MPLS Working Group Kamran Raza
Internet Draft Sami Boutros
Intended status: Standards Track
Expires: August 18, 2013 Cisco Systems
February 19, 2013
Disabling IPoMPLS and P2P PW LDP Applications
draft-ietf-mpls-ldp-ip-pw-capability-03.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 to its peer its
disinterest in such non-negotiated applications. 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 8
5.2. Application Control capability in a Capability message 8
6. Operational Examples 8
6.1. Disabling IPoMPLS and P2P PW apps. on an ICCP session 9
6.2. Disabling IPoMPLS application on a L2VPN/PW T-LDP session 9
6.3. Disabling IPoMPLS app.dynamically on an estab. IP/PW session 9
6.4. Disabling unwanted state advertisement by a dual-stack LSR 10
7. Security Considerations 10
8. IANA Considerations 10
9. References 11
9.1. Normative References 11
9.2. Informative References 11
10. 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 the corresponding feature capability is successfully
negotiated between the peers.
While new LDP features and applications, such as Typed Wildcard FEC
[RFC5918], Inter-Chassis Communication Protocol [ICCP], mLDP
[RFC6388], and L2VPN 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 LDP speakers to exchange application
state unnecessarily 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 reasons, an 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 to be deployed 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 IPv6 prefix labels to
the peer is unnecessary, as well as wasteful, from the point of view
of LSR memory/CPU and network resource consumption.
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 LSR for exchanging LDP applications
state, which introduces operational overhead and complexity.
This document proposes an LDP Capabilities [RFC5561] based solution
by which an LDP speaker may announce to its peer(s) its disinterest
(or non-support/disability) 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 dynamically
disable or enable such an application 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 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 Pseudowires.
3. Non-negotiated LDP applications
For the applications that existed prior to the definition of LDP
Capabilities framework [RFC5561], an LDP speaker typically
advertises, without waiting for any capabilities exchange and
negotiation, its corresponding application state to its peers right
after the session establishment. These early LDP applications
include:
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 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, disables the advertisement
of any state related to the application towards the sender. This new
capability can also be sent later in a Capability message to either
disable enabled applications or to enable previously disabled
applications.
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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
TLV 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;
thus S-bit MUST be set to 1 both in an Initialization and Capability
message.
The capability data associated with this TLV is one or more
Application Control Elements, where each element indicates
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
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
|AppType|D|Rsvd1| Rsvd2 |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
Figure 2: Format of an "Application Control Element"
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Where:
AppType: Defines the (non-negotiated) application type. The value of
this field is defined as:
1: IPv4 Label switching
2: IPv6 Label switching
3: P2P PW FEC128 signaling
4: P2P PW FEC129 signaling
0, 5-15: Reserved.
D bit: Controls the advertisement of state for the application:
1: Disable state advertisement
0: Enable state advertisement
When sent in an Initialization message, D bit MUST be set to 1.
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.
From now onward, this document uses the 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 the 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. If a receiver receives such
a malformed TLV, it SHOULD discard this TLV and continue processing
rest of the message.
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
capability TLV for a given application type as an update to its
existing policy for given type.
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To understand capability updates from an example, let us consider 2
LSRs, S (LDP speaker) and P (LDP peer), both of which support all the
non-negotiated applications listed earlier. By default, these LSR
will advertise state for these applications, as configured, to their
peer as soon as an LDP session is established. Now assume that P
receives an Application Control capability in the Initialization
message with "IPv6 Label switching" and "P2P PW FEC129" applications
disabled. This updates P's outbound policy towards S to advertise
state related to only "IPv4 Label switching" and "P2P PW FEC 128"
applications. Later, P receives another capability update from S via
a Capability message with "IPv6 Label switching" enabled and "P2P PW
FEC128" disabled. This results in P's outbound policy towards S to
advertise both IPv4 and IPv6 Label switching state, and disable both
P2P PW FEC128 and FEC 129 signaling. Finally, P receives another
update from S via a Capability message that specifies to disable all
four non-negotiated applications, resulting P outbound policy towards
S 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 an LSR to
disable receipt of unwanted/unnecessary state from its LDP peer. This
capability is uni-lateral 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 conforms to the procedures defined in the Section
6 of LDP Capabilities [RFC5561].
After this capability is successfully negotiated (i.e. sent by an LSR
and received/understood by its peer), then the receiving LSR MUST NOT
advertise any state related to the disabled applications towards the
capability sending LSR 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]. 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.
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5.1. Application Control Capability in an Initialization message
LDP Capabilities [RFC5561] framework dictates that the S-bit of
capability parameter in an Initialization message MUST be set to 1
and SHOULD be ignored on receipt.
An LDP speaker determines (e.g. via some local configuration or
default policy) if it needs 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 capability sending 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 one
or more of its IPoMPLS and/or P2P PW signaling applications get
disabled, or if previously disabled application gets enabled again.
In this case, the LDP speaker constructs the TLV with appropriate
application control element(s) and sends the corresponding capability
TLV in a Capability message.
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 peer
withdraws/advertises application state from/to the capability sending
LDP speaker according to the capability update.
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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 to exchange ICCP state related to dual-homed devices
connected to these LSRs. Let us assume that both LSRs are
provisioned not to exchange any state for IPoMPLS (IPv4/IPv6) and
P2P PW (FEC128/129) application.
To indicate their disinterest in these applications, the LSRs 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 receiving LSR will
disable advertisement of IPv4/IPv6 bindings (addresses and labels),
as well as P2P PW FEC128/129 signaling, towards its peer after
session establishment.
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 to exchange label bindings for FEC 128/129. Given
that there is no need to exchange IP (v4/v6) address/label bindings
amongst the PE LSRs over a PW T-LDP session in most typical
deployments, let us assume that LSRs are provisioned to disable
IPoMPLS (IPv4/IPv6)application on given PW session.
To indicate their disinterest in IPoMPLS application over PW T-LDP
session, the LSRs will follow/apply the same procedures to disable
IPv4 and IPv6 label switching as described in previous section. As a
result, only P2P PW related state will be exchanged between these
LSRs over this T-LDP session.
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
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,
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LSR2 will disable IPoMPLS application(s) towards LSR1 and withdraw
all previous IP label/address state from LSR1. To withdraw label and
address bindings from its peer, LSR2 MAY use a single Prefix FEC
Typed Wildcard Label Withdraw message [RFC5918] and an Address
Withdraw message respectively.
This dynamic disability of IPoMPLS application does 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 a new capability parameter TLV and requests
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following LDP TLV code point assignment by IANA from LDP "TLV Type
Name Space" registry:
o "Application Control Capability" TLV (requested codepoint: 0x50C)
9. References
9.1. 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.
9.2. 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, March 2012.
[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.
10. 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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