IS-IS Flooding Reduction in MSDC
draft-xu-lsr-isis-flooding-reduction-in-msdc-04
The information below is for an old version of the document.
| Document | Type |
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|---|---|---|---|
| Authors | Xiaohu Xu , Luyuan Fang , Jeff Tantsura , Shaowen Ma | ||
| Last updated | 2023-08-03 (Latest revision 2020-12-22) | ||
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draft-xu-lsr-isis-flooding-reduction-in-msdc-04
Network Working Group X. Xu
Internet-Draft China Mobile
Intended status: Standards Track L. Fang
Expires: 4 February 2024 eBay
J. Tantsura
Nvidia
S. Ma
Google
3 August 2023
IS-IS Flooding Reduction in MSDC
draft-xu-lsr-isis-flooding-reduction-in-msdc-04
Abstract
IS-IS is commonly used as an underlay routing protocol for MSDC
(Massively Scalable Data Center) networks. For a given IS-IS router
within the CLOS topology, it would receive multiple copies of exactly
the same LSP from multiple IS-IS neighbors. In addition, two IS-IS
neighbors may send each other the same LSP simultaneously. The
unnecessary link-state information flooding wastes the precious
process resource of IS-IS routers greatly due to the fact that there
are too many IS-IS neighbors for each IS-IS router within the CLOS
topology. This document proposes some extensions to IS-IS so as to
reduce the IS-IS flooding within MSDC networks greatly. The
reduction of the IS-IS flooding is much beneficial to improve the
scalability of MSDC networks.
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 4 February 2024.
Copyright Notice
Copyright (c) 2023 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 (https://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
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provided without warranty as described in the Revised BSD License.
Table of Contents
1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . 2
2. Terminology . . . . . . . . . . . . . . . . . . . . . . . . . 5
3. Modifications to Current IS-IS Behaviors . . . . . . . . . . 5
3.1. IS-IS Routers as Non-DIS . . . . . . . . . . . . . . . . 5
3.2. Controllers as DIS . . . . . . . . . . . . . . . . . . . 6
4. Acknowledgements . . . . . . . . . . . . . . . . . . . . . . 6
5. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 6
6. Security Considerations . . . . . . . . . . . . . . . . . . . 6
7. References . . . . . . . . . . . . . . . . . . . . . . . . . 6
7.1. Normative References . . . . . . . . . . . . . . . . . . 6
7.2. Informative References . . . . . . . . . . . . . . . . . 7
Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . 7
1. Introduction
IS-IS is commonly used as an underlay routing protocol for Massively
Scalable Data Center (MSDC) networks where CLOS is the most popular
topology.
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For a given IS-IS router within the CLOS topology, it would receive
multiple copies of exactly the same LSP from multiple IS-IS
neighbors. In addition, two IS-IS neighbors may send each other the
same LSP simultaneously. The unnecessary link-state information
flooding wastes the precious process resource of IS-IS routers
greatly and therefore IS-IS could not scale very well in MSDC
networks.
As a result, some MSDC operators had to choose BGP as the routing
protocol in their data centers [RFC7938]. However, with the
emergence of high-performance Ethernet networks for AI and high
performance computing (HPC), the visibility of the whole network
topology, and even the link load information, is crucial for the end-
to-end path load-balancing. As a result, link-state routing
protocols, such as IS-IS, would have to be reconsidered as the
routing protocol for large-scale AI and HPC Ethernet networks. Of
course, the prerequisite is the scaling issue associated with link-
state routing protocols as mentioned above could be addressed.
This document describes a pragmatic approach to the above scaling
issue. The basic idea is as follows: instead of flooding link-state
information across neighboring IS-IS routers with the MSDC network
fabric, link-state information originated from each IS-IS routers
would be collected to centralized controllers, which in turn reflect
the collected link-state information to all IS-IS routers within the
MSDC. As shown in Figure 1, all IS-IS routers within a MDSC network
fabric are connected to one or more centralized controllers via a
dedicated Local Area Network (LAN) , referred to as link-state
collection and distribution LAN, which is used for link-state
information collection and distribution purpose. For redundancy,
there should be at least two link-state collection and distribution
LANs.
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+----------+ +----------+
|Controller| |Controller|
+----+-----+ +-----+----+
|DIS |Candidate DIS
| |
| |
---+---------+---+----------+-----------+---+---------+-LS Collection&Distribution LAN
| | | | |
|Non-DIS |Non-DIS |Non-DIS |Non-DIS |Non-DIS
| | | | |
| +---+--+ | +---+--+ |
| |Router| | |Router| |
| *------*- | /*---/--* |
| / \ -- | // / \ |
| / \ -- | // / \ |
| / \ --|// / \ |
| / \ /*- / \ |
| / \ // | -- / \ |
| / \ // | -- / \ |
| / /X | -- \ |
| / // \ | / -- \ |
| / // \ | / -- \ |
| / // \ | / -- \ |
| / // \ | / -- \ |
| / // \ | / -- \ |
| / // \ | / -- \ |
+-+- //* +\\+-/-+ +---\-++
|Router| |Router| |Router|
+------+ +------+ +------+
Figure 1
With the assistance of a controller acting as IS-IS Designated
Intermediate System (DIS) for the link-state collection and
distribution LAN, IS-IS routers within the MSDC network don't need to
exchange any IS-IS Protocol Datagram Units (PDUs) other than Hello
packets among them. In order to obtain the full topology information
(i.e., the fully synchronized link-state database) of the MSDC's
network, these IS-IS routers would exchange the link-state
information with the controller being elected as IS-IS DIS for the
link-state collection and distribution LAN instead.
To further suppress the flooding of multicast IS-IS PDUs originated
from IS-IS routers over the link-state collection and distribution
LAN, IS-IS routers would not send multicast IS-IS Hello packets over
the link-state collection and distribution LAN. Instead, they just
wait for IS-IS Hello packets originated from the controller being
elected as IS-IS DIS initially. Once an IS-IS DIS for the link-state
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collection and distribution LAN has been discovered, they start to
send IS-IS Hello packets directly (as unicasts) to the IS-IS DIS
periodically. In addition, IS-IS routers would send IS-IS PDUs to
the IS-IS DIS for the link-state collection and distribution LAN as
unicasts as well. In contrast, the controller being elected as IS-IS
DIS would send IS-IS PDUs as before. As a result, IS-IS routers
would not receive IS-IS PDUs from one another unless these IS-IS PDUs
are forwarded as unknown unicasts over the link-state collection and
distribution LAN. Through the above modifications to the current IS-
IS router behaviors, the IS-IS flooding is greatly reduced, which is
much beneficial to improve the scalability of MSDC networks.
2. Terminology
This memo makes use of the terms defined in [RFC1195].
3. Modifications to Current IS-IS Behaviors
3.1. IS-IS Routers as Non-DIS
After the bidirectional exchange of IS-IS Hello packets among IS-IS
routers, IS-IS routers would originate Link State PDUs (LSPs)
accordingly. However, these self-originated LSPs need not to be
exchanged directly among them anymore. Instead, these LSPs just need
to be sent solely to the controller being elected as IS-IS DIS for
the link-state collection and distribution LAN.
To further reduce the flood of multicast IS-IS PDUs over the link-
state collection and distribution LAN, IS-IS routers SHOULD send IS-
IS PDUs as unicasts. More specifically, IS-IS routers SHOULD send
unicast IS-IS Hello packets periodically to the controller being
elected as IS-IS DIS. In other words, IS-IS routers would not send
any IS-IS Hello packet over the link-state collection and
distribution LAN until they have found an IS-IS DIS for the link-
state collection and distribution LAN. Note that IS-IS routers
SHOULD NOT be elected as IS-IS DIS for the link-state collection and
distribution LAN (This is done by setting the DIS Priority of those
IS-IS routers to zero). As a result, IS-IS routers would not see
each other over the link-state collection and distribution LAN. In
other word, IS-IS routers would not establish adjacencies with one
other. Furthermore, IS-IS routers SHOULD send all the types of IS-IS
PDUs to the controller being elected as IS-IS DIS as unicasts as
well.
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To avoid the data traffic from being forwarded across the link-state
collection and distribution LAN, the cost of all IS-IS routers'
interfaces to the link-state collection and distribution LAN SHOULD
be set to the maximum value.
When a given IS-IS router lost its connection to the link-state
collection and distribution LAN, it SHOULD actively establish
adjacency with all of its IS-IS neighbors within the CLOS network.
As such, it could obtain the full LSDB of the CLOS network while
flooding its self-originated LSPs to the remaining part of the whole
CLOS network through these IS-IS neighbor.
3.2. Controllers as DIS
The controller being elected as IS-IS DIS would send IS-IS PDUs as
multicasts or unicasts as before. And it SHOULD accept and process
those unicast IS-IS PDUs originated from IS-IS routers. Upon
receiving any new LSP from a given IS-IS router, the controller being
elected as DIS MUST flood it immediately to the link-state collection
and distribution LAN for two purposes: 1) implicitly acknowledging
the receipt of that LSP; 2) synchronizing that LSP to all the other
IS-IS routers.
Furthermore, to decrease the frequency of advertising Complete
Sequence Number PDU (CSNP) on the controller being elected as DIS,
it's RECOMMENDED that IS-IS routers SHOULD send an explicit
acknowledgement with a Partial Sequence Number PDU (PSNP) upon
receiving a new LSP from the controller being elected as DIS.
4. Acknowledgements
The authors would like to thank Peter Lothberg and Erik Auerswald for
his valuable comments and suggestions on this document.
5. IANA Considerations
TBD.
6. Security Considerations
TBD.
7. References
7.1. Normative References
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[RFC1195] Callon, R., "Use of OSI IS-IS for routing in TCP/IP and
dual environments", RFC 1195, DOI 10.17487/RFC1195,
December 1990, <https://www.rfc-editor.org/info/rfc1195>.
[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>.
7.2. Informative References
[RFC4136] Pillay-Esnault, P., "OSPF Refresh and Flooding Reduction
in Stable Topologies", RFC 4136, DOI 10.17487/RFC4136,
July 2005, <https://www.rfc-editor.org/info/rfc4136>.
[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>.
Authors' Addresses
Xiaohu Xu
China Mobile
Email: xuxiaohu_ietf@hotmail.com
Luyuan Fang
eBay
Email: luyuanf@gmail.com
Jeff Tantsura
Nvidia
Email: jefftant.ietf@gmail.com
Shaowen Ma
Google
Email: shaowen@google.com
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