Internet DRAFT - draft-hegde-ospf-advertising-te-protocols
draft-hegde-ospf-advertising-te-protocols
OSPF WG S. Hegde
Internet-Draft C. Bowers
Intended status: Standards Track Juniper Networks
Expires: January 17, 2018 July 16, 2017
Advertising TE protocols in OSPF
draft-hegde-ospf-advertising-te-protocols-01
Abstract
This document defines a mechanism to indicate which traffic
engineering protocols are enabled on a link in OSPF. It does so by
introducing a new Traffic-Engineering Protocol sub-TLV for the Link
TLV in the OSPFv2 TE Opaque LSA. This document also describes
mechanisms to address backward compatibility issues for routers that
have not yet been upgraded to software that understands this new sub-
TLV.
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 RFC 2119 [RFC2119].
Status of This Memo
This Internet-Draft is submitted in full conformance with the
provisions of BCP 78 and BCP 79.
Internet-Drafts are working documents of the Internet Engineering
Task Force (IETF). Note that other groups may also distribute
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Internet-Drafts are draft documents valid for a maximum of six months
and may be updated, replaced, or obsoleted by other documents at any
time. It is inappropriate to use Internet-Drafts as reference
material or to cite them other than as "work in progress."
This Internet-Draft will expire on January 17, 2018.
Copyright Notice
Copyright (c) 2017 IETF Trust and the persons identified as the
document authors. All rights reserved.
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Table of Contents
1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . 2
2. Motivation . . . . . . . . . . . . . . . . . . . . . . . . . 3
2.1. Explicit and unambiguous indication of TE protocol . . . 3
2.2. Limit increases in link state advertisements . . . . . . 4
3. Solution . . . . . . . . . . . . . . . . . . . . . . . . . . 4
3.1. Traffic-engineering protocol sub-TLV . . . . . . . . . . 4
4. Backward compatibility . . . . . . . . . . . . . . . . . . . 6
4.1. Scenario with upgraded RSVP-TE transit router but RSVP-
TE ingress router not upgraded . . . . . . . . . . . . . 6
4.2. Scenario with upgraded RSVP-TE ingress router but RSVP-
TE transit router not upgraded . . . . . . . . . . . . . 7
4.3. Need for a long term solution . . . . . . . . . . . . . . 8
4.4. Interaction with the Extended Link Opaque LSA . . . . . . 8
5. Security Considerations . . . . . . . . . . . . . . . . . . . 8
6. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 8
7. References . . . . . . . . . . . . . . . . . . . . . . . . . 9
7.1. Normative References . . . . . . . . . . . . . . . . . . 9
7.2. Informative References . . . . . . . . . . . . . . . . . 9
Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . 9
1. Introduction
OSPF extensions for traffic engineering are specified in [RFC3630].
[RFC3630] defines several link attributes such as administrative
group, maximum link bandwidth, and shared risk link groups (SRLGs)
which can be used by traffic engineering applications. Additional
link attributes for traffic engineering have subsequently been
defined in other documents as well. Most recently [RFC7471] defined
link attributes for delay, loss, and measured bandwidth utilization.
All of the TE link attributes specified in [RFC3630] and [RFC7471]
are carried in sub-TLVs in the Link TLV of the TE Opaque LSA.
The primary consumers of these traffic engineering link attributes
have been RSVP-based applications that use the advertised link
attributes to compute paths which will subsequently be signalled
using RSVP-TE. However, these traffic engineering link attributes
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have also been used by other applications, such as IP/LDP fast-
reroute using loop-free alternates as described in [RFC7916]. In the
future, it is likely that traffic engineering applications based on
Segment Routing [I-D.ietf-spring-segment-routing] will also use these
link attributes.
Existing OSPF standards do not provide a mechanism to explicitly
indicate whether or not RSVP has been enabled on a link. In general,
implementations have used the presence of the Link TLV in the TE
Opaque LSA to infer that RSVP is enabled on a link.
This document defines a standard way to indicate whether or not RSVP,
segment routing, or another future protocol is enabled on a link. In
this way, implementations will not have to infer whether or not RSVP
is enabled based on the presence of different sub-TLVs, but can use
the explicit indication. When network operators want to use a non-
RSVP traffic engineering application (such as IP/LDP FRR or segment
routing), they will be able to advertise traffic engineer sub-TLVs
and explicitly indicate what traffic engineering protocols are
enabled on a link.
2. Motivation
The motivation of this document is to provide a mechanism to
advertise TE attributes for current and future applications without
ambiguity. The following objectives help to accomplish this in a
range of deployment scenarios.
1. Advertise TE attributes for the link for variety of applications.
2. Allow the solution to be backward compatible so that nodes that
do not understand the new advertisement do not cause issues for
existing RSVP deployment.
3. Allow the solution to be extensible for any new applications that
need to look at TE attributes.
4. Allow the TE protocol enabled on a link to be communicated
unambiguously.
5. The solution should try to limit any increases to the quantity
and size of link state advertisements.
2.1. Explicit and unambiguous indication of TE protocol
Communicating unambiguously which TE protocol is enabled on a link is
important to be able to share this information with other consumers
through other protocols, aside from just the IGP. For example, for a
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network running both RSVP-TE and SR, it will be useful to communicate
which TE protocols are enabled on which links via BGP-LS [RFC7752] to
a central controller. Typically, BGP-LS relies on the IGP to
distribute IGP topology and traffic engineering information so that
only a few BGP-LS sessions with the central controller are needed.
In order for a router running a BGP-LS session to a central
controller to correctly communicate what TE protocols are enabled on
the links in the IGP domain, that information first needs to be
communicated unambiguously within the IGP itself.
2.2. Limit increases in link state advertisements
Over the years, the size of the networks running OSPF has grown both
in terms of the total number of nodes as well as the number of links
interconnecting those nodes. OSPF has proven to be quite scalable.
With the advent of cloud scale computing, we expect the demands
placed on OSPF by network operators to continue to grow as networks
become larger and more richly interconnected. If we expect OSPF to
continue to scale to meet this challenge, then as we evolve OSPF, we
should be careful to limit the increases in both the quantity and
size of link state advertisements to the amount necessary to solve
the problem at hand. The solution described in this draft attempts
to do that.
3. Solution
3.1. Traffic-engineering protocol sub-TLV
A new Traffic-Engineering Protocol sub-TLV is added to the Link TLV
in the OSPFv2 TE Opaque LSA. The Traffic-Engineering Protocol sub-
TLV indicates the protocols enabled on the link. The sub-TLV has
flags in the value field to indicate the protocol enabled on the
link. The length field is variable to allow the flags field to grow
for future requirements.
Type : TBD suggested value 40
Length: Variable
Value :
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
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Flags |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
Figure 1: Traffic-Engineering Protocol sub-TLV
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Type : TBA (suggested value 40)
Length: variable (in bytes)
Value: The value field consists of bits indicating the protocols
enabled on the link. This document defines the two protocol values
below.
+----------+-------------------------------+
| Value | Protocol Name |
+----------+-------------------------------+
|0x01 | RSVP |
+----------+-------------------------------+
|0x02 | Segment Routing |
+----------+-------------------------------+
Figure 2: Flags for the protocols
The RSVP flag is set to one to indicate that RSVP-TE is enabled on a
link. The RSVP flag is set to zero to indicate that RSVP-TE is not
enabled on a link.
The Segment Routing flag is set to one to indicate that Segment
Routing is enabled on a link. The Segment Routing flag is set to
zero to indicate that Segment Routing is not enabled on a link.
All undefined flags MUST be set to zero on transmit and ignored on
receipt.
An implementation that supports the TE Protocol sub-TLV and sends the
Link TLV MUST advertise the TE protocol sub-TLV in the Link TLV, even
when both the RSVP and SR flags are set to zero. In other words,
whenever the TE protocol sub-TLV is supported, it MUST be sent, even
if no TE protocols are enabled on the link. This allows a receiving
router to determine whether or not the sending router is capable of
sending the TE Protocol sub-TLV.
A router supporting the TE protocol sub-TLV which receives an
advertisement for a link containing the Link TLV with the TE protocol
sub-TLV present SHOULD respect the values of the flags in the TE
protocol sub-TLV. The receiving router SHOULD only consider links
with a given TE protocol enabled for inclusion in a path using that
TE protocol. Conversely, links for which the TE protocol sub-TLV is
present, but for which the TE protocol flag is not set to one, SHOULD
NOT be included in any TE CSPF computations on the receiving router
for the protocol in question.
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However, if the SR protocol flag is set to zero on a link but the
adjacency-sids are advertised for that link, applications MAY use the
adjacency-sid for other purposes, for example OAM.
The ability for a receiving router to determine whether or not the
sending router is capable of sending the TE protocol sub-TLV is also
used for backward compatibility as described in Section 4.
An implementation that supports the TE protocol sub-TLV SHOULD be
able to advertise TE attribute sub-TLVs without enabling RSVP-TE
signalling on the link.
4. Backward compatibility
Routers running older software that do not understand the new
Traffic-Engineering protocol sub-TLV will continue to interpret the
presence of the Link TLV in the TE Opaque LSA to mean that RSVP is
enabled a link. A network operator may not want to or be able to
upgrade all routers in the domain at the same time. There are two
backward compatibility scenarios to consider depending on whether the
router that doesn't understand the new TE protocol sub-TLV is an
RSVP-TE ingress router or an RSVP-TE transit router.
4.1. Scenario with upgraded RSVP-TE transit router but RSVP-TE ingress
router not upgraded
An upgraded RSVP-TE transit router is able to explicitly indicate
that RSVP is not enabled on a link by advertising the TE protocol
sub-TLV with the RSVP flag set to zero. However, an RSVP-TE ingress
router that has not been upgraded to understand the new TE protocol
sub-TLV will not understand that RSVP-TE is not enabled on the link,
and may include the link on a path computed for RSVP-TE. When the
network tries to signal an explicit path LSP using RSVP-TE through
that link, it will fail. In order to avoid this scenario, an
operator can use the mechanism described below.
For this scenario, the basic idea is to use the existing
administrative group link attribute as a means of preventing existing
RSVP implementations from using a link. The network operator defines
an administrative group to mean that RSVP is not enabled on a link.
We refer to this admin group the RSVP-not-enabled admin group. If
the operator needs to advertise a TE sub-TLV (maximum link bandwidth,
for example) on a link, but doesn't want to enable RSVP on that link,
then the operator also advertises the RSVP-not-enabled admin group on
that link. The operator can then use existing mechanisms to exclude
links advertising the RSVP-not-enabled admin group from the
constrained shortest path first (CSPF) computation used by RSVP.
This will prevent RSVP implementations from attempting to signal
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RSVP-TE LSPs across links that do not have RSVP enabled. Once the
entire network domain is upgraded to understand the TE protocol sub-
TLV in this draft, the configuration involving the RSVP-not-enabled
admin group is no longer needed for this network.
To be clear, the RSVP-not-enabled admin group is an arbitrary admin
group chosen by a network operator for this purpose. It is not a
value that would need to be standardized.
4.2. Scenario with upgraded RSVP-TE ingress router but RSVP-TE transit
router not upgraded
The other scenario to consider is when the RSVP-TE ingress router has
been upgraded to understand the TE protocol sub-TLV, but the RSVP-TE
transit router has not. In this case, the transit router has not
been upgraded, so it is not yet capable of sending the TE protocol
sub-TLV. If the transit router has RSVP-TE enabled on a link, we
would like for the RSVP-TE ingress router to still be able to use the
link for RSVP-TE paths. While it is possible to describe a solution
for this scenario that makes use of administrative groups, we
describe a simpler solution below.
The solution for this scenario relies on the following observation.
If the RSVP-TE ingress router can understand that the transit router
is not capable of sending the TE protocol sub-TLV, then it can
continue inferring whether or not RSVP-TE is enabled on the transit
router links based on the presence of the Link TLV in the TE Opaque
LSA, just as it does today.
To accomplish this, we require an upgraded router to send the TE
protocol sub-TLV if it sends the OSPF TE Link TLV, even when both the
RSVP and SR flags are set to zero. In other words, whenever the TE
protocol sub-TLV is supported, it MUST be sent, even if no TE
protocols are enabled on the link. see Section 3. This allows the
receiving router to interpret the absence of the TE-protocol sub-TLV
in the OSPF TE Link TLV to mean that the sending router has not been
upgraded. This allows the upgraded RSVP-TE ingress router to
distinguish between transit routers that have been upgraded and those
that haven't. When the transit router has been upgraded, then the
RSVP-TE ingress router uses the information in the TE protocol sub-
TLV. When the transit router has not been upgraded, then RSVP-TE
ingress router contines to infer whether or not RSVP-TE is enabled on
the transit router links based on the presence of TE sub-TLVs, just
as it does today. The solution for this scenario requires no
configuration on the part of network operators.
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4.3. Need for a long term solution
The use of the adminstrative group link attribute to prevent an RSVP-
TE ingress router from computing a path using a given link is an
effective short term workaround to allow networks to incrementally
upgrade the routers to software that understands the new TE-protocol
sub-TLV. One might also consider a long term solution based solely
on the use of operator-defined adminstrative groups to communicate
the TE protocol enabled on a link. However, we do not consider this
workaround to be an effective long term solution because it relies on
operator configuration that would have to be maintained in the long
term. As discussed in Section 2, continuing to have to infer which
TE protocol is enabled on a link would also limit our ability to
communicate this information unambiguously in an interoperable manner
for use by other applications such as central controllers.
4.4. Interaction with the Extended Link Opaque LSA
The Extended Link TLV and the Extended Link Opaque LSA were
introduced in [RFC7684] with the initial purpose of associating
Adjacency SIDs with links for segment routing. A pure segment
routing deployment that does not make use of any of the traffic
engineering attributes carried in the Link TLV in the TE Opaque LSA
does not need to advertise the Link TLV in the TE Opaque LSA. It
only needs to advertise Extended Link TLV in the Extended Link Opaque
LSA for the link. If the operator wants to make use of any traffic
engineering attributes defined for the Link TLV in the TE Opaque LSA,
then the routers in the network need to advertise the Link TLV in the
TE Opaque LSA to carry the TE attributes as well the Extended Link
TLV in the Extended Link Opaque LSA to carry the Adjacency SIDs.
5. Security Considerations
This document does not introduce any further security issues other
than those discussed in [RFC3630].
6. IANA Considerations
This specification updates one OSPF registry:
The Types for sub-TLVs of the TE Link TLV Registry
i) Traffic-engineering Protocol sub-tlv = Suggested value 35
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7. References
7.1. Normative References
[I-D.ietf-spring-segment-routing]
Filsfils, C., Previdi, S., Decraene, B., Litkowski, S.,
and R. Shakir, "Segment Routing Architecture", draft-ietf-
spring-segment-routing-09 (work in progress), July 2016.
[RFC2119] Bradner, S., "Key words for use in RFCs to Indicate
Requirement Levels", BCP 14, RFC 2119,
DOI 10.17487/RFC2119, March 1997,
<http://www.rfc-editor.org/info/rfc2119>.
[RFC3630] Katz, D., Kompella, K., and D. Yeung, "Traffic Engineering
(TE) Extensions to OSPF Version 2", RFC 3630,
DOI 10.17487/RFC3630, September 2003,
<http://www.rfc-editor.org/info/rfc3630>.
[RFC7471] Giacalone, S., Ward, D., Drake, J., Atlas, A., and S.
Previdi, "OSPF Traffic Engineering (TE) Metric
Extensions", RFC 7471, DOI 10.17487/RFC7471, March 2015,
<http://www.rfc-editor.org/info/rfc7471>.
7.2. Informative References
[RFC7684] Psenak, P., Gredler, H., Shakir, R., Henderickx, W.,
Tantsura, J., and A. Lindem, "OSPFv2 Prefix/Link Attribute
Advertisement", RFC 7684, DOI 10.17487/RFC7684, November
2015, <http://www.rfc-editor.org/info/rfc7684>.
[RFC7752] Gredler, H., Ed., Medved, J., Previdi, S., Farrel, A., and
S. Ray, "North-Bound Distribution of Link-State and
Traffic Engineering (TE) Information Using BGP", RFC 7752,
DOI 10.17487/RFC7752, March 2016,
<http://www.rfc-editor.org/info/rfc7752>.
[RFC7916] Litkowski, S., Ed., Decraene, B., Filsfils, C., Raza, K.,
Horneffer, M., and P. Sarkar, "Operational Management of
Loop-Free Alternates", RFC 7916, DOI 10.17487/RFC7916,
July 2016, <http://www.rfc-editor.org/info/rfc7916>.
Authors' Addresses
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Shraddha Hegde
Juniper Networks
Embassy Business Park
Bangalore, KA 560093
India
Email: shraddha@juniper.net
Chris Bowers
Juniper Networks
1194 N. Mathilda Ave.
Sunnyvale, CA 94089
US
Email: cbowers@juniper.net
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