Per-Interface MIP Addressing Requirements and Design Considerations
draft-ietf-mpls-tp-mip-mep-map-07
Network Working Group A. Farrel
Internet-Draft Juniper Networks
Intended status: Informational H. Endo
Expires: October 24, 2013 Hitachi, Ltd.
R. Winter
NEC
Y. Koike
NTT
M. Paul
Deutsche Telekom
April 22, 2013
Per-Interface MIP Addressing Requirements and Design Considerations
draft-ietf-mpls-tp-mip-mep-map-07
Abstract
The Framework for Operations, Administration and Maintenance (OAM)
within the MPLS Transport Profile (MPLS-TP) describes how Maintenance
Entity Group Intermediate Points (MIPs) may be situated within
network nodes at the incoming and outgoing interfaces.
This document elaborates on important considerations for internal MIP
addressing. More precisely it describes important restrictions for
any mechanism that specifies a way of forming OAM messages so that
they can be targeted at MIPs on incoming or MIPs on outgoing
interfaces and forwarded correctly through the forwarding engine.
Furthermore, the document includes considerations for node
implementations where there is no distinction between the incoming
and outgoing MIP.
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
working documents as Internet-Drafts. The list of current Internet-
Drafts is at http://datatracker.ietf.org/drafts/current/.
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 October 24, 2013.
Farrel, et al. Expires October 24, 2013 [Page 1]
Internet-Draft Internal MIP Considerations April 2013
Copyright Notice
Copyright (c) 2013 IETF Trust and the persons identified as the
document authors. All rights reserved.
This document is subject to BCP 78 and the IETF Trust's Legal
Provisions Relating to IETF Documents
(http://trustee.ietf.org/license-info) in effect on the date of
publication of this document. Please review these documents
carefully, as they describe your rights and restrictions with respect
to this document. Code Components extracted from this document must
include Simplified BSD License text as described in Section 4.e of
the Trust Legal Provisions and are provided without warranty as
described in the Simplified BSD License.
Table of Contents
1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . . 3
2. Requirements notation . . . . . . . . . . . . . . . . . . . . 3
3. Terminology . . . . . . . . . . . . . . . . . . . . . . . . . 3
4. Summary of the Problem Statement . . . . . . . . . . . . . . . 4
5. Requirements and Design Considerations for Internal-MIP
Adressing . . . . . . . . . . . . . . . . . . . . . . . . . . 6
6. Security Considerations . . . . . . . . . . . . . . . . . . . 10
7. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 10
8. Acknowledgments . . . . . . . . . . . . . . . . . . . . . . . 10
9. References . . . . . . . . . . . . . . . . . . . . . . . . . . 11
9.1. Normative References . . . . . . . . . . . . . . . . . . . 11
9.2. Informative References . . . . . . . . . . . . . . . . . . 11
Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . . 11
Farrel, et al. Expires October 24, 2013 [Page 2]
Internet-Draft Internal MIP Considerations April 2013
1. Introduction
The Framework for Operations, Administration and Maintenance (OAM)
within the MPLS Transport Profile (MPLS-TP)(the MPLS-TP OAM
Framework, [RFC6371]) distinguishes two configurations for
Maintenance Entity Group Intermediate Points (MIPs) on a node. It
defines per-node MIPs and per-interface MIPs, where a per-node MIP is
a single MIP per node in an unspecified location within the node and
per-interface MIPs are two (or more) MIPs per node on each side of
the forwarding engine.
In-band OAM messages are sent using the Generic Associated Channel
(G-ACh) [RFC5586]. OAM messages for the transit points of
pseudowires (PWs) or Label Switched Paths (LSPs) are delivered using
the expiration of the MPLS shim header time-to-live (TTL) field. OAM
messages for the end points of PWs and LSPs are simply delivered as
normal.
OAM messages delivered to end points or transit points are
distinguished from other (data) packets so that they can be processed
as OAM. In LSPs, the mechanism used is the presence of the Generic
Associated Channel Label (GAL) in the Label Stack Entry (LSE) under
the top LSE [RFC5586]. In PWs, the mechanism used is the presence of
the PW Associated Channel Header (PWACH) [RFC4385] or the presence of
a GAL [RFC6423].
In case multiple MIPs are present on a single node, these mechanisms
alone provide no way to address one particular MIP out of the set of
MIPs. A mechanism that addresses this shortcoming has to obey a few
important design considerations which are discussed in this document.
Note that the acronym "OAM" is used in conformance with [RFC6291].
2. Requirements notation
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 [RFC2119].
3. Terminology
In this document we use the term in-MIP (incoming MIP) to refer to
the MIP which processes OAM messages before they pass through the
forwarding engine of a node. An out-MIP (outgoing MIP) processes OAM
messages after they have passed the forwarding engine of the node.
The two together are referred to as internal MIPs.
Farrel, et al. Expires October 24, 2013 [Page 3]
Internet-Draft Internal MIP Considerations April 2013
4. Summary of the Problem Statement
Figure 1 shows an abstract functional representation of an MPLS-TP
node. It is decomposed as an incoming interface, a forwarding engine
(FW), and an outgoing interface. As per the discussion in [RFC6371],
MIPs may be placed in each of the functional interface components.
------------------------
|----- -----|
| MIP | | MIP |
| | ---- | |
----->-| In |->-| FW |->-| Out |->----
| i/f | ---- | i/f |
|----- -----|
------------------------
Figure 1: Abstract Functional Representation of an MPLS-TP Node
Several distinct OAM functions are required within this architectural
model for both PWs and LSPs such as:
o Connectivity Verification (CV) between a MEP and a MIP
o traceroute over an MPLS-TP LSP and/or an MPLS-TP PW containing
MIPs
o data-plane loopback configuration at a MIP
o diagnostic tests
The MIPs in these OAM functions may equally be the MIPs at the
incoming or outgoing interfaces.
Per-interface MIPs have the advantage that they enable a more
accurate localization and identification of faults and diagnostic
tests. In particular, the identification of whether a problem is
located between nodes or on a particular node and where on that node
is greatly enhanced. For obvious reasons, it is important to narrow
the cause of a fault down quickly to initiate a timely, and well-
directed maintenance action to resume normal network operation.
The following two figures illustrate the fundamental difference of
using per-node and per-interface MEPs and MIPs for OAM. Figure 2
depicts OAM using per-node MIPs and MEPs. For reasons of exposition
we pick a location for the MIPs on the nodes but the standard does
not mandate the exact location for the per-node model. Figure 3 on
the other hand shows the same basic network but for OAM operations
per-interface maintenance points are configured. Note that these
figures are merely examples. It is important to note that per-
interface MEPs or per-interface MIPs MUST logically be placed at a
point before (for in-MIP) or after (for out-MIP) passing the
Farrel, et al. Expires October 24, 2013 [Page 4]
Internet-Draft Internal MIP Considerations April 2013
forwarding engine as defined in [RFC6371]. It MUST be assured that
all traffic for which the MEP/MIP is associated with must pass
through or be terminated at that point.
Customer| Operator's administrative | Customer
Domain | Domain | Domain
------> |<--------------------------------------->| <------
CE1 | T-PE/PE1 S-PE/P1 T-PE/PE2 | CE2
| <--------> <--------> <--------> |
+---+ | +-+ +-+ +-+ +-+ +-+ +-+ +-+ +-+ +-+ | +---+
| | | | | | | | | | | | | | | | | | | | | | | |
| | | | | | | | | | | | | | | | | | | | | | | |
+---+ | +-+ +-+ +-+ +-+ +-+ +-+ +-+ +-+ +-+ | +---+
| In FW Out In FW Out In FW Out |
| |
FWD PW/LSP | o-------------------------- > |
| V-------------*-------------V |
| MEP1 MIP1 MEP2 |
BWD PW/LSP | <---------------------------o |
| V-------------*-------------V |
| MEP1' MIP1' MEP2'|
(S1)<============>
(S2)<==========================>
Figure 2: Example of OAM relying on per-node MIPs and MEPs
To illustrate the difference between these two modes of operation, we
use fault detection as an example. Consider the case where the
client traffic between CE1 and CE2 experiences a fault. Also assume
that an on-demand CV test between PE1 and PE2 was successful. The
scenario in Figure 2 therefore leaves the forwarding engine (FW) of
PE2, the out-going interface of PE2, the transmission line between
PE2 and CE2 or CE2 itself as a potential location of the fault as on-
demand CV can only be performed on segment S2.
The per-interface model in Figure 3 allows more fine-grained OAM
operations to be performed. At first, CV on segment S'4 and in
addition CV on segment S'5 can help to rule out e.g. the forwarding
engine of PE2. This is of course only a single example, and other
OAM functions and scenarios are trivially conceivable. The basic
message is that with the per-interface OAM model, an operator can
configure smaller segments on a transport path to which OAM
operations apply. This enables a more fine-grained scoping of OAM
operations such as fault localization and performance monitoring
which gives operators better information to deal with adverse
Farrel, et al. Expires October 24, 2013 [Page 5]
Internet-Draft Internal MIP Considerations April 2013
networking conditions.
Customer Operator's administrative Customer
Domain Domain Domain
------->|<--------------------------------------->|<------
CE1 | T-PE/PE1 S-PE/P1 T-PE/PE2 | CE2
| <--------> <--------> <--------> |
+---+ | +-+ +-+ +-+ +-+ +-+ +-+ +-+ +-+ +-+ | +---+
| | | | | | | | | | | | | | | | | | | | | | | |
| | | | | | | | | | | | | | | | | | | | | | | |
+---+ | +-+ +-+ +-+ +-+ +-+ +-+ +-+ +-+ +-+ | +---+
| In FW Out In FW Out In FW Out |
| |
FWD PW/LSP | o-----------------------------------> |
| V-------*------*------*-----*-------V |
| MEP1 MIP1 MIP2 MIP3 MIP4 MEP2|
| |
BWD PW/LSP | <-----------------------------------o |
| MEP1' MIP1' MIP2' MIP3' MIP4' MEP2'|
(S'1)<======>
(S'2)<=============>
(S'3)<====================>
(S'4)<==========================>
(S'5)<==================================>
Figure 3: Example of OAM relying on per-interface MIPs and MEPs
5. Requirements and Design Considerations for Internal-MIP Adressing
OAM messages for transit points of PWs or LSPs are delivered using
the expiration of the time-to-live (TTL) field in the top LSE of the
MPLS packet header. OAM messages for the end points of PWs and LSPs
are simply delivered as normal. These messages are distinguished
from other (data) packets so that they can be processed as OAM. In
LSPs, the mechanism used is the presence of the Generic Associated
Channel Label (GAL) in the LSE under the top LSE [RFC5586]. In PWs,
the mechanism used is the presence of the PW Associated Channel
Header [RFC4385] or the presence of a GAL [RFC6423]. In addition,
two sets of identifiers exist that can be used to address MIPs which
are defined in [RFC6370] and [I-D.ietf-mpls-tp-itu-t-identifiers]
Any solution for sending OAM messages to the in and out-MIPs must fit
within these existing models of handling OAM.
Farrel, et al. Expires October 24, 2013 [Page 6]
Internet-Draft Internal MIP Considerations April 2013
Additionally, many MPLS-TP nodes are implemented in a way that all
queuing and the forwarding function is performed at the incoming
interface. The abstract functional representation of such a node is
shown in Figure 4. As shown in the figure, the outgoing interfaces
are minimal and for this reason it may not be possible to include MIP
functions on those interfaces. This is in particular the case for
existing deployed implementations.
Any solution that attempts to send OAM messages to the outgoing
interface of an MPLS-TP node must not cause any problems when such
implementations are present (such as leaking OAM packets with a TTL
of 0).
------------------
|------------ |
| MIP | |
| ---- | |
----->-| In | FW | |-->--|->---
| i/f ---- | |
|------------ |
------------------
Figure 4: Abstract Functional Representation of Some Existing MPLS-TP
Nodes
OAM must operate on MPLS-TP nodes that are branch points on point-to-
multipoint (P2MP) trees. That means that it must be possible to
target individual outgoing MIPs as well as all outgoing MIPs in the
abstract functional representation shown in Figure 5, as well as to
handle the P2MP node implementations as shown in Figure 6 without
causing problems.
Farrel, et al. Expires October 24, 2013 [Page 7]
Internet-Draft Internal MIP Considerations April 2013
--------------------------
| -----|
| | MIP |
| ->-| |->----
| | | Out |
| | | i/f |
| | -----|
|----- | -----|
| MIP | ---- | | MIP |
| | | |- | |
----->-| In |->-| FW |--->-| Out |->----
| i/f | | |- | i/f |
|----- ---- | -----|
| | -----|
| | | MIP |
| | | |
| ->-| Out |->----
| | i/f |
| -----|
--------------------------
Figure 5: Abstract Functional Representation of an MPLS-TP Node
Supporting P2MP
------------------
| ->-|->----
| | |
|------------ | |
| | | |
| MIP ---- | | |
| | | |- |
----->-| In | FW | |--->-|->----
| i/f | | |- |
| ---- | | |
| | | |
|------------ | |
| | |
| ->-|->----
------------------
Figure 6: Abstract Functional Representation of Some Existing MPLS-TP
Nodes Supporting P2MP
In summary, the solution for OAM message delivery must behave as
follows:
Farrel, et al. Expires October 24, 2013 [Page 8]
Internet-Draft Internal MIP Considerations April 2013
o Delivery of OAM messages to the correct MPLS-TP node.
o Delivery of OAM instructions to the correct MIP within an MPLS-TP
node.
o Forwarding of OAM packets exactly as data packets.
o Packet inspection at the incoming and outgoing interfaces must be
minimized.
The first and second bullet point are obvious. The third bullet
point however is also vital. To illustrate the importance, a
rejected solution is depicted in Figure 7. In the figure, all data
and non-local OAM is handled as normal. Local OAM is intercepted at
the incoming interface and delivered to the MIP at the incoming
interface. If the OAM is intended for the incoming MIP it is handled
there with no issue. If the OAM is intended for the outgoing MIP it
is forwarded to that MIP using some internal messaging system that is
implementation-specific.
------------------------
|----- -----|
local OAM ----->-| MIP |----->------| MIP |
| | ---- | |
data =====>=| In |=>=| FW |=>=| Out |=>==== data
non-local OAM ~~~~~>~| i/f |~>~| |~>~| i/f |~>~~~~ non-local OAM
|----- ---- -----|
------------------------
Figure 7: OAM Control Message Delivery Bypassing the Forwarding
Engine
This solution is fully functional for the incoming MIP. It also
supports control of data loopback for the outgoing MIP, and can
adequately perform some OAM features such as interface identity
reporting at the outgoing MIP.
However, because the OAM message is not forwarded through the
forwarding engine, this solution cannot correctly perform OAM
loopback, connectivity verification, LSP tracing, or performance
measurement.
The last bullet point is also an important requirement for any
solution to the internal-MIP addressing problem. Since OAM packets
that target an out-MIP need to be sent through the forwarding engine
and treated exactly as regular data packets, the determination of
whether to forward the packet or process it at the incoming MIP needs
to be fast and therefore the processing overhead must be kept to a
minimum. In addition, there are a few OAM procedures that operate at
line rate such as OAM loopback. This adds to the requirement of
Farrel, et al. Expires October 24, 2013 [Page 9]
Internet-Draft Internal MIP Considerations April 2013
minimal processing overhead for both the in-MIP and out-MIP.
Most of the above superficially appears to be an implementation
matter local to an individual node, the format of the message needs
to be standardised so that:
o A MEP can correctly target the outgoing MIP of a specific MPLS-TP
node.
o A node can correctly filter out any OAM messages that were
intended for its upstream neighbor's outgoing MIP, but which were
not handled there because the upstream neighbor is an
implementation as shown in Figure 4 or Figure 6.
Note that the last bullet point describes a safety net and an
implementation should avoid that this situation ever arises.
6. Security Considerations
OAM security is discussed in [RFC6371] and security aspects specific
to MPLS-TP in general are outlined in
[I-D.ietf-mpls-tp-security-framework].
OAM can provide useful information for detecting and tracing security
attacks.
OAM can also be used to illicitly gather information or for denial of
service attacks and other types of attack. Implementations therefore
are required to offer security mechanisms for OAM. Deployments are
strongly advised to use such mechanisms.
Mixing of per-node and per-interface OAM on a single node is not
advised as OAM message leakage could be the result.
7. IANA Considerations
This revision of this document does not make any requests of IANA.
8. Acknowledgments
The authors gratefully acknowledge the substantial contributions of
Zhenlong Cui. We would also like to thank Eric Gray, Sami Boutros and
Shahram Davari for interesting input to this document through
discussions.
Farrel, et al. Expires October 24, 2013 [Page 10]
Internet-Draft Internal MIP Considerations April 2013
9. References
9.1. Normative References
[I-D.ietf-mpls-tp-itu-t-identifiers]
Winter, R., Gray, E., Helvoort, H., and M. Betts, "MPLS-TP
Identifiers Following ITU-T Conventions",
draft-ietf-mpls-tp-itu-t-identifiers-08 (work in
progress), February 2013.
[RFC2119] Bradner, S., "Key words for use in RFCs to Indicate
Requirement Levels", BCP 14, RFC 2119, March 1997.
[RFC4385] Bryant, S., Swallow, G., Martini, L., and D. McPherson,
"Pseudowire Emulation Edge-to-Edge (PWE3) Control Word for
Use over an MPLS PSN", RFC 4385, February 2006.
[RFC5586] Bocci, M., Vigoureux, M., and S. Bryant, "MPLS Generic
Associated Channel", RFC 5586, June 2009.
[RFC6370] Bocci, M., Swallow, G., and E. Gray, "MPLS Transport
Profile (MPLS-TP) Identifiers", RFC 6370, September 2011.
[RFC6371] Busi, I. and D. Allan, "Operations, Administration, and
Maintenance Framework for MPLS-Based Transport Networks",
RFC 6371, September 2011.
[RFC6423] Li, H., Martini, L., He, J., and F. Huang, "Using the
Generic Associated Channel Label for Pseudowire in the
MPLS Transport Profile (MPLS-TP)", RFC 6423,
November 2011.
9.2. Informative References
[I-D.ietf-mpls-tp-security-framework]
Fang, L., Niven-Jenkins, B., Mansfield, S., and R.
Graveman, "MPLS-TP Security Framework",
draft-ietf-mpls-tp-security-framework-09 (work in
progress), February 2013.
[RFC6291] Andersson, L., van Helvoort, H., Bonica, R., Romascanu,
D., and S. Mansfield, "Guidelines for the Use of the "OAM"
Acronym in the IETF", BCP 161, RFC 6291, June 2011.
Farrel, et al. Expires October 24, 2013 [Page 11]
Internet-Draft Internal MIP Considerations April 2013
Authors' Addresses
Adrian Farrel
Juniper Networks
Email: adrian@olddog.co.uk
Hideki Endo
Hitachi, Ltd.
Email: hideki.endo.es@hitachi.com
Rolf Winter
NEC
Email: rolf.winter@neclab.eu
Yoshinori Koike
NTT
Email: koike.yoshinori@lab.ntt.co.jp
Manuel Paul
Deutsche Telekom
Email: Manuel.Paul@telekom.de
Farrel, et al. Expires October 24, 2013 [Page 12]