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
OSPF Flooding Reduction in Massively Scalable Data Centers (MSDCs)
draft-xu-lsr-ospf-flooding-reduction-in-msdc-04
Abstract
OSPF is one of the used underlay routing protocol for MSDC (Massively
Scalable Data Center) networks. For a given OSPF router within the
CLOS topology, it would receive multiple copies of exactly the same
LSA from multiple OSPF neighbors. In addition, two OSPF neighbors
may send each other the same LSA simultaneously. The unnecessary
link-state information flooding wastes the precious process resource
of OSPF routers greatly due to the presence of too many OSPF
neighbors for each OSPF router within the CLOS topology. This
document proposes extensions to OSPF so as to reduce the OSPF
flooding within such MSDC networks. The reduction of the OSPF
flooding is much beneficial to improve the scalability of MSDC
networks. These modifications are applicable to both OSPFv2 and
OSPFv3.
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/.
Internet-Drafts are draft documents valid for a maximum of six months
and may be updated, replaced, or obsoleted by other documents at any
Xu, et al. Expires June 24, 2021 [Page 1]
Internet-Draft December 2020
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.
Copyright Notice
Copyright (c) 2020 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 extracted from this document must
include Simplified BSD License text as described in Section 4.e of
the Trust Legal Provisions and are provided without warranty as
described in the Simplified BSD License.
Table of Contents
1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . 2
2. Terminology . . . . . . . . . . . . . . . . . . . . . . . . . 4
3. Modifications to Legacy OSPF Behaviors . . . . . . . . . . . 4
3.1. OSPF Routers as Non-DRs . . . . . . . . . . . . . . . . . 4
3.2. Controllers as DR/BDR . . . . . . . . . . . . . . . . . . 5
4. Acknowledgements . . . . . . . . . . . . . . . . . . . . . . 5
5. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 5
6. Security Considerations . . . . . . . . . . . . . . . . . . . 6
7. References . . . . . . . . . . . . . . . . . . . . . . . . . 6
7.1. Normative References . . . . . . . . . . . . . . . . . . 6
7.2. Informative References . . . . . . . . . . . . . . . . . 6
Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . 6
1. Introduction
OSPF is commonly used as an underlay routing protocol for Massively
Scalable Data Center (MSDC) networks where CLOS is the most popular
topology. MSDCs are also called Large-Scale Data Centers.
For a given OSPF router within the CLOS topology, it would receive
multiple copies of exactly the same LSA from multiple OSPF neighbors.
In addition, two OSPF neighbors may send each other the same LSA
simultaneously. The unnecessary link-state information flooding
significantly wastes the precious process resource of OSPF routers
and therefore OSPF could not scale very well in MSDC networks.
Xu, et al. Expires June 24, 2021 [Page 2]
Internet-Draft December 2020
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 an 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|
+----+-----+ +-----+----+
|DR |BDR
| |
| |
---+---------+---+----------+-----------+---+---------+-Management LAN
| | | | |
|Non-DR |Non-DR |Non-DR |Non-DR |Non-DR
| | | | |
| +---+--+ | +---+--+ |
| |Router| | |Router| |
| *------*- | /*---/--* |
| / \ -- | // / \ |
| / \ -- | // / \ |
| / \ --|// / \ |
| / \ /*- / \ |
| / \ // | -- / \ |
| / \ // | -- / \ |
| / /X | -- \ |
| / // \ | / -- \ |
| / // \ | / -- \ |
| / // \ | / -- \ |
| / // \ | / -- \ |
| / // \ | / -- \ |
| / // \ | / -- \ |
+-+- //* +\\+-/-+ +---\-++
|Router| |Router| |Router|
+------+ +------+ +------+
Figure 1
With the assistance of these controllers which are acting as OSPF
Designated Router (DR)/Backup Designated Router (BDR) for the
management LAN, OSPF routers within the MSDC network don't need to
exchange any other types of OSPF packet than the OSPF Hello packet
among them. As specified in [RFC2328], these Hello packets are used
for the purpose of establishing and maintaining neighbor
relationships and ensuring bidirectional communication between OSPF
neighbors, and even the DR/BDR election purpose in the case where
those OSPF routers are connected to a broadcast network. In order to
obtain the full topology information (i.e., the fully synchronized
Xu, et al. Expires June 24, 2021 [Page 3]
Internet-Draft December 2020
link-state database) of the MSDC's network, these OSPF routers only
need to exchange the link-state information with the controllers
being elected as OSPF DR/BDR for the management LAN instead.
To further suppress the flooding of multicast OSPF packets originated
from OSPF routers over the management LAN, OSPF routers would not
send multicast OSPF Hello packets over the management LAN. Instead,
they just wait for OSPF Hello packets originated from the controllers
being elected as OSPF DR/BDR initially. Once OSPF DR/BDR for the
management LAN have been discovered, they start to send OSPF Hello
packets directly (as unicasts) to OSPF DR/BDR periodically. In
addition, OSPF routers would send other types of OSPF packets (e.g.,
Database Descriptor packet, Link State Request packet, Link State
Update packet, Link State Acknowledgment packet) to OSPF DR/BDR for
the management LAN as unicasts as well. In contrast, the controllers
being elected as OSPF DR/BDR would send OSPF packets as specified in
[RFC2328]. As a result, OSPF routers within the MSDC would not
receive OSPF packets from one another unless these OSPF packets are
forwarded as unknown unicasts over the management LAN. Through these
modifications to the legacy OSPF router behaviors, the OSPF flooding
is greatly reduced, which is much beneficial to improve the overall
scalability of MSDC networks. These modifications specified in this
document are applicable to both OSPFv2 [RFC2328] and OSPFv3
[RFC5340].
The mechanism for OSPF refresh and flooding reduction in stable
topologies as described in [RFC4136] may be considered as well.
2. Terminology
This memo makes use of the terms defined in [RFC2328].
3. Modifications to Legacy OSPF Behaviors
3.1. OSPF Routers as Non-DRs
After the exchange of OSPF Hello packets among OSPF routers, the OSPF
neighbor relationship among them would transition to and remain in
the 2-WAY state. OSPF routers would originate Router-LSAs and/or
Network-LSAs accordingly depending upon the link-types. Note that
the neighbors in the 2-WAY state would be advertised in the Router-
LSAs and/or Network-LSA. This is slightly different from the legacy
OSPF router behavior as specified in [RFC2328] where the neighbors in
the TWO-WAY state would not be advertised. However, these self-
originated LSAs need not to be exchanged directly among them anymore.
Instead, these LSAs only need to be sent solely to the controllers
being elected as OSPF DR/BDR for the management LAN.
Xu, et al. Expires June 24, 2021 [Page 4]
Internet-Draft December 2020
To further reduce the flood of multicast OSPF packets over the
management LAN, OSPF routers SHOULD send OSPF packets as unicasts.
More specifically, OSPF routers SHOULD send unicast OSPF Hello
packets periodically to the controllers being elected as OSPF DR/BDR.
In other words, OSPF routers SHOULD NOT send any OSPF Hello packet
over the management LAN until they have found an OSPF DR/BDR for the
management LAN. Note that OSPF routers, within the MSDC, SHOULD NOT
be elected as OSPF DR/BDR for the management LAN (This is done by
setting the Router Priority of those OSPF routers to zero). As a
result, OSPF routers would not see each other over the management
LAN. Furthermore, OSPF routers SHOULD send all other types of OSPF
packets than OSPF Hello packets to the controllers being elected as
OSPF DR/BDR as unicasts as well.
To avoid the data traffic from being forwarded across the management
LAN, the cost of all OSPF routers' interfaces to the management LAN
SHOULD be set to the maximum value.
When a given OSPF router lost its connection to the management LAN,
it SHOULD actively establish FULL adjacency with all of its OSPF
neighbors within the MSDC network. As such, it could obtain the full
LSDB of the MSDC network while flooding its self-originated LSAs to
the remaining part of the whole network. That's to say, for a given
OSPF router within the MSDC network, it would not actively establish
FULL adjacency with its OSPF neighbor in the 2-WAY state by default.
However, it SHOULD NOT refuse to establish FULL adjacency with a
given OSPF neighbors when receiving Database Description Packets from
that OSPF neighbor.
3.2. Controllers as DR/BDR
The controllers being elected as OSPF DR/BDR would send OSPF packets
as multicasts or unicasts as per [RFC2328]. In addition, Link State
Acknowledgment packets are RECOMMENDED to be sent as unicasts rather
than multicasts.
4. Acknowledgements
The authors would like to thank Acee Lindem and Mohamed Boucadair for
their valuable comments and suggestions on this document.
5. IANA Considerations
TBD.
Xu, et al. Expires June 24, 2021 [Page 5]
Internet-Draft December 2020
6. Security Considerations
TBD.
7. References
7.1. Normative References
[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>.
[RFC2328] Moy, J., "OSPF Version 2", STD 54, RFC 2328,
DOI 10.17487/RFC2328, April 1998,
<https://www.rfc-editor.org/info/rfc2328>.
[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>.
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
Xu, et al. Expires June 24, 2021 [Page 6]
Internet-Draft December 2020
Shaowen Ma
Juniper
Email: mashao@juniper.net
Xu, et al. Expires June 24, 2021 [Page 7]