Internet DRAFT - draft-li-dynamic-flooding-isis
draft-li-dynamic-flooding-isis
Internet Engineering Task Force T. Li
Internet-Draft Arista Networks
Intended status: Informational March 18, 2018
Expires: September 19, 2018
Dynamic Flooding for IS-IS
draft-li-dynamic-flooding-isis-01
Abstract
Routing with link state protocols in dense network topologies can
result in sub-optimal convergence times due to the overhead
associated with flooding. This can be addressed by decreasing the
flooding topology so that it is less dense.
This document discusses extensions to the IS-IS routing protocol to
support a solution to flooding in dense subgraphs.
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 September 19, 2018.
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Copyright (c) 2018 IETF Trust and the persons identified as the
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the Trust Legal Provisions and are provided without warranty as
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Table of Contents
1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . 2
1.1. Requirements Language . . . . . . . . . . . . . . . . . . 3
2. Area Leader TLV . . . . . . . . . . . . . . . . . . . . . . . 3
3. Area System IDs TLV . . . . . . . . . . . . . . . . . . . . . 3
4. Flooding Path TLV . . . . . . . . . . . . . . . . . . . . . . 4
5. Acknowledgements . . . . . . . . . . . . . . . . . . . . . . 5
6. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 5
7. Security Considerations . . . . . . . . . . . . . . . . . . . 5
8. References . . . . . . . . . . . . . . . . . . . . . . . . . 6
8.1. Normative References . . . . . . . . . . . . . . . . . . 6
8.2. Informative References . . . . . . . . . . . . . . . . . 6
Author's Address . . . . . . . . . . . . . . . . . . . . . . . . 6
1. Introduction
In recent years, there has been increased focused on how to address
the dynamic routing of networks that have a bipartite (a.k.a. spine-
leaf), Clos [Clos], or Fat Tree [Leiserson] topology. Conventional
Interior Gateway Protocols (IGPs, i.e. IS-IS [ISO10589], OSPF
[RFC5340]) under-perform, redundantly flooding information throughout
the dense topology, leading to overloaded control plane inputs and
thereby creating operational issues. For practical considerations,
network architects have resorted to applying unconventional
techniques to address the problem, applying BGP in the data center
[RFC7938], however it is very clear that using an Exterior Gateway
Protocol as an IGP is sub-optimal, if only due to the configuration
overhead.
This problem is discussed in more detail in [Architecture], along
with an architectural solution for the problem. The remainder of
this document is focused on describing extensions to the IS-IS
protocol to implement that architecture. Three additions appear to
be necessary.
1. A TLV that an IS may inject into its LSP to indicate its
preference for becoming Area Leader.
2. A TLV to carry the list of system IDs that compromise the
flooding topology for the area.
3. A TLV to carry the adjacency matrix for the flooding topology for
the area.
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1.1. 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 RFC 2119 [RFC2119].
2. Area Leader TLV
The Area Leader TLV allows a system to indicate its eligibility and
priority for becoming Area Leader. Intermediate Systems (routers)
not advertising this TLV are not eligible to become Area Leader.
The Area Leader is the router with the numerically highest Area
Leader priority in the area. In the event of ties, the router with
the numerically highest system ID is the Area Leader. Due to
transients during database flooding, different routers may not agree
on the Area Leader.
The format of the Area Leader TLV is:
0 1 2
0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| TLV Type | TLV Length | Priority |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
TLV Type: XXX
TLV Length: 1
Priority: 0-255, unsigned integer
3. Area System IDs TLV
The Area System IDs TLV is used by the Area Leader to enumerate the
system IDs that it has used in computing the flooding topology.
Conceptually, the Area Leader creates a list of system IDs for all
routers in the area, assigning indices to each system, starting with
index 0.
Because the space in a single TLV is small, it may require more than
one TLV to encode all of the system IDs in the area. This TLV may
recur in multiple LSP segments so that all system IDs can be
advertised.
The format of the Area System IDs TLV is:
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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
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| TLV Type | TLV Length | Starting Index |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Ending Index |L| Reserved | System IDs ...
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
System IDs continued ....
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
TLV Type: YYY
TLV Length: 9 + (ID length * N)
Starting index: The index of the first system ID that appears in
this TLV.
Ending index: The index of the last system ID that appears in this
TLV.
L (Last): This bit is set if the ending index of this TLV is the
last index in the full list of system IDs for the area.
System IDs: A concatenated list of system IDs for the area.
4. Flooding Path TLV
The Flooding Path TLV is used to denote a path in the flooding
topology. The goal is an efficient encoding of the links of the
topology. A single link is a simple case of a path that only covers
two nodes. A connected path may be described as a sequence of
indices: (I1, I2, I3, ...), denoting a link from the system with
index 1 to the system with index 2, a link from the system with index
2 to the system with index 3, and so on.
If a path exceeds the size that can be stored in a single TLV, then
the path may be distributed across multiple TLVs by the replication
of a single system index.
Complex topologies that are not a single path can be described using
multiple TLVs.
The Flooding Path TLV contains a list of system indices relative to
the systems advertised through the Area System IDs TLV. At least 2
indices must be included in the TLV. Due to the lenth restriction of
TLVs, this TLV can contain at most 126 system indices.
The Flooding Path TLV has the format:
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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
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| TLV Type | TLV Length | Starting Index |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Index 2 | Additional indices ...
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
TLV Type: ZZZ
TLV Length: 9 + Length of Matrix octet contents
Starting index: The index of the first system in the path.
Index 2: The index of the next system in the path.
Additional indices: A sequence of additional indices to systems
along the path.
Matrix: The concatenated rows of the upper right triangular
portion of the adjacency matrix for the flooding topology, padded
with 0 bits to an octet boundary.
5. Acknowledgements
The author would like to thank Adam Sweeney for his diligent review.
6. IANA Considerations
This memo requests that IANA allocate and assign three code points
from the IS-IS TLV Codepoints registry. One for each of the
following TLVs:
1. Area Leader TLV
2. Area System IDs TLV
3. Flooding Path TLV
7. Security Considerations
This document introduces no new security issues. Security of routing
within a domain is already addressed as part of the routing protocols
themselves. This document proposes no changes to those security
architectures.
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8. References
8.1. Normative References
[ISO10589]
International Organization for Standardization,
"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, Nov. 2002.
[RFC2119] Bradner, S., "Key words for use in RFCs to Indicate
Requirement Levels", BCP 14, RFC 2119,
DOI 10.17487/RFC2119, March 1997,
<https://www.rfc-editor.org/info/rfc2119>.
8.2. Informative References
[Architecture]
Li, T., "An Architecture for Dynamic Flooding on Dense
Graphs", Internet draft draft-li-dynamic-flooding, Jan.
2018.
[Clos] Clos, C., "A Study of Non-Blocking Switching Networks",
The Bell System Technical Journal Vol. 32(2), DOI
10.1002/j.1538-7305.1953.tb01433.x, March 1953,
<http://dx.doi.org/10.1002/j.1538-7305.1953.tb01433.x>.
[Leiserson]
Leiserson, C., "Fat-Trees: Universal Networks for
Hardware-Efficient Supercomputing", IEEE Transactions on
Computers 34(10):892-901, 1985.
[RFC5340] Coltun, R., Ferguson, D., Moy, J., and A. Lindem, "OSPF
for IPv6", RFC 5340, DOI 10.17487/RFC5340, July 2008,
<https://www.rfc-editor.org/info/rfc5340>.
[RFC7938] Lapukhov, P., Premji, A., and J. Mitchell, Ed., "Use of
BGP for Routing in Large-Scale Data Centers", RFC 7938,
DOI 10.17487/RFC7938, August 2016,
<https://www.rfc-editor.org/info/rfc7938>.
Author's Address
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Tony Li
Arista Networks
5453 Great America Parkway
Santa Clara, California 95054
USA
Email: tony.li@tony.li
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