Internet DRAFT - draft-basavaraj-ospf-graceful-restart-enhancements
draft-basavaraj-ospf-graceful-restart-enhancements
INTERNET-DRAFT Vijayalaxmi Basavaraj
Intended Status: Informational Ankur Dubey
Updates: 3623, 5187 Sami Boutros
VMware
Acee Lindem
Cisco
Expires: January 8, 2020 July 7, 2019
OSPF Graceful Restart Enhancements
draft-basavaraj-ospf-graceful-restart-enhancements-01
Abstract
This document describes enhancements to the OSPF graceful restart
procedures to improve routing convergence in some OSPF network
deployments. This document updates RFC 3623 and RFC 5187.
Status of this Memo
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Copyright and License Notice
Copyright (c) 2019 IETF Trust and the persons identified as the
document authors. All rights reserved.
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Provisions Relating to IETF Documents
(http://trustee.ietf.org/license-info) in effect on the date of
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Table of Contents
1 Introduction . . . . . . . . . . . . . . . . . . . . . . . . . 3
1.1 Terminology . . . . . . . . . . . . . . . . . . . . . . . . 3
2 Graceful Restart Enhancements . . . . . . . . . . . . . . . . . 3
2.1 Stub Link Network Scenarios . . . . . . . . . . . . . . . . 3
2.2 Multiple Failure Scenarios . . . . . . . . . . . . . . . . . 4
3 Security Considerations . . . . . . . . . . . . . . . . . . . . 4
4. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 4
5. References . . . . . . . . . . . . . . . . . . . . . . . . . . 4
5.1 Normative References . . . . . . . . . . . . . . . . . . . 4
5.2 Informative References . . . . . . . . . . . . . . . . . . 4
Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . . 5
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1 Introduction
This document describes the enhancements to the current Graceful
restart OSPF procedure to improve routing convergence in certain OSPF
network deployment scenarios. The goal is for both the restarting
OSPF node and the helper OSPF node to terminate the OSPF graceful
restart procedure faster and not wait for the grace period expiry in
those network scenarios and hence improve the overall OSPF network
convergence.
1.1 Terminology
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 Graceful Restart Enhancements
In this section we will describe couple of issues with OSPF Graceful
Restart (GR) in some network deployment scenarios, and a proposal to
enhance the OSPF GR procedure to achieve faster OSPF routing
convergence in those scenarios.
2.1 Stub Link Network Scenarios
--------- --------- ---------
|Router1|---Area 0----|Router2|---Area 1---|Router3|
--------- --------- ---------
Figure1: OSPF topology with Graceful restart
As described in figure 1, Router2 is an area border router (ABR) with
OSPF links in 2 areas. Furthermore. Router2 has formed full
adjacencies only in Area 0. In Area 1, Router2 has an OSPF link
enabled but Router2 couldn't form any adjacency either because
Router3 is down or Router3 does not have OSPF enabled. Hence, Router2
will only have a stub link in Area 1.
On restart, the ABR router Router2, having only a stub link in the
Area 1, will never receive its pre-restart LSA in this area and will
never form an adjacency, Router2 will have to wait for the grace
period expiry leading to slower OSPF routing convergence.
For this we propose, if no OSPF control packets were received within
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the dead interval on a link in Area 1 as per the above network
scenario, Router2 MUST mark the link as stub and MUST not wait for
the grace period to form an adjacency on this link to successfully
Exit GR.
2.2 Multiple Failure Scenarios
In scenarios where more than one router is restarting at the same
time in the same OSPF area and StrictLSAChecking is disabled,
restarting OSPF routers will end up waiting the entire grace interval
to exit GR.
If the restarting routers receive a Grace Link State Advertisements
(LSA) from another router in a given area after restart, and the
helper routers receive grace LSAs from more than one router, this
will indicate that there have been multiple failures. Therefore, the
helper and restarting routers MUST terminate GR and avoid any
unnecessary delay in OSPF routing convergence.
3 Security Considerations
This document does not introduce any additional security constraints.
4. IANA Considerations
None
5. References
5.1 Normative References
[KEYWORDS] Bradner, S., "Key words for use in RFCs to Indicate
Requirement Levels", BCP 14, RFC 2119, March 1997.
[RFC3623] Moy, J., Pillay-Esnault, P., and A. Lindem, "Graceful OSPF
Restart", RFC 3623, November 2003.
[RFC5187] Pillay-Esnault, P., and A. Lindem, "OSPFv3 Graceful
Restart", RFC 5187, June 2008.
5.2 Informative References
[RFC2328] Moy, J., "OSPF Version 2", STD 54, RFC 2328, April 1998.
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Authors' Addresses
Sami Boutros
VMware
Email: boutross@vmware.com
Ankur Dubey
VMware
Email: adubey@vmware.com
Vijayalaxmi Basavaraj
VMware
Email: vbasavaraj@vmware.com
Acee Lindem
Cisco
Email: acee@cisco.com
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