IS-IS Flooding Reduction in MSDC
draft-xu-lsr-isis-flooding-reduction-in-msdc-03
Network Working Group X. Xu
Internet-Draft Alibaba, Inc
Intended status: Standards Track L. Fang
Expires: June 24, 2021 Expedia, Inc
J. Tantsura
Apstra, Inc.
S. Ma
Juniper
December 21, 2020
IS-IS Flooding Reduction in MSDC
draft-xu-lsr-isis-flooding-reduction-in-msdc-03
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
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provisions of BCP 78 and BCP 79.
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Internet-Drafts are draft documents valid for a maximum of six months
and may be updated, replaced, or obsoleted by other documents at any
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time. It is inappropriate to use Internet-Drafts as reference
material or to cite them other than as "work in progress."
This Internet-Draft will expire on June 24, 2021.
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Table of Contents
1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . 2
2. Terminology . . . . . . . . . . . . . . . . . . . . . . . . . 4
3. Modifications to Current IS-IS Behaviors . . . . . . . . . . 4
3.1. IS-IS Routers as Non-DIS . . . . . . . . . . . . . . . . 4
3.2. Controllers as DIS . . . . . . . . . . . . . . . . . . . 5
4. Acknowledgements . . . . . . . . . . . . . . . . . . . . . . 5
5. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 5
6. Security Considerations . . . . . . . . . . . . . . . . . . . 5
7. References . . . . . . . . . . . . . . . . . . . . . . . . . 5
7.1. Normative References . . . . . . . . . . . . . . . . . . 5
7.2. Informative References . . . . . . . . . . . . . . . . . 6
Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . 6
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. 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.
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To simplify the network management task, centralized controllers are
becoming fundamental network elements in most MSDCs. One or more
controllers are usually connected to all routers within the MSDC
network via a Local Area Network (LAN) which is dedicated for network
management purpose (called management LAN), as shown in Figure 1.
+----------+ +----------+
|Controller| |Controller|
+----+-----+ +-----+----+
|DIS |Candidate DIS
| |
| |
---+---------+---+----------+-----------+---+---------+-Management 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 management 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 management LAN instead.
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To further suppress the flooding of multicast IS-IS PDUs originated
from IS-IS routers over the management LAN, IS-IS routers would not
send multicast IS-IS Hello packets over the management 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
management 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 management 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
management 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 management LAN.
To further reduce the flood of multicast IS-IS PDUs over the
management 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 management LAN until they have found an IS-IS DIS for the
management LAN. Note that IS-IS routers SHOULD NOT be elected as IS-
IS DIS for the management 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 management 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.
To avoid the data traffic from being forwarded across the management
LAN, the cost of all IS-IS routers' interfaces to the management LAN
SHOULD be set to the maximum value.
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When a given IS-IS router lost its connection to the management 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 management 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
[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>.
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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>.
Authors' Addresses
Xiaohu Xu
Alibaba, Inc
Email: 13910161692@qq.com
Luyuan Fang
Expedia, Inc
Email: luyuanf@gmail.com
Jeff Tantsura
Apstra, Inc.
Email: jefftant.ietf@gmail.com
Shaowen Ma
Juniper
Email: mashao@juniper.net
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