the same reservation style as the
protected LSP. This must be correctly reflected in the
SESSION_ATTRIBUTE object.
Detour LSPs are regular LSPs in operation. Once a detour path is
successfully computed and the detour LSP is established, the PLR
need not compute detour routes again, unless (1) the contents of
FAST_REROUTE have changed, or (2) the downstream interface and/or
the nexthop router for a protected LSP have changed. The PLR may
recompute detour routes at any time.
6.3.1 Make-Before-Break with Detour LSPs
If the sender-template specific method is used, it is possible to
do make-before-break with detour LSPs. This is done by using two
different IP addresses belonging to the PLR (which were not used in
the SENDER_TEMPLATE of the protected LSP). If the current detour
LSP uses the first IP address in its SENDER_TEMPLATE, then the new
detour LSP should be signaled using the second IP address in its
SENDER_TEMPLATE. Once the new detour LSP has been created, the
current detour LSP can be torn down. By alternating the use of
these IP addresses, the current and new detour LSPs will have
different SENDER_TEMPLATES and, thus, different state in the
downstream LSRs.
This make-before-break mechanism, changing the PLR IP address in
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the DETOUR object instead, is not feasible with the path-specific
method because the PATH messages for new and current detour LSPs
may be merged if they share a common next-hop.
6.3.2 Message Handling
LSRs must process the detour LSPs independent of the protected LSPs
to avoid triggering the LSP loop detection procedure described in
[RSVP-TE].
The PLR MUST not mix the messages for the protected and the detour
LSPs. When a PLR receives Resv, ResvTear and PathErr messages from
the downstream detour destination, the messages MUST not be forwarded
upstream. Similarly, when a PLR receives ResvErr and ResvConf
messages from a protected LSP, it MUST not propagate them onto the
associated detour LSP.
A session tear-down request is normally originated by the sender via
PathTear messages. When a PLR node receives a PathTear message from
upstream, it MUST delete both the protected and the detour LSPs. The
PathTear messages MUST propagate to both protected and detour LSPs.
During error conditions, the LSRs may send ResvTear messages to fix
problems on the failing path. When a PLR node receives the ResvTear
messages from downstream for a protected LSP, as long as a detour is
up, the ResvTear messages MUST not be sent further upstream.
PathErrs should be treated similiarly.
6.3.3 Local Reroute of Traffic onto Detour LSP
When the PLR detects a failure on the protected LSP, the PLR MUST
rapidly switch packets to the protected LSP's backup LSP instead of
the protected LSP's normal out-segment. The goal of this technique
is to effect the redirection within 10s of milliseconds.
L32 L33 L34 L35
R1-------R2-------R3-------R4-------R5
| |
L46 | L47 | L44
R6---------------R7
Protected LSP: [R1->R2->R3->R4->R5]
Detour LSP: [R2->R6->R7->R4]
Example 3: Redirect to Detour
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In Example 3 above, if the link [R2->R3] fails, then R2 would do
the following. Any traffic received on link [R1->R2] with label
L32 would be sent out link [R2->R6] with label L46 (along the
detour LSP) instead of out link [R3->R4] with lable L34 (along the
protected LSP). The Merge Point, R4, would recognize that packets
received on link [R7->R4] with label L44 should be sent out link
[R4->R5] with label L35, and thus merged with the protected LSP.
6.4 Signaling for Facility Protection
A PLR may use one or more bypass tunnels to protect against the
failure of a link and/or a node. These bypass tunnels may be
setup in advance or may be dynamically created as new protected
LSPs are signaled.
6.4.1. Discovering Downstream Labels
To support facility backup, it is necessary for the PLR to
determine a label which will indicate to the MP that packets
received with that label should be switched along the protected
LSP. This can be done without explicitly signaling the backup path
if the MP uses a label space global to that LSR.
As described in Section 5, the head-end LSR MUST set the "label
recording requested" flag in the SESSION_ATTRIBUTE object for LSPs
requesting local protection. This will cause (as specified in
[RSVP- TE]) all LSRs to record their INBOUND labels and to note via
a flag if the label is global to the LSR. Thus, when a protected
LSP is first signaled through a PLR, the PLR can examine the RRO in
the Resv message and learn about the incoming labels that are used
by all downstream nodes for this LSP.
When MPs use per-interface-label spaces, the PLR must send Path
messages (for each protected LSP using a bypass tunnel) via that
bypass tunnel prior to the failure in order to discover the
appropriate MP label. The signaling procedures for this are in
Section 6.4.3 below.
6.4.2. Procedures for the PLR before Local Repair
A PLR which determines to use facility-backup to protect a given
LSP should select a bypass tunnel to use taking into account
whether node protection is to be provided, what bandwidth was
requested and whether a bandwidth guarantee is desired, and what
link attribute filters were specified in the FAST_REROUTE object.
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The selection of a bypass tunnel for a protected LSP is performed
by the PLR when the LSP is first setup.
6.4.3. Procedures for the PLR during Local Repair
When the PLR detects a link or/and node failure condition, it needs
to reroute the data traffic onto the bypass tunnel and to start
sending the control traffic for the protected LSP onto the bypass
tunnel.
The backup tunnel is identified using the sender-template-specific
method. The procedures to follow are similar to those described in
Section 6.3.
- The SESSION is unchanged.
- The SESSION_ATTRIBUTE is unchanged except as follows:
The "Local protection desired", "Bandwidth protection desired",
and "Node protection desired" flags SHOULD be cleared.
The "Label recording desired" MAY be modified.
- The IPv4 (or IPv6) tunnel sender address of the SENDER_TEMPLATE
is set to an address belonging to the PLR.
- The RSVP_HOP object MUST contain an IP source address
belonging to the PLR. Consequently, the MP will send messages
back to the PLR using as a destination that IP address.
- The PLR MUST generate an EXPLICIT_ROUTE object toward the
egress. Detailed ERO processing is described below.
- The RRO object may need to be updated, as described in Section
6.5.
The PLR sends Path, PathTear, and ResvConf messages via the backup
tunnel. The MP sends Resv, ResvTear, and PathErr messages by
directly addressing them to the address in the RSVP_HOP object
contents as specified in [RSVP].
If it is necessary to signal the backup prior to failure to
determine the MP label to use, then the same Path message is sent.
In this case, the PLR SHOULD continue to send Path messages for the
protected LSP along the normal route. PathTear messages should be
duplicated, with one sent along the normal route and one sent thru
the bypass tunnel. The MP should duplicate the Resv and ResvTear
messages and sent them to both the PLR and the LSR indicated by the
protected LSP's RSVP_HOP object.
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6.4.4. Processing backup tunnel's ERO
Procedures for ERO processing are described in [RSVP-TE]. This
section describes additional ERO update procedures for Path messages
which are sent over bypass tunnels. If normal ERO processing rules
were followed, the Merge Point would examine the first sub-object and
likely reject it (Bad initial sub-object). This is because the
unmodified ERO might contain the IP address of a bypassed node (in
the case of a NNHOP Backup Tunnel), or of an interface which is
currently down (in the case of a NHOP Backup Tunnel). For this
reason, the PLR invoke the following ERO procedures before sending a
Path message via a bypass tunnel.
Sub-objects belonging to abstract nodes which precede the Merge Point
are removed, along with the first sub-object belonging to the MP. A
sub-object identifying the Backup Tunnel destination is then added.
More specifically, the PLR MUST:
- remove all the sub-objects proceeding the first address belonging
to the MP.
- replace this first MP address with an IP address of the MP.
(Note that this could be same address that was just removed.)
6.5. PLR Procedures During Local Repair
In addition to the technique specific signaling and packet
treatment, there is common signaling which should be followed.
During fast reroute, for each protected LSP containing an RRO
object, the PLR obtains the RRO from the protected LSP's stored
RESV. The PLR MUST update the IPv4 or IPv6 sub-object it inserted
into the RRO by setting the "Local protection in use" and "Local
Protection Available" flags.
6.5.1. Notification of local repair
In many situations, the route used during a Local Repair will be less
than optimal. The purpose of Local Repair is to keep high priority
and loss sensitive traffic flowing while a more optimal re-routing of
the tunnel can be effected by the head-end of the tunnel. Thus the
head-end needs to know of the failure so it may re-signal an LSP
which is optimal.
To provide this notification, the PLR SHOULD send a Path Error
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message with error code of "Notify" (Error code =25) and an error
value field of ss00 cccc cccc cccc where ss=00 and the sub-code = 3
("Tunnel locally repaired") (see [RSVP-TE])
Additionally a head-end may also detect that an LSP needs to be moved
to a more optimal path by noticing failures reported via the IGP.
Note that in the case of inter-area TE LSP (TE LSP spanning areas),
the head-end LSR will need to rely exclusively on Path Error messages
to be informed of failures in another area.
6.5.2 Revertive Behavior
Upon a failure event, a protected TE LSP is locally repaired by the
PLR. There are two basic strategies for restoring the TE LSP to a
full working path.
- Global revertive mode: The head-end LSR of each tunnel is
responsible for reoptimizing the TE LSPs that used the failed
resource. There are several potential reoptimization triggers -
RSVP error messages, inspection of OSPF LSAs or ISIS LSPs, and
timers. Note that this re-optimization process may proceed as
soon as the failure is detected. It is not tied to the
restoration of the failed resource.
- Local revertive mode: Upon detecting that the resource is
restored, the PLR re-signals each of TE LSPs that used to be
routed over the restored resource. Every TE LSP successfully
resignaled along the restored resource is switched back.
There are several circumstances where a local revertive mode might
not be desirable. In the case of resource flapping (not an uncommon
failure type), this could generate multiple traffic disruptions.
Therefore, in the local revertive mode, the PLR should implement a
means to dampen the re-signaling process in order to limit
potential disruptions due to flapping.
In the local revertive mode, any TE LSP will be switched back,
without any distinction, as opposed to the global revertive mode
where the decision to reuse the restored resource is taken by the
head-end LSR based on the TE LSP attributes. When the head-end
learns of the failure, it may reoptimize the protected LSP tunnel
along a different and more optimal path, because it has a more
complete view of the resources and TE LSP constraints; this means
that the old LSP which has been reverted to may not be optimal any
longer. Note that in the case of inter-area LSP, where the TE LSP
path computation might be done on some Path Computation Server, the
reoptimization process can still be triggered on the Head-End
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LSP. The local revertive mode is optional.
However, there are circumstances where the Head-end does not have
the ability to reroute the TE LSP (e.g if the protected LSP is
pinned down, as may be desirable if the paths are determined using
an off-line optimization tool) or if Head-end does not have the
complete TE topology information (depending on the path computation
scenario). In those cases, the local revertive might be a
interesting option.
It is recommended that one always use the globally revertive mode.
Note that a link or node "failure" may be due to the facility being
permanently taken out of service. Local revertive mode is
optional. When used in combination, the global mode may rely
solely on timers to do the reoptimization. When local revertive
mode is not used, head-end LSRs SHOULD react to RSVP error messages
and/or IGP indications in order to make a timely response.
Interoperability: If a PLR is configured with the local revertive
mode but the MP is not, any attempt from the PLR to resignal the TE
LSP over the restored resource would fail as the MP will not send
any Resv message. The PLR will still refresh the TE LSP over the
backup tunnel. The TE LSP will not revert to the restored resource;
instead it will continue to use the backup until it is
re-optimized.
7. Merge Node Behavior
An LSR is a Merge Point if it receives the Path message for a
protected LSP and one or more messages for a backup LSP which is
merged into that protected LSP. In the one-to-one backup
technique, the LSR is aware that it is a merge node prior to
failure. In the facility backup technique, the LSR may not know
that it is a Merge Point until a failure occurs and it receives a
backup LSP's Path message. Therefore, an LSR which is on the path
of a protected LSP SHOULD always assume that it is a merge point.
When a MP receives a backup LSP's Path message thru a bypass
tunnel, the Send_TTL in the Common Header may not match the TTL of
the IP packet within which the Path message was transported. This
is expected behavior.
7.1. Handling Backup Path Messages Before Failure
There are two circumstances where a Merge Point will receive Path
messages for a backup path prior to failure. In the first case, if
a PLR is providing local protection via the one-to-one backup
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technique, the detour will be signaled and must be properly handled
by the MP. In this case, the backup LSP may be signaled via the
sender-template-specific method or via the path-specific method.
In the second case, if the Merge Point does not provide labels
global to the MP and record them in a Label sub-object of the RRO
or if the PLR does not use such recorded information, the PLR may
signal the backup path, as described above in Section 6.4.1, to
determine the label to use if the PLR is providing protection
according to the facility backup technique. In this case, the
backup LSP is signaled via the sender-template-specific method.
The reception of a backup LSP's path message does not indicate that
a failure has occured and the incoming protected LSP will no longer
be used.
7.1.1. Merginging Backup Paths using the Sender-Template Specific Method
An LSR may receive multiple Path messages for one or more backup
LSPs and, possibly, the protected LSP. Each of these Path messages
will have a different SENDER_TEMPLATE. The protected LSP can be
recognized because it will either include the FAST_REROUTE object,
have the "local protection desired" flag set in the
SESSION_ATTRIBUTE object or both.
If the outgoing interface and next-hop LSR are the same, then the
Path messages are eligible for merging. Similar to that specified
in [RSVP-TE] for merging of RESV messages, only those Path messages
whose ERO from that LSR to the egress is the same can be merged.
If merging occurs and one of the Path messages merged was for the
protected LSP, then the final Path message to be sent MUST be that
of the protected LSP. This merges the backup LSPs into the
protected LSP at that LSR. Once the final Path message has been
identified, the MP MUST start to refresh it downstream
periodically.
If merging occurs and all the Path messages were for backup LSPs,
then the DETOUR object, if any, should be altered as specified in
Section 8.1
7.1.2. Merging Detours using the Path-Specific Method
An LSR (that is, an MP) may receive multiple Path messages from
different interfaces with identical SESSION and SENDER_TEMPLATE
objects. In this case, Path state merging is REQUIRED.
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The merging rule is the following:
For all Path messages that do not have either a FAST_REROUTE or a
DETOUR object, or the MP is the egress of the LSP, no merging is
required. The messages are processed according to [RSVP-TE].
Otherwise, the MP MUST record the Path state as well as their
incoming interface. If the Path messages do not share outgoing
interface and next-hop LSR, the MP MUST consider them as independent
LSPs, and MUST NOT merge them.
For all the Path messages that share the same outgoing interface and
next-hop LSR, the MP runs the following procedure to select one of
them as the Path message to forward downstream.
1. Eliminate from consideration those that traverse nodes that
other Path messages want to avoid.
2. If one LSP is originated from this node, this must be
the final LSP. Quit.
3. If only one Path message contains FAST_REROUTE object, this
becomes the chosen Path message. Quit.
4. If there are several LSPs, and not all of them have a DETOUR
object, then eliminate those with DETOUR from consideration.
5. If several candidates remain (that is, there are both detour
and protected LSPs), prefer the ones with FAST_REROUTE object.
6. If none found, prefer the ones without DETOUR object. If none
found, prefer the ones with DETOUR object.
7. If several candidate Path message still remain, it is a local
decision to choose which one will be the final LSP. The decision
can be based on the number of IP hops in ERO, bandwidth
requirements, or others.
Once the final Path message has been identified, the MP MUST start to
refresh it downstream periodically. Other LSPs are considered merged
at this node. For bandwidth reservation on the outgoing link, any
merging should be considered to have occured before bandwidth is
reserved. Thus, even though Fixed Filter is specified, multiple
detours and/or their protected LSP which are to be merged due to
sharing an outgoing interface and next-hop LSR will reserve only
the bandwidth of the final Path message on that outgoing
interface.
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7.1.2.1. An Example on Path Message Merging
R7---R8---R9-\
| | | \
R1---R2---R3---R4---R5---R6
Protected LSP: [R1->R2->R3->R4->R5->R6]
R2's Detour: [R2->R7->R8->R9->R4->R5->R6]
R3's Detour: [R3->R8->R9->R5->R6]
Example 4: Path Message Merging
In Example 4 above, R8 will receive Path messages that have the
same SESSION and SENDER_TEMPLATE from detours for R2 and R3.
During merging at R8 since detour R3 has a shorter ERO path length
(that is, ERO is [R9->R5->R6], and path length is 3), R8 will
select it as the final LSP, and only propagate its Path messages
downstream. Upon receiving a Resv (or a ResvTear) message, R8 must
relay on the messages toward both R2 and R3.
R5 needs to merge as well, and will select the main LSP, since it
has the FAST_REROUTE object. Thus, the detour LSP terminates at
R5.
7.1.3. Message Handling for Merged Detours
When an LSR receives a ResvTear for an LSP, the LSR must determine
whether it has an alternate associated LSP. For instance, if the
ResvTear was received for a protected LSP, but an associated backup
LSP has not received a ResvTear, then the LSR has an alternate
associated LSP. If the LSR does not have an alternate associated
LSP, then the MP MUST propogate the ResvTear toward the LSP's
ingress and, for each backup LSP merged into that LSP at this LSR,
the ResvTear SHOULD also be propogated along the backup LSP.
The MP may receive PathTear messages for some of the merging LSPs.
PathTear messages SHOULD NOT be propagated downstream until the MP
has received PathTear messages for each of the merged LSPs.
However, the fact that one or more of the merged LSPs has been torn
down should be reflected in the downstream message, such as by
changing the DETOUR object, if any.
7.2. Handling Failures
When a downstream LSR detects a local link failure, for any
protected LSPs routed over the failed link, Path and Resv state
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MUST NOT be cleared and PathTear and ResvErr messages MUST NOT be
sent immediately; if this is not the case, then the facility backup
technique will not work. Further a downstream LSR SHOULD reset the
refresh timers for these LSPs as if they had just been refreshed.
This is to allow time for the PLR to begin refreshing state via the
bypass tunnel. State MUST be removed if it has not been refreshed
before the refresh timer expires. This allows the facility backup
technique to work without requiring that it signal backup paths
thru the bypass tunnel before failure.
After a failure has occured, the MP must still send Resv messages
for the backup LSPs associated with the protected LSPs which have
failed. If the backup LSP was sent through a bypass tunnel, then
the PHOP object in its Path message will have the IP address of the
associated PLR. This will ensure that Resv state is refreshed.
Once the local link has recovered, the MP may or may not accept
Path messages for existing protected LSPs which had failed over to
their backup.
8. Behavior of all LSRs
The objects defined and the techniques defined in this document
require behavior from all LSRs in the traffic-engineered network,
even if that LSR is not along the path of a protected LSP.
First, if a DETOUR object is included in the backup LSP's path
message for the sender-template-specific method, the LSRs in the
traffic-engineered network should support the DETOUR object.
Second, if the Path-Specific Method is to be supported for
the one-to-one backup technique, it is necessary that the LSRs in
the traffic-engineered network be capable of merging detours as
specified below in Section 8.1.
It is possible to avoid specific LSRs which do not support this
behavior by assigning an link attribute to all the links of those
LSPs and then requesting that backup paths exclude that link
attribute.
8.1. Merging Detours in Path-Specific Method
If multiple Path Messages for different detours are received with
the same SESSION, SENDER_TEMPLATE, outgoing interface and next-hop
LSR, then the LSR must function as a Detour Merge Point and merge
the detour Path Messages. This merging should occur as specified
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in Section 7.1.2 and shown in Example 4.
In addition, it is necessary to update the DETOUR object to reflect
the merging which has taken place. This is done using the
following algorithm to format the outgoing DETOUR object for the
final LSP:
- Combine all the (PLR_ID, Avoid_Node_ID) pairs from all the
DETOUR objects of all merged LSPs, and create a new object with
all listed. Ordering is insignificant.
9. Security Considerations
This document does not introduce new security issues. The security
considerations pertaining to the original RSVP protocol [RSVP] remain
relevant.
It should be noted that the facility backup technique requires that
a PLR and its selected Merge Point will trust RSVP messages
received from each other.
10. IANA Guidelines
IANA [RFC-IANA] will assign RSVP C-class numbers for FAST_ROUTE and
DETOUR objects. Currently, in production networks, FAST_REROUTE uses
C-class 205, and DETOUR uses C-class 63.
11. Intellectual Property Considerations
Cisco Systems and Juniper Networks may have intellectual property
rights claimed in regard to some of the specification contained in
this document
12. Full Copyright Statement
Copyright (C) The Internet Society (2002). All Rights Reserved.
This document and translations of it may be copied and furnished to
others, and derivative works that comment on or otherwise explain it
or assist in its implementation may be prepared, copied, published
and distributed, in whole or in part, without restriction of any
kind, provided that the above copyright notice and this paragraph are
included on all such copies and derivative works. However, this
document itself may not be modified in any way, such as by removing
Pan et al. [Page 32]
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the copyright notice or references to the Internet Society or other
Internet organizations, except as needed for the purpose of
developing Internet standards in which case the procedures for
copyrights defined in the Internet Standards process must be
followed, or as required to translate it into languages other than
English.
The limited permissions granted above are perpetual and will not be
revoked by the Internet Society or its successors or assigns.
This document and the information contained herein is provided on an
"AS IS" basis and THE INTERNET SOCIETY AND THE INTERNET ENGINEERING
TASK FORCE DISCLAIMS ALL WARRANTIES, EXPRESS OR IMPLIED, INCLUDING
BUT NOT LIMITED TO ANY WARRANTY THAT THE USE OF THE INFORMATION
HEREIN WILL NOT INFRINGE ANY RIGHTS OR ANY IMPLIED WARRANTIES OF
MERCHANTABILITY OR FITNESS FOR A PARTICULAR PURPOSE.
13. Acknowledgments
We would like to acknowledge input and helpful comments from Rob
Goguen, Tony Li, Yakov Rekhter and Curtis Villamizar. Especially,
we thank those, who have been involved in interoperability testing
and field trails, and provided invaluable ideas and suggestions.
They are Rob Goguen, Carol Iturralde, Brook Bailey, Safaa Hasan,
Richard Southern, and Bijan Jabbari.
14. Normative References
[RSVP] R. Braden, Ed., et al, "Resource ReSerVation protocol (RSVP)
-- version 1 functional specification," RFC2205, September 1997.
[RSVP-TE] D. Awduche, et al, "RSVP-TE: Extensions to RSVP for LSP
tunnels", RFC3029, December 2001.
[RFC-WORDS] Bradner, S., "Key words for use in RFCs to Indicate
Requirement Levels", RFC 2119, March 1997.
[RFC-IANA] T. Narten and H. Alvestrand, "Guidelines for Writing an
IANA Considerations Section in RFCs", RFC 2434.
15. Author Information
Ping Pan
CIENA Corp.
10480 Ridgeview Court
Pan et al. [Page 33]
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Cupertino, CA 95014
e-mail: ppan@ciena.net
phone: +1 408 366 4991
Der-Hwa Gan
Juniper Networks
1194 N.Mathilda Ave
Sunnyvale, CA 94089
e-mail: dhg@juniper.net
phone: +1 408 745 2074
George Swallow
Cisco Systems, Inc.
250 Apollo Drive
Chelmsford, MA 01824
email: swallow@cisco.com
phone: +1 978 244 8143
Jean Philippe Vasseur
Cisco Systems, Inc.
300 Apollo Drive
Chelmsford, MA 01824
email: jpv@cisco.com
phone: +1 978 497 6238
Dave Cooper
Global Crossing
960 Hamlin Court
Sunnyvale, CA 94089
email: dcooper@gblx.net
phone: +1 916 415 0437
Alia Atlas
Avici Systems
101 Billerica Avenue
N. Billerica, MA 01862
email: aatlas@avici.com
phone: +1 978 964 2070
Markus Jork
Avici Systems
101 Billerica Avenue
N. Billerica, MA 01862
email: mjork@avici.com
phone: +1 978 964 2142
Pan et al. [Page 34]
