Internet DRAFT - draft-zzhang-mpls-rmr-rsvp-p2mp
draft-zzhang-mpls-rmr-rsvp-p2mp
mpls Z. Zhang
Internet-Draft A. Deshmukh
Intended status: Standards Track R. Singh
Expires: January 3, 2019 Juniper Networks
July 2, 2018
RSVP-TE P2MP Tunnels on RMR
draft-zzhang-mpls-rmr-rsvp-p2mp-00
Abstract
This document specifies the optimization in RSVP-TE P2MP tunnel
signaling over Resilient MPLS Rings (RMR).
Requirements Language
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.
Status of This Memo
This Internet-Draft is submitted in full conformance with the
provisions of BCP 78 and BCP 79.
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This Internet-Draft will expire on January 3, 2019.
Copyright Notice
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to this document. Code Components extracted from this document must
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Table of Contents
1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . . 3
2. Specification . . . . . . . . . . . . . . . . . . . . . . . . . 4
2.1. RMR Object . . . . . . . . . . . . . . . . . . . . . . . . 4
2.2. Procedures . . . . . . . . . . . . . . . . . . . . . . . . 5
2.2.1. PATH Message/State . . . . . . . . . . . . . . . . . . 5
2.2.2. RESV Message/State . . . . . . . . . . . . . . . . . . 6
3. Security Considerations . . . . . . . . . . . . . . . . . . . . 6
4. Acknowledgements . . . . . . . . . . . . . . . . . . . . . . . 6
5. References . . . . . . . . . . . . . . . . . . . . . . . . . . 6
5.1. Normative References . . . . . . . . . . . . . . . . . . . 6
5.2. Informative References . . . . . . . . . . . . . . . . . . 6
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1. Introduction
Traditional RSVP-TE P2MP tunnel signaling could be quite involving.
With RMR, this could be significantly simplifed:
There is no need for ERO/RRO/SERO/SRRO or hop by hop rouing. The
tunnel ingress simply sends PATH messages in one or both directions
of the ring, depending on how leaves are best reached. The <S2L Sub-
LSP Descriptor List> only needs to list the tunnel leaves, and a
transit router does not need to "branch" a PATH message into multiple
ones Therefore, unless there are many tunnel leaves on a huge ring, a
single PATH message is enough. In the rare situation of a large
tunnel with many leaves to list, a small number of PATH messages
should suffice. Additionally, there is no need to signal and
maintain individual sub-LSPs (one for each leaf) any more. As a
result, corresponding PATH/RESV state is also reduced. Each node
only needs to maintain a single PATH state and a single RESV state
for each P2MP tunnel, and the RESV state does not need to track
individual leaves - it just need to track if a RESV is received from
downstream and/or if this node itself is a leaf.
A RESV message is triggered to the PHOP when the RESV state is first
created (either because the node is a leaf or because a RESV message
is received from downstream) and it is refreshed periodically. A
RESV Tear is sent when the RESV state is deleted (when the node is no
longer a Leaf and the RESV from downstream has timed out or a RESV
Tear is received).
Optionally, the tunnel ingress may not need to list any/all leaves.
It could simply send the PATH message around the ring, with the <S2L
Sub-LSP Descriptor List> listing the root itself. Through methods
outside the scope of this document, a node determines if it is a leaf
of the tunnel, and if yes, it will send back a RESV message. With
this, a single PATH message is surely enough.
In this document, leaves in <S2L Sub-LSP Descriptor List> are
referred to as explicit leaves, and leaves not listed there but self-
determined by ring nodes are referred to as implicit leaves. There
could be both explicit and implicit leaves for a tunnel. The ingress
allows implicit leaves by including itself as the last one in the
<S2L Sub-LSP Descriptor List>.
Optionally, the RESV message could also include a <S2L Sub-LSP
Descriptor List> to list all the leaves on the established tunnel so
that the each node knows its downstream leaves. In that case, when
the set of downstream leaves changes, a RESV message with the new
<S2L Sub-LSP Descriptor List> is triggered.
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Adding/removing explicit leaves is straighforward. The ingress
simply sends a triggered PATH message with new <S2L Sub-LSP
Descriptor List>. As it passes around the ring, each node determines
if it is an explicit leaf and updates its state accordingly. The
triggered PATH message does not have to go all the way to the last
leaf - if on a node the <S2L Sub-LSP Descriptor List> in the to-be-
sent PATH message is the same as what was sent before, the triggered
PATH message will not be sent further.
To indicate that the tunnel signaling is with above mentioned RMR
optimizations, a new object is included in the PATH message to
specify the Ring ID and direction.
Link/Node protection is achieved by tunneling packets to the next
node using the Ring LSP to that node in the other direction. This
does not need any additional signaling but is based on a reasonable
premise that unicast Ring LSPs are always in place. Once the ingress
learns the failure (through IGP discovery or through other error
detection/notification mechanisms), global repair kicks in to reach
some leaves via PATH message sent in the other direction. Before
global repair is finished, traffic continues to flow in the original
path except that at the failure point it is tunneled to the next
node.
If an RMR is just part of a general RSVP network the optimization can
also be applied on the ring nodes. If the tunnel ingress knows the
leaves that are on the ring, it could put all those leaves in the
single PATH message and construct the ERO/SERO only towards the entry
points on the ring. The entry points then includes the RMR object in
the PATH messages that they send. For leaves beyond the ring, the
ingress may include the exit points on the ring as loose hops in the
ERO/SERO, and when a ring node needs to send the PATH message off the
ring, it removes the RMR object. Details will be provided in future
revisions of this document.
2. Specification
2.1. RMR Object
The RMR object is a new object of the following:
o Class Name: RMR
o Class-Num: TBA1 (to be assigned by IANA)
o C-Type: TBA2 (to be assigned by IANA)
The format of the object content following the common object header
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is the folowing:
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
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Ring ID (4 octets) |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
|D| Flags | Reserved |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
Following the 4-octect Ring ID, there is an 8-bit Flags field. The
first bit of the Flags field indicates the direction. If it is set,
it is clockwise direction. Otherwise, it is anti-clockwise.
2.2. Procedures
This section describes the differces in the procedures for ring nodes
to set up RSVP-TE P2MP tunnels across the ring, compared to the
conventional non-RMR-aware case. For now it is assumed that all
nodes (ingress, tranist, and leaves) on the tunnel are on the ring.
More details will be provided in future revisions.
2.2.1. PATH Message/State
The tunnel ingress includes the RMR object with the Ring ID and the
direction flag bit set accordingly. The explicit tunnel leaves are
encoded in the <S2L Sub-LSP Descriptor List>, and no ERO/SERO is
included. If the tunnel allows implicit leaves, the descriptor list
encodes the ingress itself as the last element. The message is sent
to the next node on the ring in the direction specified in the RMR
object, w/o using ERO/SERO or hop-by-hop routing.
When a node recevies a PATH message with the RMR object, it checks if
itself is listed in the <S2L Sub-LSP Descriptor List>, or if the <S2L
Sub-LSP Descriptor List> encodes the tunnel ingress as the last
element and this node itself is an implicit leaf. If yes, it creates
corresponding RESV state and sends a RESV message to the PHOP.
The receiving node removes itself from the <S2L Sub-LSP Descriptor
List> in the PATH message, and saves the list locally. The PATH
message is sent to the next node on the ring in the specified
direction if one of the following conditions is met:
o The <S2L Sub-LSP Descriptor List> encodes the tunnel ingress
itself as the last element.
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o The <S2L Sub-LSP Descriptor List> is not empty and either the PATH
state is newly created or the <S2L Sub-LSP Descriptor List> is
different from the previously saved one.
If <S2L Sub-LSP Descriptor List> is empty and different from the
previously saved one, a PATH Teardown is sent instead with the saved
<S2L Sub-LSP Descriptor List>.
2.2.2. RESV Message/State
A ring node may know that it is a leaf when the PATH message is first
processed as described in the previous section. In case of implicit
leaves, it may become a leaf after the PATH messages has been
processed. A non-leaf node may also receive a RESV message from its
NHOP. In all cases, the node creates RESV state and sends a RESV
message to the PHOP, w/o encoding RRO/SRRO.
If a ring node was a leaf but stops being a leaf, either because it
is no longer listed in the <S2L Sub-LSP Descriptor List> or it is no
longer an implicit leaf, it removes/updates corresponding local
state. A RESV Teardown is sent to the PHOP if there is no RESV
received from its downstream.
3. Security Considerations
This document does not introduce new security risks?
4. Acknowledgements
5. References
5.1. Normative References
[I-D.ietf-mpls-rmr] Kompella, K. and L. Contreras, "Resilient MPLS
Rings", draft-ietf-mpls-rmr-04 (work in
progress), March 2017.
5.2. Informative References
Authors' Addresses
Zhaohui Zhang
Juniper Networks
EMail: zzhang@juniper.net
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Abhishek Deshmukh
Juniper Networks
EMail: adeshmukh@juniper.net
Ravi Singh
Juniper Networks
EMail: ravis@juniper.net
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