IS-IS Point-to-Multipoint operation
draft-lamparter-isis-p2mp-00
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| Authors | Christian Franke , David Lamparter | ||
| Last updated | 2015-07-06 | ||
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draft-lamparter-isis-p2mp-00
Network Working Group C. Franke
Internet-Draft D. Lamparter
Intended status: Standards Track NetDEF
Expires: January 08, 2016 July 07, 2015
IS-IS Point-to-Multipoint operation
draft-lamparter-isis-p2mp-00
Abstract
This document describes a new mode operation for IS-IS. In addition
to the existing LAN and point-to-point modes of operation, a point-
to-multipoint mode is defined. This mode is useful for operation
both on networks with more than two routers where multicast is
expensive in comparison to unicast, as well on networks where
creating a LAN pseudonode cannot adequately reflect metrics.
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 08, 2016.
Copyright Notice
Copyright (c) 2015 IETF Trust and the persons identified as the
document authors. All rights reserved.
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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
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described in the Simplified BSD License.
Table of Contents
1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . 2
2. P2MP Pseudocircuits . . . . . . . . . . . . . . . . . . . . . 3
2.1. Pseudocircuit behaviour . . . . . . . . . . . . . . . . . 3
2.1.1. Representation in LSPs . . . . . . . . . . . . . . . 3
2.1.2. Forwarding . . . . . . . . . . . . . . . . . . . . . 4
2.2. Neighbor IS discovery . . . . . . . . . . . . . . . . . . 4
2.2.1. Manual configuration . . . . . . . . . . . . . . . . 4
2.2.2. Lower layer autodiscovery . . . . . . . . . . . . . . 4
2.2.3. Multicast autodiscovery . . . . . . . . . . . . . . . 4
2.3. Adjacency formation . . . . . . . . . . . . . . . . . . . 5
2.4. Pseudocircuit teardown . . . . . . . . . . . . . . . . . 5
3. PDU generation and processing . . . . . . . . . . . . . . . . 6
3.1. LSP, CSNP, PSNP and all other non-Hello PDU types . . . . 6
3.2. LAN and P2P Hellos . . . . . . . . . . . . . . . . . . . 6
3.3. P2MP Hello PDUs . . . . . . . . . . . . . . . . . . . . . 6
3.3.1. Without Three-way Adjacency TLV . . . . . . . . . . . 6
3.3.2. With Three-way Adjacency TLV . . . . . . . . . . . . 7
4. PDU encoding . . . . . . . . . . . . . . . . . . . . . . . . 7
4.1. P2MP Hello PDU . . . . . . . . . . . . . . . . . . . . . 7
5. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 8
6. Configuration model . . . . . . . . . . . . . . . . . . . . . 9
7. Security Considerations . . . . . . . . . . . . . . . . . . . 9
8. Privacy Considerations . . . . . . . . . . . . . . . . . . . 9
9. Acknowledgements . . . . . . . . . . . . . . . . . . . . . . 9
10. References . . . . . . . . . . . . . . . . . . . . . . . . . 9
10.1. Normative References . . . . . . . . . . . . . . . . . . 9
10.2. Informative References . . . . . . . . . . . . . . . . . 9
Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . 10
1. Introduction
The core functionality of the protocol outlined in this document
consists of an additional Subnetwork dependent function per Section 8
of ISO/IEC 10589:2002 [IS-IS]. In that regard, the next section can
be understood as new section "8.5 Point-to-multipoint networks".
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The outlined protocol is remotely similar to the derelict section
"8.3 ISO 8208 subnetworks" [X.25] in that multiple point-to-point
adjacencies are established on an interface.
Point-to-multipoint operation of IS-IS is thus not a new idea; in
fact section 6.2 already mentions "multipoint links." This document
re-enables the concept.
2. P2MP Pseudocircuits
In place of ISO 8473 call management [CLNS] establishing sessions,
this document establishes pairwise "pseudocircuits" between two IS on
a common medium. Multiple such pseudocircuits can normally exist on
one P2MP interface.
Each pseudocircuit operates, aside from subnetwork attachment
procedures, exactly as a PtP link.
It should be noted that while the Multicast autodiscovery mechanism
requires broadcast capability, no other part of the protocol does.
The P2MP interface type can be used on non-transitive and/or non-
broadcast interfaces.
2.1. Pseudocircuit behaviour
An implementation maintains a set of pseudocircuits per P2MP
interface. Each pseudocircuit is uniquely identified by the local
interface and peer's SNPA address.
Each participating system MUST use a consistent SNPA address per
local interface. A change in SNPA address results in all neighbors
treating the interface as distinct from the previous one. A system
MAY support multiple SNPA addresses per interface by treating them as
distinct interfaces.
Unnumbered media are not supported by this protocol. Each
participant on a link MUST have an unique SNPA address on that link.
As pseudocircuits are dynamic in nature, they must be created and
destroyed as needed.
2.1.1. Representation in LSPs
Pseudocircuits are represented in LSPs as a regular PtP circuit would
be. As a result, their treatment in SPF calculations is also
identical to PtP circuits.
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2.1.2. Forwarding
In scenarios where pseudocircuits do not form a full mesh of all
participants on a medium, the best path for a packet may be through
the same interface as the one it was received on.
Systems implementing this specification MUST therefore support
forwarding packets on the same interface that they were received on.
This applies only to interfaces configured for P2MP operation.
2.2. Neighbor IS discovery
The discovery machinery produces as output a "candidate neighbor
list," which is a list of possible neighbor's SNPAs and is maintained
per P2MP interface. Additional information (metric, etc.) MAY be
associated with the SNPA, but this is not part of the discovery
mechanism.
The candidate neighbor list is conceptual in nature; adding and
removing entries results in pseudocircuit creation and deletion. It
need not be implemented as an actual list.
The list is the union of the result of each of the following sources
of neighbor information. A neighbor may be listed by multiple
sources: it MUST NOT be removed while any source still lists it.
The IS-IS implementation SHOULD provide user configuration to disable
individual mechanisms and/or filter candidate neighbors both as a
security and as misconfiguration preventing measure.
2.2.1. Manual configuration
A list of neighbor IS MAY be configured by the user, providing
possible neighbor's SNPAs on an interface.
2.2.2. Lower layer autodiscovery
Lower protocol layers (VPLS, IEEE 802.11) may be able to provide a
list of attached neighbors. This list MAY be fed into the candidate
neighbor list.
2.2.3. Multicast autodiscovery
For broadcast capable networks, this document defines an
autodiscovery mechanism based on multicasting Hello packets. This
mechanism MAY be disabled by the user, but MUST be implemented for
all lower layer link types with (limited or full) broadcast
capability.
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Multicast autodiscovery P2MP Hello PDUs are distinguished by not
containing a RFC5303 Three-Way Adjacency TLV. Receiving such a Hello
places the sending IS on the candidate list for as long as the PDU's
holdtime indicates.
A system MAY implement a receive-only passive multicast autodiscovery
mode where it adds candidates (forms pseudocircuits) on receiving
P2MP Hello PDUs, but does not send such PDUs itself.
If either passive or full multicast autodiscovery is enabled,
receiving a P2MP Hello PDU with a Three-Way Adjacency TLV also adds
the neighbor to the candidate list.
2.3. Adjacency formation
Since there is no underlying protocol layer partitioning the link
into actual PtP circuits in this case, additional handling is
required on bringing up the individual pseudocircuit adjacencies.
To prevent different pseudocircuits from "bleeding" into each other,
implementations of this protocol MUST enable [RFC5303] on all P2MP
pseudocircuits, with changes as follows:
o Received IIH PDUs on P2MP pseudocircuits without the Point-to-
Point Three-Way Adjacency option MUST be discarded. The TLV is
not optional on pseudocircuit adjacencies but rather mandatory.
2.4. Pseudocircuit teardown
Pseudocircuits are destroyed when their PtP state machine has
transitioned into "Down" state and they are no longer listed as
candidates by any discovery mechanism. The conditions for
pseudocircuit removal are thus:
o PtP adjacency timeout functionality (IS-IS section 8.2.6 [IS-IS])
has moved the pseudocircuit to Down state, or it never moved out
of Down state
o The holdtime of any multicast autodiscovery P2MP Hello PDUs has
expired.
o Manual configuration or lower layer autodiscovery no longer lists
the neighbor.
As long as a pseudocircuit is present, its PtP state machine will, as
expected for PtP circuits, trigger transmission of further Hello
PDUs, even when it is in Down state.
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3. PDU generation and processing
3.1. LSP, CSNP, PSNP and all other non-Hello PDU types
All PDU types that are not Hello PDUs, e.g. L1/L2 LSP PDUs, L1/L2
CSNP/PSNP PDUs, FS-LSP, FS-CSNP and FS-PSNP PDUs are processed on
P2MP interfaces by dispatching them to an individual pseudocircuit by
looking up the PDU's source address in the interface's list of P2MP
pseudocircuits. This includes all functions defined in Section 7 of
ISO/IEC 10589:2002 [IS-IS] and PDUs added in [RFC7176] and [RFC7356].
While possible, this document does not suggest sending such PDUs to
multicast destinations. All systems MUST send these PDUs to unicast
lower layer destinations so that they are received only by the
pseudocircuit's neighbor system. However, systems SHOULD NOT check
the destination address on receipt to allow future optimisations.
3.2. LAN and P2P Hellos
Received LAN and P2P Hello PDUs MUST be discarded when received on an
interface configured for P2MP operation. The system MAY notify the
operator of such a misconfiguration.
TODO: hitless migration possible?
3.3. P2MP Hello PDUs
P2MP Hello PDUs are divided in two categories depending on the
presence of a RFC5303 Three-way Adjacency TLV.
3.3.1. Without Three-way Adjacency TLV
For each P2MP interface that has the multicast autodiscovery
mechanism enabled, a system periodically sends P2MP Hello PDUs
without Three-way Adjacency TLV to a lower layer specific multicast
address. The periodic timer SHOULD be configurable and is subject to
jitter per Section 10.1 of ISO/IEC 10589:2002 [IS-IS].
On receipt, such PDUs are not processed on any pseudocircuit's PtP
state machine. They are processed on pseudocircuit management level
as described in :
o If no pseudocircuit matches the PDU's lower layer source address,
one is created for that address
o The pseudocircuit is held in existence at least until the PDU's
holdtime expires.
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No information other than the neighbor's SNPA is carried from the PDU
onto the pseudocircuit, thus most TLVs that are normally valid in
Hellos become pointless. However, all TLVs that affect PDU
processing (in particular authentication TLVs) are processed
normally.
On IEEE 802 lower layers that support 48bit MAC addresses, the
AllIntermediateSystems multicast address (09-00-2B-00-00-05) is used
as destination when sending these PDUs.
3.3.2. With Three-way Adjacency TLV
P2MP Hello PDUs with a RFC5303 Three-way Adjacency TLV are both
processed and generated by the PtP Hello state machine (Section 8.2
of ISO/IEC 10589:2002 [IS-IS]) of their associated pseudocircuit.
This implies that received PDUs are dispatched by looking up their
source SNPA address among the pseudocircuits associated with the
receiving interface (possibly creating a pseudocircuit).
For Hello PDUs sent by the pseudocircuit's PtP Hello state machine,
the destination SNPA address is set to the pseudocircuit's neighbor
SNPA address.
TLV validity and processing is exactly as for PtP Hellos.
4. PDU encoding
(Note this section follows ISO 10589 section 9, particularly in
numbering bits starting at 1 for the LSB.)
4.1. P2MP Hello PDU
Figure 1: P2MP Hello PDU format
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MSB LSB MSB LSB
8 7 6 5 4 3 2 1 8 7 6 5 4 3 2 1
+---+---+---+---+---+---+---+---+ - + - + - + - + - + - + - + - +
| 0x83 (Protocol Discriminator) |
+---+---+---+---+---+---+---+---+
| Length Indicator |
+---+---+---+---+---+---+---+---+
| 0x01 (Version/ID Extension) |
+---+---+---+---+---+---+---+---+
| ID Length |
+---+---+---+---+---+---+---+---+
| R R R | TBD-PDU (PDU Type)|
+---+---+---+---+---+---+---+---+
| 0x01 (Version) |
+---+---+---+---+---+---+---+---+
| R R R R R R R R |
+---+---+---+---+---+---+---+---+
| Maximum Area Addresses |
+---+---+---+---+---+---+---+---+
| R R R R R R |CircTyp|
+---+---+---+---+---+---+---+---+
| Source ID |
: (ID Length) :
: :
+---+---+---+---+---+---+---+---+---+---+---+---+---+---+---+---+
| Holding Time |
+---+---+---+---+---+---+---+---+---+---+---+---+---+---+---+---+
| PDU Length |
+---+---+---+---+---+---+---+---+---+---+---+---+---+---+---+---+
: Variable Length Fields (TLVs) :
: :
All fields function exactly as for Point-to-Point IS-IS hello PDUs,
as specified in Section 9.7 of ISO/IEC 10589:2002 [IS-IS].
Note the Local Circuit ID field is absent. Its function is replaced
by [RFC5303].
5. IANA Considerations
IANA is requested to allocate a value from the "IS-IS PDU Registry"
as follows:
Type: TBD-PDU
Description: P2MP-HELLO-PDU
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Reference: This document
Applicability of sub-TLVs for this PDU (per "TLV Codepoints
Registry") is per the "IIH" column.
6. Configuration model
TODO: YANG model.
7. Security Considerations
TODO.
8. Privacy Considerations
TODO.
9. Acknowledgements
TODO.
10. References
10.1. Normative References
[IS-IS] ISO/IEC, "Intermediate System to Intermediate System
Intra-Domain Routing Exchange Protocol for use in
Conjunction with the Protocol for Providing the
Connectionless-mode Network Service (ISO 8473)", ISO/IEC
10589:2002, Second Edition, 2002.
[RFC2119] Bradner, S., "Key words for use in RFCs to Indicate
Requirement Levels", BCP 14, RFC 2119, March 1997.
[RFC5303] Katz, D., Saluja, R., and D. Eastlake, "Three-Way
Handshake for IS-IS Point-to-Point Adjacencies", RFC 5303,
October 2008.
10.2. Informative References
[CLNS] ISO/IEC, "Protocol for providing the connectionless-mode
network service: Protocol specification", ISO/IEC
8473-1:1998, 1998.
[RFC7176] Eastlake, D., Senevirathne, T., Ghanwani, A., Dutt, D.,
and A. Banerjee, "Transparent Interconnection of Lots of
Links (TRILL) Use of IS-IS", RFC 7176, May 2014.
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[RFC7356] Ginsberg, L., Previdi, S., and Y. Yang, "IS-IS Flooding
Scope Link State PDUs (LSPs)", RFC 7356, September 2014.
[X.25] ISO/IEC, "X.25 Packet Layer Protocol for Data Terminal
Equipment", ISO/IEC 8208:2000, 2000.
Authors' Addresses
Christian Franke
NetDEF
Leipzig
DE
Email: chris@opensourcerouting.org
David Lamparter
NetDEF
Leipzig 04103
Germany
Email: david@opensourcerouting.org
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