draft-ietf-ospf-link-overload-04.txt   draft-ietf-ospf-link-overload-05.txt 
Open Shortest Path First IGP S. Hegde Open Shortest Path First IGP S. Hegde
Internet-Draft Juniper Networks, Inc. Internet-Draft Juniper Networks, Inc.
Intended status: Standards Track P. Sarkar Intended status: Standards Track P. Sarkar
Expires: August 22, 2017 H. Gredler Expires: August 27, 2017 H. Gredler
Individual Individual
M. Nanduri M. Nanduri
Microsoft Corporation Microsoft Corporation
L. Jalil L. Jalil
Verizon Verizon
February 18, 2017 February 23, 2017
OSPF Link Overload OSPF Link Overload
draft-ietf-ospf-link-overload-04 draft-ietf-ospf-link-overload-05
Abstract Abstract
When a link is being prepared to be taken out of service, the traffic 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 needs to be diverted from both ends of the link. Increasing the
metric to the highest metric on one side of the link is not metric to the highest metric on one side of the link is not
sufficient to divert the traffic flowing in the other direction. sufficient to divert the traffic flowing in the other direction.
It is useful for routers in an OSPFv2 or OSPFv3 routing domain to be It is useful for routers in an OSPFv2 or OSPFv3 routing domain to be
able to advertise a link being in an overload state to indicate able to advertise a link being in an overload state to indicate
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Internet-Drafts are working documents of the Internet Engineering Internet-Drafts are working documents of the Internet Engineering
Task Force (IETF). Note that other groups may also distribute Task Force (IETF). Note that other groups may also distribute
working documents as Internet-Drafts. The list of current Internet- working documents as Internet-Drafts. The list of current Internet-
Drafts is at http://datatracker.ietf.org/drafts/current/. Drafts is at http://datatracker.ietf.org/drafts/current/.
Internet-Drafts are draft documents valid for a maximum of six months Internet-Drafts are draft documents valid for a maximum of six months
and may be updated, replaced, or obsoleted by other documents at any and may be updated, replaced, or obsoleted by other documents at any
time. It is inappropriate to use Internet-Drafts as reference time. It is inappropriate to use Internet-Drafts as reference
material or to cite them other than as "work in progress." material or to cite them other than as "work in progress."
This Internet-Draft will expire on August 22, 2017. This Internet-Draft will expire on August 27, 2017.
Copyright Notice Copyright Notice
Copyright (c) 2017 IETF Trust and the persons identified as the Copyright (c) 2017 IETF Trust and the persons identified as the
document authors. All rights reserved. document authors. All rights reserved.
This document is subject to BCP 78 and the IETF Trust's Legal This document is subject to BCP 78 and the IETF Trust's Legal
Provisions Relating to IETF Documents Provisions Relating to IETF Documents
(http://trustee.ietf.org/license-info) in effect on the date of (http://trustee.ietf.org/license-info) in effect on the date of
publication of this document. Please review these documents publication of this document. Please review these documents
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3.2. Link scope flooding . . . . . . . . . . . . . . . . . . . 4 3.2. Link scope flooding . . . . . . . . . . . . . . . . . . . 4
4. Link-Overload sub-TLV . . . . . . . . . . . . . . . . . . . . 4 4. Link-Overload sub-TLV . . . . . . . . . . . . . . . . . . . . 4
4.1. OSPFv2 Link-overload sub-TLV . . . . . . . . . . . . . . 4 4.1. OSPFv2 Link-overload sub-TLV . . . . . . . . . . . . . . 4
4.2. OSPFv3 Link-Overload sub-TLV . . . . . . . . . . . . . . 5 4.2. OSPFv3 Link-Overload sub-TLV . . . . . . . . . . . . . . 5
5. Elements of procedure . . . . . . . . . . . . . . . . . . . . 5 5. Elements of procedure . . . . . . . . . . . . . . . . . . . . 5
5.1. Point-to-point links . . . . . . . . . . . . . . . . . . 6 5.1. Point-to-point links . . . . . . . . . . . . . . . . . . 6
5.2. Broadcast/NBMA links . . . . . . . . . . . . . . . . . . 6 5.2. Broadcast/NBMA links . . . . . . . . . . . . . . . . . . 6
5.3. Point-to-multipoint links . . . . . . . . . . . . . . . . 7 5.3. Point-to-multipoint links . . . . . . . . . . . . . . . . 7
5.4. Unnumbered interfaces . . . . . . . . . . . . . . . . . . 7 5.4. Unnumbered interfaces . . . . . . . . . . . . . . . . . . 7
5.5. Hybrid Broadcast and P2MP interfaces . . . . . . . . . . 7 5.5. Hybrid Broadcast and P2MP interfaces . . . . . . . . . . 7
6. Backward compatibility . . . . . . . . . . . . . . . . . . . 7 6. Backward compatibility . . . . . . . . . . . . . . . . . . . 8
7. Applications . . . . . . . . . . . . . . . . . . . . . . . . 7 7. Applications . . . . . . . . . . . . . . . . . . . . . . . . 8
7.1. Pseudowire Services . . . . . . . . . . . . . . . . . . . 8 7.1. Pseudowire Services . . . . . . . . . . . . . . . . . . . 8
7.2. Controller based Traffic Engineering Deployments . . . . 8 7.2. Controller based Traffic Engineering Deployments . . . . 9
8. Security Considerations . . . . . . . . . . . . . . . . . . . 9 7.3. L3VPN Services and sham-links . . . . . . . . . . . . . . 10
9. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 9 7.4. Hub and spoke deployment . . . . . . . . . . . . . . . . 10
10. Acknowledgements . . . . . . . . . . . . . . . . . . . . . . 10 8. Security Considerations . . . . . . . . . . . . . . . . . . . 11
11. References . . . . . . . . . . . . . . . . . . . . . . . . . 10 9. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 11
11.1. Normative References . . . . . . . . . . . . . . . . . . 10 10. Acknowledgements . . . . . . . . . . . . . . . . . . . . . . 11
11.2. Informative References . . . . . . . . . . . . . . . . . 11 11. References . . . . . . . . . . . . . . . . . . . . . . . . . 11
Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . 11 11.1. Normative References . . . . . . . . . . . . . . . . . . 11
11.2. Informative References . . . . . . . . . . . . . . . . . 12
Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . 13
1. Introduction 1. Introduction
When a node is being prepared for a planned maintenance or upgrade, When a node is being prepared for a planned maintenance or upgrade,
[RFC6987] provides mechanisms to advertise the node being in an [RFC6987] provides mechanisms to advertise the node being in an
overload state by setting all outgoing link costs to MAX-METRIC overload state by setting all outgoing link costs to MAX-METRIC
(0xffff). These procedures are specific to the maintenance activity (0xffff). These procedures are specific to the maintenance activity
on a node and cannot be used when a single link attached to the node on a node and cannot be used when a single link attached to the node
requires maintenance. requires maintenance.
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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 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 | | Type | Length |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Remote IP address | | Remote IP address |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
Figure 1: Link-Overload sub-TLV for OSPFv2 Figure 1: Link-Overload sub-TLV for OSPFv2
Type : TBA (suggested value 4) Type : TBA (suggested value 4)
Length: 4 Length: 4
Value: Remote IPv4 address. The remote IP4 address is used to Value: Remote IPv4 address. The remote IP4 address is used to
identify the particular link that is in the overload state when there identify the particular link that is in the overload state when there
are multiple parallel links between two nodes. are multiple parallel links between two nodes.
4.2. OSPFv3 Link-Overload sub-TLV 4.2. OSPFv3 Link-Overload sub-TLV
The OSPFv3 Link-Overload sub-TLV is carried in the link local scope The OSPFv3 Link-Overload sub-TLV is carried in the link local scope
OSPFV3 RI LSA as defined in [RFC7770]. The area scope advertisement OSPFv3 RI LSA as defined in [RFC7770].
of Link-Overload sub-TLV will be carried in the Router-Link TLV as
defined in the [I-D.ietf-ospf-ospfv3-lsa-extend]and will be described
in a separate document. 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
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 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 | | Type | Length |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
Figure 2: Link-Overload sub-TLV for OSPFv3 Figure 2: Link-Overload sub-TLV for OSPFv3
Type : TBA (Suggested value 4) Type : TBA (Suggested value 4)
Length: 0 Length: 0
The area scope advertisement of Link-Overload sub-TLV for OSPFv3 will
be described in a separate document.
5. Elements of procedure 5. Elements of procedure
The Link-Overload sub-TLV indicates that the link identified by the The Link-Overload sub-TLV indicates that the link identified by the
sub-TLV is overloaded. The node that has the link to be taken out of sub-TLV is overloaded. The node that has the link to be taken out of
service SHOULD originate the Link-Overload sub-TLV in the Extended service SHOULD originate the Link-Overload sub-TLV in the Extended
Link TLV in the Extended Link Opaque LSA as defined in [RFC7684] for Link TLV in the Extended Link Opaque LSA as defined in [RFC7684] for
OSPFv2. The Link-Overload information is carried as a property of OSPFv2. The Link-Overload information is carried as a property of
the link and is flooded across the area. This information can be the link and is flooded across the area. This information can be
used by ingress routers or controllers to take special actions. An used by ingress routers or controllers to take special actions. An
application specific to this use case is described in Section 7.2. application specific to this use case is described in Section 7.2.
The precise action taken by the remote node at the other end of the The precise action taken by the remote node at the other end of the
link identified as overloaded depends on the link type. link identified as overloaded depends on the link type.
5.1. Point-to-point links 5.1. Point-to-point links
The node that has the link to be taken out of service SHOULD set The node that has the link to be taken out of service SHOULD set
metric of the link to MAX-METRIC (0xffff) and re- originate the metric of the link to MAX-METRIC (0xffff) and re- originate the
Router-LSA. The TE metric SHOULD be set to MAX-TE-METRIC-1 Router-LSA. The TE metric SHOULD be set to MAX-TE-METRIC -1
(0xfffffffe) and the node SHOULD re-originate the TE Link Opaque (0xfffffffe) and the node SHOULD re-originate the TE Link Opaque
LSAs. When a Link-Overload sub-TLV is received for a point-to-point LSAs. When a Link-Overload sub-TLV is received for a point-to-point
link, the remote node SHOULD identify the local link which link, the remote node SHOULD identify the local link which
corresponds to the overloaded link and set the metric to MAX-METRIC corresponds to the overloaded link and set the metric to MAX-METRIC
(0xffff). The remote node MUST re-originate the router-LSA with the (0xffff)and the remote node SHOULD re-originate the router-LSA with
changed metric. The TE metric SHOULD be set to MAX-TE-METRIC-1 the changed metric. The TE metric SHOULD be set to MAX-TE-METRIC -1
(0xfffffffe) and the TE opaque LSA for the link MUST be re-originated (0xfffffffe) and the TE opaque LSA for the link SHOULD be re-
with new value. originated with new value.
In multi-topology deployments [RFC4915], the Link-Overload sub-TLV Extended link opaque LSAs and the Extended link TLV are not scoped
carried in an Extended Link opaque LSA corresponds to all the for multi-topology [RFC4915]. In multi-topology deployments
topologies the link belongs to. The receiver node SHOULD change the [RFC4915], the Link-Overload sub-TLV carried in an Extended Link
metric in the reverse direction corresponding to all the topologies opaque LSA corresponds to all the topologies the link belongs to.
to which the reverse link belongs. The receiver node SHOULD change the metric in the reverse direction
corresponding to all the topologies to which the reverse link belongs
and re-originate the Router LSA as defined in [RFC4915].
When the originator of the Link-Overload sub-TLV purges the Extended When the originator of the Link-Overload sub-TLV purges the Extended
Link Opaque LSA/E-Router-LSA or re-originates it without the Link- Link Opaque LSA or re-originates it without the Link-Overload sub-
Overload sub-TLV, the remote node must re-originate the appropriate TLV, the remote node must re-originate the appropriate LSAs with the
LSAs with the metric and TE metric values set to their original metric and TE metric values set to their original values.
values.
5.2. Broadcast/NBMA links 5.2. Broadcast/NBMA links
Broadcast or NBMA networks in OSPF are represented by a star topology Broadcast or NBMA networks in OSPF are represented by a star topology
where the Designated Router (DR) is the central point to which all where the Designated Router (DR) is the central point to which all
other routers on the broadcast or NBMA network connect logically. As other routers on the broadcast or NBMA network connect logically. As
a result, routers on the broadcast or NBMA network advertise only 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 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, or advertise adjacencies with each other. For the Broadcast links,
the MAX-METRIC on the remote link cannot be changed since all the the MAX-METRIC on the remote link cannot be changed since all the
neighbours are on same link. Setting the link cost to MAX-METRIC neighbours are on same link. Setting the link cost to MAX-METRIC
would impact paths going via all neighbours. would impact paths going via all neighbours.
The node that has the link to be taken out of service SHOULD set The node that has the link to be taken out of service SHOULD set
metric of the link to MAX-METRIC(0xffff) and re-originate the Router- metric of the link to MAX-METRIC(0xffff) and re-originate the Router-
LSA. The TE metric SHOULD be set to MAX-TE-METRIC-1(0xfffffffe) and LSA. The TE metric SHOULD be set to MAX-TE-METRIC -1(0xfffffffe) and
the node SHOULD re-originate the TE Link Opaque LSAs. For a the node SHOULD re-originate the TE Link Opaque LSAs. For a
broadcast link, the two part metric as described in [RFC8042] is broadcast link, the two part metric as described in [RFC8042] is
used. The node originating the Link-Overload sub-TLV MUST set the used. The node originating the Link-Overload sub-TLV MUST set the
metric in the Network-to-Router Metric sub-TLV to MAX-METRIC 0xffff metric in the Network-to-Router Metric sub-TLV to MAX-METRIC 0xffff
for OSPFv2 and OSPFv3 and re-originate the LSAs the TLV is carried- for OSPFv2 and OSPFv3 and re-originate the LSAs the TLV is carried-
in. The nodes that receive the two part metric should follow the in. The nodes that receive the two part metric should follow the
procedures described in [RFC8042]. The backward compatibility procedures described in [RFC8042]. The backward compatibility
procedures described in [RFC8042] should be followed to ensure loop procedures described in [RFC8042] should be followed to ensure loop
free routing. free routing.
skipping to change at page 7, line 20 skipping to change at page 7, line 31
to-point links. When a Link-Overload sub-TLV is received for a to-point links. When a Link-Overload sub-TLV is received for a
point-to-multipoint link the remote node SHOULD identify the point-to-multipoint link the remote node SHOULD identify the
neighbour which corresponds to the overloaded link and set the metric neighbour which corresponds to the overloaded link and set the metric
to MAX-METRIC (0xffff). The remote node MUST re-originate the to MAX-METRIC (0xffff). The remote node MUST re-originate the
Router-LSA with the changed metric and flood into the OSPF area. Router-LSA with the changed metric and flood into the OSPF area.
5.4. Unnumbered interfaces 5.4. Unnumbered interfaces
Unnumbered interface do not have a unique IP addresses and borrow Unnumbered interface do not have a unique IP addresses and borrow
address from other interfaces. [RFC2328] describes procedures to address from other interfaces. [RFC2328] describes procedures to
handle unnumbered interfaces. The link-data field in the Extended handle unnumbered interfaces in the context of the Router LSA. We
Link TLV carries the interface-id instead of the IP address. The apply a similar procedure to the Extended Link TLV carrying the Link-
Link-Overload sub-TLV carries the remote interface-id in the Remote- Overload sub-TLV in to handle unnumbered interfaces. The link-data
ip-address field if the interface is unnumbered. Procedures to field in the Extended Link TLV carries the interface-id instead of
obtain interface-id of the remote side are defined in [RFC4203]. the IP address. The Link-Overload sub-TLV carries the remote
interface-id in the remote-ip-address field if the interface is
unnumbered. Procedures to obtain interface-id of the remote side are
defined in [RFC4203].
5.5. Hybrid Broadcast and P2MP interfaces 5.5. Hybrid Broadcast and P2MP interfaces
Hybrid Broadcast and P2MP interfaces represent a broadcast network Hybrid Broadcast and P2MP interfaces represent a broadcast network
modeled as P2MP interfaces. [RFC6845] describes procedures to handle modeled as P2MP interfaces. [RFC6845] describes procedures to handle
these interfaces. Operation for the Hybrid interfaces is similar to these interfaces. Operation for the Hybrid interfaces is similar to
the P2MP interfaces. When a Link-Overload sub-TLV is received for a the P2MP interfaces. When a Link-Overload sub-TLV is received for a
hybrid link the remote node SHOULD identify the neighbour which hybrid link the remote node SHOULD identify the neighbour which
corresponds to the overloaded link and set the metric to MAX-METRIC corresponds to the overloaded link and set the metric to MAX-METRIC
(0xffff). All the remote nodes connected to originator MUST re- (0xffff). All the remote nodes connected to originator MUST re-
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6. Backward compatibility 6. Backward compatibility
The mechanism described in the document is fully backward compatible. The mechanism described in the document is fully backward compatible.
It is required that the originator of the Link-Overload sub-TLV as It is required that the originator of the Link-Overload sub-TLV as
well as the node at the remote end of the link identified as well as the node at the remote end of the link identified as
overloaded understand the extensions defined in this document. In overloaded understand the extensions defined in this document. In
the case of broadcast links, the backward compatibility procedures as the case of broadcast links, the backward compatibility procedures as
described in [RFC8042] are applicable. described in [RFC8042] are applicable.
7. Applications 7. Applications
7.1. Pseudowire Services
---------PE3----------------PE4---------- 7.1. Pseudowire Services
| |
| |
CE1---------PE1----------------PE2---------CE2
| |
| |
-----------------------------------------
Private VLAN
Figure 3: Pseudowire Services
Many service providers offer pseudo-wire services to customers using Many service providers offer pseudo-wire services to customers using
L2 circuits. The IGP protocol that runs in the customer network L2 circuits. The IGP protocol that runs in the customer network
would also run over the pseudo-wire to create seamless private would also run over the pseudo-wire to create seamless private
network for the customer. Service providers want to offer overload network for the customer. Service providers want to offer overload
kind of functionality when the PE device is taken-out for kind of functionality when the PE device is taken-out for
maintenance. The provider should guarantee that the PE is taken out maintenance. The provider should guarantee that the PE is taken out
for maintenance only after the service is successfully diverted on an for maintenance only after the service is successfully diverted on an
alternate path. There can be large number of customers attached to a alternate path. There can be large number of customers attached to a
PE node and the remote end-points for these pseudo-wires are spread PE node and the remote end-points for these pseudo-wires are spread
across the service provider's network. It is a tedious and error- across the service provider's network. It is a tedious and error-
prone process to change the metric for all pseudo-wires in both prone process to change the metric for all pseudo-wires in both
directions. The link-overload feature simplifies the process by directions. The link-overload feature simplifies the process by
increasing the metric on the link in the reverse direction as well so increasing the metric on the link in the reverse direction as well so
that traffic in both directions is diverted away from the PE that traffic in both directions is diverted away from the PE
undergoing maintenance. The Link-Overload feature allows the link to undergoing maintenance. The Link-Overload feature allows the link to
be used as a last resort link so that traffic is not disrupted when be used as a last resort link so that traffic is not disrupted when
alternative paths are not available. alternative paths are not available.
When the PE1 node is going for maintenance, service provider sets the Private VLAN
PE1 to overload state. The PE1 going in overload state triggers all =======================================
the CEs connected to the PE to set their pseudowire links passing via | |
PE1 to link-overload state. The mechanisms used to communicate | |
between PE1 and CE1 is outside the scope of this document. CE1 sets | ------PE3---------------PE4------CE3
the link-overload state on its link and modifies the metric to | / \
MAX_METRIC and floods the information, the remote end of the link | / \
also sets the metric on the link to MAX-METRIC and the traffic from CE1---------PE1----------PE2---------CE2
both directions gets diverted away from the link. | \
| \
| ------CE4
| |
| |
| |
=================================
Private VLAN
Figure 3: Pseudowire Services
In the example shown in Figure 3, when the PE1 node is going for
maintenance, service providers set the PE1 to overload state. The
PE1 going in overload state triggers all the CEs (In this example
CE1)connected to the PE to set their pseudowire links passing via PE1
to link-overload state. The mechanisms used to communicate between
PE1 and CE1 is outside the scope of this document. CE1 sets the
link-overload state on its private VLAN connecting CE3, CE2 and CE4
and modifies the metric to MAX_METRIC and floods the information, the
remote end of the link at CE3, CE2, and CE4 also set the metric on
the link to MAX-METRIC and the traffic from both directions gets
diverted away from the link.
7.2. Controller based Traffic Engineering Deployments 7.2. Controller based Traffic Engineering Deployments
In controller-based deployments where the controller participates in
the IGP protocol, the controller can also receive the link-overload
information as a warning that link maintenance is imminent. Using
this information, the controller can find alternate paths for traffic
which use 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 traffic
engineering constraints, the controller might temporarily relax those
constraints and put the service on a different path.
_____________ _____________
| | | |
-------------| Controller |-------------- -------------| Controller |--------------
| |____________ | | | |____________ | |
| | | |
|--------- Primary Path ------------------| |--------- Primary Path ------------------|
PE1---------P1----------------P2---------PE2 PE1---------P1----------------P2---------PE2
| | | |
| | | |
|________P3________| |________P3________|
Alternate Path Alternate Path
Figure 4: Controller based Traffic Engineering Figure 4: Controller based Traffic Engineering
In controller-based deployments where the controller participates in
the IGP protocol, the controller can also receive the link-overload
information as a warning that link maintenance is imminent. Using
this information, the controller can find alternate paths for traffic
which use 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 traffic
engineering constraints, the controller might temporarily relax those
constraints and put the service on a different path.
In the above example, PE1->PE2 LSP is set-up to satisfy a constraint In the above example, PE1->PE2 LSP is set-up to satisfy a constraint
of 10 GB bandwidth on each link. The links P1->P3 and P3->P2 have of 10 Gbps bandwidth on each link. The links P1->P3 and P3->P2 have
only 1 GB capacity and there is no alternate path satisfying the only 1 Gbps capacity and there is no alternate path satisfying the
bandwidth constraint of 10GB. When P1->P2 link is being prepared for bandwidth constraint of 10GB. When P1->P2 link is being prepared for
maintenance, the controller receives the link-overload information, maintenance, the controller receives the link-overload information,
as there is no alternate path available which satisfies the as there is no alternate path available which satisfies the
constraints, controller chooses a path that is less optimal and constraints, controller chooses a path that is less optimal and
temporarily sets up an alternate path via P1->P3->P2. Once the 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 traffic is diverted, the P1->P2 link can be taken out of service for
maintenance/upgrade. maintenance/upgrade.
7.3. L3VPN Services and sham-links
Many service providers offer L3VPN services to customers and CE-PE
links run OSPF [RFC4577]. When PE goes for maintenance, all the
links on the PE can be set to link-overlaod state which will gurantee
that the traffic from CEs also gets diverted. The interaction
between OSPF and BGP is outside the scope of this document.
Another useful usecase is when ISPs provide sham-link services to
customers [RFC4577].When PE goes for maintenance, all sham-links on
the PE can be set to link-overload 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 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. When a Hub node goes down for maintenance, all links on
the Hub can be set to link-overload state and traffic gets divered
from spoke sites as well without having to make configuration changes
on the spokes.
8. Security Considerations 8. Security Considerations
This document does not introduce any further security issues other This document does not introduce any further security issues other
than those discussed in [RFC2328] and [RFC5340]. than those discussed in [RFC2328] and [RFC5340].
9. IANA Considerations 9. IANA Considerations
This specification updates one OSPF registry: This specification updates one OSPF registry:
OSPF Extended Link TLVs Registry OSPF Extended Link TLVs Registry
skipping to change at page 10, line 22 skipping to change at page 11, line 36
i) TBD - Link-Overload sub-TLV i) TBD - Link-Overload sub-TLV
BGP-LS Link NLRI Registry [RFC7752] BGP-LS Link NLRI Registry [RFC7752]
i)TBD - Link-Overload sub-TLV i)TBD - Link-Overload sub-TLV
10. Acknowledgements 10. Acknowledgements
Thanks to Chris Bowers for valuable inputs and edits to the document. Thanks to Chris Bowers for valuable inputs and edits to the document.
Thanks to Jeffrey Zhang and Acee Lindem for inputs. Thanks to Thanks to Jeffrey Zhang and Acee Lindem for inputs. Thanks to
Karsten Thomann for careful review and inputs. Karsten Thomann for careful review and inputs on the applications
where link-overload is useful.
11. References 11. References
11.1. Normative References 11.1. Normative References
[RFC6845] Sheth, N., Wang, L., and J. Zhang, "OSPF Hybrid Broadcast [RFC6845] Sheth, N., Wang, L., and J. Zhang, "OSPF Hybrid Broadcast
and Point-to-Multipoint Interface Type", RFC 6845, and Point-to-Multipoint Interface Type", RFC 6845,
DOI 10.17487/RFC6845, January 2013, DOI 10.17487/RFC6845, January 2013,
<http://www.rfc-editor.org/info/rfc6845>. <http://www.rfc-editor.org/info/rfc6845>.
skipping to change at page 11, line 7 skipping to change at page 12, line 22
S. Shaffer, "Extensions to OSPF for Advertising Optional S. Shaffer, "Extensions to OSPF for Advertising Optional
Router Capabilities", RFC 7770, DOI 10.17487/RFC7770, Router Capabilities", RFC 7770, DOI 10.17487/RFC7770,
February 2016, <http://www.rfc-editor.org/info/rfc7770>. February 2016, <http://www.rfc-editor.org/info/rfc7770>.
[RFC8042] Zhang, Z., Wang, L., and A. Lindem, "OSPF Two-Part [RFC8042] Zhang, Z., Wang, L., and A. Lindem, "OSPF Two-Part
Metric", RFC 8042, DOI 10.17487/RFC8042, December 2016, Metric", RFC 8042, DOI 10.17487/RFC8042, December 2016,
<http://www.rfc-editor.org/info/rfc8042>. <http://www.rfc-editor.org/info/rfc8042>.
11.2. Informative References 11.2. Informative References
[I-D.ietf-ospf-ospfv3-lsa-extend]
Lindem, A., Mirtorabi, S., Roy, A., and F. Baker, "OSPFv3
LSA Extendibility", draft-ietf-ospf-ospfv3-lsa-extend-06
(work in progress), February 2015.
[RFC2119] Bradner, S., "Key words for use in RFCs to Indicate [RFC2119] Bradner, S., "Key words for use in RFCs to Indicate
Requirement Levels", BCP 14, RFC 2119, Requirement Levels", BCP 14, RFC 2119,
DOI 10.17487/RFC2119, March 1997, DOI 10.17487/RFC2119, March 1997,
<http://www.rfc-editor.org/info/rfc2119>. <http://www.rfc-editor.org/info/rfc2119>.
[RFC2328] Moy, J., "OSPF Version 2", STD 54, RFC 2328, [RFC2328] Moy, J., "OSPF Version 2", STD 54, RFC 2328,
DOI 10.17487/RFC2328, April 1998, DOI 10.17487/RFC2328, April 1998,
<http://www.rfc-editor.org/info/rfc2328>. <http://www.rfc-editor.org/info/rfc2328>.
[RFC4203] Kompella, K., Ed. and Y. Rekhter, Ed., "OSPF Extensions in [RFC4203] Kompella, K., Ed. and Y. Rekhter, Ed., "OSPF Extensions in
Support of Generalized Multi-Protocol Label Switching Support of Generalized Multi-Protocol Label Switching
(GMPLS)", RFC 4203, DOI 10.17487/RFC4203, October 2005, (GMPLS)", RFC 4203, DOI 10.17487/RFC4203, October 2005,
<http://www.rfc-editor.org/info/rfc4203>. <http://www.rfc-editor.org/info/rfc4203>.
[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, <http://www.rfc-editor.org/info/rfc4577>.
[RFC4915] Psenak, P., Mirtorabi, S., Roy, A., Nguyen, L., and P. [RFC4915] Psenak, P., Mirtorabi, S., Roy, A., Nguyen, L., and P.
Pillay-Esnault, "Multi-Topology (MT) Routing in OSPF", Pillay-Esnault, "Multi-Topology (MT) Routing in OSPF",
RFC 4915, DOI 10.17487/RFC4915, June 2007, RFC 4915, DOI 10.17487/RFC4915, June 2007,
<http://www.rfc-editor.org/info/rfc4915>. <http://www.rfc-editor.org/info/rfc4915>.
[RFC5340] Coltun, R., Ferguson, D., Moy, J., and A. Lindem, "OSPF [RFC5340] Coltun, R., Ferguson, D., Moy, J., and A. Lindem, "OSPF
for IPv6", RFC 5340, DOI 10.17487/RFC5340, July 2008, for IPv6", RFC 5340, DOI 10.17487/RFC5340, July 2008,
<http://www.rfc-editor.org/info/rfc5340>. <http://www.rfc-editor.org/info/rfc5340>.
[RFC6987] Retana, A., Nguyen, L., Zinin, A., White, R., and D. [RFC6987] Retana, A., Nguyen, L., Zinin, A., White, R., and D.
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