TEAS Working Group Vishnu Pavan Beeram (Ed)
Internet Draft Juniper Networks
Intended status: Proposed Standard Ina Minei
Google, Inc
Rob Shakir
British Telecom
Ebben Aries
Facebook
Dante Pacella
Verizon
Tarek Saad
Cisco Systems
Markus Jork
Juniper Networks
Expires: April 5, 2016 October 5, 2015
Implementation Recommendations to Improve the Scalability of RSVP-TE
Deployments
draft-ietf-teas-rsvp-te-scaling-rec-00
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Copyright Notice
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Abstract
The scale at which RSVP-TE Label Switched Paths (LSPs) get deployed
is growing continually and the onus is on RSVP-TE implementations
across the board to keep up with this increasing demand.
This document makes a set of implementation recommendations to help
RSVP-TE deployments push the envelope on scaling and advocates the
use of a couple of techniques - "Refresh Interval Independent RSVP
(RI-RSVP)" and "Per-Peer flow-control" - for improving scaling.
Conventions used in this document
The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT",
"SHOULD", "SHOULD NOT", "RECOMMENDED", "MAY", and "OPTIONAL" in this
document are to be interpreted as described in RFC-2119 [RFC2119].
Table of Contents
1. Introduction...................................................3
2. Recommendations................................................4
2.1. "RFC2961 specific" Recommendations........................4
2.1.1. Basic Pre-Requisites.................................4
2.1.2. Making Acknowledgements mandatory....................4
2.1.3. Clarifications on reaching Rapid Retry Limit (Rl)....4
2.2. Refresh Interval Independent RSVP.........................5
2.2.1. Capability Advertisement.............................6
2.2.2. Compatibility........................................6
2.3. Per-Peer RSVP Flow Control................................7
2.3.1. Capability Advertisement.............................7
2.3.2. Compatibility........................................8
2.4. Other Recommendations.....................................8
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2.4.1. Summary FRR..........................................8
3. Security Considerations........................................8
4. IANA Considerations............................................9
4.1. Capability Object Values..................................9
5. References.....................................................9
5.1. Normative References......................................9
5.2. Informative References...................................10
6. Acknowledgments...............................................10
Appendix A. Recommended Defaults.................................10
Authors' Addresses...............................................11
1. Introduction
The scale at which RSVP-TE [RFC3209] Label Switched Paths (LSPs) get
deployed is growing continually and there is considerable onus on
RSVP-TE implementations across the board to keep up with this
increasing demand in scale.
The set of RSVP Refresh Overhead Reduction procedures [RFC2961]
serves as a powerful toolkit for RSVP-TE implementations to help
cover a majority of the concerns about soft-state scaling. However,
even with these tools in the toolkit, analysis of existing
implementations [RFC5439] indicates that the processing required
under certain scale may still cause significant disruption to an
LSR.
This document builds on the scaling work and analysis that has been
done so far and makes a set of concrete implementation
recommendations to help RSVP-TE deployments push the envelope
further on scaling - push higher the threshold above which an LSR
struggles to achieve sufficient processing to maintain LSP state.
This document advocates the use of a couple of techniques - "Refresh
Interval Independent RSVP (RI-RSVP)" and "Per-Peer flow-control" -
for significantly cutting down the amount of processing cycles
required to maintain LSP state. "RI-RSVP" helps completely eliminate
RSVP's reliance on refreshes and refresh-timeouts while "Per-Peer
Flow-Control" enables a busy RSVP speaker to apply back pressure to
its peer(s). In order to reap maximum scaling benefits, it is
strongly RECOMMENDED that implementations support both the
techniques, but it is possible for an implementation to support just
one but not the other.
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2. Recommendations
2.1. "RFC2961 specific" Recommendations
The implementation recommendations discussed in this section are
based on the proposals made in [RFC2961] and act as pre-requisites
for implementing either or both of the techniques discussed in
Sections 2.2 and 2.3.
2.1.1. Basic Pre-Requisites
An implementation that supports either or both of the techniques
discussed in Sections 2.2 and 2.3:
- SHOULD indicate support for RSVP Refresh Overhead Reduction
extensions (as specified in Section 2 of [RFC2961]) by default,
with the ability to override the default via configuration.
- MUST support reliable delivery of Path/Resv and the corresponding
Tear/Err messages using the procedures specified in [RFC2961].
- MUST support retransmit of all RSVP-TE messages using exponential-
backoff, as specified in Section 6 of [RFC2961].
2.1.2. Making Acknowledgements mandatory
The reliable message delivery mechanism specified in [RFC2961]
states that "Nodes receiving a non-out of order message containing a
MESSAGE_ID object with the ACK_Desired flag set, SHOULD respond with
a MESSAGE_ID_ACK object."
In an implementation that supports either or both of the techniques
discussed in Sections 2.2 and 2.3, nodes receiving a non-out of
order message containing a MESSAGE ID object with the ACK-Desired
flag set, MUST respond with a MESSAGE_ID_ACK object. This
improvement to the predictability of the system in terms of reliable
message delivery is key for being able to take any action based on a
non-receipt of an ACK.
2.1.3. Clarifications on reaching Rapid Retry Limit (Rl)
According to section 6 of [RFC2961] "The staged retransmission will
continue until either an appropriate MESSAGE_ID_ACK object is
received, or the rapid retry limit, Rl, has been reached." The
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following clarifies what actions, if any, a router should take once
Rl has been reached.
If it is the retransmission of Tear/Err messages and Rl has been
reached, the router need not take any further actions. If it is the
retransmission of Path/Resv messages and Rl has been reached, then
the router starts periodic retransmission of these messages. The
retransmitted messages MUST carry MESSAGE_ID object with ACK_Desired
flag set. This periodic retransmission SHOULD continue until an
appropriate MESSAGE_ID ACK object is received indicating
acknowledgement of the (retransmitted) Path/Resv message. The
configurable periodic retransmission interval SHOULD be less than
the regular refresh interval. A default periodic retransmission
interval of 30 seconds is RECOMMENDED by this document.
2.2. Refresh Interval Independent RSVP
The RSVP protocol relies on periodic refreshes for state
synchronization between RSVP neighbors and for recovery from lost
RSVP messages. It relies on refresh timeout for stale state cleanup.
The primary motivation behind introducing the notion of "Refresh
Interval Independent RSVP" (RI-RSVP) is to completely eliminate
RSVP's reliance on refreshes and refresh timeouts. This is done by
simply increasing the refresh interval to a fairly large value.
[RFC2961] and [RFC5439] do talk about increasing the value of the
refresh-interval to provide linear improvement on transmission
overhead, but also point out the degree of functionality that is
lost by doing so. This section revisits this notion, but also
proposes sufficient recommendations to make sure that there is no
loss of functionality incurred by increasing the value of the
refresh interval.
An implementation that supports RI-RSVP:
- MUST support all the recommendations made in Section 2.1
- MUST make the default value of the configurable refresh interval
be a large value (10s of minutes). A default value of 20 minutes
is RECOMMENDED by this document.
- MUST implement coupling the state of individual LSPs with the
state of the corresponding RSVP-TE signaling adjacency. When an
RSVP-TE speaker detects RSVP-TE signaling adjacency failure, the
speaker MUST act as if the all the Path and Resv state learnt via
the failed signaling adjacency has timed out.
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- MUST make use of Node-ID based Hello Session ([RFC3209],
[RFC4558]) for detection of RSVP-TE signaling adjacency failures;
A default value of 9 seconds is RECOMMENDED by this document for
the configurable node hello interval (as opposed to the 5ms
default value proposed in Section 5.3 of [RFC3209]).
- (If Bypass FRR [RFC4090] is supported,) MUST implement procedures
specified in [RI-RSVP-FRR] which describes methods to facilitate
FRR that works independently of the refresh-interval.
- MUST indicate support for RI-RSVP via the CAPABILITY object in
Hello messages.
2.2.1. Capability Advertisement
An implementation supporting the RI-RSVP recommendations MUST set a
new flag "RI-RSVP Capable" in the CAPABILITY object signaled in
Hello messages.
The new flag that will be introduced to CAPABILITY object is
specified below.
0 1 2 3
0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Length | Class-Num(134)| C-Type (1) |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Reserved |I|T|R|S|
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
I bit
Indicates that the sender supports RI-RSVP.
Any node that sets the new I-bit in its CAPABILITY object MUST also
set Refresh-Reduction-Capable bit in common header of all RSVP-TE
messages.
2.2.2. Compatibility
The RI-RSVP functionality MUST be activated only between peers that
indicate their support for this functionality. The RI-RSVP specific
Bypass FRR procedures discussed in [RI-RSVP-FRR] introduce a few new
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protocol extensions and those MUST get activated only if the
participating nodes support RI-RSVP functionality.
2.3. Per-Peer RSVP Flow Control
The set of recommendations discussed in this section provide an RSVP
speaker with the ability to apply back pressure to its peer(s) to
reduce/eliminate RSVP-TE control plane congestion.
An implementation that supports "Per-Peer RSVP Flow Control":
- MUST support all the recommendations made in Section 2.1
- MUST use lack of ACKs from a peer as an indication of peer's RSVP-
TE control plane congestion. If congestion is detected, the local
system MUST throttle RSVP-TE messages to the affected peer. This
MUST be done on a per-peer basis. (Per-peer throttling MAY be
implemented by a traffic shaping mechanism that proportionally
reduces the RSVP signaling packet rate as the number of
outstanding Acks increases. And when the number of outstanding
Acks decreases, the send rate would be adjusted up again.)
- SHOULD use a Retry Limit (Rl) value of 7 (Section 6.2 of
[RFC2961], suggests using 3).
- SHOULD prioritize Tear/Error over trigger Path/Resv (messages that
bring up new LSP state) sent to a peer when the local system
detects RSVP-TE control plane congestion in the peer.
- MUST indicate support for all recommendations in this section via
the CAPABILITY object in Hello messages.
2.3.1. Capability Advertisement
An implementation supporting the "Per-Peer Flow Control"
recommendations MUST set a new flag "Per-Peer Flow Control Capable"
in the CAPABILITY object signaled in Hello messages.
The new flag that will be introduced to CAPABILITY object is
specified below.
0 1 2 3
0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Length | Class-Num(134)| C-Type (1) |
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+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Reserved |F|I|T|R|S|
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
F bit
Indicates that the sender supports Per-Peer RSVP Flow Control
Any node that sets the new I-bit in its CAPABILITY object MUST also
set Refresh-Reduction-Capable bit in common header of all RSVP-TE
messages.
2.3.2. Compatibility
The "Per-Peer Flow Control" functionality MUST be activated only if
both peers support it. If a peer hasn't indicated that it is capable
of participating in "Per-Peer Flow Control", then it is risky to
assume that the peer would always acknowledge a non-out of order
message containing a MESSAGE ID object with the ACK-Desired flag
set.
2.4. Other Recommendations
The following scaling recommendations have no interdependency with
any of the techniques/recommendations specified in Sections 2.2 and
2.3. These are stand-alone functionalities that help improve RSVP-TE
scalability.
2.4.1. Summary FRR
If Bypass FRR [RFC4090] is supported by an implementation, it SHOULD
support the procedures discussed in [SUMMARY-FRR]. These procedures
reduce the amount of RSVP signaling required for Fast Reroute
procedures and subsequently improve the scalability of RSVP-TE
signaling when undergoing FRR convergence post a link or node
failure.
3. Security Considerations
This document does not introduce new security issues. The security
considerations pertaining to the original RSVP protocol [RFC2205]
and RSVP-TE [RFC3209] and those that are described in [RFC5920]
remain relevant.
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4. IANA Considerations
4.1. Capability Object Values
[RFC5063] defines the name space for RSVP Capability Object Values.
The name space is managed by IANA.
IANA registry: RSVP PARAMETERS
Subsection: Capability Object Values
A Capability flag called "RI-RSVP Capable" is defined in Section
2.2.1 of this document. The bit number for this flag is TBD.
A Capability flag called "Per-Peer Flow Control Capable" is defined
in Section 2.3.1 of this document. The bit number for this flag is
TBD.
5. References
5.1. Normative References
[RFC2119] Bradner, S., "Key words for use in RFCs to Indicate
Requirement Levels", BCP 14, RFC 2119, March 1997.
[RFC2205] Braden, R., "Resource Reservation Protocol (RSVP)",
RFC 2205, September 1997.
[RFC2961] Berger, L., "RSVP Refresh Overhead Reduction
Extensions", RFC 2961, April 2001.
[RFC3209] Awduche, D., "RSVP-TE: Extensions to RSVP for LSP
Tunnels", RFC 3209, December 2001.
[RFC4090] Pan, P., "Fast Reroute Extensions to RSVP-TE for LSP
Tunnels", RFC 4090, May 2005.
[RFC4558] Ali, Z., "Node-ID Based Resource Reservation (RSVP)
Hello: A Clarification Statement", RFC 4558, June 2006.
[RFC5063] Satyanarayana, A., "Extensions to GMPLS Resource
Reservation Protocol Graceful Restart", RFC5063, October
2007.
[RI-RSVP-FRR] Ramachandran, C., "Refresh Interval Independent FRR
Facility Protection", draft-chandra-mpls-ri-rsvp-frr,
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(work in progress)
[SUMMARY-FRR] Taillon, M., "RSVP-TE Summary Fast Reroute Extensions
for LSP Tunnels", draft-mtaillon-mpls-summary-frr-
rsvpte-00, (work in progress)
5.2. Informative References
[RFC5439] Yasukawa, S., "An Analysis of Scaling Issues in MPLS-TE
Core Networks", RFC 5439, February 2009.
[RFC5920] Fang, L., "Security Framework for MPLS and GMPLS
Networks", RFC5920, July 2010.
6. Acknowledgments
The authors would like to thank Yakov Rekhter for initiating this
work and providing valuable inputs. They would like to thank
Raveendra Torvi and Chandra Ramachandran for participating in the
many discussions that led to the recommendations made in this
document. They would also like to thank Adrian Farrel for providing
detailed review comments.
Appendix A. Recommended Defaults
(a) Refresh-Interval (R)- 20 minutes (Section 2.2)
Given that an implementation supporting RI-RSVP doesn't rely on
refreshes for state sync between peers, the RSVP refresh interval is
sort of analogous to IGP refresh interval, the default of which is
typically in the order of 10s of minutes. Choosing a default of 20
minutes allows the refresh timer to be randomly set to a value in
the range [10 minutes (0.5R), 30 minutes (1.5R)].
(b) Node Hello-Interval - 9 Seconds (Section 2.2)
[RFC3209] defines the hello timeout as 3.5 times the hello interval.
Choosing 9 seconds for the node hello-interval gives a hello timeout
of 3.5*9 = 31.5 seconds. This puts the hello timeout value to be in
the same ballpark as the IGP hello timeout value.
(c) Retry-Limit (Rl) - 7 (Section 2.3)
Choosing 7 as the retry-limit results in an overall rapid retransmit
phase of 31.5 seconds. This nicely matches up with the 31.5 seconds
hello timeout.
(d) Periodic Retransmission Interval - 30 seconds (Section 2.1.3)
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If the Retry-Limit (Rl) is 7, then it takes about 30 (31.5 to be
precise) seconds for the 7 rapid retransmit steps to max out. (The
last delay from message 6 to message 7 is 16 seconds). The 30
seconds interval also matches the traditional default refresh time.
Authors' Addresses
Vishnu Pavan Beeram (Ed)
Juniper Networks
Email: vbeeram@juniper.net
Ina Minei
Google, Inc
Email: inaminei@google.com
Rob Shakir
British Telecom
Email: rob.shakir@bt.com
Ebben Aries
Facebook
Email: exa@fb.com
Dante Pacella
Verizon
Email: dante.j.pacella@verizon.com
Tarek Saad
Cisco Systems
Email: tsaad@cisco.com
Markus Jork
Juniper Networks
Email: mjork@juniper.net
Beeram, et al Expires April 5, 2016 [Page 11]
