Network Working Group Kamran Raza
Internet Draft Cisco Systems
Intended status: Standards Track
Expires: October 19, 2011 Sami Boutros
Cisco Systems
April 20, 2011
LDP IP and PW Capability
draft-raza-mpls-ldp-ip-pw-capability-01.txt
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Abstract
Currently, no LDP capability is exchanged for LDP applications like
IP label switching and L2VPN/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 "incapability" or
disability or non-support for IP label switching or L2VPN/PW
application, hence disabling corresponding application state exchange
over the established LDP session.
Table of Contents
1. Introduction 3
2. Conventions used in this document 3
3. Non-negotiated LDP applications 4
3.1. Application Control Capabilities 4
3.1.1. IP Label Switching Capability TLV 4
3.1.2. PW Signaling Capability TLV 5
3.2. Procedures for Application Control Capabilities in an
Initialization message 6
3.3. Procedures for Application Control capabilities in a
Capability message 7
4. Operational Examples 8
4.1. Disabling IP/PW label applications on an ICCP session 8
4.2. Disabling IP Label Switching application on a PW session 8
4.3. Disabling IP application dynamically on an established
IP/PW session 9
5. Security Considerations 9
6. IANA Considerations 9
7. Conclusions 10
8. References 10
8.1. Normative References 10
8.2. Informative References 10
9. Acknowledgments 10
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1. Introduction
LDP Capabilities [RFC5561] introduced a mechanism to negotiate LDP
capabilities for a given feature amongst peer LSRs. This mechanism
insures that no unnecessary state is exchanged between peer LSRs
unless corresponding feature capability is successfully negotiated
between peers.
While new features and applications, such as Typed Wildcard FEC
[RFC5918], Inter-Chassis Communication Protocol [ICCP], mLDP
[MLDP], make use of LDP capabilities framework for their feature
negotiation, the earlier LDP features and applications like IP label
switching and L2VPN/PW signaling [RFC4447] 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. To avoid
this unnecessary state advertisement and exchange, currently customers
are typically required to configure/define some sort of LDP state
(label) filtering policies on the box, which introduces operational
overhead and complexity.
This document proposes a solution by which an LDP speaker may announce
its "incapability" (or disability) to its peer for IP Label Switching
and/or L2VPN/PW Signaling application at session establishment time.
This helps avoiding unnecessary state exchange for such feature
applications. The proposal also state the mechanics to enable
previously disabled application later during the session lifetime.
The document introduces two new LDP Capabilities for IP label
switching and L2VPN/PW applications 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 "IP unicast", unless
otherwise explicitly stated.
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3. Non-negotiated LDP applications
For the applications that existed before LDP Capabilities [RFC5561]
mechanics were defined, LDP speaker may advertise relevant
application state to its peers after session establishment without
waiting for any capabilities exchange and negotiation.
Currently, the most important non-negotiated applications include:
o IP [v4 and v6] label switching
o L2VPN/PW signaling
To disable unnecessary state exchange for such LDP applications, two
new capabilities are being introduced in this document. These new
capabilities allow an LDP speaker to notify its LDP peer at the
session establishment time when one or more LDP "Non-negotiated
applications" are not required/configured on the sender side. Upon
receipt of such capability, if supported, the receiving LDP speaker
MUST disable the advertisement of application state towards the
sender. These capabilities can also be sent later in a Capability
message to either disable these applications, or to enable
previously disabled applications.
3.1. Application Control Capabilities
To control advertisement of state related to non-negotiated LDP
applications, namely IP Label switching and L2VPN/PW signaling, two
new capability TLVs are defined as described in the following
subsections.
3.1.1. IP Label Switching Capability TLV
The IP Label Switching capability is a new Capability Parameter
defined with the following format:
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
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
|1|0| IP Label Sw. Cap (IANA) | Length (2) |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
|1| Reserved | AF Bitmap |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
The value of the U-bit for the IP capability parameter TLV MUST be
set to 1 so that a receiver MUST silently ignore this TLV if unknown
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to it, and continue processing the rest of the message. Once
advertised, this capability cannot be withdrawn and hence the S-bit
must always be set to 1 both in Initialization message and Capability
message. The capability data associated with this TLV is 1 octet long
"Address Family Bitmap", and hence the TLV length MUST be set to 2.
The Capability data "Address Family Bitmap" is defined as:
7 6 5 4 3 2 1 0
+-+-+-+-+-+-+-+-+
| AF bitmap |
+-+-+-+-+-+-+-+-+
Where:
bit0: IPv4 label switching application
bit1: IPv6 label switching application
bit2-7: Reserved.
A bit in the bitmap is set to 0 or 1 to disable or enable
respectively a corresponding IP application.
As described earlier, "IP Label Switching" Capability Parameter TLV
MAY be included by an LDP speaker in an Initialization message to
signal to its peer LSR that state exchange for IPv4 and/or IPv6
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 IPv4/v6 label switching application(s).
3.1.2. PW Signaling Capability TLV
The "PW Signaling" capability is a new Capability Parameter defined
with the following format:
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
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
|1|0| PW Sig. Cap (IANA) | Length (2) |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
|1| Reserved |E| Reserved |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
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The value of the U-bit for the PW capability parameter 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. Once
advertised, this capability cannot be withdrawn and hence the S-bit
MUST always be set to 1 in Initialization message or Capability
message. The capability data associated with this TLV is 1 octet long
and hence the TLV length MUST be set to 2.
The capability data is defined as following byte:
7 6 5 4 3 2 1 0
+-+-+-+-+-+-+-+-+
|E| Reserved |
+-+-+-+-+-+-+-+-+
Where E-bit (Enable bit) is used to control PW signaling application
by setting it to 0 and 1 to disable and enable the application
respectively.
As described earlier, PW Signaling Capability Parameter TLV MAY be
included by an LDP speaker in an Initialization message to signal to
its peer LSR that state exchange for PW application need to be
disabled on given peer session. This TLV can also be sent later in a
Capability message to enable/disable the PW Signaling application.
3.2. Procedures for Application Control Capabilities 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.
An LDP speaker determines (e.g. via some local configuration or
default policy) if they need to disable IP and/or L2VPN/PW
applications with a peer LSR. If there is a need to disable, then the
IP and/or PW application capability TLVs need to be included in the
Initialization message with respective application bits set to 0 to
indicate application disable, where the application bit refers to a
bit in "Address Family Bitmap" of the "IP Label Switching" Capability
or E-bit in "PW Signaling" Capability.
An LDP speaker that supports the "IP Label Switching" and/or "PW
Signaling" capability MUST interpret those TLVs in a received
Initialization message such that it disables the advertisement of the
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application state towards the sender LSR for IP (v4 and/or v6) and/or
L2VPN/PW applications if their application control bits are set to 0.
If a receiving LDP speaker does not understand the capability TLVs,
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.
Once this capability has been sent by sender LSR and received and
understood by the receiver LSR, then both these LSRs MUST NOT
exchange any state related to the disabled applications until and
unless these applications are explicitly enabled again (e.g. via the
same Capability TLV sent in a Capability message with corresponding
application control bit set to 1).
"IP Label Switching" and "PW Signaling" capability TLVs are
unilateral/uni-directional in nature. This means that the receiving
LSR may not need 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].
3.3. Procedures for Application Control capabilities in a Capability
message
If the LDP peer supports "Dynamic Announcement Capability" [RFC5561],
then an LDP speaker can send IP Label Switching and/or PW Signaling
capability in a Capability message. 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 IP and/or L2VPN/PW signaling applications gets disabled, or if
previously disabled IP and/or L2VPN/PW applications gets enabled
again. In this case, LDP speaker constructs the TLVs with appropriate
application control bitmap and sends the corresponding capability
TLVs in a Capability message. Furthermore, the LDP speaker also
withdraws application(s) related advertised state (such as label
bindings) from its peer.
Upon receipt of those TLVs in a Capability message, the receiving LDP
speaker reacts in the same manner as it reacts upon the receipt of
those TLVs in an Initialization message. Additionally, the receiving
LDP speaker withdraws the application(s) related advertised state
(such as label bindings) from the sending LDP speaker. If the
receiving LDP speaker does not understand or support either Dynamic
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Announcement capability or received Application Control capability
TLV ("IP Label Switching" or "PW Signaling"), it MUST respond with
"Unsupported Capability" notification to the sender of the Capability
message.
4. Operational Examples
4.1. Disabling IP/PW label applications on an ICCP session
Consider two PE routers, LSR1 and LSR2, which understand/support "IP
Label Switching" and "PW Signaling" capability TLVs. These LSR 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
label bindings related to IP (v4/v6) prefixes and PW layer2 FEC
(FEC128/129) with LSR2.
To indicate its "disability" for the IP/PW applications, the LSR1
will include both the "IP Label Switching" capability TLV (with
bit0-1 of "Address Family Bitmap" set to 0) and "PW Signaling"
capability TLV (with E-bit set to 0) in the Initialization message.
Upon receipt of those TLVs in Initialization message, the LSR2 will
disable any IP/PW address/label binding state advertisement towards
LSR1 after session establishment.
The LSR1 will also disable any IP/PW address/label binding state
towards LSR2, irrespective of the fact whether or not LSR2 could
disable the corresponding application state advertisement towards
LSR1.
4.2. Disabling IP Label Switching application on a L2VPN/PW session
Now, consider LSR1 and LSR2 have an established session due to
L2VPN/PW application just to exchange PW (FEC128/129) label
bindings for VPWS/VPLS services amongst them. 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 IP (v4/v6) application on given PW session towards LSR2.
To indicate its disability for IP application, the LSR1 will include
the "IP Label Switching" capability TLV in the Initialization
message with bit0-1 (IPv4, IPv6) in "Address Family Bitmap" set to
zero. Upon receipt of this TLV in Initialization message, the LSR2
will disable any IP address/label binding state advertisement
towards LSR1.
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The LSR1 will also disable any IP address/label binding state
towards LSR2, irrespective of the fact whether or not LSR2 could
disable the corresponding IP application state advertisement towards
LSR1.
4.3. Disabling IP application dynamically on an established IP/PW
session
Assume that LSRs from previous sections were initially provisioned to
exchange both IP and PW state over the session between them, and also
support "Dynamic Announcement" capability [RFC5561]. Now, assume that
LSR1 is dynamically provisioned to disable IP label switching with
LSR2. In this case, LSR1 will first withdraw all its IP label state
by sending a single Label Withdraw message with IP Prefix Typed
Wildcard FEC using the mechanics described in [RFC5918], and Address
Withdraw message to withdraw its addresses. LSR1 will also send IP
Label Switching capability TLV in Capability message towards LSR2
with bit0-1 (IPv4, IPv6) in "Address Family Bitmap" set to zero. Upon
receipt of this TLV, LSR2 will also disable IP label switching
towards LSR1 and withdraw all previous IP application label/address
state using the same mechanics as described earlier for LSR1. The
disability of IP label switching dynamically should not impact
L2VPN/PW application on given session, and both LSRs should continue
to exchange PW Signaling application related state.
5. 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].
6. IANA Considerations
The document introduces following two new capability parameter TLVs
and requests following LDP TLV code point assignment by IANA:
o "IP Label Switching" Capability TLV (requested codepoint: 0x50C)
o "PW Signaling" Capability TLV (requested codepoint: 0x50D)
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7. 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 applications.
8. References
8.1. Normative References
[RFC5561] Thomas, B., Raza, K., Aggarwal, S., Aggarwal, R., and Le
Roux, JL., "LDP Capabilities", RFC 5561, July 2009.
[RFC5918] Asati, R., Minei, I., and Thomas, B. "Label Distribution
Protocol Typed Wildcard FEC", RFC 5918, August 2010.
[ICCP] Martini, L., Salam, S., and Matsushima, S., "Inter-Chassis
Communication Protocol for L2VPN PE Redundancy", draft-
ietf-pwe3-iccp-04.txt, Work in Progress, October 2010.
[MLDP] Minei, I., Kompella, K., Wijnands, I., and Thomas, B., "LDP
Extensions for Point-to-Multipoint and Multipoint-to-
Multipoint Label Switched Paths", draft-ietf-mpls-ldp-p2mp
-10.txt, Work in Progress, July 2010.
[RFC4447] L. Martini, Editor, E. Rosen, El-Aawar, T. Smith, G. Heron,
"Pseudowire Setup and Maintenance using the Label
Distribution Protocol", RFC 4447, April 2006.
[RFC2119] Bradner, S., "Key words for use in RFCs to Indicate
Requirement Levels", BCP 14, RFC2119, March 1997.
8.2. Informative References
[RFC5036] Andersson, L., Menei, I., and Thomas, B., Editors, "LDP
Specification", RFC 5036, September 2007.
[RFC5920] Fang, L. et al., "Security Framework for MPLS and GMPLS
Networks", RFC 5920, July 2010.
9. 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.
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Authors' Addresses
Kamran Raza
Cisco Systems, Inc.,
2000 Innovation Drive,
Kanata, 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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