MPLS Working Group Kamran Raza
Internet Draft Sami Boutros
Intended status: Standards Track
Expires: February 17, 2013 Cisco Systems
August 18, 2012
Disabling IPoMPLS and P2P PW LDP Applications
draft-ietf-mpls-ldp-ip-pw-capability-02.txt
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Abstract
Currently, no LDP capability is exchanged for LDP applications like
IP label switching and L2VPN P2P PW signaling. When an LDP session
comes up, an LDP speaker may unnecessarily advertise its local state
for such LDP applications even when the peer session may be
established for some other applications like ICCP. This document
proposes a solution by which an LDP speaker announces its disinterest
in such non-negotiated application. This, in turn, disables the
advertisement of corresponding application state, which would have
otherwise be advertised by default, over the established LDP session.
Table of Contents
1. Introduction 3
2. Conventions used in this document 4
3. Non-negotiated LDP applications 4
4. Controlling State Exchange for Non-negotiated LDP Applications 5
4.1. Application Control Capability 5
5. Capabilities Procedures 7
5.1. Application Control Capability in an Initialization message 7
5.2. Application Control capability in a Capability message 8
6. Operational Examples 8
6.1. Disabling IPoMPLS and P2P PW application on an ICCP session 8
6.2. Disabling IPoMPLS application on a L2VPN/PW T-LDP session 9
6.3. Disabling IPoMPLS appl. dynamically on an IP/PW session 9
6.4. Disabling unwanted state advert. by an IP dual-stack LSR 10
7. Security Considerations 10
8. IANA Considerations 10
9. Conclusions 11
10. References 11
10.1. Normative References 11
10.2. Informative References 11
11. Acknowledgments 12
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1. Introduction
LDP Capabilities [RFC5561] introduced a mechanism to negotiate LDP
capabilities for a given feature amongst peer LSRs. The capability
mechanism insures that no unnecessary state is exchanged between peer
LSRs unless corresponding feature capability is successfully
negotiated between peers.
While new LDP features and applications, such as Typed Wildcard FEC
[RFC5918], Inter-Chassis Communication Protocol [ICCP], mLDP
[RFC6388], and P2MP PW [P2MP-PW] make use of LDP capabilities
framework for their feature negotiation, the earlier LDP features and
applications like IP label switching and L2VPN P2P PW signaling
[RFC4447] [RFC4762] may cause unnecessary state exchange between LDP
peers even when the given application is not enabled on one of the
LDP speakers participating in a given session.
For example, when bringing up and using an LDP peer session with a
remote PE LSR for purely ICCP signaling purposes, the LDP speaker may
unnecessarily advertise labels for IP (unicast) prefixes to this ICCP
related LDP peer as per its default behavior.
Another example of unnecessary state advertisement can be cited when
LDP is used in an IP dual-stack environment. For instance, an LSR
that is locally enabled for both IPv4 and IPv6 label switching may
advertise address/label bindings for both IPv4 and IPv6 address
families towards an LDP peer that is interested in IPv4 only. In this
case, the advertisement of IPv6 addresses and IPv4 prefix labels to
the peer is unnecessary, as well as wasteful from LSR memory/CPU and
network resource consumption point of view.
To avoid this unnecessary state advertisement and exchange, currently
an operator is typically required to configure and define some sort
of filtering policies on the box for LDP state exchange, which
introduces operational overhead and complexity.
This document proposes an LDP Capabilities [RFC5561] based solution
by which an LDP speaker may announce its disinterest (or non-
support/disability) to its peer for IP Label Switching and/or L2VPN
P2P PW Signaling application at the time of session establishment.
This helps avoiding unnecessary state exchange for such feature
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applications. The proposal also states the mechanics to disable or
enable an application dynamically during the session lifetime. The
document introduces a new LDP capability to implement this proposal.
2. 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].
The term "IP" in this document refers to both "IPv4 unicast" and
"IPv6 unicast" address families.
This document uses shorthand terms "IPoMPLS" to refer to IP Label
switching application, and "P2P PW" to refer to L2VPN PW signaling
for FEC 128 and FEC 129 P2P PWs.
3. Non-negotiated LDP applications
For the applications that existed before LDP Capabilities [RFC5561]
procedures were defined, an LDP speaker typically advertises relevant
application state to its peers after session establishment without
waiting for any capabilities exchange and negotiation. These LDP
applications are:
o IPv4/IPv6 label switching ("IPoMPLS")
o L2VPN P2P PW signaling ("P2P PW")
To disable unnecessary state exchange for such LDP applications, a
new capability is being introduced in this document. This new
capability controls the advertisement of application state and
enables an LDP speaker to notify its LDP peer its disinterest in one
or more of these "Non-negotiated" LDP applications at the time of
session establishment. Upon receipt of such capability, the receiving
LDP speaker, if supporting the capability, MUST disable the
advertisement of any state related to the application towards the
sender. Moreover, the sender LSR SHOULD also disable the
advertisement of corresponding application state towards the peer.
This new capability can also be sent later in a Capability message to
either disable these applications, or to enable previously disabled
applications dynamically.
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4. Controlling State Exchange for Non-negotiated LDP Applications
To control advertisement of state related to non-negotiated LDP
applications, namely IPoMPLS and P2P PW signaling, a new capability
TLVs is defined as follows.
4.1. Application Control Capability
The "Application Control Capability" is a new Capability Parameter
TLV defined in accordance with section 3 of LDP Capabilities
specification [RFC5561]. The format of this new TLV is as follows:
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
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
|U|F| App Control Cap. (IANA) | Length |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
|S| Reserved | |
+-+-+-+-+-+-+-+-+
| |
~ Application Control Element(s) ~
| |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
Figure 1: Format of an "Application Control Capability" TLV
The value of the U-bit for the TLV MUST be set to 1 so that a
receiver MUST silently ignore this TLV if unknown to it, and continue
processing the rest of the message. Whereas, The value of F-bit MUST
be set to 0. Once advertised, this capability cannot be withdrawn and
hence the S-bit MUST be set to 1 both in Initialization message and
Capability message.
The capability data associated with this TLV is one or more
Application Control Elements, where each element defines
enabling/disabling of state advertisement for a given application.
The format of an Application Control Element is defined as follows:
0 1
0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| App |D|Rsvd1| Rsvd2 |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
Figure 2: Format of an "Application Control Element"
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Where:
App: Defines the (non-negotiated) application type. The value of this
field is defined as:
0: IPv4 Label switching
1: IPv6 Label switching
2: P2P PW FEC128 signaling
3: P2P PW FEC129 signaling
4-15: Reserved.
D bit: Controls the advertisement of state for the application as
follows
1: Disable state advertisement
0: Enable state advertisement
Rsvd1, Rsvd2: Reserved for future use. MBZ on transmit and ignored on
receipt.
The "Length" field of "Application Control Capability" TLV depends on
the number of Application Control Elements present in the TLV. For
example, if there are two elements present, then the Length field is
set to 5 octets. A receiver of this capability TLV can deduce number
of application control elements present in the TLV by using Length
field.
For now onward, this document uses term "element" to refer to an
application control element.
As described earlier, "Application Control Capability" TLV MAY be
included by an LDP speaker in an Initialization message to signal to
its peer LSR that state exchange for one or more application(s) need
to be disabled on a given peer session. This TLV can also be sent
later in a Capability message to selectively enable or disable these
applications. An "Application Control Capability" TLV MUST contain
elements with distinct application types and the TLV MUST NOT contain
the same application type more than once.
To control more than one application, a sender LSR can either send a
single capability TLV in a message with multiple elements present, or
can send separate messages with capability TLV specifying one or more
elements. A receiving LSR, however, MUST treat each incoming message
with capability TLV as an incremental update to the existing control.
To understand capability updates from an example, let us consider 2
LSR peers, R1 (sender) and R2 (receiver), both of which support all
the non-negotiated applications listed earlier. By default, these LSR
will advertise state for these applications to their peer as soon as
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an LDP session is established. Now assume that R2 receives an
Application Control capability in the Initialization message with
"IPv6 Label switching" and "P2P PW FEC129" applications disabled.
This updates R2's outbound policy towards R1 to advertise state
related to only "IPv4 Label switching" and "P2P PW FEC 128"
applications. Now, R2 receives a capability update from R1 via a
Capability message with "IPv6 Label switching" enabled and "P2P PW
FEC128" disabled. This updates R2's outbound policy towards R1 to
advertise both IPv4 and IPv6 Label switching state, and disable both
P2P PW FEC128 and FEC 129 signaling. Finally, R2 receives another
update from R1 via Capability message that specifies to disable all 4
non-negotiated applications, resulting R2 outbound policy towards R1
to block/disable state for all these applications, and only advertise
state for any other application, if present.
5. Capabilities Procedures
The "Application Control" capability conveys the desire of a sending
LSR to disable receipt of unwanted/unnecessary state from a peer.
Hence, this capability is unilateral and uni-directional in nature,
and a receiving LSR is not required to send a similar capability TLV
in an Initialization or Capability message towards the sender. This
unilateral behavior also conforms to the procedures defined in the
Section 6 of LDP Capabilities [RFC5561].
After this capability is successfully negotiated (i.e. sent by a
sender and received/understood by the receiver), then both
participating LSRs MUST NOT exchange any state related to the
disabled applications until and unless these applications are
explicitly enabled again via a capability update.
If a receiving LDP speaker does not understand the Application
Control capability TLV, then it MUST respond to the sender with
"Unsupported TLV" Notification as described in LDP Capabilities
[RFC5561]. Upon receipt of such Notification, the sender MAY still
continue to block/disable its outbound state advertisement towards
the peer for the requested disabled applications. If a receiving LDP
speaker does not understand or does not support an application
specified in an application control element, it SHOULD silently
ignore/skip such an element and continue processing rest of the TLV.
5.1. Application Control Capability in an Initialization message
LDP Capabilities [RFC5561] dictate that the S-bit of capability
parameter in an Initialization message MUST be set to 1 and SHOULD be
ignored on receipt.
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An LDP speaker determines (e.g. via some local configuration or
default policy) if they need to disable IPoMPLS and/or P2P PW
applications with a peer LSR. If there is a need to disable, then the
"Application Control Capability" TLV needs to be included in the
Initialization message with respective application control elements
included with their D bit set to 1.
An LDP speaker that supports the "Application Control" capability
MUST interpret the capability TLV in a received Initialization
message such that it disables the advertisement of the application
state towards the sender LSR for IPoMPLS and/or P2P PW applications
if their application control element's D bit is set to 1.
5.2. Application Control capability in a Capability message
If the LDP peer supports "Dynamic Announcement Capability" [RFC5561],
then an LDP speaker may send Application Control capability in a
Capability message towards the peer. Once advertised, these
capabilities cannot be withdrawn and hence the S-bit of the TLV MUST
be set to 1 when sent in a Capability message.
An LDP speaker may decide to send this TLV towards an LDP peer if any
of its IPoMPLS and/or P2P PW signaling applications get disabled, or
if previously disabled application gets enabled again. In this case,
LDP speaker constructs the TLV with appropriate application control
elements and sends the corresponding capability TLV in a Capability
message. Furthermore, the LDP speaker also withdraws/advertises
application(s) related state (such as address/label bindings) from/to
its peer according to the capability update.
Upon receipt of this TLV in a Capability message, the receiving LDP
speaker reacts in the same manner as it reacts upon the receipt of
this TLV in an Initialization message. Additionally, the receiving
LDP speaker withdraws/advertises application state from/to the
sending peer according to the capability update.
6. Operational Examples
6.1. Disabling IPoMPLS and P2P PW applications on an ICCP session
Consider two PE routers, LSR1 and LSR2, which understand/support
"Application Control" capability TLV, and have an established LDP
session due to ICCP application in order to exchange ICCP state
related to dual-homed devices connected to these LSRs. Let us assume
that LSR1 is provisioned not to exchange any state for IPoMPLS
(IPv4/IPv6) and P2P PW (FEC128/129) application with LSR2.
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To indicate its disinterest in these applications, the LSR1 will
include an "Application Control" capability TLV (with 4 application
control elements corresponding to these 4 applications with D bit
set to 1 for each one) in the Initialization message. Upon receipt
of this TLV in Initialization message, the LSR2 will disable
advertisement of IPv4/IPv6 bindings (addresses and labels), as well
as P2P PW FEC128/129 signaling, towards LSR1 after session
establishment.
The LSR1 will also disable similar state advertisement for these
applications towards LSR2 independently, irrespective of the fact
whether or not LSR2 could disable the corresponding application
state advertisement towards LSR1.
6.2. Disabling IPoMPLS application on a L2VPN/PW T-LDP session
Now, consider LSR1 and LSR2 have an established T-LDP session for
P2P PW application just to exchange label bindings for FEC 128/129.
Since in most typical deployments, there is no need to exchange IP
(v4/v6) address/label bindings amongst the PE LSRs, let us assume
that LSR1 is provisioned to disable IPoMPLS (IPv4/IPv6)application
on given PW session towards LSR2.
To indicate its disinterest in IPoMPLS application over PW T-LDP
session, the LSR1 will follow/apply the same procedures to disable
IPv4 and IPv6 label switching as described in previous section.
Similarly, LSR2 will behave accordingly by disabling state
advertisement for IPoMPLS application towards LSR1.
6.3. Disabling IPoMPLS application dynamically on an established IP/PW
session
Assume that LSRs from previous sections were initially provisioned to
exchange both IPoMPLS and P2P PW state over the session between them,
and also support "Dynamic Announcement" Capability [RFC5561]. Now,
assume that LSR1 is dynamically provisioned to disable IPoMPLS
(IPv4/IPv6) over T-LDP session with LSR2. In this case, LSR1 will
first disable its future outbound application state towards LSR2, and
also withdraw all its previously advertised IPoMPLS state (labels and
addresses) by sending a single Prefix FEC Typed Wildcard Label
Withdraw message [RFC5918], and an Address Withdraw message
respectively towards LSR2. LSR1 will also send Application Control
capability TLV in a Capability message towards LSR2 with application
control elements defined for IPv4 and IPv6 label switching with D bit
set to 1. Upon receipt of this TLV, LSR2 will also disable IPoMPLS
applications towards LSR1 and withdraw all previous IP label/address
state using the same mechanics as described earlier for LSR1. This
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dynamic disability of IPoMPLS application will not impact L2VPN P2P
PW application on the given session, and both LSRs should continue to
exchange PW Signaling application related state.
6.4. Disabling unwanted state advertisement by an IP dual-stack LSR
In IP dual-stack scenarios, an LSR2 may advertise unnecessary state
(label/address bindings) towards peer LSR1 corresponding to IPv6
label switching application once a session is established mainly for
exchanging state for IPv4. The similar scenario also applies when
advertising IPv4 label switching state on a session meant for IPv6.
The Application Control capability and its procedures defined in this
document can help to avoid such unnecessary state advertisement.
Consider IP dual-stack environment where LSR2 is enabled for IPoMPLS
application for both IPv4 and IPv6, but LSR1 is enabled for (or
interested in) only IPv4oMPLS. To avoid receiving unwanted state
advertisement for IPv6oMPLS application from LSR2, LSR1 can send
"Application Control" capability with element for IPv6 label
switching with D bit set to 1 in the Initialization message towards
LSR2 at the time of session establishment. Upon receipt of this
capability, LSR2 will disable all IPv6 label and address binding
advertisement towards LSR1. If IPv6oMPLS is later enabled on LSR1,
LSR1 can update the capability by sending Application Control
capability in Capability message towards LSR2 to enable IPv6oMPLS
application dynamically.
[LDPv6] specification section 7 also suggests an alternate way to
avoid the unnecessary state advertisement in the above scenario.
7. Security Considerations
The proposal introduced in this document does not introduce any new
security considerations beyond that already apply to the base LDP
specification [RFC5036] and [RFC5920].
8. IANA Considerations
The document defines following a new capability parameter TLV and
requests following LDP TLV code point assignment by IANA from LDP
"TLV Type Name Space" registry:
o "Application Control Capability" TLV (requested codepoint: 0x50C)
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9. Conclusions
The document proposed a solution using LDP Capabilities [RFC5561]
mechanics to disable unnecessary state exchange, if/as desired,
between LDP peers for currently non-negotiated IP/PW LDP
applications.
10. References
10.1. Normative References
[RFC5036] L. Andersson, I. Minei, and B. Thomas, "LDP Specification",
RFC 5036, September 2007.
[RFC5561] B. Thomas, K. Raza, S. Aggarwal, R. Aggarwal, and JL. Le
Roux, "LDP Capabilities", RFC 5561, July 2009.
[RFC2119] S. Bradner, "Key words for use in RFCs to Indicate
Requirement Levels", BCP 14, RFC2119, March 1997.
10.2. Informative References
[RFC5918] R. Asati, I. Minei, and B. Thomas, "Label Distribution
Protocol Typed Wildcard FEC", RFC 5918, August 2010.
[RFC4447] L. Martini, E. Rosen, El-Aawar, T. Smith, and G. Heron,
"Pseudowire Setup and Maintenance using the Label
Distribution Protocol", RFC 4447, April 2006.
[RFC4762] M. Lasserre, and V. Kompella, "Virtual Private LAN Service
(VPLS) Using Label Distribution Protocol (LDP) Signaling",
RFC 4762, January 2007.
[P2MP-PW] Martini, L. et. al, "Signaling Root-Initiated Point-to-
Multipoint Pseudowires using LDP", draft-ietf-pwe3-p2mp-pw-
04.txt, Work in Progress, October 2011.
[ICCP] L. Martini, S. Salam, A. Sajassi, and S. Matsushima,
"Inter-Chassis Communication Protocol for L2VPN PE
Redundancy", draft-ietf-pwe3-iccp-09.txt, Work in Progress,
July 2012.
[RFC6388] I. Minei, I. Wijnand, K. Kompella, and B. Thomas, "LDP
Extensions for P2MP and MP2MP LSPs", RFC 6388, November
2011.
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[LDPv6] R. Asati, et al., "Updates to LDP for IPv6", draft-ietf-
mpls-ldp-ipv6-07.txt, Work in Progress, June 2012.
[RFC5920] L. Fang, et al., "Security Framework for MPLS and GMPLS
Networks", RFC 5920, July 2010.
11. Acknowledgments
The authors would like to thank Eric Rosen for his valuable input and
comments.
This document was prepared using 2-Word-v2.0.template.dot.
Authors' Addresses
Kamran Raza
Cisco Systems, Inc.,
2000 Innovation Drive,
Ottawa, ON K2K-3E8, Canada.
E-mail: skraza@cisco.com
Sami Boutros
Cisco Systems, Inc.
3750 Cisco Way,
San Jose, CA 95134, USA.
E-mail: sboutros@cisco.com
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