Internet DRAFT - draft-ietf-rtgwg-routing-timer-param-sync
draft-ietf-rtgwg-routing-timer-param-sync
Network Working Group S. Bryant
Internet-Draft Huawei Technologies
Intended status: Standards Track A. Atlas
Expires: May 1, 2018 C. Bowers
Juniper Networks
October 28, 2017
Routing Timer Parameter Synchronization
draft-ietf-rtgwg-routing-timer-param-sync-00
Abstract
This document describes a mechanism for a link state routing protocol
to coordinate the value of a routing timer parameter amongst routers
in the flooding domain. The document also defines the solution to
one specific case: the agreement of a common convergence timer value
for use by routers in network convergence.
Status of This Memo
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provisions of BCP 78 and BCP 79.
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This Internet-Draft will expire on May 1, 2018.
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described in the Simplified BSD License.
Table of Contents
1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . 2
2. Requirements Language . . . . . . . . . . . . . . . . . . . . 3
3. Overview of Mechanism . . . . . . . . . . . . . . . . . . . . 3
4. Protocol Details . . . . . . . . . . . . . . . . . . . . . . 4
4.1. ISIS . . . . . . . . . . . . . . . . . . . . . . . . . . 4
4.2. OSPF . . . . . . . . . . . . . . . . . . . . . . . . . . 5
5. Convergence Time . . . . . . . . . . . . . . . . . . . . . . 6
5.1. Required Properties . . . . . . . . . . . . . . . . . . . 6
5.2. Definition of the Convergence Timer . . . . . . . . . . . 7
6. IANA considerations . . . . . . . . . . . . . . . . . . . . . 7
6.1. ISIS . . . . . . . . . . . . . . . . . . . . . . . . . . 7
6.2. OSPF . . . . . . . . . . . . . . . . . . . . . . . . . . 8
6.3. Routing Timer Parameter Synchronization Registry . . . . 8
7. Security Considerations . . . . . . . . . . . . . . . . . . . 8
8. Acknowledgments . . . . . . . . . . . . . . . . . . . . . . . 9
9. Contributing Authors . . . . . . . . . . . . . . . . . . . . 9
10. References . . . . . . . . . . . . . . . . . . . . . . . . . 9
10.1. Normative References . . . . . . . . . . . . . . . . . . 9
10.2. Informative References . . . . . . . . . . . . . . . . . 9
Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . 10
1. Introduction
There exist use cases where it desirable for a network to use a
common value for a routing timer parameter across all nodes. In the
past, these types of use case have been addressed by setting the
parameter to a constant value in the protocol definition itself, or
by requiring that the same value of the parameter be configured at
every node.
Setting the routing timer parameter to a constant value in the
protocol definition makes it difficult to change the parameter, since
a change would require formal modification to the protocol. In
practice, such a change is impractical, so the constant value needs
to be chosen conservatively. This may impose a fundamental
restriction on the eventual use of the protocol.
Manual or "static" configuration of the timer parameter is fraught
for two reasons. First, it is can be difficult to ensure that the
correct, identical, value is installed in all of the routers.
Second, if any change is introduced into the network that results in
a need to change the value (for example due to a change in hardware
or software version) then all of the routers need to be reconfigured
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to use the new timer parameter value. Such consistency may be
ensured by deploying automated means such as enforcing the new value
by invoking the management interface of all involved routers. For
example, a central management entity may be responsible for
communicating the new configuration value by means of vendor-specific
command line interface (CLI), NETCONF[RFC6241], etc. This approach
may be attractive if all involved nodes expose technology-agnostic
and vendor-independent interfaces to modify a given network-wide
configuration parameter.
This document describes a protocol extension that propagates a
routing timer parameter throughout the flooding domain, which can be
used as an alternative to the centralized approach described above.
The method of choosing between one or more different advertised
values, the flooding scope, and the action to be taken when the
parameter changes MUST be provided in the definition of the parameter
type.
This document also creates one parameter type: Convergence Timer
intended for use in IP Fast-reroute applications [RFC5714] [RFC5715].
Note that this protocol is only intended to be used for the
propagation of parameters needed to support the operation of the
routing system. It MUST NOT be used as a general purpose parameter
exchange protocol, and in particular it MUST NOT be used as a
parameter negotiation protocol, since such use may degrade the
ability of the underlying link-state routing protocol to carry our
its essential purpose.
2. Requirements Language
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 [RFC2119].
3. Overview of Mechanism
Routing Timer parameter values that can be disseminated by means of
the attribute defined in this specification MUST be defined as a
configurable parameter or a default parameter in the corresponding
specification.
A new information element is introduced into the routing protocol
that specifies the parameter. Each router taking part in the
parameter synchronization is expected to advertise a specific value
of the parameter, which that router determines based mainly on
considerations local to that router. In general, different routers
in the flooding domain may advertise different values of the
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parameter. How the values advertised by a router are determined is
out of scope of this document.
A router receiving the parameter values advertised by all routers in
the flooding domain will use a well-defined method to select the
operational value of the parameter that it uses in the running of the
protocol. All routers MUST use the same method applied to the same
set of advertised parameter values. All routers SHALL therefore
choose the same operational value for the parameter.
Note the operational value for the parameter selected SHOULD NOT
directly affect the value for the parameter advertised by a router,
since this introduces a form of negotiation leading to additional
routing protocol traffic and possibly to instability in the routing
protocol.
The method of selecting from a range of advertised parameter values
MUST be provided in the parameter definition.
The definition of the parameter MUST specify the action to be taken
when a new parameter value is advertised that would cause a change in
the selected value.
The definition of the parameter MUST specify the action to be taken
in the legacy/migration case, where not all routers advertise the
parameter.
4. Protocol Details
This section describes the protocol extensions needed to implement
this functionality.
4.1. ISIS
A new Routing Timer Parameter Synchronization (RTPS) sub-TLV is
introduced into the IS-IS Router CAPABILITY TLV (TLV #242 defined in
[RFC7981]). The setting of the S-bit in TLV #242 (indicating whether
the parameter should be leaked between levels) MUST be included in
the specific routing parameter definition.
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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
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Type | Length | Sub-Type | Duration .
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
. Duration continued |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
Figure 1: Routing Timer Parameter Synchronization ISIS Sub-TLV
The Type (1 octet) of this sub-TLV to be assigned by IANA.
Length is variable (minimum value 5, multiple of 5 octets) and
represents the total Length of the field.
Sub-Type consists of a one octet identifier of the timer type.
Duration is a 32 bit value representing is the length of the timer in
milliseconds. This is capable of expressing a time in the range 1ms
to just under 50 days.
4.2. OSPF
A new Routing Timer Parameter Synchronization TLV is defined for the
OSPF Router Information LSA. This new TLV may be carried in a type
10 or type 11 OSPF Opaque LSA depending on the required flooding
scope.
The specification of a the specific routing timer parameter MUST
define the appropriate flooding scope(s) for that parameter.
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
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Type | Length |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Sub-Type | Duration .
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
. Durn. cont. |
+-+-+-+-+-+-+-+-+
Figure 2: Routing Timer Parameter Synchronization OSPF TLV
The Type (2 octets) of this sub-TLV to be assigned by IANA.
Length is variable (minimum value 5, multiple of 5 octets) and
represents the total Length of the field.
Sub-Type consists of a one octet identifier of the timer type.
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Duration is a 32 bit value representing is the length of the timer in
milliseconds. This is capable of expressing a time in the range 1ms
to just under 50 days.
5. Convergence Time
Routers running a fast-reroute mechanism such as Maximally Redundant
Tree (MRT) [RFC7812] fast re-route require a network wide convergence
time value so that know how long they need continue using the repair
path before it is safe to use the base path. This time is set to be
the worst case time that any router will take to calculate the new
topology, and to make the necessary changes to the FIB.
The time taken by a router to complete each phase of the transition
will be dependent on the size of the network and the design and
implementation of the router. It can therefore be expected that the
optimum delay will need to be tuned from time to time as the network
evolves.
5.1. Required Properties
The Convergence Time mechanism MUST have the following properties:
o The operational convergence delay time MUST be consistent among
all routers that are converging on the new topology.
o The operational convergence delay time MUST be the highest delay
time advertised by any router in the new topology.
o The mechanism MUST increase the delay when a new router in
introduced to the network that requires a higher delay than
is currently in use.
o When the router that had the longest delay requirements is
removed from the topology, the convergence delay timer
value MUST, within some reasonable time, be reduced to
the longest delay required by the remaining routers.
o It MUST be possible for a router to change the
convergence delay timer value that it requires.
o A router which is in multiple routing areas, or is running
multiple routing protocols MAY signal a different loop-free
convergence delay for each area.
How a router determines the time that it needs to execute each
convergence phase is an implementation issue, and outside the scope
of this specification. However a router that dynamically determines
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its proposed delay value must do so in such a way that it does not
cause the synchronized value to continually fluctuate.
5.2. Definition of the Convergence Timer
It is RECOMMENDED that the routing convergence timer be limited to a
maximum of 60 seconds.
The routing convergence timer value selected is the largest value
advertised.
If a routing protocol message is issued that changes the Convergence
Timer value, but does not change the topology, the new timer value
MUST be taken into consideration during the next network transition,
but MUST NOT instigate a new transition.
If a routing protocol message is issued that changes both the
Convergence Timer value and the topology, a transition is instigated
and the new timer value MUST be taken into consideration.
The convergence mechanism MUST specify the action to be taken if a
timer change (only) message and a topology change message are
independently generated during the hold-off time.
A router running ISIS that supports convergence timer synchronization
SHOULD advertise the Routing Timer Parameter Synchronization sub-TLV
with the value of the Convergence Timer in the Duration field of this
sub-TLV. The S-bit is set to zero indicating that the Convergence
Timer RPTS sub-TLV MUST NOT be leaked between levels.
A router running OSPF that supports convergence timer synchronization
SHOULD advertise the Routing Timer Parameter Synchronization TLV
with the value of the Convergence Timer in the Duration field of this
TLV. The TLV SHOULD only be carried in the type 10 Opaque LSA which
prevents propagation outside the OSPF area.
6. IANA considerations
6.1. ISIS
IANA is requested to allocate a new Sub-TLVs for TLV 242 from the IS-
IS TLV Codepoints name space.
Value Description Reference
----------------------------------------------
TBD Routing Timer Parameter This Document
Synchronization
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6.2. OSPF
IANA is requested to allocate a new OSPF Router Information (RI) TLV
from the Open Shortest Path First (OSPF) Parameters name space
Value TLV Name Reference
--------------------------------------------------
TBD Routing Timer Parameter This document
Synchronization
A value in the range 12 to 32767 is requested.
6.3. Routing Timer Parameter Synchronization Registry
IANA is requested to create a new Routing Timer Parameter
Synchronization Registry within its own name space, and to allocate
one value from it.
Value Name Reference
------------------------------------------------
0 Reserved This document
1 Convergence Timer This document
2..255 Reserved This document
Allocations within this registry require IETF Consensus. This link
state protocol extension MUST NOT be used for any purpose other than
one associated with the routing system timer parameters.
7. Security Considerations
The introduction of this parameter advertising mechanism does not
introduce a significant vulnerability into the base routing protocol
and is secured in exactly the same way as the other TLVs that are
carried.
In specifying a new parameter, consideration must be given to the
impact of the additional parameter, and in particular the rate of
change of that parameter, on the dynamics of the link-state routing
protocol in use. In the specific case of the Convergence Timer, the
amount of data being carried and the rate of change of the parameter
value will have a negligible impact on the link-state routing
protocol in use.
A rouge router deliberately introducing an anomalous parameter value
is just as capable of introducing many other anomalies into the
routing domain.
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As far as possible, care should be taken to validate that the
parameter is reasonable.
In the specific case of the Convergence Time RTPS, the following
considerations apply.
If an abnormally large timer value is proposed by a router, the there
is a danger that the convergence process will take an excessive time.
If during that time the routing protocol signals the need for another
transition, the transition will be abandoned and the default best
case (traditional) convergence mechanism used.
It is RECOMMENDED that implementations prohibit the configuration of
a router convergence timer value in excess of 60 seconds.
8. Acknowledgments
The authors thank Les Ginsberg and the other authors of
[I-D.ietf-isis-segment-routing-msd] and
[I-D.ietf-ospf-segment-routing-msd] , Mohamed Boucadair for their
review comments and proposed text, and Tom Petch for his review
comments.
9. Contributing Authors
Mike Shand
Independent
mike@mshand.org.uk
10. References
10.1. Normative References
[RFC2119] Bradner, S., "Key words for use in RFCs to Indicate
Requirement Levels", BCP 14, RFC 2119,
DOI 10.17487/RFC2119, March 1997, <https://www.rfc-
editor.org/info/rfc2119>.
[RFC7981] Ginsberg, L., Previdi, S., and M. Chen, "IS-IS Extensions
for Advertising Router Information", RFC 7981,
DOI 10.17487/RFC7981, October 2016, <https://www.rfc-
editor.org/info/rfc7981>.
10.2. Informative References
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[I-D.ietf-isis-segment-routing-msd]
Tantsura, J., Chunduri, U., Aldrin, S., and L. Ginsberg,
"Signaling MSD (Maximum SID Depth) using IS-IS", draft-
ietf-isis-segment-routing-msd-04 (work in progress), June
2017.
[I-D.ietf-ospf-segment-routing-msd]
Tantsura, J., Chunduri, U., Aldrin, S., and P. Psenak,
"Signaling MSD (Maximum SID Depth) using OSPF", draft-
ietf-ospf-segment-routing-msd-05 (work in progress), June
2017.
[RFC5714] Shand, M. and S. Bryant, "IP Fast Reroute Framework",
RFC 5714, DOI 10.17487/RFC5714, January 2010,
<https://www.rfc-editor.org/info/rfc5714>.
[RFC5715] Shand, M. and S. Bryant, "A Framework for Loop-Free
Convergence", RFC 5715, DOI 10.17487/RFC5715, January
2010, <https://www.rfc-editor.org/info/rfc5715>.
[RFC6241] Enns, R., Ed., Bjorklund, M., Ed., Schoenwaelder, J., Ed.,
and A. Bierman, Ed., "Network Configuration Protocol
(NETCONF)", RFC 6241, DOI 10.17487/RFC6241, June 2011,
<https://www.rfc-editor.org/info/rfc6241>.
[RFC7812] Atlas, A., Bowers, C., and G. Enyedi, "An Architecture for
IP/LDP Fast Reroute Using Maximally Redundant Trees (MRT-
FRR)", RFC 7812, DOI 10.17487/RFC7812, June 2016,
<https://www.rfc-editor.org/info/rfc7812>.
Authors' Addresses
Stewart Bryant
Huawei Technologies
Email: stewart.bryant@gmail.com
Alia Atlas
Juniper Networks
Email: akatlas@gmail.com
Chris Bowers
Juniper Networks
Email: cbowers@juniper.net
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