Internet DRAFT - draft-ietf-ospf-link-overload
draft-ietf-ospf-link-overload
Open Shortest Path First IGP S. Hegde
Internet-Draft Juniper Networks, Inc.
Intended status: Standards Track P. Sarkar
Expires: August 8, 2018 Arrcus, Inc.
H. Gredler
Individual
M. Nanduri
ebay Corporation
L. Jalil
Verizon
February 4, 2018
OSPF Graceful Link shutdown
draft-ietf-ospf-link-overload-16
Abstract
When a link is being prepared to be taken out of service, the traffic
needs to be diverted from both ends of the link. Increasing the
metric to the highest value on one side of the link is not sufficient
to divert the traffic flowing in the other direction.
It is useful for the routers in an OSPFv2 or OSPFv3 routing domain to
be able to advertise a link as being in a graceful-shutdown state to
indicate impending maintenance activity on the link. This
information can be used by the network devices to re-route the
traffic effectively.
This document describes the protocol extensions to disseminate
graceful-link-shutdown information in 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/.
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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
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 August 8, 2018.
Copyright Notice
Copyright (c) 2018 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 . . . . . . . . . . . . . . . . . . . . . . . . 3
2. Motivation . . . . . . . . . . . . . . . . . . . . . . . . . 3
3. Flooding Scope . . . . . . . . . . . . . . . . . . . . . . . 4
4. Protocol Extensions . . . . . . . . . . . . . . . . . . . . . 4
4.1. OSPFv2 graceful-link-shutdown sub-TLV . . . . . . . . . . 4
4.2. Remote IPv4 Address Sub-TLV . . . . . . . . . . . . . . . 4
4.3. Local/Remote Interface ID Sub-TLV . . . . . . . . . . . . 5
4.4. OSPFv3 Graceful-Link-Shutdown sub-TLV . . . . . . . . . . 6
4.5. BGP-LS Graceful-Link-Shutdown TLV . . . . . . . . . . . . 6
4.6. Distinguishing parallel links . . . . . . . . . . . . . . 7
5. Elements of procedure . . . . . . . . . . . . . . . . . . . . 8
5.1. Point-to-point links . . . . . . . . . . . . . . . . . . 9
5.2. Broadcast/NBMA links . . . . . . . . . . . . . . . . . . 9
5.3. Point-to-multipoint links . . . . . . . . . . . . . . . . 10
5.4. Unnumbered interfaces . . . . . . . . . . . . . . . . . . 10
5.5. Hybrid Broadcast and P2MP interfaces . . . . . . . . . . 10
6. Backward compatibility . . . . . . . . . . . . . . . . . . . 10
7. Applications . . . . . . . . . . . . . . . . . . . . . . . . 11
7.1. Overlay Network . . . . . . . . . . . . . . . . . . . . . 11
7.2. Controller based Deployments . . . . . . . . . . . . . . 12
7.3. L3VPN Services and sham-links . . . . . . . . . . . . . . 13
7.4. Hub and spoke deployment . . . . . . . . . . . . . . . . 13
8. Security Considerations . . . . . . . . . . . . . . . . . . . 13
9. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 13
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10. Acknowledgements . . . . . . . . . . . . . . . . . . . . . . 14
11. References . . . . . . . . . . . . . . . . . . . . . . . . . 14
11.1. Normative References . . . . . . . . . . . . . . . . . . 14
11.2. Informative References . . . . . . . . . . . . . . . . . 15
Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . 16
1. Introduction
This document describes a mechanism for gracefully taking a link out
of service while allowing it to be used if no other path is
available.It also provides a mechanism to divert the traffic from
both directions of the link.
Many OSPFv2 or OSPFv3 deployments run on overlay networks provisioned
by means of pseudo-wires or L2-circuits. Prior to devices in the
underlying network going offline for maintenance, it is useful to
divert the traffic away from the node before the maintenance is
actually performed. Since the nodes in the underlying network are
not visible to OSPF, the existing stub router mechanism described in
[RFC6987] cannot be used. In a service provider's network, there may
be many CE-to-CE connections that run over a single PE. It is
cumbersome to change the metric on every CE-to-CE connection in both
directions. This document provides a mechanism to change the metric
of the link on remote side and also use the link as a last-resort-
link if no alternate paths are available. An application specific to
this use case is described in detail in Section 7.1.
This document provides mechanisms to advertise graceful-link-shutdown
state in the flexible encodings provided by OSPFv2 Prefix/Link
Attribute Advertisement [RFC7684] and E-Router-LSA
[I-D.ietf-ospf-ospfv3-lsa-extend] fr OSPFv3. Throughout this
document, OSPF is used when the text applies to both OSPFv2 and
OSPFv3. OSPFv2 or OSPFv3 is used when the text is specific to one
version of the OSPF protocol.
2. Motivation
The motivation of this document is to reduce manual intervention
during maintenance activities. The following objectives help to
accomplish this in a range of deployment scenarios.
1. Advertise impending maintenance activity so that traffic from
both directions can be diverted away from the link.
2. Allow the solution to be backward compatible so that nodes that
do not understand the new advertisement, do not cause routing
loops.
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3. Advertise the maintenance activity to other nodes in the network
so that LSP ingress routers/controllers can learn about the
impending maintenance activity and apply specific policies to re-
route the LSPs for traffic-engineering based deployments.
4. Allow the link to be used as a last resort link to prevent
traffic disruption when alternate paths are not available.
3. Flooding Scope
The graceful-link-shutdown information is flooded in area-scoped
Extended Link Opaque LSA [RFC7684] for OSPFv2 and E-Router-LSA for
OSPFv3 [I-D.ietf-ospf-ospfv3-lsa-extend]. The Graceful-Link-Shutdown
sub-TLV MAY be processed by the head-end nodes or the controller as
described in the Section 7. The procedures for processing the
Graceful-Link-Shutdown sub-TLV are described in Section 5.
4. Protocol Extensions
4.1. OSPFv2 graceful-link-shutdown sub-TLV
The Graceful-Link-Shutdown sub-TLV identifies the link as being
gracefully shutdown. It is advertised in extended Link TLV of the
Extended Link Opaque LSA as defined in [RFC7684].
0 1 2 3
0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Type | Length |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
Figure 1: Graceful-Link-Shutdown sub-TLV for OSPFv2
Type : TBA (suggested value 7)
Length: 0
4.2. Remote IPv4 Address Sub-TLV
This sub-TLV specifies the IPv4 address of remote endpoint on the
link. It is advertised in the Extended Link TLV as defined in
[RFC7684]. This sub-TLV is optional and MAY be advertised in an
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area-scoped Extended Link Opaque LSA to identify the link when there
are multiple parallel links between two nodes.
0 1 2 3
0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Type | Length |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Remote IPv4 address |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
Figure 2: Remote IPv4 Address Sub-TLV
Type : TBA (suggested value 8)
Length: 4
Value: Remote IPv4 address. The remote IPv4 address is used to
identify a particular link on the remote side when there are multiple
parallel links between two nodes.
4.3. Local/Remote Interface ID Sub-TLV
This sub-TLV specifies local and remote interface identifiers. It is
advertised in the Extended Link TLV as defined in [RFC7684]. This
sub-TLV is optional and MAY be advertised in an area-scoped Extended
Link Opaque LSA to identify the link when there are multiple parallel
unnumbered links between two nodes. The local interface-id is
generally readily available. One of the mechanisms to obtain remote
interface-id is described in [RFC4203].
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0 1 2 3
0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Type | Length |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Local Interface ID |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Remote Interface ID |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
Figure 3: Local/Remote Interface ID Sub-TLV
Type : TBA (suggested value 9)
Length: 8
Value: 4 octets of Local Interface ID followed by 4 octets of Remote
interface ID.
4.4. OSPFv3 Graceful-Link-Shutdown sub-TLV
The Graceful-Link-Shutdown sub-TLV is carried in the Router-Link TLV
as defined in the [I-D.ietf-ospf-ospfv3-lsa-extend] for OSPFv3. The
Router-Link TLV contains the neighbour interface-id and can uniquely
identify the link on the remote node.
0 1 2 3
0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Type | Length |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
Figure 4: Graceful-Link-Shutdown sub-TLV for OSPFv3
Type : TBA (Suggested value 7)
Length: 0
4.5. BGP-LS Graceful-Link-Shutdown TLV
BGP-LS as defined in [RFC7752] is a mechanism to distribute network
information to the external entities using BGP routing protocol.
Graceful-link-shutdown is an important link information that the
external entities can use for various use cases as defined in
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Section 7. BGP Link NLRI is used to carry the link information. A
new TLV called Graceful-Link-Shutdown is defined to describe the link
attribute corresponding to graceful-link-shutdown state. The TLV
format is as described in [RFC7752] sec 3.1. There is no value field
and length field is set to zero for this TLV.
0 1 2 3
0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Type | Length |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
Figure 5: Graceful-Link-Shutdown TLV for BGP-LS
Type : TBA (Suggested value 1121)
Length: 0
4.6. Distinguishing parallel links
++++++++++I.w I.y +++++++++
|Router A|------------------|Router B |
| |------------------| |
++++++++++I.x I.z++++++++++
Figure 6: Parallel Linkls
Consider two routers A and B connected with two parallel point-to-
point interfaces. I.w and I.x represent the Interface address on
Router A's side and I.y and I.z represent Interface addresses on
Router B's side. The extended link opaque LSA as described in
[RFC7684] describes links using link-type, Link-ID and Link-data.
For ex. Link with address I.w is described as below on Router A.
Link-type = Point-to-point
Link-ID: Router-ID of B
Link-Data = I.w
A third node (controller or head-end) in the network cannot
distinguish the Interface on router B which is connected to this
particular Interface with the above information. Interface with
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address I.y or I.z could be chosen due to this ambiguity. In such
cases Remote-IPv4 Address sub-TLV should be originated and added to
the Extended Link TLV. The use cases as described in Section 7
require controller or head-end nodes to interpret the graceful-link-
shutdown information and hence the need for the Remote IPv4 address
sub-TLV. I.y is carried in the Extended Link TLV which unambiguously
identifies the interface on the remote side. OSPFv3 Router-link-TLV
as described in [I-D.ietf-ospf-ospfv3-lsa-extend] contains Interface
ID and neighbor's Interface-ID which can uniquely identify connecting
interface on the remote side and hence OSPFv3 does not require
seperate Remote-IPv6 address to be advertised along with the OSPFv3-
Graceful-Link-Shutdown sub-TLV.
5. Elements of procedure
As defined in [RFC7684] every link on the node will have a separate
Extended Link Opaque LSA. The node that has the link to be taken out
of service MUST advertise the Graceful-Link-Shutdown sub-TLV in the
Extended Link TLV of the Extended Link Opaque LSA as defined in
[RFC7684] for OSPFv2 and Router-Link TLV of E-Router-LSA for OSPFv3.
The Graceful-Link-Shutdown sub-TLV indicates that the link identified
by the sub-TLV is subjected to maintenance.
For the purposes of changing the metric OSPFv2 and OSPFv3 Router-LSAs
need to be re-orignated and for Traffic Engineering metric, TE Opaque
LSAs [RFC3630] in OSPFv2 and Intra-area-TE-LSA [RFC5329]in OSPFv3
need to be re-originated.
The Graceful-Link-Shutdown information is advertised as a property of
the link and is flooded through the area. This information can be
used by ingress routers or controllers to take special actions. An
application specific to this use case is described in Section 7.2.
When a link is ready to carry traffic, the Graceful-Lnk-Shutdown sub-
TLV MUST be removed from the Extended Link TLV/Router-Link TLV and
the corresponding LSAs MUST be readvertised. Similarly, metric MUST
be set to original values and corresponding LSAs MUST be
readvertised.
The procedures described in this draft may be used to divert the
traffic away from the link in scenarios other than link-shutdown or
link-replacement activity.
The precise action taken by the remote node at the other end of the
link identified for graceful-shutdown depends on the link type.
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5.1. Point-to-point links
The node that has the link to be taken out of service MUST set metric
of the link to MaxLinkMetric (0xffff) and re-originate its router-
LSA. The Traffic Engineering metric of the link SHOULD be set to
(0xffffffff) and the node SHOULD re-originate the corresponding TE
Link Opaque LSAs. When a Graceful-Link-Shutdown sub-TLV is received
for a point-to-point link, the remote node MUST identify the local
link which corresponds to the graceful-shutdown link and set its
metric to MaxLinkMetric (0xffff) and the remote node MUST re-
originate its router-LSA with the changed metric. When TE is
enabled, the Traffic Engineering metric of the link SHOULD be set to
(0xffffffff) and follow procedures of [RFC5817]. Similarly, the
remote node SHOULD set the Traffic Engineering metric of the link to
0xffffffff and SHOULD re-originate the TE Link Opaque LSA for the
link with the new value.
The Extended link opaque LSAs and the Extended link TLV are not
scoped for multi-topology [RFC4915]. In multi-topology deployments
[RFC4915], the Graceful-Link-Shutdown sub-TLV advertised in an
Extended Link opaque LSA corresponds to all the topologies which
include the link. The receiver node SHOULD change the metric in the
reverse direction for all the topologies which include the remote
link and re-originate the router-LSA as defined in [RFC4915].
When the originator of the Graceful-Link-Shutdown sub-TLV purges the
Extended Link Opaque LSA or re-originates it without the Graceful-
Link-Shutdown sub-TLV, the remote node must re-originate the
appropriate LSAs with the metric and TE metric values set to their
original values.
5.2. Broadcast/NBMA links
Broadcast or NBMA networks in OSPF are represented by a star topology
where the Designated Router (DR) is the central point to which all
other routers on the broadcast or NBMA network logically connect. As
a result, routers on the broadcast or NBMA network advertise only
their adjacency to the DR. Routers that do not act as DR do not form
or advertise adjacencies with each other. For the Broadcast links,
the MaxLinkMetric on the remote link cannot be changed since all the
neighbors are on same link. Setting the link cost to MaxLinkMetric
would impact paths going via all neighbors.
The node that has the link to be taken out of service MUST set metric
of the link to MaxLinkMetric (0xffff) and re-originate the Router-
LSA. The Traffic Engineering metric of the link SHOULD be set to (
0xffffffff) and the node SHOULD re-originate the corresponding TE
Link Opaque LSAs. For a broadcast link, the two part metric as
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described in [RFC8042] is used. The node originating the Graceful-
Link-Shutdown sub-TLV MUST set the metric in the Network-to-Router
Metric sub-TLV to MaxLinkMetric (0xffff) for OSPFv2 and OSPFv3 and
re-originate the corresponding LSAs. The nodes that receive the two-
part metric should follow the procedures described in [RFC8042]. The
backward compatibility procedures described in [RFC8042] should be
followed to ensure loop free routing.
5.3. Point-to-multipoint links
Operation for the point-to-multipoint links is similar to the point-
to-point links. When a Graceful-Link-Shutdown sub-TLV is received
for a point-to-multipoint link the remote node MUST identify the
neighbour which corresponds to the graceful-shutdown link and set its
metric to MaxLinkMetric (0xffff). The remote node MUST re-originate
the router-LSA with the changed metric for the correponding neighbor.
5.4. Unnumbered interfaces
Unnumbered interfaces do not have a unique IP address and borrow
their address from other interfaces. [RFC2328] describes procedures
to handle unnumbered interfaces in the context of the router-LSA. We
apply a similar procedure to the Extended Link TLV advertising the
Graceful-Link-Shutdown sub-TLV in order to handle unnumbered
interfaces. The link-data field in the Extended Link TLV includes
the Local interface-id instead of the IP address. The Local/Remote
Interface ID sub-TLV MUST be advertised when there are multiple
parallel unnumbered interfaces between two nodes. One of the
mechanisms to obtain the interface-id of the remote side is defined
in [RFC4203].
5.5. Hybrid Broadcast and P2MP interfaces
Hybrid Broadcast and P2MP interfaces represent a broadcast network
modeled as P2MP interfaces. [RFC6845] describes procedures to handle
these interfaces. Operation for the Hybrid interfaces is similar to
the P2MP interfaces. When a Graceful-Link-Shutdown sub-TLV is
received for a hybrid link, the remote node MUST identify the
neighbor which corresponds to the graceful-shutdown link and set its
metric to MaxLinkMetric (0xffff). All the remote nodes connected to
originator MUST re-originate the router-LSA with the changed metric
for the neighbor.
6. Backward compatibility
The mechanisms described in the document are fully backward
compatible. It is required that the node adverting the Graceful-
Link-Shutdown sub-TLV as well as the node at the remote end of the
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graceful-shutdown link support the extensions described herein for
the traffic to diverted from the graceful-shutdown link. If the
remote node doesn't support the capability, it will still use the
graceful-shutdown link but there are no other adverse effects. In
the case of broadcast links using two-part metrics, the backward
compatibility procedures as described in [RFC8042] are applicable.
7. Applications
7.1. Overlay Network
Many service providers offer L2 services to a customer connecting
different locations. The customer's IGP protocol creates a seamless
private network (overlay network) across the locations for the
customer. Service providers want to offer graceful-shutdown
functionality when the PE device is taken-out for maintenance. There
can be large number of customers attached to a PE node and the remote
end-points for these L2 attachments circuits are spread across the
service provider's network. It is a tedious and error-prone process
to change the metric for all corresponding L2 circuits in both
directions. The graceful-link-shutdown feature simplifies the
process by increasing the metric on the CE-CE overlay link so that
traffic in both directions is diverted away from the PE undergoing
maintenance. The Graceful-Link-Shutdown feature allows the link to
be used as a last resort link so that traffic is not disrupted when
alternate paths are not available.
------PE3---------------PE4------CE3
/ \
/ \
CE1---------PE1----------PE2---------CE2
\
\
------CE4
Figure 7: Overlay Network
In the example shown in Figure 7, when the PE1 node is going out of
service for maintenance, a service provider sets the PE1 to stub-
router state and communicates the pending maintenance action to the
overlay customer networks. The mechanisms used to communicate
between PE1 and CE1 is outside the scope of this document. CE1 sets
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the graceful-link-shutdown state on its links connecting CE3, CE2 and
CE4 and changes the metric to MaxLinkMetric and re-originates the
corresponding LSA. The remote end of the link at CE3, CE2, and CE4
also set the metric on the link to MaxLinkMetric and the traffic from
both directions gets diverted away from PE1.
7.2. Controller based Deployments
In controller-based deployments where the controller participates in
the IGP protocol, the controller can also receive the graceful-link-
shutdown information as a warning that link maintenance is imminent.
Using this information, the controller can find alternate paths for
traffic which uses the affected link. The controller can apply
various policies and re-route the LSPs away from the link undergoing
maintenance. If there are no alternate paths satisfying the
constraints, the controller might temporarily relax those constraints
and put the service on a different path. Increasing the link metric
alone does not specify the maintenance activity as the metric could
increase in events such as LDP-IGP synchronisation. An explicit
indication from the router using the graceful-link-shutdown sub-TLV
is needed to inform the Controller or head-end routers.
_____________
| |
-------------| Controller |--------------
| |____________ | |
| |
|--------- Primary Path ------------------|
PE1---------P1----------------P2---------PE2
| |
| |
|________P3________|
Alternate Path
Figure 8: Controller based Traffic Engineering
In the above example, PE1->PE2 LSP is set-up to satisfy a constraint
of 10 Gbps bandwidth on each link. The links P1->P3 and P3->P2 have
only 1 Gbps capacity and there is no alternate path satisfying the
bandwidth constraint of 10Gbps. When P1->P2 link is being prepared
for maintenance, the controller receives the graceful-link-shutdown
information, as there is no alternate path available which satisfies
the constraints, the controller chooses a path that is less optimal
and temporarily sets up an alternate path via P1->P3->P2. Once the
traffic is diverted, the P1->P2 link can be taken out of service for
maintenance/upgrade.
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7.3. L3VPN Services and sham-links
Many service providers offer L3VPN services to customers and CE-PE
links run OSPF [RFC4577]. When PE is taken out of service for
maintenance, all the links on the PE can be set to graceful-link-
shutdown state which will gurantee that the traffic to/from dual-
homed CEs gets diverted. The interaction between OSPF and BGP is
outside the scope of this document. [RFC6987] based mechanism with
summaries and externals advertised with high metrics could also be
used to achieve the same functionality when implementations support
high metrics advertisement for summaries and externals.
Another useful usecase is when ISPs provide sham-link services to
customers [RFC4577]. When PE goes out of service for maintenance,
all sham-links on the PE can be set to graceful-link-shutdown state
and traffic can be divered from both ends without having to touch the
configurations on the remote end of the sham-links.
7.4. Hub and spoke deployment
OSPF is largely deployed in Hub and Spoke deployments with a large
number of spokes connecting to the Hub. It is a general practice to
deploy multiple Hubs with all spokes connecting to these Hubs to
achieve redundancy. The [RFC6987] mechanism can be used to divert
the spoke-to-spoke traffic from the overloaded hub router. The
traffic that flows from spokes via the hub into an external network
may not be diverted in certain scenarios.When a Hub node goes down
for maintenance, all links on the Hub can be set to graceful-link-
shutdown state and traffic gets divered from the spoke sites as well
without having to make configuration changes on the spokes.
8. Security Considerations
This document utilizes the OSPF packets and LSAs described in
[RFC2328] , [RFC5340] , [RFC3630] and [RFC5329]. The authentication
procedures described in [RFC2328] for OSPFv2 and [RFC4552] for OSPFv3
are applicable to this document as well. This document does not
introduce any further security issues other than those discussed in
[RFC2328] and [RFC5340].
9. IANA Considerations
This specification updates one OSPF registry:
OSPFv2 Extended Link TLV Sub-TLVs
i) Graceful-Link-Shutdown Sub-TLV - Suggested value 7
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ii) Remote IPv4 Address Sub-TLV - Suggested value 8
iii) Local/Remote Interface ID Sub-TLV - Suggested Value 9
OSPFv3 Extended-LSA sub-TLV Registry
i) Graceful-Link-Shutdown sub-TLV - suggested value 7
BGP-LS Node Descriptor, Link Descriptor, Prefix Descriptor, and
Attribute TLVs [RFC7752]
i)Graceful-Link-Shutdown TLV - Suggested 1121
10. Acknowledgements
Thanks to Chris Bowers for valuable inputs and edits to the document.
Thanks to Jeffrey Zhang, Acee Lindem and Ketan Talaulikar for inputs.
Thanks to Karsten Thomann for careful review and inputs on the
applications where graceful-link-shutdown is useful.
Thanks to Alia Atlas, Deborah Brungard, Alvaro Retana, Andrew G.
Malis and Tim Chown for valuable inputs.
11. References
11.1. Normative References
[I-D.ietf-ospf-ospfv3-lsa-extend]
Lindem, A., Roy, A., Goethals, D., Vallem, V., and F.
Baker, "OSPFv3 LSA Extendibility", draft-ietf-ospf-ospfv3-
lsa-extend-23 (work in progress), January 2018.
[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>.
[RFC3630] Katz, D., Kompella, K., and D. Yeung, "Traffic Engineering
(TE) Extensions to OSPF Version 2", RFC 3630,
DOI 10.17487/RFC3630, September 2003,
<https://www.rfc-editor.org/info/rfc3630>.
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[RFC5329] Ishiguro, K., Manral, V., Davey, A., and A. Lindem, Ed.,
"Traffic Engineering Extensions to OSPF Version 3",
RFC 5329, DOI 10.17487/RFC5329, September 2008,
<https://www.rfc-editor.org/info/rfc5329>.
[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>.
[RFC5817] Ali, Z., Vasseur, JP., Zamfir, A., and J. Newton,
"Graceful Shutdown in MPLS and Generalized MPLS Traffic
Engineering Networks", RFC 5817, DOI 10.17487/RFC5817,
April 2010, <https://www.rfc-editor.org/info/rfc5817>.
[RFC6845] Sheth, N., Wang, L., and J. Zhang, "OSPF Hybrid Broadcast
and Point-to-Multipoint Interface Type", RFC 6845,
DOI 10.17487/RFC6845, January 2013,
<https://www.rfc-editor.org/info/rfc6845>.
[RFC6987] Retana, A., Nguyen, L., Zinin, A., White, R., and D.
McPherson, "OSPF Stub Router Advertisement", RFC 6987,
DOI 10.17487/RFC6987, September 2013,
<https://www.rfc-editor.org/info/rfc6987>.
[RFC7684] Psenak, P., Gredler, H., Shakir, R., Henderickx, W.,
Tantsura, J., and A. Lindem, "OSPFv2 Prefix/Link Attribute
Advertisement", RFC 7684, DOI 10.17487/RFC7684, November
2015, <https://www.rfc-editor.org/info/rfc7684>.
[RFC7752] Gredler, H., Ed., Medved, J., Previdi, S., Farrel, A., and
S. Ray, "North-Bound Distribution of Link-State and
Traffic Engineering (TE) Information Using BGP", RFC 7752,
DOI 10.17487/RFC7752, March 2016,
<https://www.rfc-editor.org/info/rfc7752>.
[RFC8042] Zhang, Z., Wang, L., and A. Lindem, "OSPF Two-Part
Metric", RFC 8042, DOI 10.17487/RFC8042, December 2016,
<https://www.rfc-editor.org/info/rfc8042>.
11.2. Informative References
[RFC4203] Kompella, K., Ed. and Y. Rekhter, Ed., "OSPF Extensions in
Support of Generalized Multi-Protocol Label Switching
(GMPLS)", RFC 4203, DOI 10.17487/RFC4203, October 2005,
<https://www.rfc-editor.org/info/rfc4203>.
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[RFC4552] Gupta, M. and N. Melam, "Authentication/Confidentiality
for OSPFv3", RFC 4552, DOI 10.17487/RFC4552, June 2006,
<https://www.rfc-editor.org/info/rfc4552>.
[RFC4577] Rosen, E., Psenak, P., and P. Pillay-Esnault, "OSPF as the
Provider/Customer Edge Protocol for BGP/MPLS IP Virtual
Private Networks (VPNs)", RFC 4577, DOI 10.17487/RFC4577,
June 2006, <https://www.rfc-editor.org/info/rfc4577>.
[RFC4915] Psenak, P., Mirtorabi, S., Roy, A., Nguyen, L., and P.
Pillay-Esnault, "Multi-Topology (MT) Routing in OSPF",
RFC 4915, DOI 10.17487/RFC4915, June 2007,
<https://www.rfc-editor.org/info/rfc4915>.
Authors' Addresses
Shraddha Hegde
Juniper Networks, Inc.
Embassy Business Park
Bangalore, KA 560093
India
Email: shraddha@juniper.net
Pushpasis Sarkar
Arrcus, Inc.
Email: pushpasis.ietf@gmail.com
Hannes Gredler
Individual
Email: hannes@gredler.at
Mohan Nanduri
ebay Corporation
2025 Hamilton Avenue
San Jose, CA 98052
US
Email: mnanduri@ebay.com
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Luay Jalil
Verizon
Email: luay.jalil@verizon.com
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