Networking Working Group P. Psenak, Ed.
Internet-Draft C. Filsfils
Intended status: Standards Track S. Litkowski
Expires: 9 September 2023 Cisco Systems
D. Voyer
Bell Canada
A. Dhamija
Rakuten
S. Hegde
Juniper Networks, Inc.
G. Van de Velde
Nokia
8 March 2023
IGP Unreachable Prefix Announcement
draft-ppsenak-lsr-igp-ureach-prefix-announce-02
Abstract
In the presence of summarization, there is a need to signal loss of
reachability to an individual prefix covered by the summary in order
to enable fast convergence away from paths to the node which owns the
prefix which is no longer reachable. This document describes how to
use existing protocol mechanisms in IS-IS and OSPF to advertise such
prefix reachability loss.
Requirements Language
The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT",
"SHOULD", "SHOULD NOT", "RECOMMENDED", "NOT RECOMMENDED", "MAY", and
"OPTIONAL" in this document are to be interpreted as described in BCP
14 [RFC2119][RFC8174] when, and only when, they appear in all
capitals, as shown here.
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/.
Psenak, et al. Expires 9 September 2023 [Page 1]
Internet-Draft IGP Unreachable Prefix Announcement March 2023
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 9 September 2023.
Copyright Notice
Copyright (c) 2023 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 Revised BSD License text as
described in Section 4.e of the Trust Legal Provisions and are
provided without warranty as described in the Revised BSD License.
Table of Contents
1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . 3
2. Supporting UPA in IS-IS . . . . . . . . . . . . . . . . . . . 3
2.1. Advertisement of UPA in IS-IS . . . . . . . . . . . . . . 4
2.2. Propagation of UPA in IS-IS . . . . . . . . . . . . . . . 5
3. Supporting UPA in OSPF . . . . . . . . . . . . . . . . . . . 5
3.1. Advertisement of UPA in OSPF . . . . . . . . . . . . . . 6
3.2. Propagation of UPA in OSPF . . . . . . . . . . . . . . . 6
4. Generation of the UPA . . . . . . . . . . . . . . . . . . . . 6
5. Signaling the UPA origin . . . . . . . . . . . . . . . . . . 7
5.1. Signaling the UPA origin in ISIS . . . . . . . . . . . . 7
5.2. Signaling the UPA origin in OSPFv2 . . . . . . . . . . . 7
5.3. Signaling the UPA origin in OSPFv3 . . . . . . . . . . . 7
5.4. Treatement of the U-Flag and UP-Flag . . . . . . . . . . 9
6. Deployment Considerations for UPA . . . . . . . . . . . . . . 9
7. Processing of the UPA . . . . . . . . . . . . . . . . . . . . 10
8. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 10
8.1. ISIS Prefix Attribute Flags Sub-TLV . . . . . . . . . . . 10
8.2. OSPFv2 Extended Prefix TLV Flags . . . . . . . . . . . . 10
8.3. OSPFv3 Extended-LSA Sub-TLVs . . . . . . . . . . . . . . 11
8.4. OSPFv3 Extended Prefix TLV Flags . . . . . . . . . . . . 11
9. Security Considerations . . . . . . . . . . . . . . . . . . . 11
10. Acknowledgements . . . . . . . . . . . . . . . . . . . . . . 11
11. References . . . . . . . . . . . . . . . . . . . . . . . . . 12
11.1. Normative References . . . . . . . . . . . . . . . . . . 12
11.2. Informative References . . . . . . . . . . . . . . . . . 13
Psenak, et al. Expires 9 September 2023 [Page 2]
Internet-Draft IGP Unreachable Prefix Announcement March 2023
Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . 14
1. Introduction
Link-state IGP protocols like IS-IS and OSPF are primarily used to
distribute routing information between routers belonging to a single
Autonomous System (AS) and to calculate the reachability for IPv4 or
IPv6 prefixes advertised by the individual nodes inside the AS. Each
node advertises the state of its local adjacencies, connected
prefixes, capabilities, etc. The collection of these states from all
the routers inside the area form a link-state database (LSDB) that
describes the topology of the area and holds additional state
information about the prefixes, router capabilities, etc.
The growth of networks running a link-state routing protocol results
in the addition of more state which leads to scalability and
convergence challenges. The organization of networks into levels/
areas and IGP domains helps limit the scope of link-state information
within certain boundaries. However, the state related to prefix
reachability often requires propagation across a multi-area/level
and/or multi-domain IGP network. Techniques such as summarization
have been used traditionally to address the scale challenges
associated with advertising prefix state outside of the local area/
domain. However, this results in suppression of the individual
prefix state that is useful for triggering fast-convergence
mechanisms outside of the IGPs - e.g., BGP PIC Edge [I-D.ietf-rtgwg-
bgp-pic].
This document describes how the use of existing protocol mechanisms
can support the necessary functionality without the need for any
protocol extensions. The functionality being described is called
Unreachable Prefix Announcement (UPA).
Similarly, when an egress router needs to be taken out for
maintenance, the traffic is drained from the node before taking it
down. This is typically achieved by setting OL-bit together with
using max-metric for all prefixes advertised by the node in ISIS, or
by setting max-metric on all-links and prefixes advertised by the
node in OSPF. When prefixes from such node are summarized by the
ABR/ASBR, nodes outside of the area or domain are unaware of such
prefixes becoming unreachable. This document proposes protocol
extensions to carry information about such prefixes in a backward
compatible manner.
2. Supporting UPA in IS-IS
[RFC5305] defines the encoding for advertising IPv4 prefixes using 4
octets of metric information. Section 4 specifies:
Psenak, et al. Expires 9 September 2023 [Page 3]
Internet-Draft IGP Unreachable Prefix Announcement March 2023
"If a prefix is advertised with a metric larger then MAX_PATH_METRIC
(0xFE000000, see paragraph 3.0), this prefix MUST NOT be considered
during the normal SPF computation. This allows advertisement of a
prefix for purposes other than building the normal IP routing table.
"
Similarly, [RFC5308] defines the encoding for advertising IPv6
prefixes using 4 octets of metric information. Section 2 states:
"...if a prefix is advertised with a metric larger than
MAX_V6_PATH_METRIC (0xFE000000), this prefix MUST NOT be considered
during the normal Shortest Path First (SPF) computation. This will
allow advertisement of a prefix for purposes other than building the
normal IPv6 routing table."
This functionality can be used to advertise a prefix (IPv4 or IPv6)
in a manner which indicates that reachability has been lost - and to
do so without requiring all nodes in the network to be upgraded to
support the functionality.
2.1. Advertisement of UPA in IS-IS
Existing nodes in a network that do not suport UPA will not use UPAs
during the route calculation, but will continue to flood them. This
allows flooding of such advertisements to occur without the need to
upgrade all nodes in a network.
Recognition of the advertisement as UPA is only required on routers
which have a use case for this information. Area Border Routers
(ABRs), which would be responsible for propagating UPA advertisements
into other areas would need to recognize such advertisements.
As per the definitions referenced in the preceding section, any
prefix advertisement with a metric value greater than 0xFE000000 can
be used for purposes other than normal routing calculations. Such an
advertisement can be interpreted by the receiver as a UPA.
Optionally, an implementation may use local configuration to limit
the set of metric values which will be interpreted as UPA. The only
restriction is that such values MUST be greater than 0xFE000000.
UPA in ISIS is supported for all IS-IS Sub-TLVs Advertising Prefix
Reachability, e.g., SRv6 Locator [I-D.ietf-lsr-isis-srv6-extensions],
Extended IP reachability [RFC5305], MT IP Reach [RFC5120], IPv6 IP
Reach [RFC5308], MT IPv6 IP Reach [RFC5120], IPv4 Algorithm Prefix
Reachability TLV [I-D.ietf-lsr-ip-flexalgo], and IPv6 Algorithm
Prefix Reachability TLV [I-D.ietf-lsr-ip-flexalgo]
Psenak, et al. Expires 9 September 2023 [Page 4]
Internet-Draft IGP Unreachable Prefix Announcement March 2023
2.2. Propagation of UPA in IS-IS
ISIS allows propagation of IP prefixes in both directions between
level 1 and level 2. For reachable prefixes this is only done if the
prefix is reachable in source level - e.g., the prefix needs to be
reachable in level 1 to be propagated to level 2 and vice verse.
Such requirement of reachability MUST NOT be applied for UPAs, as
they are propagating unreachability.
ISIS L1/L2 routers may wish to advertise received UPAs into other
areas (upwards and/or downwards). When propagating UPAs the original
metric value MUST be preserved. The cost to reach the originator of
the received UPA MUST NOT be considered when readvertising the UPA.
3. Supporting UPA in OSPF
[RFC2328] Appendix B defines the following architectural constant for
OSPF:
"LSInfinity The metric value indicating that the destination
described by an LSA is unreachable. Used in summary-LSAs and AS-
external-LSAs as an alternative to premature aging (see
Section 14.1). It is defined to be the 24-bit binary value of all
ones: 0xffffff."
[RFC5340] Appendix B states:
"Architectural constants for the OSPF protocol are defined in
Appendix B of OSPFV2."
indicating that these same constants are applicable to OSPFv3.
[RFC2328] section 14.1. also describes the usage of LSInfinity as a
way to indicate loss of prefix reachability:
"Premature aging can also be used when, for example, one of the
router's previously advertised external routes is no longer
reachable. In this circumstance, the router can flush its AS-
external-LSA from the routing domain via premature aging. This
procedure is preferable to the alternative, which is to originate a
new LSA for the destination specifying a metric of LSInfinity."
UPA in OSPFv2 is supported for OSPFv2 Summary-LSA [RFC2328], AS-
external-LSAs [RFC2328], NSSA AS-external LSA.[RFC3101], and OSPFv2
Extended Prefix TLV [I-D.ietf-lsr-ip-flexalgo].
Psenak, et al. Expires 9 September 2023 [Page 5]
Internet-Draft IGP Unreachable Prefix Announcement March 2023
UPA in OSPFv3 is supported for Inter-Area-Prefix-LSA [RFC5340], AS-
External-LSA [RFC5340], NSSA-LSA [RFC5340], E-Inter-Area-Prefix-LSA
[RFC8362], E-AS-External-LSA [RFC8362], E-Type-7-LSA [RFC8362], and
SRv6 Locator LSA [I-D.ietf-lsr-ospfv3-srv6-extensions].
3.1. Advertisement of UPA in OSPF
Using the existing mechanism already defined in the standards, as
described in previous section, an advertisement of the inter-area or
external prefix inside OSPF or OSPFv3 LSA that has the age set to
value lower than MaxAge and metic set to LSInfinity can be
interpreted by the receiver as a UPA.
Existing nodes in a network which receive UPA advertisements will
propagate it following existing standard procedures defined by OSPF.
OSPF Area Border Routers (ABRs), which would be responsible for
propagating UPA advertisements into other areas would need to
recognize such advertisements.
3.2. Propagation of UPA in OSPF
Advertising prefix reachability between OSPF areas assumes prefix
reachability in a source area. Such requirement of reachability MUST
not be applied for UPAs, as they are propagating unreachability.
OSPF ABRs may wish to advertise received UPAs into other connected
areas. When doing so, the original LSInfinity metric value in UPA
MUST be preserved. The cost to reach the originator of the received
UPA MUST NOT be considered when readvertising the UPA to connected
areas.
4. Generation of the UPA
UPA MAY be generated by the ABR or ASBR that is performing the
summarization, when all of the following conditions are met:
- reachability of a prefix that was reachable earlier was lost
- a summary address which covers the prefix is being advertised by
the ABR/ASBR
Implementations are free to limit the UPA generation to specific
prefixes, e.g. host prefixes, SRv6 locators, or similar. Such
filtering is optional and MAY be controlled via configuration.
Psenak, et al. Expires 9 September 2023 [Page 6]
Internet-Draft IGP Unreachable Prefix Announcement March 2023
5. Signaling the UPA origin
In ISIS a prefix can be advertised with metric higher than
0xFE000000, or in OSPF with metric LSInfinity, for various reasons.
Even though in all cases the treatment of such metric is specified
for both OSPF and ISIS, having an explicit way to signal that the
prefix was advertised in order to signal unreachability is useful to
distinguish it from other cases where the prefix with such metric is
advertised.
5.1. Signaling the UPA origin in ISIS
Two new bits in the IPv4/IPv6 Extended Reachability Attribute Flags
[RFC7794] are defined:
U-Flag: - Unreachable Prefix Flag (Bit TBD). When set, it
indicates that the prefix is unreachable due to the unplanned
reason.
UP-Flag: - Unreachable Planned Prefix Flag (Bit TBD). When set,
it indicates that the prefix is unreachable due to the planned
reason, e.g., planned maintenance.
The prefix that is advertised with U or UP flag MUST have the metric
set to a value larger than 0xFE000000. If the prefix metric is less
than or equal 0xFE000000, both of these flags MUST be ignored.
5.2. Signaling the UPA origin in OSPFv2
Two new bits in Flags field of the OSPFv2 Extended Prefix TLV
[RFC7684] are defined:
U-Flag: - Unreachable Prefix Flag (Bit TBD). When set, it
indicates that the prefix is unreachable due to the unplanned
reason.
UP-Flag: - Unreachable Planned Prefix Flag (Bit TBD). When set,
it indicates that the prefix is unreachable due to the planned
reason, e.g., planned maintenance.
The prefix that is advertised with U or UP flag MUST have the
metric set to a value LSInfinity. If the prefix metric is not
equal to LSInfinity, both of these flags MUST be ignored.
5.3. Signaling the UPA origin in OSPFv3
A new Prefix Attribute Flags sub-TLV is defined as a sub-TLV of the
following OSPFv3 TLVs as defined in [RFC8362]:
Psenak, et al. Expires 9 September 2023 [Page 7]
Internet-Draft IGP Unreachable Prefix Announcement March 2023
Intra-Area Prefix TLV
Inter-Area Prefix TLV
External Prefix TLV
It MUST appear only once in the parent TLV and has the following
format:
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 |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Prefix Attribute Flags |
+- -+
| ... |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
where:
Type: TBD
Length: variable, dependent on the size of the Prefix Attribute
Flags. MUST be a multiple of 4 octets.
Prefix Attribute Flags: individual bits representing the flags.
Bits in Prefix Attribute Flags are defined/sent starting with Bit 0
defined below. Additional bit definitions that may be defined in the
future SHOULD be assigned in ascending bit order so as to minimize
the number of bits that will need to be transmitted.
Undefined bits MUST be transmitted as 0 and MUST be ignored on
receipt.
Bits that are NOT transmitted MUST be treated as if they are set to 0
on receipt.
Two new bits in OSPFv3 Prefix Atribute Flags are defined:
U-Flag: - Unreachable Prefix Flag (Bit TBD). When set, it
indicates that the prefix became unreachable due to the unplanned
reason.
UP-Flag: - Unreachable Planned Prefix Flag (Bit TBD). When set,
it indicates that the prefix became unreachable due to the planned
reason, e.g., planned maintenance.
Psenak, et al. Expires 9 September 2023 [Page 8]
Internet-Draft IGP Unreachable Prefix Announcement March 2023
The prefix that is advertised with U or UP flag MUST have the metric
set to a value LSInfinity. If the prefix metric is not equal to
LSInfinity, both of these flags MUST be ignored.
5.4. Treatement of the U-Flag and UP-Flag
U-Flag and UP-Flag are optional flags that have informative
character. Treatment of these flags on the receiver is optional and
the usage of them is outside of scope of this document.
6. Deployment Considerations for UPA
The intent of UPA is to provide an event driven signal of the
transition of a destination from reachable to unreachable. It is not
intended to advertise a persistent state. UPA advertisements should
therefore be withdrawn after a modest amount of time, that would
provides sufficient time for UPA to be flooded network-wide and acted
upon by receiving nodes, but limits the presence of UPA in the
network to a short time period. The time the UPA is kept in the
network SHOULD also reflect the intended use-case for which the UPA
was advertised.
As UPA advertisements in ISIS are advertised in existing Link State
PDUs (LSPs) and the unit of flooding in IS-IS is an LSP, it is
recommended that, when possible, UPAs are advertised in LSPs
dedicated to this type of advertisement. This will minimize the
number of LSPs which need to be updated when UPAs are advertised and
withdrawn.
In OSPF and OSPFv3, each inter-area and external prefix is advertised
in it's own LSA, so the above optimisation does not apply to OSPF.
It is also recommended that implementations limit the number of UPA
advertisements which can be originated at a given time.
UPA is not meant to address an area/domain partition. When an area
partitions, while multiple ABRs advertise the same summary, each of
the ABRs can only reach portion of the summarized prefix. As a
result, depending on which ABR the traffic is using to enter a
partitioned area, the traffic could be dropped or be delivered to its
final destination. UPA does not make the problem of an area
partition any worse. In case of an area partition each of the ABRs
will generate UPAs for the destinations for which the reachability
was lost locally. As the UPA propagates to the nodes outside of a
partitioned area, it may result in such nodes picking an alternative
egress node for the traffic, if such alternate egress node exists.
If such alternate egress node resides outside of a partitioned area,
traffic will be restored. If such alternate egress node resides in a
Psenak, et al. Expires 9 September 2023 [Page 9]
Internet-Draft IGP Unreachable Prefix Announcement March 2023
partitioned area and is covered by the summary, the trafic will be
dropped if it enters a partitioned area via the ABR that can not
reach the alternate egress node - resulting in similar behavior as
without the UPA. Above is similarly applicable to a domain
partition.
7. Processing of the UPA
Processing of the received UPAs is optional and SHOULD be controlled
by the configuration at the receiver. The receiver itself, based on
its configuration, decides what the UPA will be used for and what
applications, if any, will be notified when UPA is received.
8. IANA Considerations
8.1. ISIS Prefix Attribute Flags Sub-TLV
This document adds two new bits in the "IS-IS Bit Values for Prefix
Attribute Flags Sub-TLV" registry:
Bit #: TBD
Description: U-Flag
Reference: This document (Section 5.1).
Bit #: TDB
Description: UP-Flag
Reference: This document (Section 5.1).
8.2. OSPFv2 Extended Prefix TLV Flags
This document adds two new bits in the "OSPFv2 Extended Prefix TLV
Flags" registry:
Bit #: TBD
Description: U-Flag
Reference: This document (Section 5.2).
Bit #: TDB
Description: UP-Flag
Reference: This document (Section 5.2).
Psenak, et al. Expires 9 September 2023 [Page 10]
Internet-Draft IGP Unreachable Prefix Announcement March 2023
8.3. OSPFv3 Extended-LSA Sub-TLVs
This document adds new Sub-TLV in the "OSPFv3 Extended-LSA Sub-TLVs"
registry:
Value: TBD
Description: Prefix Attribute Flags sub-TLV
Reference: This document (Section 5.3).
The L2BM column is set to X.
8.4. OSPFv3 Extended Prefix TLV Flags
This document defines a new "OSPFv3 Extended Prefix TLV Flags"
registry under "Open Shortest Path First v3 (OSPFv3) Parameters".
This document adds two new bits in the newly defined "OSPFv3 Extended
Prefix TLV Flags" registry:
Bit #: TBD
Description: U-Flag
Reference: This document (Section 5.3).
Bit #: TDB
Description: UP-Flag
Reference: This document (Section 5.3).
9. Security Considerations
The use of UPAs introduces the possibility that an attacker could
inject a false, but apparently valid, UPA. However, the risk of this
occurring is no greater than the risk today of an attacker injecting
any other type of false advertisement .
The risks can be reduced by the use of existing security extensions
as described in [RFC5304] and [RFC5310] for IS-IS, in [RFC2328][ and
[RFC7474] for OSPFv2, and in [RFC5340] and [RFC4552] for OSPFv3.
10. Acknowledgements
The authors would like to thank Kamran Raza and Michael MacKenzie for
their contribution to the overall solution proposed in this document.
Psenak, et al. Expires 9 September 2023 [Page 11]
Internet-Draft IGP Unreachable Prefix Announcement March 2023
11. References
11.1. Normative References
[ISO10589] ISO, "Intermediate system to Intermediate system intra-
domain routeing information exchange protocol for use in
conjunction with the protocol for providing the
connectionless-mode Network Service (ISO 8473)", November
2002.
[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>.
[RFC3101] Murphy, P., "The OSPF Not-So-Stubby Area (NSSA) Option",
RFC 3101, DOI 10.17487/RFC3101, January 2003,
<https://www.rfc-editor.org/info/rfc3101>.
[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>.
[RFC5120] Przygienda, T., Shen, N., and N. Sheth, "M-ISIS: Multi
Topology (MT) Routing in Intermediate System to
Intermediate Systems (IS-ISs)", RFC 5120,
DOI 10.17487/RFC5120, February 2008,
<https://www.rfc-editor.org/info/rfc5120>.
[RFC5304] Li, T. and R. Atkinson, "IS-IS Cryptographic
Authentication", RFC 5304, DOI 10.17487/RFC5304, October
2008, <https://www.rfc-editor.org/info/rfc5304>.
[RFC5305] Li, T. and H. Smit, "IS-IS Extensions for Traffic
Engineering", RFC 5305, DOI 10.17487/RFC5305, October
2008, <https://www.rfc-editor.org/info/rfc5305>.
[RFC5308] Hopps, C., "Routing IPv6 with IS-IS", RFC 5308,
DOI 10.17487/RFC5308, October 2008,
<https://www.rfc-editor.org/info/rfc5308>.
Psenak, et al. Expires 9 September 2023 [Page 12]
Internet-Draft IGP Unreachable Prefix Announcement March 2023
[RFC5310] Bhatia, M., Manral, V., Li, T., Atkinson, R., White, R.,
and M. Fanto, "IS-IS Generic Cryptographic
Authentication", RFC 5310, DOI 10.17487/RFC5310, February
2009, <https://www.rfc-editor.org/info/rfc5310>.
[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>.
[RFC7474] Bhatia, M., Hartman, S., Zhang, D., and A. Lindem, Ed.,
"Security Extension for OSPFv2 When Using Manual Key
Management", RFC 7474, DOI 10.17487/RFC7474, April 2015,
<https://www.rfc-editor.org/info/rfc7474>.
[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>.
[RFC7794] Ginsberg, L., Ed., Decraene, B., Previdi, S., Xu, X., and
U. Chunduri, "IS-IS Prefix Attributes for Extended IPv4
and IPv6 Reachability", RFC 7794, DOI 10.17487/RFC7794,
March 2016, <https://www.rfc-editor.org/info/rfc7794>.
[RFC8174] Leiba, B., "Ambiguity of Uppercase vs Lowercase in RFC
2119 Key Words", BCP 14, RFC 8174, DOI 10.17487/RFC8174,
May 2017, <https://www.rfc-editor.org/info/rfc8174>.
[RFC8362] Lindem, A., Roy, A., Goethals, D., Reddy Vallem, V., and
F. Baker, "OSPFv3 Link State Advertisement (LSA)
Extensibility", RFC 8362, DOI 10.17487/RFC8362, April
2018, <https://www.rfc-editor.org/info/rfc8362>.
11.2. Informative References
[I-D.ietf-lsr-ip-flexalgo]
Britto, W., Hegde, S., Kaneriya, P., Shetty, R., Bonica,
R., and P. Psenak, "IGP Flexible Algorithms (Flex-
Algorithm) In IP Networks", Work in Progress, Internet-
Draft, draft-ietf-lsr-ip-flexalgo-08, 19 December 2022,
<https://datatracker.ietf.org/doc/html/draft-ietf-lsr-ip-
flexalgo-08>.
Psenak, et al. Expires 9 September 2023 [Page 13]
Internet-Draft IGP Unreachable Prefix Announcement March 2023
[I-D.ietf-lsr-isis-srv6-extensions]
Psenak, P., Filsfils, C., Bashandy, A., Decraene, B., and
Z. Hu, "IS-IS Extensions to Support Segment Routing over
IPv6 Dataplane", Work in Progress, Internet-Draft, draft-
ietf-lsr-isis-srv6-extensions-19, 14 November 2022,
<https://datatracker.ietf.org/doc/html/draft-ietf-lsr-
isis-srv6-extensions-19>.
[I-D.ietf-lsr-ospfv3-srv6-extensions]
Li, Z., Hu, Z., Talaulikar, K., and P. Psenak, "OSPFv3
Extensions for SRv6", Work in Progress, Internet-Draft,
draft-ietf-lsr-ospfv3-srv6-extensions-09, 14 January 2023,
<https://datatracker.ietf.org/doc/html/draft-ietf-lsr-
ospfv3-srv6-extensions-09>.
Authors' Addresses
Peter Psenak (editor)
Cisco Systems
Pribinova Street 10
Bratislava 81109
Slovakia
Email: ppsenak@cisco.com
Clarence Filsfils
Cisco Systems
Brussels
Belgium
Email: cfilsfil@cisco.com
Stephane Litkowski
Cisco Systems
La Rigourdiere
Cesson Sevigne
France
Email: slitkows@cisco.com
Daniel Voyer
Bell Canada
Email: daniel.voyer@bell.ca
Amit Dhamija
Rakuten
Email: amit.dhamija@rakuten.com
Psenak, et al. Expires 9 September 2023 [Page 14]
Internet-Draft IGP Unreachable Prefix Announcement March 2023
Shraddha Hegde
Juniper Networks, Inc.
Embassy Business Park
Bangalore, KA
560093
India
Email: shraddha@juniper.net
Gunter Van de Velde
Nokia
Antwerp
Belgium
Email: gunter.van_de_velde@nokia.com
Psenak, et al. Expires 9 September 2023 [Page 15]