Internet DRAFT - draft-minei-ldp-operational-experience
draft-minei-ldp-operational-experience
Network Working Group Loa Andersson
Internet Draft Ina Minei
Expiration Date: January 2006 Bob Thomas
Category: Informational Editors
July 2005
Experience with the LDP protocol
draft-minei-ldp-operational-experience-01.txt
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Abstract
The purpose of this memo is to document how some of the requirements
specified in RFC 1264 for advancing protocols developed by working
groups within the IETF Routing Area to Draft Standard have been
satisfied by LDP (Label Distribution Protocol). Specifically, this
report documents operational experience with LDP, requirement 5 of
section 5.0 in RFC 1264.
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Table of Contents
1 Introduction .......................................... 3
2 Operational experience ................................ 3
2.1 Environment and duration .............................. 3
2.2 Applications and motivation ........................... 4
2.3 Protocol features ..................................... 4
2.4 Security concerns ..................................... 4
2.5 Implementations and inter-operability ................. 5
2.6 Operational experience ................................ 5
3 Intellectual Property Statement ....................... 6
4 Acknowledgments ....................................... 6
5 References ............................................ 7
5.1 Normative References .................................. 7
5.2 Informative References ................................ 7
6 Editors' Addresses .................................... 7
Full Copyright Statement .............................. 8
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1. Introduction
The purpose of this memo is to document how some of the requirements
specified in RFC 1264 for advancing protocols developed by working
groups within the IETF Routing Area to Draft Standard have been sat-
isfied by LDP. Specifically, this report documents operational expe-
rience with LDP, requirement 5 of section 5.0 in RFC 1264.
LDP was originally published as RFC 3036 in January 2001. It was
produced by the MPLS Working Group of the IETF and was jointly
authored by Loa Andersson, Paul Doolan, Nancy Feldman, Andre Fredette
and Bob Thomas.
2. Operational experience
This section discusses operational experience with the protocol. The
information is based on a survey sent to the MPLS Working Group in
October 2004. The questionnaire can be found in the MPLS Working
Group mail archives for October 2004.
11 responses were received, all but two requesting confidentiality.
The survey results are summarized to maintain confidentiality. The
networks surveyed span different geographic locations: US, Europe and
Asia. Both academic and commercial networks responded to the survey.
2.1. Environment and duration
The size of the deployments ranges from less than 20 Label Switching
Routers (LSRs) to over 1000 LSRs. Eight out of the 11 deployments
use LDP in the edge and the core, two on the edge only and one in the
core only.
Sessions exist to peers discovered via both the basic and the
extended discovery mechanisms. In half the cases, more than one adja-
cency (and as many as four adjacencies) are maintained per session.
The average number of LDP sessions on an LSR ranges from under 10 to
just over 80. The responses are spread as follows: under 10: 4
responses, 20-50: 4 responses, over 80: 1 response.
In the surveyed networks, the time LDP has been deployed ranges from
under one year to over 4 years. The responses are spread out as fol-
lows: under 1 year - 3 responses, 2 years - 2 responses, 3 years -3
responses and over 4 years - 3 responses.
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2.2. Applications and motivation
Nine out of the 11 responses list L3VPNs as the application driving
the LDP deployment in the network.
The list of applications is as follows. L3VPNs: 9, pseudo-wires: 4
current (and one planned deployment), L2VPNs: 4, forwarding based on
labels: 2, BGP-free core: 1
There are two major options for label distribution protocols, LDP and
RSVP-TE. One of the key differences between the two is that RSVP-TE
has support for Traffic Engineering (TE), while LDP does not. The
reasons cited for picking LDP as the label distribution protocol are:
o The deployment does not require traffic engineering - 6
o Inter-operability concerns if a different protocol is used - 5
o Equipment vendor only supports LDP - 5
o Ease of configuration - 4
o Ease of management - 3
o Scalability concerns with other protocols - 3
o Required for a service offering of the service provider - 1
2.3. Protocol features
All deployments surveyed use the downstream unsolicited label distri-
bution mode. All but one deployment use liberal label retention (one
uses conservative).
LSP setup is established with both independent and ordered control.
Five of the deployments use both control modes in the same network.
The number of LDP FECs advertised and LDP routes installed falls in
one of two categories: 1) roughly the same as the number of LSRs in
the network and 2) roughly the same as the number of IGP routes in
the network. Of the 8 responses were received. 6 were in the first
category and 2 in the second.
2.4. Security concerns
A security concern was raised by one of the operators with respect
to the lack of a mechanism for securing LDP Hellos.
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2.5. Implementations and inter-operability
Eight out of the 11 responses state that more than one implementation
(and as many as four different ones) are deployed in the same net-
work.
The consensus is that although implementations differ, no inter-oper-
ability issues exist. The challenges listed by providers running mul-
tiple implementations are:
o Different flexibility in picking which FECs to advertise labels
for.
o Different flexibility in setting transport and LDP router-id
addresses.
o Different default utilization of LDP labels for traffic resolu-
tion. Some vendors use LDP for both VPN and IPv4 traffic forward-
ing, while other vendors allow only VPN traffic to resolve via
LDP. The challenge is to restrict the utilization of LDP labels
to VPN traffic in a mixed-vendor environment.
o Understanding the differences in the implementations.
2.6. Operational experience
In general, operators reported stable implementations and steady
improvement in resiliency to failure and convergence times over the
years. Some operators reported that no issues were found with the
protocol since deploying.
The operational issues reported fall in three categories:
1. Configuration issues. Both the session and adjacency endpoints
must be allowed by the firewall filters. Misconfiguration of
the filters causes sessions to drop (if already established) or
not to establish.
2. Vendor bugs. These include traffic blackholing, unnecessary
label withdrawals and changes, session resets and problems
migrating from older versions of the technology. Most reports
stated that the problems reported occurred in early versions of
the implementations.
3. Protocol issues.
- The synchronization required between LDP and the IGP was listed
as the main protocol issue. Two issues were reported. 1) Slow
convergence, due to the fact that LDP convergence time is tied to
the IGP convergence time. 2) Traffic blackholing on a link-up
event. When an interface comes up, the LDP session may come up
slower than the IGP session. This results in dropping MPLS traf-
fic for a link-up event (not a failure but a restoration). This
issue is described in more detail in [LDP-SYNC].
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- Silent failures. Failure not being propagated to the head end of
the LSP when setting up LSPs using independent control.
3. Intellectual Property Statement
The IETF takes no position regarding the validity or scope of any
Intellectual Property Rights or other rights that might be claimed to
pertain to the implementation or use of the technology described in
this document or the extent to which any license under such rights
might or might not be available; nor does it represent that it has
made any independent effort to identify any such rights. Information
on the procedures with respect to rights in RFC documents can be
found in BCP 78 and BCP 79.
Copies of IPR disclosures made to the IETF Secretariat and any assur-
ances of licenses to be made available, or the result of an attempt
made to obtain a general license or permission for the use of such
proprietary rights by implementers or users of this specification can
be obtained from the IETF on-line IPR repository at
http://www.ietf.org/ipr.
The IETF invites any interested party to bring to its attention any
copyrights, patents or patent applications, or other proprietary
rights that may cover technology that may be required to implement
this standard. Please address the information to the IETF at ietf-
ipr@ietf.org.
4. Acknowledgments
The editors would like to thank the operators who participated in the
survey for their valuable input: Shane Amante, Niclas Comstedt, Bruno
Decraene, Mourad Kaddache, Kam Lee Yap, Lei Wang and Otto Kreiter.
Not all who participated are listed here, due to confidentiality
requests. Those listed have given their consent.
Also, a big thank you to Scott Bradner who acted as an independent
third party ensuring anonymity of the responses.
The editors would like to thank Rajiv Papneja, Halit Ustundag and Loa
Andersson for their input to the survey questionnaire.
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5. References
5.1. Normative References
[RFC1264] Hinden, R., "Internet Engineering Task Force Internet Rout-
ing Protocol Standardization Criteria", RFC 1264, October 1991.
[RFC2026] Bradner, S., "The Internet Standards Process -- Revision
3", RFC 2026, October 1996.
[RFC3036] Andersson, L., Doolan, P., Feldman, N., Fredette, A. and
B. Thomas, "LDP Specification", RFC 3036, January 2001.
[RFC3815] Cucchiara,J., Sjostrand, H. and Luciani, J., "Definitions
of Managed Objects for the Multiprotocol Label Switching (MPLS),
Label Distribution Protocol (LDP)", RFC 3815, June 2004.
5.2. Informative References
[RFC1321] Rivest, R., "The MD5 Message-Digest Algorithm," RFC 1321,
April 1992.
[LDP-SYNC] Jork, M., Atlas, A. and Fang, L., "LDP IGP Synchroniza-
tion", draft-jork-ldp-igp-sync-00
6. Editors' Addresses
Loa Andersson
Acreo AB
Isafjordsgatan 22
Kista, Sweden
email: loa.andersson@acreo.se
loa@pi.se
Ina Minei
Juniper Networks
1194 N.Mathilda Ave
Sunnyvale, CA 94089
e-mail: ina@juniper.net
Bob Thomas
Cisco Systems, Inc.
1414 Massachusetts Ave
Boxborough, MA 01719
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email: rhthomas@cisco.com
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Andersson, et al. [Page 8]
