Network Working Group H. Chen
Internet-Draft Futurewei
Intended status: Standards Track D. Cheng
Expires: January 8, 2020 Individual
M. Toy
Verizon
Y. Yang
IBM
A. Wang
China Telecom
X. Liu
Volta Networks
Y. Fan
Casa Systems
L. Liu
Fujitsu
July 7, 2019
Flooding Topology Computation Algorithm
draft-cc-lsr-flooding-reduction-04
Abstract
This document proposes an algorithm for a node to compute a flooding
topology, which is a subgraph of the complete topology per underline
physical network. When every node in an area automatically
calculates a flooding topology by using a same algorithm and floods
the link states using the flooding topology, the amount of flooding
traffic in the network is greatly reduced. This would reduce
convergence time with a more stable and optimized routing
environment.
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].
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 https://datatracker.ietf.org/drafts/current/.
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Internet-Drafts are draft documents valid for a maximum of six months
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This Internet-Draft will expire on January 8, 2020.
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Table of Contents
1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . 2
2. Terminology . . . . . . . . . . . . . . . . . . . . . . . . . 3
3. Flooding Topology . . . . . . . . . . . . . . . . . . . . . . 3
3.1. Flooding Topology Construction . . . . . . . . . . . . . 3
4. Algorithms to Compute Flooding Topology . . . . . . . . . . . 4
4.1. Algorithm with Considering Degree . . . . . . . . . . . . 5
4.2. Algorithm with Considering Others . . . . . . . . . . . . 5
5. Security Considerations . . . . . . . . . . . . . . . . . . . 6
6. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 6
7. Acknowledgements . . . . . . . . . . . . . . . . . . . . . . 7
8. References . . . . . . . . . . . . . . . . . . . . . . . . . 7
8.1. Normative References . . . . . . . . . . . . . . . . . . 7
8.2. Informative References . . . . . . . . . . . . . . . . . 7
Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . 7
1. Introduction
For some networks such as dense Data Center (DC) networks, the
existing Link State (LS) flooding mechanism is not efficient and may
have some issues. The extra LS flooding consumes network bandwidth.
Processing the extra LS flooding, including receiving, buffering and
decoding the extra LSs, wastes memory space and processor time. This
may cause scalability issues and affect the network convergence
negatively.
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This document proposes an algorithm for a node to compute a flooding
topology, which is a subgraph of the complete topology per underline
physical network. When every node in an area automatically
calculates a flooding topology by using a same algorithm and floods
the link states using the flooding topology, the amount of flooding
traffic in the network is greatly reduced. This would reduce
convergence time with a more stable and optimized routing
environment.
There may be multiple algorithms for computing a flooding topology.
Users can select one they prefer, and smoothly switch from one to
another.
2. Terminology
LSA: A Link State Advertisement in OSPF.
LSP: A Link State Protocol Data Unit (PDU) in IS-IS.
LS: A Link Sate, which is an LSA or LSP.
FT: Flooding Topology.
FTC: Flooding Topology Computation.
3. Flooding Topology
For a given network topology, a flooding topology is a sub-graph or
sub-network of the given network topology that has the same
reachability to every node as the given network topology. Thus all
the nodes in the given network topology MUST be in the flooding
topology. All the nodes MUST be inter-connected directly or
indirectly. As a result, LS flooding will in most cases occur only
on the flooding topology, that includes all nodes but a subset of
links. Note even though the flooding topology is a sub-graph of the
original topology, any single LS MUST still be disseminated in the
entire network.
3.1. Flooding Topology Construction
Many different flooding topologies can be constructed for a given
network topology. For example, a chain connecting all the nodes in
the given network topology is a flooding topology. A circle
connecting all the nodes is another flooding topology. A tree
connecting all the nodes is a flooding topology. In addition, the
tree plus the connections between some leaves of the tree and branch
nodes of the tree is a flooding topology.
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The following parameters need to be considered for constructing a
flooding topology:
o Degree: The degree of the flooding topology is the maximum degree
among the degrees of the nodes on the flooding topology. The
degree of a node on the flooding topology is the number of
connections on the flooding topology it has to other nodes.
o Number of links: The number of links on the flooding topology is a
key factor for reducing the amount of LS flooding. In general,
the smaller the number of links, the less the amount of LS
flooding.
o Diameter: The diameter of the flooding topology is the shortest
distance between the two most distant nodes on the flooding
topology. It is a key factor for reducing the network convergence
time. The smaller the diameter, the less the convergence time.
o Redundancy: The redundancy of the flooding topology means a
tolerance to the failures of some links and nodes on the flooding
topology. If the flooding topology is split by some failures, it
is not tolerant to these failures. In general, the larger the
number of links on the flooding topology is, the more tolerant the
flooding topology to failures.
Note that the flooding topology constructed by a node is dynamic in
nature, that means when the base topology (the entire topology graph)
changes, the flooding topology (the sub-graph) MUST be re-computed/
re-constructed to ensure that any node that is reachable on the base
topology MUST also be reachable on the flooding topology.
4. Algorithms to Compute Flooding Topology
There are many algorithms to compute a flooding topology. A simple
and efficient one is briefed below.
o Select a node R0 according to a rule such as the node with the
smallest node ID;
o Build a tree using R0 as root of the tree; and then
o Connect each node whose degree is one to the tree to have a
flooding topology.
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4.1. Algorithm with Considering Degree
The algorithm starts from node R0 as root with a given maximum degree
MaxD, a candidate queue Cq = {(R0, D = 0, PHs = { })}, and an empty
flooding topology FT = { }. Cq contains one element (R0, D = 0, PHs
= { }), where node R0 is the root, D = 0 indicates that the Degree (D
for short) of R0 is 0 (i.e., the number of links on the flooding
topology connected to R0 is 0), PHs = { } indicates that the Previous
Hops (PHs for short) of R0 is empty.
1. Finding and removing the first element with node A in Cq that is
not on FT and one PH's D in PHs < MaxD.
If there is no element with a node in Cq whose PHs != { } and one
PH in PHs whose D < MaxD,
then MaxD++ and restarts algorithm from R0, MaxD, Cq =
{(R0,D=0,PHs = { })}, FT = { };
otherwise (i.e., A with one PH's D in PHs < MaxD or PHs = { }),
if PHs = { } (i.e., A is the root),
then mark A on FT and add A with D=0 and PHs={ } into FT;
otherwise (i.e., A is not the root. Assume that PH is the
first one in PHs whose D < MaxD), PH's D++, mark A on FT and
add A with D=1 and PHs={PH} to FT.
2. If all the nodes are on the FT, then goto step 4;
3. Suppose that node Xi (i = 1, 2,..., n) is connected to node A and
not on FT, and X1, X2,..., Xn are in an increasing order by their
IDs (i.e., X1's ID < X2's ID < ... < Xn's ID). If Xi is not in
Cq, then add it into the end of Cq with D = 0 and PHs = {A};
otherwise (i.e., Xi is in Cq), add A into Xi's PHs and elements
in PHs are in an increasing order by their degrees first and then
IDs; Goto step 1.
4. For each node B in FT whose D is one, find a link L attached to B
such that L's remote node R whose D and ID are minimum; increase
B's D and R's D by one. Return FT.
4.2. Algorithm with Considering Others
There may be some contraints on some nodes in a network. For
example, in a spine-and-leaf network, there may be a constraint on
the degree of every leaf node on the flooding topology, which is that
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the degree of every leaf node is not greater than a given number
ConMaxD such as ConMaxD = 2. For each of the other nodes such as the
spine nodes, there is no such constraint, that is that ConMaxD is a
huge number for each of these nodes.
Step 1 of the algorithm described above is updated below to consider
this constraint. In addition to checking constraint PH's D < MaxD,
step 1 checks another constraint PH's D < PH's ConMaxD.
1. Finding and removing the first element with node A in Cq that is
not on FT and one PH's D in PHs < MaxD and PH's D < PH's ConMaxD.
If there is no element with a node in Cq whose PHs != { } and one
PH in PHs whose D < MaxD and PH's D < PH's ConMaxD,
then MaxD++ and restarts algorithm from R0, MaxD, Cq =
{(R0,D=0,PHs = { })}, FT = { };
otherwise (i.e., node A with one PH's D in PHs < MaxD and PH's D
< PH's ConMaxD or PHS = { }),
if PHs = { } (i.e., A is the root),
then mark A on FT and add A with D=0 and PHs={ } into FT;
otherwise (i.e., A is not the root. Assume that PH is the
first one in PHs whose D < MaxD and PH's D < PH's ConMaxD),
PH's D++, mark A on FT and add A with D=1 and PHs={PH} to FT.
5. Security Considerations
This document does not introduce any new security issue.
6. IANA Considerations
Under Registry Name: "IGP Algorithm Type For Computing Flooding
Topology" under an existing "Interior Gateway Protocol (IGP)
Parameters" IANA registries (refer to Section 7.3. IGP
[I-D.ietf-lsr-dynamic-flooding]), IANA is requested to assign one
value of IGP Algorithm Type For Computing Flooding Topology as
follows:
+==========+========================================+=============+
|Type Value| Type Name | reference |
+==========+========================================+=============+
| 1 | Breadth First Minimum Degree Algorithm |This document|
+----------+----------------------------------------+-------------+
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7. Acknowledgements
The authors would like to thank Acee Lindem, Zhibo Hu, Robin Li,
Stephane Litkowski and Alvaro Retana for their valuable suggestions
and comments on this draft.
8. References
8.1. Normative References
[I-D.ietf-lsr-dynamic-flooding]
Li, T., Psenak, P., Ginsberg, L., Chen, H., Przygienda,
T., Cooper, D., Jalil, L., and S. Dontula, "Dynamic
Flooding on Dense Graphs", draft-ietf-lsr-dynamic-
flooding-03 (work in progress), June 2019.
[RFC1195] Callon, R., "Use of OSI IS-IS for routing in TCP/IP and
dual environments", RFC 1195, DOI 10.17487/RFC1195,
December 1990, .
[RFC2119] Bradner, S., "Key words for use in RFCs to Indicate
Requirement Levels", BCP 14, RFC 2119,
DOI 10.17487/RFC2119, March 1997,
.
[RFC2328] Moy, J., "OSPF Version 2", STD 54, RFC 2328,
DOI 10.17487/RFC2328, April 1998,
.
8.2. Informative References
[I-D.ietf-rtgwg-spf-uloop-pb-statement]
Litkowski, S., Decraene, B., and M. Horneffer, "Link State
protocols SPF trigger and delay algorithm impact on IGP
micro-loops", draft-ietf-rtgwg-spf-uloop-pb-statement-10
(work in progress), January 2019.
[RFC8126] Cotton, M., Leiba, B., and T. Narten, "Guidelines for
Writing an IANA Considerations Section in RFCs", BCP 26,
RFC 8126, DOI 10.17487/RFC8126, June 2017,
.
Authors' Addresses
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Huaimo Chen
Futurewei
Boston
USA
Email: huaimo.chen@futurewei.com
Dean Cheng
Individual
Santa Clara
USA
Email: deanccheng@gmail.com
Mehmet Toy
Verizon
USA
Email: mehmet.toy@verizon.com
Yi Yang
IBM
Cary, NC
United States of America
Email: yyietf@gmail.com
Aijun Wang
China Telecom
Beiqijia Town, Changping District
Beijing 102209
China
Email: wangaj.bri@chinatelecom.cn
Xufeng Liu
Volta Networks
McLean, VA
USA
Email: xufeng.liu.ietf@gmail.com
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Yanhe Fan
Casa Systems
USA
Email: yfan@casa-systems.com
Lei Liu
Fujitsu
USA
Email: liulei.kddi@gmail.com
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