Hi Jeffery,
Many thanks for your review! Please see inline...
BR,
Ran
From: ZhaohuiZhangviaDatatracker <[email protected]>
To: [email protected] <[email protected]>;
Cc: [email protected]
<[email protected]>;[email protected]
<[email protected]>;[email protected] <[email protected]>;
Date: 2025年09月05日 04:20
Subject: [Last-Call] draft-ietf-lsr-anycast-flag-05 ietf last call Rtgdir review
Document: draft-ietf-lsr-anycast-flag
Title: OSPFv2 Anycast Property Advertisement
Reviewer: Zhaohui Zhang
Review result: Has Nits
For the following two paragraphs:
[RFC7684] defines OSPFv2 Opaque LSAs based on Type-Length-Value (TLV)
tuples that can be used to associate additional attributes with
prefixes or links. The OSPFv2 Extended Prefix TLV that is contained
in the OSPFv2 Extended Prefix Opaque LSA is used to advertise
additional attributes associated with an IPv4 prefix, but the
definition of anycast flag to identify the IPv4 prefix as anycast has
not yet been defined.
The flags field of the OSPFv2 Extended Prefix TLV (Section 2.1 of
[RFC7684]) can be found in "OSPFv2 Extended Prefix TLV Flags" IANA
registry [IANA-OSPFv2-EPF].
They could be combined into the following:
[RFC7684] defines OSPFv2 Opaque LSAs based on Type-Length-Value (TLV)
tuples that can be used to associate additional attributes with
prefixes or links. The OSPFv2 Extended Prefix TLV that is contained
in the OSPFv2 Extended Prefix Opaque LSA is used to advertise
additional attributes associated with an IPv4 prefix, including a flags
field (Section 2.1 of [RFC7684]) with an "OSPFv2 Extended Prefix TLV Flags"
IANA registry [IANA-OSPFv2-EPF].
This would match the changes in the abstract (between the -04 and -05 revision)
of this draft.
Ran: Thank you for your suggestions. We've incorporated your feedback and made
the following revisions. Please let us know if this addresses your concerns.
[RFC7684] defines OSPFv2 Opaque LSAs based on Type-Length-Value (TLV)
tuples that can be used to associate additional attributes with
prefixes or links. The OSPFv2 Extended Prefix TLV that is contained
in the OSPFv2 Extended Prefix Opaque LSA is used to advertise
additional attributes associated with a prefix.
Extensions related to the anycast property of prefixes have been
specified for IS-IS [RFC9352] and OSPFv3 [RFC9513], even though those
documents are related to Segment Routing over IPv6, the anycast
property applies to any IP prefix advertisement. This document
defines a flag to advertise the anycast property for a prefix
advertisement in OSPFv2 in the Flags field of the OSPFv2 Extended
Prefix TLV Flags (section 2.1 of [RFC7684]).
2. Use-case
In the absence of the N-flag, the node specific prefixes need to be
identified from the anycast prefixs. A prefix that is advertised by
a single node and without an Anycast Flag (AC-flag) MUST be
considered node specific.
The above is not a use case, and the content is present below anyway.
I would suggest to remove the section, or give a real use case example.
I have one in mind and could provide text if you would like to include it.
Ran: Many thanks! Ketan provided a use case, which we authors have discussed.
Please see if the following content is suitable.
Section 3.3 of [RFC8402] describes an IGP-Anycast Segment and its use
with SR-MPLS. The use of an anycast segment as a waypoint in a SR TE
path is a use-case that requires consistent use of labels both for
the anycast segment but also the segment following it if that is an
adjacency SID or binding SID allocated dynamically or from the SRLB.
However, there is no indication available in OSPFv2 to convey to the
entity performing path computation using the OSPF LSDB that specific
prefix segments are anycast segments.
When computing TI-LFA [I-D.ietf-rtgwg-segment-routing-ti-lfa] repair
paths using SR segments, the requirement is to pick specific nodes
that need to be traversed to ensure loop free characteristics. This
requires picking prefix segments of those nodes that uniquely
identify those nodes. The selection of anycast prefix segments
advertised by those nodes for the TI-LFA repair path may result in
loops as the traffic may get rerouted to another node advertising the
same anycast segment. Hence, only node segments (with or without the
N-flag) and not anycast segments (with the AC-flag) are to be used
for TI-LFA repair paths.
A prefix that is advertised by a single node and without an AC-flag
MUST be considered node specific prefix.
Ran: This sentence wants be be changed to:
A prefix that is advertised by a single node and without an AC-flag
is considered node-specific prefix.
What if a prefix is advertised by multiple nodes but w/o the AC-flag?
Ran: A prefix advertised by multiple nodes without an AC-flag is considered an
anycast prefix.
5. YANG Data Model
module: ietf-ospf-anycast-flag
augment /rt:routing/rt:control-plane-protocols
/rt:control-plane-protocol/ospf:ospf/ospf:areas/ospf:area
/ospf:interfaces/ospf:interface:
+--rw anycast-flag? boolean
Should it be part of the interface or prefix configuration?
An interface could have multiple addresses, and maybe only one/some of them
may need the AC-flag?
Ran：Yingzhen and Ketan are already handling the issue.
5.2. YANG Data Model for OSPFv2 Anycast Property Advertisement
The following is the YANG module:
<CODE BEGINS> file "[email protected]"
module ietf-ospf-anycast-flag {
yang-version 1.1;
namespace
"urn:ietf:params:xml:ns:yang:ietf-ospf-anycast-flag";
prefix ospf-anycast-flag;
What does "prefix ospf-anycast-flag" mean here? Is it an interface or prefix
property?
The following mentions both interface and prefix.
import ietf-routing {
prefix rt;
reference
"RFC 8349: A YANG Data Model for Routing
Management (NMDA Version)";
}
import ietf-ospf {
prefix ospf;
reference
"RFC 9129: YANG Data Model for the OSPF Protocol";
}
identity ac-flag {
base ospf:ospfv2-extended-prefix-flag;
description
"Anycast flag. When set, it indicates that the prefix
is configured as anycast.";
}
/* Configuration */
augment "/rt:routing/rt:control-plane-protocols/"
+ "rt:control-plane-protocol/ospf:ospf/"
+ "ospf:areas/ospf:area/ospf:interfaces/ospf:interface" {
when "derived-from(/rt:routing/rt:control-plane-protocols/"
+ "rt:control-plane-protocol/rt:type, 'ospf:ospfv2')" {
description
"This augments the OSPFv2 interface configuration.";
}
description
"This augments OSPFv2 interface configuration with anycast
property advertisement.";
leaf anycast-flag {
type boolean;
default "false";
description
"Sets the prefix as an anycast address.";
}
}
}
Thanks.
Jeffrey
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